Apparatus

Abstract

An Eye shield (400, figure 4) comprising a frame (402, figure 4) and a composite lens 100, comprising a plurality of layers 101, 102, 103, 104, a power supply in electrical communication with at least

Description

TECHNICAL FIELD In general terms this invention relates to an eye shield. The eye shield comprises a frame, a composite lens comprising a heating layer, and a power supply in electrical communication with at least one of the plurality of layers of the composite lens. BACKGROUND Eye shields, such as sports goggles or diving masks, are used to create a physical barrier between part of the user’s face and the external environment. The lens or visor of such eye shields must be transparent to visible light in order to not impede the vision of the user. A problem with eye shields is their susceptibility to fogging. Fogging occurs when warm, humid air comes into contact with a cooler surface, and the moisture in the air condenses into tiny droplets on the cooler surface. In the case of eye shields, the user’s breath, perspiration and body heat can all result in warm, humid air in the vicinity of an inner surface of the eye shield lens or visor. In the case of diving masks in particular, the exterior of the eye shield lens or visor may be in direct contact with a large volume of water that is significantly cooler than the inner surface of the eye shield lens or visor, resulting in significant and persistent fogging of the eye shield. To remove the fog, divers need to flood the mask with water and clear it by exhaling through the nose. When water is removed from the air compartment, the surface pressure of the water at the inner side of the glass forms a film that wipes the glass clean of the fog forming droplets. At the same time, the temperature of the air compartment is dropped close to ambient water temperature. However, the temperature increases again due to higher surface temperature of the skin and the higher temperature from the breath of the diver that is exhaled through the diver’s nose. As such, the condensation and fogging process repeats. This is a significant issue for eye shield users such as Scuba Divers and Free Divers, as the fogged glass can prevent the viewing of critical dive computer data such as Depth, Oxygen remaining, Ascent rate, No Decompression Limits, and safety stop data. In addition to the safety concerns associated with a fogged lens, the user’s experience of their dive is worsened by having poor visibility of their surroundings. Current solutions to this problem generally aim to prevent condensation from settling on the lens or visor of the eye shield. These include anti-fog sprays, gels, and hydrophobic surface films for the inner surface of the lens or visor. None of these solutions are ideal, as they generally do not provide adequate fogging protection, and require repeated reapplications to remain even somewhat effective. That is, they provide - at best - a temporary solution. An alternative approach to solving the problem of eye shield fogging is the use of various conductive apparatuses intended to preventing condensation build-up on eye shields for eyeprotecting shields. For example, US Patent No. 4,868,929, titled “Electrically Heated Ski Goggles”, comprises an eye shield with embedded resistive wires operatively connected via a switching device to an external power source pack adapted to produce heating of the eye shield for anti-fog purposes. The use case for eye shields in diving applications is significantly more challenging than that of winter sports goggles such as those described in US Patent No. 4,868,929, because the exterior of the eye shield is in contact with an enormous volume of water that is cooler than the interior of the eye shield. Accordingly, heating the lens of the eye shield underwater requires a large amount of electrical power - ambient water at the outer surface of the eye shield has a thermal conductivity of around 0.6 W / m K, whereas air has a thermal conductivity of 0.024 W / m K. A problem to be overcome is to prevent any heating energy from simply flowing mainly to surrounding water. In addition, due to being immersed in water, eye shields for use in diving applications must be sufficiently water resistant to remain functioning underwater. There remains a need for eye shields that are capable of overcoming the fogging problem associated with the eye shield lens or visor, particularly in challenging environmental operating conditions such as those encountered in diving applications. The inventors of the present application have surprisingly found a solution to these challenges, thus providing an improved eye shield that is suitable for use in multiple applications and environments, including use as a diving mask. SUMMARY OF THE INVENTION A first aspect of the invention is an eye shield comprising: a frame; a composite lens comprising a plurality of layers; a power supply in electrical communication with at least one of the plurality of layers of the composite lens; wherein at least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCF), the TCF comprising: a) a substrate having a surface; b) a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate; c) a conductive layer, comprising carbon nanotubes (CNTs). BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1a is a schematic view of a composite lens according to the present disclosure Figure 1 b is an alternative schematic view of a composite