CN117715748A

CN117715748A - High modulus, high thermal conductivity radiative passive coolants

Info

Publication number: CN117715748A
Application number: CN202280052387.8A
Authority: CN
Inventors: 安德鲁·约翰·欧德科克; 阿尔曼·博罗曼德; 克里斯托弗·斯蒂普; 亚历克斯·奥克芬; 克里斯托弗·元庭·廖; 叶盛
Original assignee: Meta Platforms Technologies LLC
Current assignee: Meta Platforms Technologies LLC
Priority date: 2021-07-28
Filing date: 2022-07-27
Publication date: 2024-03-15

Abstract

The polymer bilayer includes a porous fluoropolymer layer directly overlying a polyethylene layer. The polyethylene layer may be porous or dense and may comprise an ultra-high molecular weight polymer. The polymer bilayer may be co-integrated with and provide passive cooling to a structure (e.g., a wearable device) exposed to high thermal loads (> 0-1000W/m 2). For example, passive cooling of AR/VR glasses at different solar loads can be achieved by a polymer bilayer that has high reflectivity at both the entire solar heating wavelength and high emissivity at long wavelength infrared. High reflectivity reduces energy absorption throughout the solar spectrum, while high emissivity promotes radiant heat transfer to the surrounding environment.

Description

High modulus, high thermal conductivity radiative passive coolants

Technical Field

The present disclosure relates generally to a high modulus, high thermal conductivity radiant passive coolant.

Background

Polymers and other organic materials may be incorporated into a variety of different optical devices and systems, including passive optical and electro-active devices, and active optical and electro-active devices, as well as electro-optical devices and systems. One or more lightweight and comfortable polymer/organic solid layers may be incorporated into wearable devices such as smart glasses and are attractive candidates for emerging technologies including virtual reality devices/augmented reality devices where a comfortable, adjustable form factor is desired.

For example, virtual Reality (VR) glasses devices or VR headset, and augmented reality (augmented reality, AR) glasses devices or AR headset may enable a user to experience a variety of events, such as interacting with a person in a computer-generated three-dimensional world simulation, or viewing data superimposed on a real-world view. For example, superimposing information onto the field of view may be achieved by an optical head-mounted display (OHMD) or by using embedded wireless glasses with a transparent heads-up display (HUD) or Augmented Reality (AR) overlay. VR/AR eyeglass devices and VR/AR head-mounted viewers may be used for a variety of purposes. For example, governments may use such devices for military training, medical professionals may use such devices to simulate surgery, and engineers may use such devices as design visualization aids. During use, these and other devices and systems may be exposed to temperature fluctuations, which may include exposure to high temperatures that adversely affect performance and/or user comfort.

Various methods and techniques may be used to provide active cooling and/or passive cooling for such devices and systems. For example, as will be appreciated, compression-based cooling methods may require excessive energy to be suitable for many applications. Other cooling methods (e.g., water cooling) typically include complex designs and accessories that make their application in all-weather wearable electronic devices such as smart glasses, AR glasses, VR headset, smart watches, etc., challenging.

For example, without being bound by theory, the all-weather wearability of AR/VR glasses may be based on their functionality and comfort under disparate solar loads, which may be included indoors (about 0W/m ² ) And outdoors (about 1000W/m) ² ) Is performed according to the operation of (a). As disclosed herein, passive cooling by material design can achieve high cooling power by reflection at solar heating spectral wavelengths (0.25 microns to 2.5 microns) and emission at long wavelength Infrared (IR) (8 microns to 14 microns). High reflectivity throughout the solar heating spectrum can provide small energy absorption in the solar spectrum, while high emissivity in the long wavelength infrared (long wavelength infrared, LWIR) allows surface radiation and exchange of heat with the atmosphere.

Despite recent advances, it would be advantageous to provide mechanical and optical systems comprising lenses and lens architectures that have high transparency and high emissivity and that inhibit or even eliminate thermal throttling due to exposure to electromagnetic radiation. Accordingly, the present disclosure relates generally to polymer layers including polymer bilayers and multilayers, and more particularly to polymer layers and bilayer architectures that exhibit high solar spectral reflectance, high transmittance and high emissivity at Long Wavelength Infrared (LWIR), high effective modulus and yield strength, high thermal conductivity, and optionally Radio Frequency (RF) transparency.

Disclosure of Invention

According to a first aspect, there is provided a layered structure comprising: an optically transparent layer comprising ultra high molecular weight polyethylene; and an IR reflecting layer overlying the optically transparent layer, wherein the layered structure has a short wavelength (0.25 μm < λ <5 μm) infrared reflectance of at least about 10% and a long wavelength (8 μm < λ <14 μm) infrared reflectance of less than about 10%.

The optically transparent layer can have a thermal conductivity of at least about 5W/mK.

The optically transparent layer may have an elastic modulus of at least about 2GPa and a tensile strength of at least about 0.7 GPa.

The IR reflecting layer may comprise an IR reflecting paint. The IR reflective coating includes nanoscale particles of a pigment, which may be selected from the group consisting of: organic dyes and metal oxides.

The IR reflecting layer may comprise a porous fluoropolymer. The porous fluoropolymer may include polyvinylidene fluoride (polyvinylidene fluoride, PVDF). The porous fluoropolymer may be selected from the group consisting of: PVDF-CTFE, PVDF-HFP, PVDF-TFE, PVDF-TrFE-TFE, and combinations thereof. The porous fluoropolymer may have a porosity of at least about 15 vol.%. The porous fluoropolymer may include a plurality of pores having an average pore size of at least about 100 nm.

The thickness of the optically transparent layer may be less than the thickness of the IR reflecting layer. The thickness of the optically transparent layer can range from about 10 microns to about 1mm, and the thickness of the IR reflecting layer can range from about 0.2mm to about 1mm.

According to a second aspect, there is provided an apparatus comprising the layered structure of the first aspect, wherein the apparatus may be selected from the group consisting of: smart watches, virtual Reality (VR) glasses, VR headset, augmented Reality (AR) glasses, AR headset, mixed Reality (MR) glasses, and MR headset.

According to a third aspect, there is provided a layered structure comprising: an optically transparent layer of ultra high molecular weight polyethylene; and an IR reflecting layer directly overlying the optically transparent layer, wherein the optically transparent layer has a thermal conductivity of at least about 5W/mK and an elastic modulus of at least about 2 GPa.

The layered structure may have a short wavelength (0.25 μm < lambda <5 μm) infrared reflectance of at least about 10% and a long wavelength (8 μm < lambda <14 μm) infrared reflectance of less than about 10%. The IR reflecting layer may comprise an IR reflecting paint.

According to a third aspect, there is provided a method comprising: forming an optically transparent layer of ultra high molecular weight polyethylene; and forming an IR reflecting layer over the optically transparent layer to produce a layered structure having a short wavelength (0.25 μm < lambda <5 μm) infrared reflectance of at least about 10% and a long wavelength (8 μm < lambda <14 μm) infrared reflectance of less than about 10%.

Forming the IR reflecting layer over the optically transparent layer may include laminating the IR reflecting layer to the optically transparent layer.

The method may further include forming a pressure sensitive adhesive layer or an optically clear adhesive layer between the optically clear layer and the IR reflecting layer.

Forming the optically transparent layer may include vacuum compression molding a fibrous polyethylene mat (fibrous polyethylene mat). The fibrous polyethylene mat may comprise a plurality of knitted or woven ultra-high molecular weight polyethylene fibers. The fibrous polyethylene mat may comprise a plurality of non-woven ultra-high molecular weight polyethylene fibers.

The method may further comprise deforming the layered structure to a compound curvature.

An exemplary polymer bilayer (e.g., film) may include a porous fluoropolymer layer and a stretched ultra-high molecular weight polyethylene (ultra-high molecular weight polyethylene, UHMWPE) layer. The polymer bilayer structure may be configured as a foam (PVDF)/membrane (UHMWPE) structure, a foam (PVDF)/foam (UHMWPE) structure, a foam (PVDF)/fibrous membrane (UHMWPE) structure, or even as a co-extruded core (PVDF foam)/shell (UHMWPE) fibrous structure. In some embodiments, the PVDF foam layer may be supported by a PVDF film layer. The polymer bilayer may be formed by lamination and may comprise or constitute a laminate. As used herein, the terms "polymer film" and "polymer layer" are used interchangeably. Furthermore, unless the context clearly indicates otherwise, reference to "a polymer film" or "a polymer layer" may include reference to "a polymer bilayer". Furthermore, for convenience, specific embodiments may be described herein with reference to polyvinylidene fluoride (PVDF) or Polyethylene (PE). However, it should be understood that embodiments directed to polyvinylidene fluoride or polyvinylidene fluoride films may be applicable to polyethylene or polyethylene films, and embodiments directed to polyethylene or polyethylene films may be applicable to polyvinylidene fluoride or polyvinylidene fluoride films.

The polymer bilayer may be co-integrated with the wearable device to provide a platform that achieves passive cooling during daytime use by combining the high emissivity of the fluoropolymer and the high transparency of the UHMWPE in the LWIR region. Furthermore, the high thermal conductivity of UHMWPE can reduce the tendency for thermal throttling by promoting heat dissipation over a larger surface area of the device, which may increase heat dissipation through convective heat transfer.

According to some embodiments, the porous fluoropolymer may include PVDF-based polymers, such as PVDF homopolymer, PVDF-CTFE, PVDF-HFP, PVDF-TFE, PVDF-TrFE, and PVDF-TrFE-TFE, and combinations and copolymers thereof, wherein CTFE is chlorotrifluoroethylene, HFP is hexafluoropropylene, TFE is tetrafluoroethylene, and TrFE is trifluoroethylene.

In some embodiments, the porous fluoropolymer may be characterized by a porosity of at least about 15vol.%, e.g., about 15vol.%, 20vol.%, 25vol.%, 30vol.%, 35vol.%, 40vol.%, 45vol.%, 50vol.%, 55vol.%, or 60vol.%, including a range between any of the foregoing values. The average pore size within the porous fluoropolymer may be at least about 100nm, such as 100nm, 200nm, 500nm, or 1000nm, including ranges between any of the foregoing values. The pore size distribution within the porous fluoropolymer layer may be unimodal, bimodal or polydisperse.

The porous fluoropolymer may be formed using a blowing agent suitable for creating porosity within the fluoropolymer layer. Exemplary blowing agents may include solid particles of: azodicarbonamide (ADC), p '-oxybisbenzenesulfonyl hydrazide (p, p' -oxybis-benzenesulfonyl hydrazide, OBSH) or sodium bicarbonate, and derivatives thereof. Another exemplary foaming agent may include supercritical CO ₂ . In another exemplary method, the porous fluoropolymer may be formed by reverse phase separation of a polymer solution in a non-solvent bath.

In some embodiments, the fluoropolymer layer may be characterized by a solar spectral reflectance of at least about 40%, such as 40%, 60%, 80%, 90%, 95%, 98%, or 99%, including ranges between any of the foregoing values, and a long wavelength infrared emissivity of at least about 40%, such as 40%, 60%, 80%, 90%, 95%, 98%, or 99%, including ranges between any of the foregoing values.

For example, the porous fluoropolymer may comprise high molecular weight polyvinylidene fluoride or ultra high molecular weight polyvinylidene fluoride. In some constructions, the porous fluoropolymer layer may have a thickness ranging from about 0.2mm to about 1.0mm, and at least one area dimension of at least about 1 cm.

The refractive index and temperature conditioning behavior, as well as other properties of the polymer film, can be determined by its chemical composition, the chemical structure of the polymer repeat units, its density and degree of crystallization, and the arrangement of crystals and/or polymer chains. Among these factors, the crystal or polymer chain arrangement may be dominant. In crystalline or semi-crystalline polymer films, the refractive index and temperature conditioning behavior may be related to the degree or extent of crystal orientation, while the degree or extent of chain alignment may produce a similar response in the amorphous phase within the polymer film.

The applied stress can be used to create a preferred arrangement of crystals or polymer chains within the polymer film and cause a corresponding change in properties along different directions of the film. As further disclosed herein, during the process of stretching a polymer film to cause a preferred arrangement of crystals/polymer chains and concomitant modification of one or more film properties, applicants have shown that the gel casting (gel casting) process and the associated liquid solvent selection can reduce the tendency of polymer chains within the cast film to entangle.

In accordance with certain examples, applicants have developed a polymer film manufacturing process for forming PVDF-based polymer films of high optical quality and emissivity with a desired temperature conditioning response. However, in PVDF and related polymers, the degree of total crystallization and crystal alignment may be limited due to entanglement of the polymer chains, as disclosed herein, the disentanglement and alignment of the polymer chains may be facilitated according to the gel casting method of the polymer solution.

The polymer solution may include one or more crystallizable polymers, one or more additives, and one or more liquid solvents. For example, gel casting may provide control of one or more of the following: the polymer composition and concentration, the choice and concentration of the liquid solvent, and the casting temperature, and may help reduce entanglement of the polymer chains and allow the polymer film to achieve higher elongation ratios (stretch ratios) during subsequent deformation steps. In some cases, one or more low molecular weight additives may be added to the polymer solution. The molecular weight distribution of the one or more crystalline polymers and the one or more additives may be mono-disperse, bimodal or polydisperse, respectively.

PVDF-based polymer films may be formed using crystallizable polymers. Exemplary crystallizable polymers may include moieties such as vinylidene fluoride (VDF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and Vinyl Fluoride (VF). As used herein, one or more of the foregoing "PVDF-family" sections may be combined with low molecular weight additives to form an anisotropic polymer film. References herein to PVDF films include references to any polymer film containing PVDF family members unless the context clearly indicates otherwise.

The crystallizable polymer component of such PVDF film may have a molecular weight ("high molecular weight") of at least about 100,000g/mol, for example, at least about 100,000g/mol, at least about 150,000g/mol, at least about 200,000g/mol, at least about 250,000g/mol, at least about 300,000g/mol, at least about 350,000g/mol, at least about 400,000g/mol, at least about 450,000g/mol, or at least about 500,000g/mol, including ranges between any of the foregoing values.

If a "low molecular weight" additive is provided, the molecular weight of the additive may be less than about 200,000g/mol, such as less than about 200,000g/mol, less than about 100,000g/mol, less than about 50,000g/mol, less than about 25,000g/mol, less than about 10,000g/mol, less than about 5000g/mol, less than about 2000g/mol, less than about 1000g/mol, less than about 500g/mol, less than about 200g/mol, or less than about 100g/mol, including ranges between any of the foregoing values.

Exemplary low molecular weight additives may include monomers, oligomers, and polymers of vinylidene fluoride (VDF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and Vinyl Fluoride (VF), as well as homopolymers, copolymers, terpolymers, derivatives, and combinations thereof. Such additives can be readily dissolved in the high molecular weight component and provide refractive indices that match the high molecular weight component. For example, the low molecular weight additive may have a refractive index ranging from about 1.38 to about 1.55 measured at 652.9 nm.

The molecular weight of the low molecular weight additive may be less than the molecular weight of the crystallizable polymer. According to one example, the crystallizable polymer may have a molecular weight of at least about 100,000g/mol, while the additive may have a molecular weight of less than about 25,000 g/mol. According to another example, the crystallizable polymer may have a molecular weight of at least about 300,000g/mol, while the additive may have a molecular weight of less than about 200,000 g/mol. According to a particular example, the crystallizable polymer may have a molecular weight of about 600,000g/mol, and the additive may have a molecular weight of about 150,000 g/mol. In some examples, the term "molecular weight" as used herein may refer to a weight average molecular weight.

Typically, the low molecular weight additive may constitute up to about 90wt.%, e.g., about 0.001wt.%, about 0.002wt.%, about 0.005wt.%, about 0.01wt.%, about 0.02wt.%, about 0.05wt.%, about 0.1wt.%, about 0.2wt.%, about 0.5wt.%, about 1wt.%, about 2wt.%, about 5wt.%, about 10wt.%, about 20wt.%, about 30wt.%, about 40wt.%, about 50wt.%, about 60wt.%, about 70wt.%, about 80wt.%, or about 90wt.% of the polymer film, including ranges between any of the foregoing values.

The choice of liquid solvent may affect the maximum crystallinity and the percentage of beta phase content of the PVDF-based polymer film. In addition, the polarity of the solvent may affect the critical polymer concentration (c) at which the polymer chains are entangled in the solution. The liquid solvent (i.e., the "solvent") may comprise a single solvent composition or a mixture of different solvents. In some embodiments, the crystallizable polymer may have a solubility in the liquid solvent of at least about 0.1g/100g (e.g., 1g/100g or 10g/100 g) at a temperature of 25 ℃ or higher (e.g., 50 ℃, 75 ℃, 100 ℃, or 150 ℃).

Exemplary liquid solvents include, but are not limited to, dimethylformamide (DMF), cyclohexanone, dimethylacetamide (DMAc), diacetone alcohol, diisobutylketone, tetramethylurea, ethyl acetoacetate, dimethyl sulfoxide (dimethyl sulfoxide, DMSO), trimethyl phosphate, N-methyl-2-pyrrolidone (N-methyl-2-pyrrosidone, NMP), butyrolactone, isophorone, triethyl phosphate, carbitol acetate, propylene carbonate, glyceryl triacetate, dimethyl phthalate, acetone, tetrahydrofuran (THF), methyl ethyl ketone, methyl isobutyl ketone, glycol ethers, glycol ether esters, and N-butyl acetate.

The polymer gel may be obtained from the polymer solution by evaporating the solvent, cooling the polymer solution, adding a relatively poor solvent to the polymer solution, or a combination thereof. The solubility of the crystalline polymer in the poor solvent may be less than 20g/100g, such as 5g/100g or 1g/100g, at a temperature of less than about 150 ℃ (e.g., 75 ℃, 25 ℃, 0 ℃, -40 ℃, or-70 ℃). The polymer gel (comprising a mixture of crystallizable polymer and liquid solvent) may be transparent, translucent or opaque. After gelation and prior to further processing (such as calendaring), the polymer gel may be washed with a secondary solvent that may replace the original solvent. A solvent evaporation step may be used to partially or completely remove the primary solvent and/or the secondary solvent.

An anisotropic polymer film, i.e., a polymer film comprising the polymer gel, may be formed by applying stress to the polymer gel. According to some examples, solid state extrusion processes may be used to orient polymer chains and form polymer films. According to a further example, a calendaring process may be used to orient the polymer chains in the gel at room temperature or at an elevated temperature. The solvent may be partially or fully removed before, during or after stretching and orienting.

The calendering process may be applied to the dried or partially dried gel prior to stretching. The gel may be calendered multiple times with a progressively smaller nip to achieve the target thickness. Any residual solvent may be removed during the calendaring process. The calendering process can be performed at room temperature and/or at a temperature of no greater than about 150 ℃ (e.g., 130 ℃, 110 ℃, 90 ℃, 70 ℃, or 50 ℃). The polymer may be stretched to an elongation ratio of at least about 1.5 (e.g., 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 15, 20, 30, or 50, including ranges between any of the foregoing values).

In an exemplary process, the dried or substantially dried polymeric material may be hot pressed to form a desired shape fed through a solid state extrusion system (i.e., extruder) at a suitable extrusion temperature. The hot pressing temperature and the extrusion temperature may both be less than about 190 ℃. That is, the hot pressing temperature and the extrusion temperature may be independently selected from: 180 ℃, 170 ℃, 160 ℃, 150 ℃, 140 ℃,130 ℃, 120 ℃, 110 ℃, 100 ℃, 90 ℃, or 80 ℃, including ranges between any of the foregoing values. According to particular embodiments, the extruded polymeric material may be further stretched, for example, using a post-extrusion uniaxial or biaxial stretching process. For example, the solid state extruder may include a bifurcated nozzle.

Stretching may include, for example, a single stretching action or multiple sequential stretching events along different in-plane directions of the polymer film. The stretching action may be limited in speed or may be limited in strain rate. In some embodiments, the polymer film may be stretched at a variable speed or a constant speed. In some embodiments, a variable strain rate or a constant strain rate (e.g., 0.5/second (sec), 1/second, 5/second, or 10/second, including ranges between any of the foregoing values) may be used to stretch the polymer film. For example, the strain rate may be reduced from an initial strain rate (e.g., 5/second) to a final strain rate (e.g., 0.5/second) throughout the stretching action and/or among different stretching events.

Some stretching processes may include two consecutive stretching events. For example, orthogonal continuous stretching (orthogonal consecutive stretching, OCS) can be used to develop structural fingerprints, such as smaller platelet thickness and higher degree of polymer chain orientation where the stretch ratio (draw ratio) is less than that used to achieve similar structural fingerprints via a comparative single-stretch (single stretching, SS) or parallel continuous stretch (parallel consecutive stretching, PCS) technique. Orthogonal continuous stretching may include stretching the polymer film first along a first in-plane axis and then subsequently stretching the polymer film along a second in-plane axis that is orthogonal to the first in-plane axis.

In one exemplary method, the cast polymeric film can be stretched along the first in-plane axis to an elongation ratio of at most about 4 (e.g., 2, 3, or 4, including ranges between any of the foregoing values), and with relaxation in the cross-machine direction stretch direction, the relaxation ratio is at least about 0.2 (e.g., 0.2, 0.3, 0.4, or 0.5, including ranges between any of the foregoing values). The polymer film may then be stretched to an elongation ratio of at least about 7 (e.g., 7, 10, 20, 30, 40, 50, or 60, including ranges between any of the foregoing values) along a second in-plane axis orthogonal to the first in-plane axis, and a relaxation ratio in the cross-direction stretch direction of at least about 0.2 (e.g., 0.2, 0.3, 0.4, or 0.5, including ranges between any of the foregoing values).

In some embodiments, the stretch ratio in the first stretching step may be less than the stretch ratio in the second stretching step. According to further embodiments, the temperature of the polymer film during the second stretching step may be higher than the temperature of the polymer film during the first stretching step. The temperature during the second stretching step may be at least about 5 ℃ (e.g., 5 ℃, 10 ℃, 15 ℃, or 20 ℃ higher than the temperature during the first stretching step, including ranges between any of the foregoing values).

In some embodiments, the PVDF polymer film may be heated and stretched in a first direction, cooled, and then heated and stretched in a second direction. In some embodiments, the polymer film may be heated and stretched in a first direction, cooled, and then heated and stretched again in the first direction. After the second stretching step, the PVDF polymer film may be cooled. The cooling action may be immediately followed by the first (or second) stretching step, wherein the polymer film may be cooled within about 10 seconds after completion of the first (or second) stretching step.

Cooling stabilizes the microstructure of the stretched polymer film. In some examples, the temperature of the polymer film during the stretching action may be above the glass transition temperature of the crystallizable polymer. In some examples, the temperature of the polymer film during the stretching action may be less than, equal to, or greater than the melt initiation temperature of the crystallizable polymer.

In various examples, the degree of relaxation perpendicular to the stretch direction may be approximately equal to the square root of the stretch ratio in the stretch direction. In some embodiments, the degree of relaxation may be substantially constant throughout the stretching process. In further embodiments, the degree of relaxation may be reduced, wherein a greater relaxation is associated with a beginning stretching step and a lesser relaxation is associated with an ending stretching step.

After extrusion or casting, the PVDF film may be uniaxially or bi-directionally oriented as a single layer or multiple layers to form an anisotropic and optically clear film. The anisotropic polymer film may be formed using a film orientation system configured to heat the polymer film in one or more different regions of the polymer film and to stretch the polymer film in at least one in-plane direction. In some embodiments, the film orientation system may be configured to stretch the polymer film (i.e., the crystallizable polymer film) in only one in-plane direction. For example, the film orientation system may be configured to apply in-plane stress to the polymer film along the x-direction while allowing the film to relax along an orthogonal in-plane direction (e.g., along the y-direction). As used herein, in some examples, relaxation of a polymer film may be accompanied by the absence of applied stress along the relaxation direction.