lens according to the present disclosure Figure 2 is a schematic of a TCF comprising a substrate having a surface and a metal-containing layer Figure 3 is a schematic of a TCF comprising a substrate having a surface, a metal-containing layer, and a conductive layer Figure 4 is a simplified illustration of an eye shield of the invention Figure 5 is a simplified illustration of an eye shield of the invention having a single composite lens Figure 6a is a schematic of nodes of a composite lens at which temperatures were determined in order to assess the defogging capability of the composite lens Figure 6b is a schematic of the temperature of various points of the composite lens when being assessed for defogging ability Figure 6c is a graph showing the average temperature determined at various points of the composite lens when heated DETAILED DESCRIPTION OF THE INVENTION The invention is an eye shield comprising: a frame; a composite lens comprising a plurality of layers; a power supply in electrical communication with at least one of the plurality of layers of the composite lens; wherein at least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCF), the TCF comprising: a) a substrate having a surface; b) a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate; c) a conductive layer, comprising carbon nanotubes (CNTs). The inventors have found that the use of a composite lens comprising a plurality of layers, wherein at least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCF) advantageously prevents fogging from occurring by keeping an internal surface temperature of the composite lens glass outside of the dew point. In addition, the composite lens comprising a heating layer can clear existing fogging in the same fashion, by heating the internal surface past the dew point. This advantageously results in significant safety benefits for users of the eye shield of the invention, and in particular divers, who as a result of the use of the eye shield of the invention are fully able to view their life support gauges and other critical equipment. The eye shield has the additional benefit of giving recreational users a better in water experience, as they will have clearer vision to enjoy the environment. Figure 1 shows a schematic view of a composite lens 100 according to the present disclosure and suitable for use in the eye shield of the first aspect of the invention. The composite lens comprises a plurality of layers 101,102,103,104. At least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCF). The TCF comprises: a substrate having a surface; a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate; and a conductive layer, comprising carbon nanotubes (CNTs). Many of the commonly available transparent conductive films used today rely upon inorganic compounds to provide the necessary conductivity. To provide the desired transparency, total film thickness is limited to about 50-100 nm. A common conductive thin film compound is indium tin oxide (ITO). ITO based thin films provide a sheet resistance of about 100 to about 300 ohms / square in useable transparency ranges. However, ITO based thin films suffer from brittleness and high costs. The inventors have surprisingly found that the use of a heating layer comprising a TCF as described herein results in a composite lens having suitable sheet resistance (Rs), chemical resistance, environmental stability and mechanical robustness for use in the eye shield of the present invention, while retaining a visual light transmittance (% VLT) of from 90% to 99%. Figures 2 and 3 show a schematic view of a transparent conductive film (TCF) according to the present disclosure. In Figure 2, the TCF comprises a substrate having a surface 201. A metal-containing layer is present on the substrate having a surface, comprising an electrically conductive arrangement 202, 203, 204 on a portion of the substrate. The electrically conductive arrangement 202, 203, 204 comprises at least one metal M, and may be a metal nanowire layer comprising the at least one metal M, or may be a metal mesh layer comprising the at least one metal M. The metal M may be copper (Cu), aluminium (Al), gold (Au), silver (Ag), or mixtures or alloys thereof. Preferably, the metal M is copper (Cu) or silver (Ag), and more preferably is copper (Cu). The metal-containing layer may comprise two different metals, such as a second metal on top of a first metal. The first metal may comprise silver (Ag) and the second metal may comprise copper (Cu). The metal-containing layer may comprise a network of interconnected metal traces with open spaces between the traces, e.g. a metal mesh. The network may be in a diamond, hexagonal, rectangular or random pattern. The metal-containing layer may comprise at least 90% open spaces. The metal traces preferably have a line width of less than about 30 microns. Metal meshes are metallic grids composed of ultra-narrow lines that provide electrical conductivity via the interconnected lines while also allowing for visible light transmittance via the spaces between the lines. Metal meshes can be created on a surface of the substrate by any viable method, including direct printing, embossing, photo patterning followed by etching, and printing followed by plating. The metal mesh can be created in a width that is sufficient for the ultimate application of the TCF. The width of the metallic lines comprising the metal mesh will depend on the method by which the metal mesh