According to some embodiments, within an exemplary orientation system, a polymer film may be heated and stretched transverse to the direction of film travel through the system. In such an embodiment, the polymer film may be held along the opposing edges by a plurality of movable clips slidably disposed along the divergent track system such that the polymer film is stretched in the transverse direction (transverse direction, TD) as it moves in the longitudinal direction (machine direction, MD) through the heating and deforming zones of the film orientation system. In some embodiments, the rate of stretching in the transverse direction and the rate of relaxation in the longitudinal direction may be independently and locally controlled. In certain embodiments, mass production may be achieved, for example, using a roll-to-roll manufacturing platform.

In certain aspects, the tensile stress may be applied uniformly or non-uniformly along the longitudinal or transverse dimensions of the polymer film. The heating of the polymer film may be accompanied by the application of a tensile stress. For example, semi-crystalline PVDF polymer films may be heated to temperatures above room temperature (about 23 ℃) to facilitate deformation of the film and formation and rearrangement of crystals and/or polymer chains therein.

The temperature of the polymer film may be maintained at a desired value or within a desired range before, during and/or after the stretching action, i.e. in the preheating zone or in a deformation zone downstream of the preheating zone, in order to improve the deformability of the polymer film relative to the unheated polymer film. The temperature of the polymer film in the deformation zone may be less than, equal to, or greater than the temperature of the polymer film in the preheating zone.

In some embodiments, the polymer film may be heated to a constant temperature throughout the stretching action. In some embodiments, one region of the polymer film may be heated to different temperatures, i.e., during and/or after the application of the tensile stress. In some embodiments, different regions of the polymer film may be heated to different temperatures. In certain embodiments, the strain achieved in response to an applied tensile stress may be at least about 20%, such as about 20%, about 50%, about 100%, about 200%, about 400%, about 500%, about 1000%, about 2000%, about 3000%, or about 4000% or more, including ranges between any of the foregoing values.

After one or more stretching actions, one or more film properties may be improved by hot pressing or hot calendaring. For example, uniaxial hot pressing may be performed in a rigid mold that applies a load along a common axis. Some compression systems may include a graphite mold, which may be enclosed in a protective atmosphere chamber or vacuum chamber. During the hot pressing process, temperature and pressure may be simultaneously applied to the stretched polymer film. Heating may be accomplished using an induction coil surrounding the graphite mold and pressure may be applied hydraulically. Calendering is a process in which a polymer film is compressed during production by passing the film between one or more pairs of heated rolls.

In some embodiments, the stretched polymeric film can be pressed or calendered to at least about 50% of its initial thickness (e.g., 50%, 60%, 70%, or 80% of its initial thickness, including ranges between any of the foregoing values) at an applied pressure of at least about 2MPa (e.g., 2MPa, 3MPa, 4MPa, 5MPa, or 10MPa, including ranges between any of the foregoing values) and at a temperature of less than about 140 ℃ (e.g., 120 ℃, 125 ℃, 130 ℃, or 135 ℃, including ranges between any of the foregoing values).

The thickness of the pressed or calendered polymer film may be less than about 500 micrometers, for example less than 400 micrometers, less than 300 micrometers, or less than 200 micrometers. According to some embodiments, after hot pressing or hot calendering, the polymer film may be further stretched using one or more additional stretching steps. In the post-hot press or post-hot calender stretching step, the polymer film may be stretched to a stretch ratio of about 5 or greater (e.g., 5, 10, 20, 40, 60, 80, 100, 120, or 140, including ranges between any of the foregoing values).

Hot pressing or hot calendaring can increase the transmittance of the polymer film and reduce haze. According to some embodiments, the applied pressure may collapse voids within the polymer film, thereby reducing the total void volume and increasing the density of the polymer matrix.

After the polymer film is deformed, the heating may be maintained for a predetermined amount of time and then the polymer film may be cooled. The cooling action may include allowing the polymer film to cool naturally at a set cooling rate, or by quenching (e.g., by purging with a cryogenic gas), which may thermally stabilize the polymer film. During the cooling action, the polymer film may relax by about 5% or more, such as about 10%.

After deformation, the crystals or chains may be at least partially aligned with the direction of the applied tensile stress. Thus, the polymer film may exhibit high optical clarity and mechanical anisotropy.

The presently disclosed anisotropic PVDF-based polymer films may be characterized as optical quality polymer films and may be formed or incorporated into optical elements (e.g., actuatable layers). The optical element may be used in a variety of display devices, such as Virtual Reality (VR) glasses, VR headset, augmented Reality (AR) glasses, and AR headset.

According to various embodiments, an "optical quality" film may be characterized in some examples by a transmittance of at least about 20% (e.g., 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%, including ranges between any of the foregoing values) and a bulk haze (bulk haze) of less than about 10% (e.g., 0%, 1%, 2%, 4%, 6%, or 8%, including ranges between any of the foregoing values) in the visible spectrum. Transparent materials generally exhibit very low absorbance and minimal light scattering.

As used herein, the terms "haze" and "clarity" may refer to optical phenomena associated with light transmission through a material, and may be due to, for example, light refraction within the material, for example, due to secondary phases or porosities and/or light reflection from one or more surfaces of the material. As will be appreciated by those skilled in the art, haze may be associated with an amount of light that experiences wide angle scattering (i.e., an angle greater than 2.5 ° from normal) and a corresponding loss of transmission contrast, while sharpness may be associated with an amount of light that experiences narrow angle scattering (i.e., an angle less than 2.5 ° from normal) and a concomitant loss of optical sharpness or "see-through quality.

According to some embodiments, the area dimensions (i.e., length and width) of the anisotropic PVDF family polymer film may independently be in the range of about 5cm to about 50cm or more, such as 5cm, 10cm, 20cm, 30cm, 40cm, or 50cm, including ranges between any of the foregoing values. Exemplary anisotropic polymer films can have an area size of about 5cm by 5cm, 10cm by 10cm, 20cm by 20cm, 50cm by 50cm, 5cm by 10cm, 10cm by 20cm, 10cm by 50cm, etc.

According to various embodiments, a polymer composition for forming an anisotropic polymer film may include a crystallizable polymer and a low molecular weight additive. Without being bound by theory, one or more low molecular weight additives may interact with the high molecular weight polymer throughout the casting and stretching process to help reduce chain entanglement and achieve better chain alignment, and in some examples, higher crystalline content within the polymer film.

In some examples, a composition having a bimodal molecular weight distribution may be cast to form a film that may be stretched to induce mechanical and piezoelectric anisotropy through crystal and/or chain rearrangement. Stretching may include applying uniaxial or biaxial stress. In some embodiments, the application of in-plane biaxial stress may be performed simultaneously or sequentially. In some embodiments, the low molecular weight additives may advantageously reduce the stretching temperature required to achieve crystal and/or chain rearrangement. In some embodiments, the polymer film may be stretched by calendaring, solid state extrusion, and/or combinations thereof.

According to various embodiments, an anisotropic PVDF-based polymer film may be formed by applying a desired stress state to a crystallizable polymer film. The polymer composition capable of crystallizing may be formed into a monolayer using a suitable gel casting operation. For example, a composition containing vinylidene fluoride may be cast and oriented as a monolayer to form a mechanically and/or optically anisotropic film. According to further embodiments, the crystallizable polymer may be cast to form a film, and such film may be laminated to form a bilayer structure.

In some embodiments, a polymer film having a bimodal molecular weight distribution can be stretched to a greater elongation ratio than a comparative polymer film (i.e., lacking the low molecular weight additive). In some examples, the elongation ratio may be greater than 4, such as 5, 10, 20, 40, or greater. The stretching action may comprise a single stretching step or multiple (i.e., continuous) stretching steps, wherein one or more of the stretching temperature and strain rate may be independently controlled.

In an exemplary method, the polymer film may be heated to a temperature from about 60 ℃ to about 170 ℃ during stretching and stretched at a strain rate of about 0.1%/sec to about 300%/sec. Further, one or both of the temperature and strain rate may remain the same or vary during the stretching action. For example, the polymer film may be stretched at a first temperature and a first strain rate (e.g., 130 ℃ and 50%/second) to achieve a first elongation ratio. Subsequently, the temperature of the polymer film may be increased and the strain rate may be decreased until a second temperature and a second strain rate (e.g., 165 ℃ and 5%/second) are achieved to achieve a second elongation ratio.

Such stretched polymer films may exhibit higher crystallinity and higher modulus of elasticity. For example, an oriented polymer film having a bimodal molecular weight distribution may have an in-plane elastic modulus of greater than about 2GPa (e.g., 3GPa, 5GPa, 10GPa, 12GPa, or 15GPa, including ranges between any of the foregoing values).

According to some embodiments, the crystalline content of the anisotropic polymer film may include, for example, crystals of poly (vinylidene fluoride), poly (trifluoroethylene), poly (chlorotrifluoroethylene), poly (hexafluoropropylene), and/or poly (vinyl fluoride), although other crystalline polymer materials are contemplated, wherein in some examples, the crystalline phase in the "crystalline" or "semi-crystalline" polymer film may comprise at least about 1% of the polymer film. For example, the crystalline content (e.g., beta phase content) of the polymer film may be at least about 1%, such as 1%, 2%, 4%, 10%, 20%, 40%, 60%, or 80%, including ranges between any of the foregoing values.

In some embodiments, the polymer film may be annealed after stretching. The annealing may be performed at a fixed or variable elongation ratio and/or a fixed or variable applied stress. Exemplary annealing temperatures may be greater than about 80 ℃, such as 100 ℃, 130 ℃, 150 ℃, 170 ℃, or 190 ℃, including ranges between any of the foregoing values. Without being bound by theory, annealing may stabilize the orientation of the polymer chains and reduce the shrinkage tendency of the polymer film.

After deformation, the crystals or chains may be at least partially aligned with the direction of the applied tensile stress. Thus, the polymer film may exhibit a high degree of birefringence, high optical clarity, a bulk haze of less than about 10%, a high piezoelectric coefficient (e.g., d ₃₁ Greater than about 5 pC/N) and/or a high electromechanical coupling coefficient (e.g., k) ₃₁ Greater than about 0.1).

In an exemplary experiment, PVDF resin was completely dissolved in various liquid solvents including DMF, cyclohexanone (CH), and a mixture of DMF and cyclohexanone. In one example, a 10wt.% solution of PVDF in DMF was prepared with continuous stirring at 60 ℃ (sample 1). In another example, a 10wt.% solution of PVDF in cyclohexanone was prepared with continuous stirring at 90 ℃ (sample 4). Other 10wt.% resin solutions (sample 2 and sample 3) were prepared using 50-50w/w solvent mixtures of DMF and cyclohexanone with continuous stirring at 80 ℃.

The corresponding samples 1-4 were kept stirring at the target temperature for 3 hours until the solution was clear. The solution was then poured into a separate container and a gel formed in a period of about 1 hour. After gelation, the gel was washed with methanol (5 times) to remove residual solvent. The washed gel was stored overnight in a fume hood to evaporate the methanol and obtain a dry white gel.

The dried gel was treated using a continuous calendering step at room temperature, with the nip decreasing with each successive pass through the calendering apparatus. The transparent film is obtained at an elongation ratio in the range of about 2 to about 5.

The calendered polymer film was heated, stretched, and then the crystalline content was measured. The stretching action included locally heating the film sample to 140 ℃, beginning to apply stress, and increasing the temperature to a target stretching temperature of about 160 ℃ at a rate of 5 ℃/minute until an applied stress of 250MPa was reached, then further increasing the film temperature to 170 ℃ at a rate of 1 ℃/minute while maintaining a stress of 250 MPa. The elongation ratio is between 10 and 12. The unannealed film is then cooled to below 40 ℃ before the applied stress is removed.

In some embodiments, the stretched film may be annealed. For example, after reaching a temperature of 170 ℃, the temperature may be further increased to an annealing temperature of 195 ℃ at a rate of 0.5 ℃/min under a constant applied stress of 250 MPa. The sample may be held at 195 ℃ for 40 minutes. The annealing process may increase the elongation ratio to a value greater than 12, for example from 12 to 15. The annealed sample may be cooled to below 40 ℃ prior to removal of the applied stress.