was made. Coarser metal meshes will typically have line widths of about 25 to 50 pm. Finer metal meshes will typically have line widths of about 2 to 10 pm. Preferably, the metal mesh has a line width of less than about 6 pm, such that the metal mesh is functionally not visible to the user of the eye shield when in use. The spacing between the metallic lines of the metal mesh depends on the desired visible light transmittance (VLT), the metal line width and the metallic grid pattern (e.g., hexagonal, rectangular, random, etc.). The metal lines are thick enough to essentially have negligible VLT (i.e., the metal lines either absorb or reflect almost all of the light). Thus the VLT for the metal mesh is defined mainly by the percent open area of the metallic grid pattern. The spacing between the metallic lines can be computed for the various geometries of the metallic grid pattern for a given metallic line width and VLT target. For coarser metal meshes with line width of 30 pm and percent open area of 90%, the spacing between metallic lines is about 550 pm for both hexagonal and square grid patterns. For finer metal meshes with line width of 5 pm and percent open area of 90%, the spacing between metallic lines is about 91 pm for both hexagonal and square grid patterns. Suitable nanowires for use in the electrically conductive arrangement of the TCF are electrically conductive, are preferably dispersible in solvents to enable formulation of a stable ink or coating fluid, have sub-micron features in at least one dimension, have an aspect ratio >1, may be solid or hollow, when coated will form an electrically conductive network on the substrate, and will have adequate adhesion to the substrate for processing (which may include the addition of a binder to the formulation). The nanowires have diameters typically ranging from about 5 nm to about 150 nm (e.g. about 31 nm to about 50 nm) and typical lengths of about 5 microns to about 70 microns (e.g. about 11 pm to about 20 pm). The concentration of metal nanowire per square meter may typically range from about 1 mg / m2to about 100 mg / m2 (e.g. about 30 mg / sq meter to about 55 mg / sq meter). The metal-containing layer may also include a binder that helps to bind the nanowires or metal mesh layer to the substrate. Suitable binders include soluble polymers such as polyvinylpyrrolidone, cellulose esters, polyacrylic polymers, and polyvinyl alcohol. The metal-containing layer may also include an optical brightener that modifies an optical property of the nanowire layer, such as to reduce the yellow hue that may be associated with silver (Ag) nanowires in particular. The metal-containing layer may be formed by any suitable method known in the art, including -but not limited to - flexo printing plates, electroless plating, electroplating, lithographic etching methods, lift-off patterning methods deployed in the printed circuits industry, laser ablation of a thin metal film, or combinations of any of these methods. Suitable methods for the deposition and / or formation of suitable metal-containing can be of the types disclosed in US Patent No. 9 / 777,167 and / or US Patent No. 9 / 777,168 and / or US Patent No. 11 / 393,607 and / or US Patent No. 11 / 943,865 and / or US Patent Application No. 2023 / 265,307 the entire contents and disclosures of which are incorporated herein by reference. The TCF of the heating layer of the composite lens comprises a substrate having a surface, a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate; and a conductive layer, comprising carbon nanotubes (CNTs). In Figure 3, the TCF comprises a substrate having a surface 301 and a metal-containing layer comprising an electrically conductive arrangement 302, 303, 304 on a portion of the substrate. The TCF further comprises a conductive layer 305. The conductive layer 305 comprises carbon nanotubes (CNTs). The conductive layer 305 is in electrical contact with at least a portion of the electrically conductive arrangement 302, 303, 304. The conductive layer 305 increases the conductivity of the heating layer, such that the metal-containing layer of the TCF can sufficiently heat the composite lens to achieve the desirable defogging effect. Carbon nanotubes suitable for use in the conductive layer of the TCF are electrically conductive, will form an electrically conductive network when deposited, are preferably dispersible in solvents to enable formulation of a stable ink or coating fluid, have sub-micron features in at least one dimension, have one dimension <2 nm, have an aspect ratio >1, will have adequate adhesion to the metal-containing layer and the substrate for processing, and will not be removable from the substrate by wiping. Suitable carbon nanotubes include single wall, few-wall, and multiwall tubes. Graphene or metal nanoparticles (such as a silver or other metal nanoparticles) may be added to reduce contact resistance between tubes. As used herein, CNT refers to single wall, multi-wall and few-wall tubes. Few-wall tubes are CNT having a median number of walls typically ranging from two to three walls, i.e. a batch of few-wall CNT may have some CNTs with greater than three walls; however, the primary component of few-wall CNT will have from two to three walls. In one preferred embodiment of the invention, the CNT used is a single walled CNT. Preferably, the CNT is a single wall CNT with a median diameter of about 0.84 nm and diameters ranging from but not