After cooling, the total crystallinity was measured using differential scanning calorimetry (differential scanning calorimetry, DSC) and the relative beta phase ratio was determined using fourier transform infrared spectroscopy (Fourier Transform Infrared Spectroscopy, FTIR). Absolute beta crystallinity is calculated as the product of total crystallinity and relative beta ratio. Modulus (i.e., storage modulus) is measured by dynamic mechanical analysis (dynamic mechanical analysis, DMA). The data in table 1 shows that gel castings using poor solvents (sample 4) can achieve higher moduli after stretching than gel castings using good solvents (sample 1). Furthermore, annealing can also increase the total crystalline content and modulus of the stretched films (sample 2 and sample 3).

Table 1: effect of solvents and annealing on PVDF film properties

In some examples, the stress applied during stretching may be in the range of about 100MPa to about 500MPa, such as 100MPa, 150MPa, 200MPa, 250MPa, 300MPa, 350MPa, 400MPa, 450MPa, or 500MPa, including ranges between any of the foregoing values. In another exemplary experiment using cyclohexane as a solvent, the film was stretched at a maximum applied stress of about 400 MPa.

According to various embodiments, the anisotropic polymer film may include a fibrous material, an amorphous material, a partially crystalline material, or a fully crystalline material. Such materials may also be mechanically anisotropic, where one or more characteristics may include compressive strength, tensile strength, shear strength, yield strength, stiffness, hardness, toughness, ductility, machinability, thermal expansion, piezoelectric response, and creep behavior may be direction dependent.

The polymer composition having a bimodal molecular weight can be formed into a monolayer using a casting operation. Alternatively, the polymer composition having a bimodal molecular weight can be cast with other polymers or other non-polymeric materials to form a multilayer polymeric film. Application of uniaxial or biaxial stress to the gel cast monolayer or multilayer film may be used to align the polymer chains and/or redirect the crystals to induce mechanical, optical and/or temperature-regulated anisotropy therein.

The crystallizable polymer and the low molecular weight additive may be independently selected to include vinylidene fluoride (VDF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), vinyl Fluoride (VF), and homopolymers, copolymers, terpolymers, derivatives, and combinations thereof. The high molecular weight component of the polymer film may have a molecular weight of at least 100,000g/mol, while the low molecular weight additive may have a molecular weight of less than 200,000g/mol and may constitute 0.1wt.% to 90wt.% of the polymer film.

The polyethylene layer may comprise "ultra high" molecular weight polyethylene (UHMWPE), and the polyethylene layer may be characterized by a molecular weight of at least about 300,000g/mol, such as at least about 300,000g/mol, at least about 500,000g/mol, at least about 1,000,000g/mol, at least about 2,000,000g/mol, or at least about 5,000,000g/mol, including ranges between any of the foregoing values.

In further embodiments, the polyethylene layer may include a low molecular weight wax, such as 50wt.% or more of a low molecular weight wax. In some embodiments, the polyethylene layer may have a thickness from about 10 microns to about 1mm, and at least one area dimension of at least about 1 cm. In an exemplary polymer bilayer, the thickness of the polyethylene layer may be less than the thickness of the porous fluoropolymer layer.

The polyethylene layer may be dense or porous. The porous polyethylene layer may be characterized by a porosity of at least about 1vol.%, e.g., about 1vol.%, 2vol.%, 4vol.%, 10vol.%, 15vol.%, 20vol.%, 25vol.%, 30vol.%, 35vol.%, 40vol.%, 45vol.%, 50vol.%, 55vol.%, or 60vol.%, including ranges between any of the foregoing values. The average pore size within the porous polyethylene layer may be at least about 50nm, such as 50nm, 100nm, 200nm, or 500nm, including ranges between any of the foregoing values, and the pore size distribution within the polyethylene layer may be unimodal, bimodal, or polydisperse.

The polyethylene layer may include an antioxidant. Exemplary antioxidants can include oligomers of hindered phenols, phosphites, thiosynergists, hydroxylamines, and hindered amine light stabilizers (hindered amine light stabilizer, HALS).

The polyethylene layer may include a pigment. Exemplary pigments may include nanoscale particles (e.g., average particle size less than about 200nm, e.g., less than 200nm, less than 100nm, or less than 50nm, including ranges between any of the foregoing values), and may include, for example, organic dyes (such as sudan blue, sudan red, or Su Danhei); metal oxides (e.g., iron chromium oxide); perylene black. In some embodiments, such IR reflecting pigments may be incorporated into an IR reflecting layer, such as an IR reflecting paint layer overlying a polyethylene layer.

In some embodiments, the polyethylene layer may be characterized by a near infrared reflectance of at least about 40%, such as at least 40%, 60%, or 80%, including ranges between any of the foregoing values. In some embodiments, the polyethylene layer may be characterized by a long wavelength infrared transmittance of at least about 40%, such as at least 40%, 60%, or 80%, including ranges between any of the foregoing values.

In some embodiments, the polyethylene layer may be characterized by a thermal conductivity of at least about 5W/mK, such as 5W/mK, 10W/mK, 15W/mK, 20W/mK, or 25W/mK, including ranges between any of the foregoing values.

In some embodiments, the polyethylene layer may be characterized by a Young's modulus of at least about 2GPa, such as 2GPa, 5GPa, 10GPa, 20GPa, 50GPa, 100GPa, or 150GPa, including ranges between any of the foregoing values, and a tensile strength of at least about 0.7GPa, such as 0.7GPa, 1GPa, 2GPa, or 3GPa, including ranges between any of the foregoing values.

The fluoropolymer layer and the polyethylene layer may be formed together continuously or separately according to various methods. In the latter case, the fluoropolymer and polyethylene films having high or ultra-high molecular weight may be independently stretched to a stretch ratio of at least 5 and then laminated to form a polymer bilayer, for example, using an optically clear adhesive or a pressure sensitive adhesive. Exemplary adhesives may be acrylic-based or epoxy-based.

An exemplary method includes forming a first layer including a porous fluoropolymer and forming a second layer including polyethylene directly on the first layer to form a polymer bilayer. In some embodiments, the polymer bilayer may be shaped to a compound curvature.

Casting operations such as melt extrusion, compression molding, solvent casting, gel casting, and the like may be used to form the polymer film. Applicants have demonstrated that enhanced stretchability can be achieved by adjusting one or more of the stretching temperature and stretching rate of the cast polymer film. In some examples, the stretching temperature may be related to the main (glass, or α) relaxation of the film and/or its low temperature (β) relaxation.

In some embodiments, the polymer, such as polyethylene, may be provided in the form of particles or powder. The particle size distribution (d 90) of exemplary polyethylene powders may be greater than about 50 microns, such as greater than 50 microns, 100 microns, 200 microns, or 300 microns, including ranges between any of the foregoing values.

If a low molecular weight additive is used, the low molecular weight additive may be provided in the form of particles or powder, and the particle size distribution (d 90) of the low molecular weight additive may be less than about 30 microns, such as 5 microns, 10 microns, 15 microns, 20 microns, or 25 microns, including ranges between any of the foregoing values. For example, the additive may comprise wax or a waxy material.

In some embodiments, the granular or powdered polyethylene may be mixed with the granular or powdered wax in a continuous mixer (LCM) at any suitable temperature. For example, the mixing temperature may be less than, equal to, or greater than the melting temperature of the wax (additive). The mixing may be adapted to impregnate the polyethylene with wax prior to casting to form a homogeneous mixture.

In some examples, a mixture of "non-entangled" polyethylene and low molecular additives may be extruded at a temperature below about 140 ℃ (e.g., 120 ℃ or 130 ℃) and above the melting point of the additives to form a polymer film. For example, the mixture may be extruded into a paste (i.e., a paste extrudate) at a temperature below the melting temperature of the unentangled polyethylene. The extruded film can have a thickness of less than about 2mm (e.g., 500 microns, 750 microns, or 1mm, including ranges between any of the foregoing values) and a porosity of less than about 10% (e.g., less than 5%, less than 2%, or less than 1%). In some embodiments, "untangled polyethylene" may refer to such high molecular weight polyethylene: it has an entanglement density less than, for example, from about 10% to about 80% of the equilibrium entanglement density, for example 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80% of the equilibrium entanglement density, including ranges between any of the foregoing values.

In an exemplary melt extrusion process, the melt may undergo pre-orientation at a Draw Down Ratio (DDR) of at least about 1 (e.g., about 1, about 2, about 3, or about 4, including ranges between any of the foregoing values). The melt may be collected on cooled rolls. The roll temperature may be below the lowest melting point of any additives included in the melt (e.g., at least about 10 ℃ below the lowest melting point of any additives included in the melt). The cast polymer may be subjected to a machine direction orientation (machine direction orientation, MDO) process to form a hard cast film having a draw ratio along the Machine Direction (MDX) of at least about 2 (e.g., at least about 2, at least about 4, or at least about 6, including ranges between any of the foregoing values).

According to further embodiments, the polymer film may be formed from a dilute solution comprising the polymer composition and the first solvent by gel casting, and then the solvent is removed. Exemplary solvents include poor solvents such as mineral oil, paraffinic oil, stearic acid, para-xylene, dodecanol, and the like. The first solvent may be removed before, during, and/or after one or more stretching actions. The first solvent may be removed directly by evaporation or by contact with a miscible second solvent followed by evaporation of the resulting co-solvent.

The cast polymer film may be stretched using a single event or multiple stretching events. Some stretching processes may include two consecutive stretching events. For example, orthogonal Continuous Stretching (OCS) may be used to develop structural fingerprints, such as smaller sheet thickness and higher degree of polymer chain orientation where the stretch ratio is smaller than that used to achieve similar structural fingerprints via either the comparative Single Stretch (SS) or Parallel Continuous Stretch (PCS) techniques. Orthogonal continuous stretching may include stretching the polymer film first along a first in-plane axis and then subsequently stretching the polymer film along a second in-plane axis that is orthogonal to the first in-plane axis.

In an exemplary OCS process, the cast polymer film may be stretched to an elongation ratio of at most about 4 (e.g., 2, 3, or 4, including ranges between any of the foregoing values) along a first in-plane axis, and with relaxation in the transverse stretching direction, the relaxation ratio is at least about 0.2 (e.g., 0.2, 0.3, 0.4, or 0.5, including ranges between any of the foregoing values). The polymer film may then be stretched to an elongation ratio of at least about 7 (e.g., 7, 10, 20, 30, 40, 50, or 60, including ranges between any of the foregoing values) along a second in-plane axis orthogonal to the first in-plane axis, and a relaxation ratio in the cross-direction stretch direction of at least about 0.2 (e.g., 0.2, 0.3, 0.4, or 0.5, including ranges between any of the foregoing values).

In some embodiments, the polyethylene film may be heated and stretched in a first direction, cooled, and then heated and stretched in a second direction. In some embodiments, the polymer film may be heated and stretched in a first direction, cooled, and then heated and stretched again in the first direction. After the second stretching step, the polyethylene film may be cooled. The cooling action may be immediately followed by the first (or second) stretching step, wherein the polyethylene film may be cooled within about 10 seconds after completion of the first (or second) stretching step. In some examples, the temperature of the polymer film during the stretching action may be above the glass transition temperature of the polymer. In some examples, the temperature of the polymer film during the stretching action may be less than, equal to, or greater than the melt initiation temperature of the polymer.

Exemplary polymers may include Ultra High Molecular Weight Polyethylene (UHMWPE). According to some embodiments, the optical properties of UHMWPE may be improved in connection with the treatment methods disclosed herein by reducing or eliminating surface defects and/or bulk defects. In some embodiments, one or more low melting point additives may be incorporated into the polymer matrix of the polymer film.

Exemplary polyethylene materials include high molecular weight polyethylene, high density polyethylene, ultra high molecular weight polyethylene, and derivatives and mixtures thereof, and may have a molecular weight (e.g., weight average molecular weight) of at least about 100,000g/mol, such as at least about 100,000g/mol, or at least about 250,000 g/mol. The ultra-high molecular weight polyethylene may have a molecular weight of at least about 300,000g/mol, such as about 300,000g/mol, about 400,000g/mol, about 500,000g/mol, about 600,000g/mol, about 700,000g/mol, about 800,000g/mol, about 900,000g/mol, about 1,000,000g/mol, about 2,000,000g/mol, or about 5,000,000g/mol, including ranges between any of the foregoing values.

In some embodiments, the polymer film comprising high molecular weight polyethylene may additionally comprise from about 5wt.% to about 50wt.% (e.g., about 5wt.%, about 10wt.%, about 20wt.%, or about 50wt.%, inclusive of ranges between any of the foregoing values) of a secondary polymer having a molecular weight of less than about 50,000g/mol (e.g., less than about 50,000g/mol, less than about 20,000g/mol, or less than about 10,000g/mol, inclusive of ranges between any of the foregoing values).

In some embodiments, the polymer film may include a low molecular weight additive. The additive may comprise low molecular weight polyethylene or polyethylene oligomers and may constitute from about 1wt.% to about 90wt.% of the polymer matrix forming the polymer film. The additives may have good solubility in high molecular weight polyethylene, high density polyethylene or ultra high molecular weight polyethylene and may be index matched to them.

Exemplary additives may include one or more of the following: hydrocarbon waxes (e.g., polyethylene-wax molecules or amide waxes), mineral oils, fluoropolymers, and the like. The molecular weight of the polyethylene-wax molecules, if used, may be at least about 400g/mol, such as 400g/mol, 1000g/mol, 2000g/mol, or 3000g/mol, including ranges between any of the foregoing values. The wax content may be at least about 2wt.%, e.g., 2wt.%, 5wt.%, 10wt.%, 20wt.%, 50wt.%, or 80wt.%, including ranges between any of the foregoing values. Suitable mineral oils may have a molecular weight of at least about 200g/mol, such as 200g/mol, 400g/mol, or 600g/mol, including ranges between any of the foregoing values. In some embodiments, up to about 1000ppm (e.g., 200ppm, 400ppm, 600ppm, 800ppm, or 1000 ppm) of fluoropolymer or other processing aid may be incorporated into the polymer matrix. The additives may be characterized by a refractive index of about 1.5 to about 1.6 (e.g., 1.55).

In some embodiments, the additives incorporated into the polymer matrix may include photothermal dyes. Exemplary photothermal dyes include 2- (2H-benzotriazol-2-yl) -4, 6-di-tert-amylphenol (BZT), azobenzene, coronatine dye, graphene, tetra-naphtalene-based dye, and metal nanoparticles (e.g., gold nanoparticles) and mixtures thereof. Photothermal dyes such as azobenzene or metal nanoparticles may be tubular by ethylene oligomers having a molecular weight of at least about 500g/mol (e.g., 500g/mol, 1000g/mol, 2000g/mol, or 3000g/mol, including ranges between any of the foregoing values). In some examples, the concentration of the photo-thermal additive within the polymer matrix may be at least about 0.5wt.%, e.g., 0.5wt.%, 1wt.%, 2wt.%, or 5wt.%, including ranges between any of the foregoing values. The tube-energized photothermal dye may be added to the polyethylene prior to or during the formation of the film, which may be stretched to form a dichroic arrangement of the dye in the polyethylene matrix.

In some embodiments, optical and mechanical properties may be particularly addressed, and the polymer film may comprise from about 60wt.% to about 90wt.% of a low molecular weight polyethylene or polyethylene oligomer. In some embodiments, thermal conductivity may be particularly targeted, and the polymer film may comprise about 1wt.% to about 10wt.% of low molecular weight polyethylene or polyethylene oligomer.

The thermal conductivity of the thermally conductive additive may be at least about 5W/mK, for example 5W/mK, 10W/mK, 15W/mK, 20W/mK, 25W/mK, 30W/mK, 35W/mK, 40W/mK, 45W/mK, 50W/mK or more, including ranges between any of the foregoing values. Exemplary thermally conductive additives include graphene, boron alkene, boron nitride (hexagonal BN), carbon nanotubes, silver nanowires, and metal nanoparticles, such as high aspect ratio metal nanoparticles. According to some embodiments, the loading of the thermally conductive additive may be in the range of about 0.01wt.% to about 1 wt.%. For example, phenolic benzotriazoles can form pi-pi interactions with polymer chains in polyethylene polymers and allow phonons to pass at very low loadings without affecting optical quality.

The molecular weight of the low molecular weight additive may be less than about 4,000g/mol, such as less than about 4,000g/mol, less than about 2,000g/mol, less than about 1,000g/mol, less than about 500g/mol, or less than about 200g/mol. Exemplary low molecular weight additives may be characterized by a melting temperature (T _m ) At least about 40 ℃, such as about 40 ℃, about 60 ℃, about 80 ℃, about 100 ℃, or about 120 ℃, including ranges between any of the foregoing values. Reference is made herein to the melting temperature (T _m ) Reference may be made to a temperature corresponding to the onset of melting.

Exemplary polyethylene polymers and oligomer-based additives may include reactive groups such as vinyl, acrylate, methacrylate, epoxy, isocyanate, hydroxyl, amine, and the like. Such additives may be cured in situ, i.e., within the polymer film by application of one or more of heat or light, or by reaction with a suitable catalyst.

In some embodiments, a variety of additives may be used. According to particular embodiments, the primary additives may be used during film processing (e.g., during extrusion, stretching, and/or calendaring). Thereafter, the primary additive may be removed, such as by washing or evaporation, and replaced by a secondary additive. The secondary additives (e.g., various phenolic benzotriazoles) may be index matched to the crystalline polyethylene polymer and may, for example, have an index of refraction from about 1.45 to about 1.6. The secondary additives may be added by soaking the film under melt conditions or in a solvent bath. The secondary additive may have a melting point below about 100 ℃.

If a secondary additive is used, the secondary additive may be a poor solvent for the polyethylene. Exemplary poor solvents may include stearic acid or saturated hydrocarbons, such as mineral oils (e.g., Mineral oil, paraffin oil, primol ^TM Oil, etc.). The secondary additives may be removed before, during or after the film stretching process, for example by evaporation or solvent exchange.

In some embodiments, the polyethylene layer may include a mat-like layer (matted layer), such as a fibrous polyethylene mat formed from ultra-high molecular weight polyethylene fibers, such as a knitted, woven or non-woven mat. For example, a mat-like polyethylene layer may be formed using vacuum compression molding of PE fibers. Exemplary processing conditions for vacuum compression molding include applying a pressure of at least about 200bar (bar) (e.g., 200bar, 500bar, 1000bar, 2000bar, or 4000bar, including ranges between any of the foregoing values) and a temperature of at least about 120 ℃ (e.g., 120 ℃, 130 ℃, 140 ℃, 150 ℃, or 160 ℃, including ranges between any of the foregoing values) over a suitable time.

According to other examples, the non-woven PE layer may comprise a fibrous mat, wherein the mat is knitted from UHMWPE fibers and then consolidated at high pressure (e.g. 10bar, 20bar, 40bar or 60 bar) and high temperature (e.g. 60 ℃, 80 ℃, 100 ℃,120 ℃ or 140 ℃). The polyethylene fibers may be coated with an unentangled PE powder prior to consolidation, wherein the powder may have a surface coverage of from about 10g/m ² To about 100g/m ² For example 10g/m ² 、20g/m ² 、40g/m ² Or 100g/m ² 。

The presently disclosed polymer films may be characterized as optical quality polymer films and may be formed or incorporated into optical elements. Such optical elements may be used in a variety of display devices, such as Virtual Reality (VR) glasses, VR headset, augmented Reality (AR) glasses, AR headset, mixed Reality (MR) glasses, and MR headset. The efficiency of these and other optical elements may depend on the degree of optical clarity and/or one or more mechanical properties of the polymer film.

For a given thickness, a "transparent" or "optically transparent" material or element may have a transmittance of at least about 85% (e.g., about 85%, 90%, 95%, 97%, 98%, 99% or 99.5%, inclusive of ranges between any of the foregoing values) and a bulk haze of less than about 5% (e.g., about 0.1%, 0.2%, 0.5%, 1%, 2%, or 5%, inclusive of ranges between any of the foregoing values) in the visible (e.g., 380nm-750 nm) and/or RF (e.g., 2GHz-20 GHz) spectrum. Transparent materials generally exhibit very low absorbance and minimal light scattering.

After extrusion or casting, the polyethylene film may be unidirectionally or bi-directionally oriented as a monolayer to form a mechanically anisotropic and optically transparent film that may also exhibit anisotropy in thermal conductivity. The anisotropic polymer film may be formed using a film orientation system configured to heat the polymer film in one or more different regions of the polymer film and to stretch the polymer film in at least one in-plane direction. In some embodiments, the film orientation system may be configured to stretch the polymer film (i.e., the crystallizable polymer film) in only one in-plane direction. For example, the film orientation system may be configured to apply in-plane stress to the polymer film along the x-direction while allowing the film to relax along an orthogonal in-plane direction (e.g., along the y-direction). As used herein, in some examples, relaxation of a polymer film may be accompanied by the absence of applied stress along the relaxation direction.

According to some embodiments, within an exemplary orientation system, a polymer film may be heated and stretched transverse to the direction of film travel through the system. In such an embodiment, the polymer film may be held along the opposing edges by a plurality of movable grippers slidably disposed along a diverging track system such that the polymer film is stretched in the Transverse Direction (TD) as it moves in the Machine Direction (MD) through the heating and deforming regions of the film orientation system. In some embodiments, the rate of stretching in the transverse direction and the rate of relaxation in the longitudinal direction may be independently and locally controlled. In certain embodiments, mass production may be achieved, for example, using a roll-to-roll manufacturing platform.

In certain aspects, the tensile stress may be applied uniformly or non-uniformly along the longitudinal or transverse dimensions of the polymer film. The heating of the polymer film may be accompanied by the application of a tensile stress. For example, semi-crystalline polymer films may be heated to temperatures above room temperature (about 23 ℃) to facilitate deformation of the film and formation and rearrangement of crystals and/or polymer chains therein.

During the stretching action, the crystalline content in the polymer film may increase. In some embodiments, stretching can change the orientation of crystals within the polymer film without substantially changing the crystalline content.

In some embodiments, a protective layer may be formed on one or both major surfaces of the polymer film. The one or more protective layers may include organic or inorganic materials and may protect the polymer film from surface damage or debris (e.g., scratches or dust). One or more protective layers, if provided, may be removed prior to one or more stretching actions, or one or more protective layers may be removed after stretching. In various examples, one or more removable protective layers may have a 90 ° peel strength of at least about 10g/cm width (e.g., 10g/cm, 20g/cm, 50g/cm, 100g/cm, 200g/cm, 500g/cm, 1000g/cm width, or greater).

After one or more stretching actions, one or more film properties may be improved by hot pressing or hot calendaring. For example, uniaxial hot pressing may be performed in a rigid mold that applies a load along a common axis. Some compression systems may include a graphite mold, which may be enclosed in a protective atmosphere chamber or vacuum chamber. During the hot pressing process, temperature and pressure may be simultaneously applied to the stretched polymer film. Heating may be accomplished using an induction coil surrounding the graphite mold and pressure may be applied hydraulically. Hot calendaring is a process in which a polymer film is compressed during production by passing the film between one or more pairs of heated rolls.

In some embodiments, the stretched polymeric film can be pressed or calendered to at least about 50% of its initial thickness (e.g., 50%, 60%, 70%, or 80% of the initial thickness, including ranges between any of the foregoing values) at an applied pressure of at least about 2MPa (e.g., 2MPa, 3MPa, 4MPa, 5MPa, or 10MPa, including ranges between any of the foregoing values) and at a temperature of less than about 140 ℃ (e.g., 120 ℃, 125 ℃, 130 ℃, or 135 ℃, including ranges between any of the foregoing values).

Hot pressing or hot calendaring can increase the transmittance and/or thermal conductivity of the polymer film. According to some embodiments, the applied pressure may collapse voids within the polymer film, thereby reducing the total void volume and increasing the density of the polymer matrix.

After the polymer film is deformed, the heating may be maintained for a predetermined amount of time and then the polymer film may be cooled. The cooling action may include allowing the polymer film to cool naturally at a set cooling rate, or by quenching (e.g., by purging with a cryogenic gas), which may thermally stabilize the polymer film.

After deformation, the crystals or chains may be at least partially aligned with the direction of the applied tensile stress. Thus, the polymer film may exhibit a high degree of optical clarity and mechanical anisotropy, including one or any combination of the following: a transmittance of at least about 85% (e.g., 85%, 90%, 95%, 97%, or 99%, inclusive of ranges between any of the foregoing) over or throughout the visible spectrum (380 nm-750 nm), a bulk haze of less than about 5% (e.g., 0%, 0.5%, 1%, 2%, 3%, 4%, or 5%, inclusive of ranges between any of the foregoing), an RF transparency of at least about 85% (e.g., 85%, 90%, 95%, 97%, or 99%, inclusive of ranges between any of the foregoing), and a specific resistivity of at least about 10 ¹⁰ Ohm/cm (ohm/cm) (e.g., 10 ¹⁰ Ohm/cm, 10 ¹² Ohm/cm or 10 ¹⁵ Ohm/cm, including any range between the foregoing values), a dielectric constant of less than about 3.5 (e.g., 3, 2.5, 2.2, or 2, including any range between the foregoing values), a loss tangent (loss tangent) of less than about 0.01 (e.g., 0.005,0.001,0.0005, including any range between the foregoing values), a modulus of elasticity of at least about 20GPa (e.g., 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa, or 100GPa, including any range between the foregoing values), a tensile strength of at least about 0.5GPa (e.g., 0.5GPa, 1GPa, or 1.5GPa, including any range between the foregoing values), a thermal conductivity of at least about 5W/mK (e.g., 5W/mK, 10W/mK, 20W/mK, 30W/mK, 40W/mK, 50W/mK, 60W/mK, 70W/mK, or 80W/mK, including any range between the foregoing values), a void of less than about 5.5%, e.g., less than about 1.5%, 3%, or 3.5%, including any of the foregoing values, and the following the valuesRanges between values), and average void sizes of less than about 100nm (e.g., 10nm, 20nm, 50nm, or 100nm, including ranges between any of the foregoing values). In some embodiments, the modulus of the polymer film may be constant or substantially constant according to frequency (e.g., in the range of 0.1Hz to 100 Hz). These and other characteristics may exhibit in-plane anisotropies from about 2:1 to about 100:1 or greater (e.g., 2:1, 3:1, 4:1, 5:1, 10:1, 20:1, 50:1, or 100:1).

The polyethylene film may comprise a fibrous material, an amorphous material, a partially crystalline material or a fully crystalline material. Such materials may also exhibit anisotropy with respect to one or more additional properties, which may include compressive strength, shear strength, yield strength, stiffness, hardness, toughness, ductility, machinability, thermal expansion, and creep behavior.

According to various embodiments, the anisotropic polyethylene film may be formed by applying a desired stress state to the crystallizable polymer film. The polymer composition capable of crystallizing may be formed into a monolayer using suitable extrusion and casting operations known to those skilled in the art. For example, the ethylene-containing composition may be extruded and oriented as a monolayer to form a mechanically and thermally conductive anisotropic film. According to further embodiments, the crystallizable polymer may be co-extruded with other polymeric materials that are either crystallizable or remain amorphous after orientation to form a multilayer structure.

After deformation, the crystals or chains may be at least partially aligned with the direction of the applied tensile stress. Thus, polyethylene films may exhibit a high degree of optical clarity and in-plane anisotropy, including an in-plane thermal conductivity of at least about 5W/mK and an elastic modulus of at least about 20 GPa.

Features from any of the embodiments described herein may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features and advantages will be more fully understood after reading the following detailed description in conjunction with the accompanying drawings and claims.

Drawings

The accompanying drawings illustrate several examples and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure.

Fig. 1 is a schematic illustration of a polymer bilayer structure comprising a porous fluoropolymer layer and an adjacent high thermal conductivity Ultra High Molecular Weight Polyethylene (UHMWPE) layer.

Fig. 2 illustrates an exemplary apparatus for forming a one-dimensional polymeric article.

FIG. 3 illustrates an exemplary apparatus for forming a two-dimensional polymeric article.

FIG. 4 is a graph of reflectance versus wavelength across the infrared spectrum for a non-optical quality polyethylene film.

FIG. 5 is a graph of reflectance versus wavelength across the infrared spectrum for a polymer article comprising a non-optical quality polyethylene film and an IR reflecting coating layer.

FIG. 6 is a graph of reflectance versus wavelength over the entire infrared spectrum for a polymer bilayer including a non-optical quality polyethylene film and a supported layer of IR reflecting PVDF foam.

FIG. 7 is a graph of reflectance versus wavelength over the entire infrared spectrum for a polymer bilayer including an optical quality polyethylene film and a supported layer of IR reflecting PVDF foam.

Fig. 8 is an illustration of exemplary augmented reality glasses.

Fig. 9 is an illustration of an exemplary virtual reality headset.

Throughout the drawings, identical reference numbers and descriptions indicate similar, but not necessarily identical elements. While the examples described herein are susceptible to various modifications and alternative forms, specific examples have been shown by way of example in the drawings and will herein be described in detail. However, the examples described herein are not intended to be limited to the particular forms disclosed. Rather, the present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims.

Detailed Description

A detailed description of the polymer layer and the polymer bilayer and their methods of manufacture will be provided below with reference to fig. 1-9. The discussion associated with fig. 1 relates to the structure and characteristics of an exemplary polymer bilayer having a high modulus and high thermal conductivity. The discussion associated with fig. 2 and 3 includes a description of an exemplary method of manufacturing forming such a polymer bilayer. The discussion associated with fig. 4-7 includes a description of the optical properties and temperature conditioning behavior of an exemplary polymer layer including an exemplary polymer bilayer. The discussion associated with fig. 8 and 9 relates to exemplary virtual reality devices and augmented reality devices that may include one or more polymeric bilayer films or fibers as disclosed herein.

Referring to fig. 1, an exemplary polymer bilayer 100 is shown that includes an ultra-high molecular weight polyethylene (UHMWPE) layer 102 directly overlying a polyvinylidene fluoride (PVDF) layer 104. In various bi-layer architectures, the polyvinylidene fluoride may be porous, while the polyethylene layer may be porous or dense. The individual polymer layers may be formed together continuously or individually and subsequently bonded. Various methods may be used to form the polymer bilayer.

A one-dimensional polymer bilayer architecture can be formed using a fiber melt spinning line in which two polymer compositions can be co-extruded into a core-shell fiber geometry (core-shell fiber geometry). The polymer may be extruded in solution or in the molten state. An exemplary fiber melt spinning apparatus is schematically illustrated in fig. 2. The apparatus 200 includes polymer inlet hoppers 205, 225 configured to feed polymer material (e.g., polyethylene and polyvinylidene fluoride) to the respective screws 210, 220. The screws 210, 220 may be configured to rotate, for example, in a reverse direction or a reverse direction.

The spinneret dies 215, 240 combine the polymeric material into a fiber 230 having a core-shell structure. The fibers 230 may be stretched in air or in a solvent bath to control the fiber cooling rate and introduce voids into the fluoropolymer and optionally into the polyethylene. The fibers 230 may be collected on a rotating spool 235. In some examples, the speed of spool 235 may be used to control the draw ratio of the as-spun fiber.

The fluoropolymer may include a blowing agent to introduce pores into the fiber core. The size and distribution of the pores may be controlled by the composition and amount of blowing agent, processing temperature and draw rate.

In some examples, the polyethylene layer may form a cladding of a bi-layer fiber. In examples of porous polyethylene layers that may be formed using solvent exchange techniques, the pore size in the cladding may be smaller than the pore size in the core. Thus, exemplary fibers can be characterized by a bimodal void size distribution.

Referring to fig. 3, an alternative apparatus for forming a polymer bilayer is schematically shown. In conjunction with the apparatus 300, a fluoropolymer film 305 having a high or ultra-high molecular weight and low entanglement density may be cast from solution, passed through a pair of rollers 340, and coated (e.g., on one major surface) with a polyethylene film 310. Polyethylene film 310 may be formed from a solution or melt phase. Suitable solvents for casting polyethylene film 310 from solution may include low molecular weight polyethylene waxes, decalin-dodecanol mixtures, paraffinic oils, mineral oils, lauric acid, stearic acid, mixtures thereof, and the like.

Air knife 315 and/or blade 335 may be used to control the thickness of polyethylene film 310. By controlling one or more of the relative rotational speed of the roller 340, the air pressure in the air knife 315, and the distance between the blade 335 and the polymer bilayer, the appropriate shear stress (i.e., shear rate) and desired strain, along with the concomitant alignment of the polyethylene chains, can be introduced to the polyethylene film 310.

The polymer bilayer may be passed sequentially through solvent bath 320 and drying oven 325 prior to entanglement onto storage roll 330. In some examples, the rotational speed differential between roller 340 and storage roller 330 may be used to stretch the polymer bilayer to a suitable stretch ratio.

The optical properties and temperature conditioning behavior of the exemplary polymer bilayer and comparative structures will be discussed below. The Fourier Transform Infrared (FTIR) reflectance data shown in fig. 4-7 provides insight into: the passive cooling properties of a bilayer of high thermal conductivity polyethylene and polyethylene comprising a highly emissive layer laminated to porous PVDF.

Referring to fig. 4, a reflectance curve 400 for a single non-optical grade polyethylene layer is shown. The reflectivity of the polyethylene film is greater than about 10%, i.e., from about 10% to about 35%, in the LWIR spectrum (λ about 8 microns-14 microns). That is, assuming a zero transmission, the LWIR emissivity of the non-optical grade polyethylene film is in the range of about 65% to about 90%, which may be insufficient to efficiently transfer the thermal energy accumulated within or upstream of the double layers.

Turning to fig. 5, a reflectivity curve 500 is shown for a composite structure including a non-optical grade polyethylene layer and an adjacent IR reflective coating. Within the long wavelength infrared spectrum, the addition of an IR reflective coating can advantageously reduce the reflectivity of the composite structure relative to the PE film alone. As shown in fig. 5, the reflectance is less than about 10%, such as less than about 5%, over the entire long wavelength infrared spectrum (λ about 8-14 microns). However, the incorporation of an IR reflective coating may also reduce reflectivity at shorter wavelengths of the infrared spectrum (0.25 microns < λ <5 microns), which may facilitate absorption (rather than reflection) of the solar heating spectrum. In the reflectance curve 500, the reflectance at shorter wavelengths of the infrared spectrum (0.25 microns < lambda <5 microns) may be about 5% or greater, for example about 10%.

Applicant has shown that a polymer bilayer comprising a polyethylene layer and a porous fluoropolymer layer directly overlying the polyethylene layer can be characterized by: the reflectivity is at least about 10%, such as at least 10%, at least 15%, or at least 20%, including ranges between any of the foregoing values, within or throughout the shorter wavelengths of the infrared spectrum (0.25 microns < lambda <5 microns), and less than about 10% within or throughout the long wavelength infrared spectrum (lambda about 8 microns-14 microns). The porous fluoropolymer layer may comprise a porous PVDF foam. In some examples, the PVDF foam may be supported by a non-porous layer of PVDF, although other polymeric support layers are also contemplated.

For example and referring to fig. 6, a reflectivity curve 600 is shown for a composite structure comprising a non-optical grade polyethylene layer and a porous PVDF foam layer supported by PVDF. As shown in fig. 6, the reflectance is greater than about 10%, such as greater than about 15%, at shorter wavelengths (0.25 microns < lambda <5 microns) of the overall infrared spectrum, while the reflectance is less than about 10%, such as less than about 5%, at longer wavelengths (lambda about 8 microns-14 microns) of the overall infrared spectrum.

Turning to fig. 7, a reflectance curve 700 is shown for a composite structure comprising an optical grade (optically transparent) polyethylene layer, a pigment layer, and a porous PVDF foam layer supported by PVDF. Where an optical grade polyethylene layer is incorporated, a pigment layer may be included, for example, between the polyethylene layer and the PVDF foam layer, which may be desirable for certain applications. As shown in fig. 7, the reflectivity for such a stack (PE/pigment/PVDF foam/PVDF support) may be greater than about 10%, such as greater than about 15% or greater than about 20%, at the shorter wavelengths of the overall infrared spectrum (0.25 microns < lambda <5 microns), while the reflectivity may be less than about 10% at the overall long wavelength infrared spectrum (lambda about 8 microns-14 microns). This combination of temperature conditioning actions can effectively passively cool a system or device secured to the PE/pigment/PVDF foam/PVDF support architecture.

As disclosed herein, the polymeric structure includes an optically transparent layer of Ultra High Molecular Weight Polyethylene (UHMWPE) that can be configured to provide a platform to achieve passive cooling in a co-integrated component or device by utilizing the transparency and high thermal conductivity of the UHMWPE layer throughout the LWIR spectrum (8 μm-14 μm), for example during exposure to sunlight. In some examples, the UHMWPE can have a molecular weight of at least about 300,000 g/mol. The high thermal conductivity of the UHMWPE layer can significantly attenuate thermal throttling by promoting thermal diffusion over a large surface area, which may increase heat dissipation through convective heat transfer.

In addition to the optical quality UHMWPE, the polymer structure may also comprise an IR reflecting layer, such as a colored IR reflecting paint layer. In connection with this, the UHMWPE layer itself may be optically transparent or colored. In some examples, the polymer structure may additionally include a porous PVDF layer. The porous PVDF layer (if provided) may be characterized by: high reflectivity in the UV spectrum, visible spectrum and near IR spectrum, and high emissivity in LWIR.

The UHMWPE layer and optional PVDF layer may be formed simultaneously, such as by coextrusion, or separately and then laminated to form a multi-layer polymeric structure. Additional film forming techniques include melt extrusion, casting, calendaring, compression molding, and the like. The stretching operation may be applied to each layer alone or to the assembled polymer structure to induce strain and produce desired optical properties (including desired temperature conditioning response).

Embodiments of the present disclosure may include or be implemented in conjunction with various types of artificial reality systems. An artificial reality is a form of reality that has been regulated in some way before being presented to a user, which may include, for example, virtual reality, augmented reality, mixed reality (or hybrid reality), or some combination and/or derivative thereof. The artificial reality content may include entirely generated content or generated content combined with captured (e.g., real world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of them may be presented in a single channel or multiple channels (e.g., stereoscopic video that produces a three-dimensional (3D) effect for a viewer). Additionally, in some embodiments, the artificial reality may also be associated with an application, product, accessory, service, or some combination thereof, for creating content in the artificial reality and/or otherwise for use in the artificial reality (e.g., performing an activity in the artificial reality), for example.

The artificial reality system may be implemented in a variety of different form factors and configurations. Some artificial reality systems may be designed to operate without a near-eye display (NED). Other artificial reality systems may include NEDs that also provide visibility to the real world (e.g., augmented reality system 800 in FIG. 8), or NEDs that visually immerse the user in artificial reality (e.g., virtual reality system 900 in FIG. 9). While some artificial reality devices may be stand-alone systems, other artificial reality devices may communicate and/or coordinate with external devices to provide an artificial reality experience to a user. Examples of such external devices include a handheld controller, a mobile device, a desktop computer, a device worn by a user, one or more other devices worn by a user, and/or any other suitable external system.

Turning to fig. 8, the augmented reality system 800 may include an eyeglass device 802 having a frame 810 configured to hold a left display device 815 (a) and a right display device 815 (B) in front of a user's eyes. Display devices 815 (a) and 815 (B) may function together or independently to present an image or series of images to a user. Although the augmented reality system 800 includes two displays, examples of the present disclosure may be implemented in an augmented reality system having a single NED or more than two nes.

In some examples, the augmented reality system 800 may include one or more sensors, such as sensor 840. The sensor 840 may generate measurement signals in response to movement of the augmented reality system 800 and may be located on substantially any portion of the frame 810. The sensor 840 may represent a position sensor, an inertial measurement unit (inertial measurement unit, IMU), a depth camera assembly, a structured light emitter and/or detector, or any combination thereof. In some examples, the augmented reality system 800 may or may not include the sensor 840, or may include more than one sensor. In examples where the sensor 840 includes an IMU, the IMU may generate calibration data based on measurement signals from the sensor 840. Examples of sensors 840 may include, but are not limited to, accelerometers, gyroscopes, magnetometers, other suitable types of sensors that detect motion, sensors for error correction of an IMU, or some combination thereof.

The augmented reality system 800 may also include a microphone array having a plurality of acoustic transducers 820 (a) to 820 (J) (collectively acoustic transducers 820). The acoustic transducer 820 may be a transducer that detects changes in air pressure caused by sound waves. Each acoustic transducer 820 may be configured to detect sound and to convert the detected sound into an electronic format (e.g., analog format or digital format). The microphone array in fig. 8 may comprise, for example, ten acoustic transducers: acoustic transducers 820 (a) and 820 (B), which may be designed to be placed within respective ears of a user; acoustic transducers 820 (C), 820 (D), 820 (E), 820 (F), 820 (G), and 820 (H), which may be positioned at different locations on frame 810; and/or acoustic transducers 820 (I) and 820 (J), which may be positioned on the corresponding neck strap 805.

In some examples, one or more of acoustic transducers 820 (a) to 820 (F) may be used as output transducers (e.g., speakers). For example, acoustic transducer 820 (a) and/or acoustic transducer 820 (B) may be an ear bud or any other suitable type of earphone or speaker.

The configuration of the acoustic transducer 820 of the microphone array may vary. Although the augmented reality system 800 is shown in fig. 8 as having ten acoustic transducers 820, the number of acoustic transducers 820 may be greater or less than ten. In some examples, using a greater number of acoustic transducers 820 may increase the amount of audio information collected and/or the sensitivity and accuracy of the audio information. Conversely, using a smaller number of acoustic transducers 820 may reduce the computational power required by the associated controller 850 to process the collected audio information. Furthermore, the position of each acoustic transducer 820 of the microphone array may vary. For example, the locations of the acoustic transducers 820 may include defined locations on the user, defined coordinates on the frame 810, an orientation associated with each acoustic transducer 820, or some combination thereof.

Acoustic transducers 820 (a) and 820 (B) may be positioned on different portions of the user's ear, such as behind the pinna, behind the tragus, and/or within the auricle (auricle) or the ear socket. Alternatively, there may be additional acoustic transducers 820 on or around the ear in addition to the acoustic transducer 820 in the ear canal. Positioning the acoustic transducer 820 close to the ear canal of the user may enable the microphone array to collect information about how sound reaches the ear canal. By positioning at least two of these acoustic transducers 820 on either side of the user's head (e.g., as binaural microphones), the augmented reality system 800 may simulate binaural hearing and capture a 3D stereo field around the user's head. In some examples, acoustic converters 820 (a) and 820 (B) may be connected to augmented reality system 800 via wired connection 830, and in other examples, acoustic converters 820 (a) and 820 (B) may be connected to augmented reality system 800 via a wireless connection (e.g., a bluetooth connection). In other examples, acoustic transducers 820 (a) and 820 (B) may not be used in conjunction with augmented reality system 800 at all.

The acoustic transducer 820 on the frame 810 can be positioned in a variety of different ways, including along the length of the temple, across the bridge, above or below the display devices 815 (a) and 815 (B), or some combination thereof. The acoustic transducer 820 may also be oriented such that the microphone array is capable of detecting sound in a wide range of directions around a user wearing the augmented reality system 800. In some examples, an optimization process may be performed during manufacture of the augmented reality system 800 to determine the relative positioning of each acoustic transducer 820 in the microphone array.

In some examples, the augmented reality system 800 may include or be connected to an external device (e.g., a paired device), such as a neck strap 805. The neck strap 805 generally represents any type or form of mating device. Thus, the following discussion of the neck strap 805 may also apply to a variety of other paired devices, such as charging boxes, smartwatches, smartphones, wrist straps, other wearable devices, hand-held controllers, tablet computers, laptop computers, other external computing devices, and the like.

As shown, the neck strap 805 may be coupled to the eyeglass apparatus 802 via one or more connectors. The connectors may be wired or wireless and may include electronic components and/or non-electronic (e.g., structural) components. In some cases, the eyeglass device 802 and the neck strap 805 can operate independently without any wired or wireless connection therebetween. While fig. 8 shows the components of the eyeglass apparatus 802 and the components of the neck strap 805 in exemplary locations on the eyeglass apparatus 802 and the neck strap 805, the components may be located elsewhere on the eyeglass apparatus 802 and/or the neck strap 805 and/or distributed differently on the eyeglass apparatus 802 and/or the neck strap 805. In some examples, the components of the eyeglass device 802 and the components of the neck strap 805 can be located on one or more additional peripheral devices paired with the eyeglass device 802, the neck strap 805, or some combination thereof.

Pairing an external device (e.g., neck strap 805) with an augmented reality eyewear device may enable the eyewear device to implement the form factor of a pair of eyewear, and still provide sufficient battery and computing power for the expansion capability. Some or all of the battery power, computing resources, and/or additional features of the augmented reality system 800 may be provided by, or shared between, the paired device and the eyeglass device, thereby generally reducing the weight, thermal profile, and form factor of the eyeglass device while still retaining the desired functionality. For example, the neck strap 805 may allow components that would otherwise be included on the eyeglass device to be included in the neck strap 805 because the user's shoulders may bear a heavier weight load than the user's head may bear. The neck strap 805 may also have a larger surface area over which heat diffuses and disperses into the surrounding environment. Thus, the neck strap 805 may achieve greater battery and computing power than would otherwise be possible on a standalone eyeglass device. Because the weight carried in the neck strap 805 is less invasive to the user than the weight carried in the eyeglass device 802, the user can afford to wear a lighter eyeglass device and carry or wear a paired device for a longer length of time than if the user were to wear a heavy, freestanding eyeglass device, thereby enabling the user to more fully integrate the artificial reality environment into his daily activities.

The neck strap 805 can be communicatively coupled with the eyeglass device 802 and/or other devices. These other devices may provide certain functionality (e.g., tracking, positioning, depth map construction, processing, storage, etc.) for the augmented reality system 800. In the example of fig. 8, the neck strap 805 may include two acoustic transducers (e.g., 820 (I) and 820 (J)) as part of the microphone array (or potentially forming its own microphone sub-array). The neck strap 805 may also include a controller 825 and a power supply 835.

The acoustic transducer 820 (I) and the acoustic transducer 820 (J) of the neck strap 805 may be configured to detect sound and convert the detected sound to an electronic format (analog or digital). In the example of fig. 8, acoustic transducer 820 (I) and acoustic transducer 820 (J) may be positioned on neck strap 805, thereby increasing the distance between acoustic transducer 820 (I) and acoustic transducer 820 (J) of the neck strap and other acoustic transducers 820 positioned on eyeglass device 802. In some cases, increasing the distance between the acoustic transducers 820 of the microphone array may increase the accuracy of beamforming performed via the microphone array. For example, if acoustic transducer 820 (C) and acoustic transducer 820 (D) detect sound and the distance between acoustic transducer 820 (C) and acoustic transducer 820 (D) is greater than, for example, the distance between acoustic transducer 820 (D) and acoustic transducer 820 (E), the determined source location of the detected sound may be more accurate than if the sound were detected by acoustic transducer 820 (D) and acoustic transducer 820 (E).

The controller 825 of the neck strap 805 may process information generated by sensors on the neck strap 805 and/or the augmented reality system 800. For example, the controller 825 may process information from the microphone array describing sounds detected by the microphone array. For each detected sound, the controller 825 may perform a direction-of-arrival (DOA) estimation to estimate the direction of the detected sound reaching the microphone array. When sound is detected by the microphone array, the controller 825 may populate the audio data set with information. In examples where the augmented reality system 800 includes an inertial measurement unit, the controller 825 may calculate all inertial and spatial operations from the IMU located on the eyeglass device 802. The connector may communicate information between the augmented reality system 800 and the neck strap 805, as well as between the augmented reality system 800 and the controller 825. Such information may be in the form of optical data, electrical data, wireless data, or any other form of data that may be transmitted. Transferring the processing of information generated by the augmented reality system 800 to the neck strap 805 may reduce the weight of the eyeglass device 802 and the amount of heat in the eyeglass device 802, making it more comfortable for the user.

The power supply 835 in the neck strap 805 can provide power to the eyeglass device 802 and/or to the neck strap 805. The power supply 835 may include, but is not limited to, a lithium ion battery, a lithium polymer battery, a disposable lithium battery, an alkaline battery, or any other form of power storage device. In some cases, power supply 835 may be a wired power supply. The inclusion of the power source 835 on the neck strap 805 rather than on the eyeglass device 802 may help better distribute the weight and heat generated by the power source 835.

As noted, some artificial reality systems may substantially replace one or more of the user's sensory perceptions of the real world with a virtual experience, rather than mixing artificial reality with real reality. One example of this type of system is a head mounted display system that covers a majority or all of the user's field of view, such as virtual reality system 900 in fig. 9. The virtual reality system 900 may include a front rigid body 902 and a strap 904 shaped to fit around the head of the user. The virtual reality system 900 may also include an output audio transducer 906 (a) and an output audio transducer 906 (B). Further, although not shown in fig. 9, front rigid body 902 may include one or more electronic components including one or more electronic displays, one or more Inertial Measurement Units (IMUs), one or more tracking emitters or detectors, and/or any other suitable device or system for creating an artificial reality experience.

The artificial reality system may include various types of visual feedback mechanisms. For example, the display device in the augmented reality system 800 and/or the display device in the virtual reality system 800 may include one or more liquid crystal displays (liquid crystal display, LCD), one or more light emitting diode (light emitting diode, LED) displays, one or more organic LED (organic light emitting diode, OLED) displays, one or more digital light projection (digital light project, DLP) microdisplays, one or more liquid crystal on silicon (liquid crystal on silicon, LCoS) microdisplays, and/or any other suitable type of display screen. These artificial reality systems may include a single display screen for both eyes, or one display screen may be provided for each eye, which may allow for additional flexibility in adjusting or correcting the user's refractive error for zooming. Some artificial reality systems may also include optical subsystems having one or more lenses (e.g., conventional concave or convex lenses, fresnel lenses, tunable liquid lenses, etc.) through which a user may view a display screen. These optical subsystems may be used for a variety of purposes, including collimating light (e.g., making objects appear farther than they are physically), amplifying light (e.g., making objects appear larger than their physical dimensions), and/or relaying light (to, for example, the eyes of a viewer). These optical subsystems may be used for direct-view architectures (e.g., single lens configurations that directly collimate light but cause so-called pincushion distortion) and/or for non-direct-view architectures (such as multi-lens configurations that produce so-called barrel distortion to eliminate pincushion distortion).

In addition to or instead of using a display screen, some artificial reality systems may include one or more projection systems. For example, the display device in the augmented reality system 800 and/or the display device in the virtual reality system 900 may include a micro LED projector that projects light (using, for example, a waveguide) into the display device, such as a transparent combiner lens that allows ambient light to pass through. The display device may refract the projected light toward the pupil of the user, and may enable the user to view both the artificial reality content and the real world at the same time. The display device may achieve this using any of a variety of different optical components, including waveguide components (e.g., holographic waveguide elements, planar waveguide elements, diffractive waveguide elements, polarizing waveguide elements, and/or reflective waveguide elements), light manipulating surfaces and elements (e.g., diffractive elements and gratings, reflective elements and gratings, and refractive elements and gratings), coupling elements, and the like. The artificial reality system may also be configured with any other suitable type or form of image projection system, such as a retinal projector used in a virtual retinal display.

The artificial reality system may also include various types of computer vision components and subsystems. For example, the augmented reality system 800 and/or the virtual reality system 900 may include one or more optical sensors, such as two-dimensional (2D) cameras or 3D cameras, structured light emitters and detectors, time-of-flight depth sensors, single beam rangefinders or scanning laser rangefinders, 3D laser radar (LiDAR) sensors, and/or any other suitable type or form of optical sensor. The artificial reality system may process data from one or more of these sensors to identify the user's location, map the real world, provide content to the user regarding the real world environment, and/or perform various other functions.

The artificial reality system may also include one or more input audio transducers and/or output audio transducers. In the example shown in fig. 9, the output audio transducers 906 (a) and 906 (B) may include voice coil speakers, ribbon speakers, electrostatic speakers, piezoelectric speakers, bone conduction transducers, cartilage conduction transducers, tragus vibration transducers, and/or any other suitable type or form of audio transducer. Similarly, the input audio transducer may include a condenser microphone, a dynamic microphone, a ribbon microphone, and/or any other type or form of input transducer. In some examples, a single transducer may be used for both audio input and audio output.

Although not shown in fig. 8, the artificial reality system may also include tactile (i.e., haptic) feedback systems, which may be incorporated into headwear, gloves, clothing, hand-held controllers, environmental devices (e.g., chairs, floor mats, etc.), and/or any other type of device or system. The haptic feedback system may provide various types of skin feedback (including vibration, force, traction, texture, and/or temperature). Haptic feedback systems may also provide various types of kinesthetic feedback, such as motion and compliance. Haptic feedback may be implemented using motors, piezoelectric actuators, fluid systems, and/or various other types of feedback mechanisms. The haptic feedback system may be implemented independently of, within, and/or in combination with other artificial reality devices.

By providing haptic sensations, auditory content, and/or visual content, an artificial reality system can create a complete virtual experience or enhance a user's real-world experience in a variety of contexts and environments. For example, an artificial reality system may assist or augment a user's perception, memory, or cognition within a particular environment. Some systems may enhance user interaction with others in the real world or may enable more immersive interaction with others in the virtual world. The artificial reality system may also be used for educational purposes (e.g., for teaching or training of schools, hospitals, government organizations, military organizations, commercial enterprises, etc.), entertainment purposes (e.g., for playing video games, listening to music, watching video content, etc.), and/or for accessibility purposes (e.g., as a hearing aid, visual aid, etc.). Examples and embodiments disclosed herein may implement or enhance the user's artificial reality experience in one or more of these contexts and environments, and/or in other contexts and environments.

The sequence of process parameters and steps described and/or illustrated herein are given by way of example only and may be varied as desired. For example, although the steps illustrated and/or described herein may be shown or discussed in a particular order, the steps need not be performed in the order illustrated or discussed. Various exemplary methods described and/or illustrated herein may also omit one or more of the steps described or illustrated herein or include additional steps in addition to those disclosed.

The previous description is provided to enable any person skilled in the art to best utilize various aspects of the examples disclosed herein. The exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the disclosure. The examples disclosed herein are to be considered in all respects as illustrative and not restrictive. In determining the scope of the present disclosure, reference should be made to any claims appended hereto and their equivalents.

The terms "connected" and "coupled" (and derivatives thereof) as used in the specification and/or claims should be interpreted as allowing for direct connection and indirect (i.e., via other elements or components) unless otherwise indicated. Furthermore, the terms "a" or "an", as used in the description and claims, are to be interpreted as meaning "at least one". Finally, for convenience in use, the terms "comprise" and "have" (and their derivatives) as used in the specification and claims may be interchangeable with, and have the same meaning as, the term "comprising.

It will be understood that when an element (e.g., a layer or region) is referred to as being formed on, deposited on, or disposed "on" or "over" another element, it can be directly on at least a portion of the other element or one or more intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or "directly over" another element, it can be on at least a portion of the other element without intervening elements present.

As used herein, in certain examples, the term "about" with respect to a particular value or range of values may refer to and include the stated value as well as all values within 10% of the stated value. Thus, for example, in some examples, a value of "50" referred to as "about 50" may include a value equal to 50±5, i.e., a value in the range of 45 to 55.

As used herein, the term "substantially" with respect to a given parameter, property, or condition may refer to and include the degree to which a person of ordinary skill in the art would understand, i.e., the given parameter, property, or condition meets a lesser degree (e.g., within acceptable manufacturing tolerances). For example, depending on the particular parameter, property, or condition that is substantially satisfied, the parameter, property, or condition may be at least about 90% satisfied, at least about 95% satisfied, or even at least about 99% satisfied.

While the transitional phrase "comprising" may be used to disclose various features, elements, or steps of a particular embodiment, it should be understood that alternative embodiments (including embodiments that may be described using the transitional phrase "consisting of … …" or "consisting essentially of … …") are implicit. Thus, for example, implicit alternative embodiments of fluoropolymers comprising or including PVDF include embodiments in which the fluoropolymer consists essentially of PVDF and embodiments in which the fluoropolymer consists of PVDF.

Claims

1. A layered structure, the layered structure comprising:

an optically transparent layer comprising ultra high molecular weight polyethylene; and

an infrared IR reflecting layer overlying the optically transparent layer, wherein the layered structure has a short wavelength (0.25 μm < λ <5 μm) infrared reflectance of at least about 10% and a long wavelength (8 μm < λ <14 μm) infrared reflectance of less than about 10%.

2. The layered structure of claim 1, wherein the optically transparent layer has a thermal conductivity of at least about 5W/mK.

3. The layered structure of claim 1 or 2, wherein the optically transparent layer has an elastic modulus of at least about 2GPa and a tensile strength of at least about 0.7 GPa.

4. The layered structure of any preceding claim, wherein the IR reflecting layer comprises an IR reflecting paint;

preferably, wherein the IR reflective coating comprises nanoscale particles of a pigment selected from the group consisting of: organic dyes and metal oxides.

5. The layered structure of any preceding claim, wherein the IR reflecting layer comprises a porous fluoropolymer;

preferably, wherein the porous fluoropolymer comprises polyvinylidene fluoride (PVDF).

6. The layered structure of claim 5, wherein the porous fluoropolymer is selected from the group consisting of: PVDF-CTFE, PVDF-HFP, PVDF-TFE, PVDF-TrFE-TFE, and combinations thereof.

7. The layered structure of claim 5 or 6, wherein the porous fluoropolymer has a porosity of at least about 15 vol.%.

8. The layered structure of any one of claims 5-7, wherein the porous fluoropolymer comprises a plurality of pores having an average pore size of at least about 100 nm.

9. The layered structure according to any preceding claim, wherein the thickness of the optically transparent layer is less than the thickness of the IR reflecting layer;

Preferably, wherein the thickness of the optically transparent layer ranges from about 10 microns to about 1mm, and the thickness of the IR reflecting layer ranges from about 0.2mm to about 1mm.

10. An apparatus comprising a layered structure according to any preceding claim, wherein the apparatus is selected from the group consisting of: smart watches, virtual Reality (VR) glasses, VR headset, augmented Reality (AR) glasses, AR headset, mixed Reality (MR) glasses, and MR headset.

11. A layered structure, the layered structure comprising:

an optically transparent layer of ultra high molecular weight polyethylene; and

an infrared IR reflecting layer directly overlying the optically transparent layer, wherein the optically transparent layer has a thermal conductivity of at least about 5W/mK and an elastic modulus of at least about 2 GPa.

12. The layered structure of claim 11, wherein the layered structure has a short wavelength (0.25 μιη < lambda <5 μιη) infrared reflectance of at least about 10% and a long wavelength (8 μιη < lambda <14 μιη) infrared reflectance of less than about 10%;

preferably, wherein the IR reflecting layer comprises an IR reflecting paint.

13. A method, the method comprising:

Forming an optically transparent layer of ultra high molecular weight polyethylene; and

an infrared IR reflecting layer is formed over the optically transparent layer to produce a layered structure having a short wavelength (0.25 μm < lambda <5 μm) infrared reflectance of at least about 10% and a long wavelength (8 μm < lambda <14 μm) infrared reflectance of less than about 10%.

14. The method of claim 13, wherein forming the IR reflecting layer over the optically transparent layer comprises laminating the IR reflecting layer to the optically transparent layer.

15. The method of claim 13 or 14, further comprising forming a pressure sensitive adhesive layer or an optically clear adhesive layer between the optically clear layer and the IR reflecting layer;

preferably, wherein forming the optically transparent layer comprises vacuum compression molding a fibrous polyethylene mat.