limited to about 0.7 nm to about 1.4 nm and a median length of about 1.1 pm and lengths ranging from but not limited to about 0.3 pm to about 3 pm. The concentration of CNT / square meter may typically range from about 1 mg / sq meter to about 25 mg / sq meter. Typically, the concentration of CNT / square meter will be from about 0.5 mg / m2 to about 5 mg / m2. The conductive layer may further comprise a curable resin binder, a catalyst that is configured to be activated and cure the resin binder, and a viscous to vapor diluent, in addition to the CNTs. The conductive binder may be an organic or inorganic polymer, may allow electron transfer, is mechanically stable, provides adequate adhesion to the metal-containing layer and the substrate for processing, may enhance cohesive strength of the conductive layer, may have a low index of refraction and high visible light transmission. Suitable binders include conductive polymers such as ionomers, for example. Suitable binders include “Nation” (a sulfonated tetrafluoroethylene based fluoropolymer-copolymer ionomer); poly(arylene ether sulfone) or “BPS”; sulfonated poly(arylene thioether sulfone) or “PATS”; ethylene copolymers containing acid groups partially neutralized using metal salts such as zinc, sodium and others, or “Surlyn” a copolymer of ethylene and methacrylic acid available from DuPont. As known to those skilled in the art, Nation is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Walther Grot of DuPont identified as CAS Registry Number 66796-30-3. The Nation binder can be dissolved in isopropanol prior to addition to the ink solution. Suitable viscosity modifiers (e.g., amine-acid adducts) are described in U.S. Published Patent Application Number 2005 / 0276924, the disclosure of which is incorporated herein by reference. The TCF may further comprise a second metal layer between the metal-containing layer as hereinbefore described and the conductive layer as hereinbefore described. The second metal layer may comprise a copper layer. The copper layer may be electroplated on the metalcontaining layer. In such cases, the TCF may have a sheet resistance of no more than 1 Ohm per square (OPS). The TCF of the heating layer as hereinbefore described may be prepared by any suitable method known in the art, such as printing processes. Typically, the metal-containing layer as hereinbefore described is deposited on the substrate having a surface as hereinbefore described herein may be prepared by the printing processes described above. If required, a patterning process to determine the desired pattern for the conductive layer comprising a CNT is applied (e.g. by any suitable lithographic printing or masking process). Alternatively, the CNT may be applied (e.g. printed) in the desired pattern over the metal-containing layer without prior masking of the metal containing layer. The desired pattern may include the entire area coated with nanowires, which may or may not be the entire area of the substrate. The CNT may be applied via dispersion of the CNT dispersed in a suitable ink. Inks appropriate for use in applying CNT to the substrate coated with metal-containing layer include solvent-based, surfactant-free, screen printable inks. Optionally, such an ink may contain a binder to promote adhesion, and, optionally, a viscosity modifier to assist the coating process. Application of the CNT, binder (and optionally the viscosity modifier) containing ink to the desired regions of the substrate carrying the metal-containing layer preferably occurs via a printing process. The resulting TCF is a conductive, flexible and stretchable material. Additionally, the areas coated with both metal nano-wire and CNT may have a visible light transmission (VLT) ranging from about 85% to about 99%, more preferably a VLT of over 98%. The visible light transmission value relates only to the coating of metal nano-wire and CNT; the visible light transmission value does not include the substrate. Suitable methods for the deposition and / or formation of suitable TCFs can be of the types disclosed in US Patent No. 9 / 777,167 and / or US Patent No. 9 / 777,168 and / or US Patent No. 11 / 393,607 and / or US Patent No. 11 / 943,865 and / or US Patent Application No. 2023 / 265,307 the entire contents and disclosures of which are incorporated herein by reference. The metal-containing layer and the conductive layer in combination preferably have a visible light transmittance (VLT) of at least 85%. More preferably, the metal-containing layer and the conductive layer in combination have a VLT of at least 90%, preferably at least 95%, such as at least 97% and more preferably at least 98%. The at least one of the plurality of layers comprising a transparent conductive film (TCF) preferably has a visible light transmission of from about 85% to about 100%, preferably of from about 90% to 100%, and more preferably of from about 95% to 100%, such as about 95%, about 96%, about 97%, about 98%, about 99%, or greater than about 99%. The TCF of the heating layer comprises a substrate having a surface. The substrate having a surface may be an adjacent surface of the immediately adjacent layer of the composite lens, such as the surface of an immediately adjacent outer layer; the surface of a thermally insulating intermediate layer; or the surface of an immediately adjacent electrically insulating inner layer. Alternatively, the TCF may be deposited on a substrate having a surface, and then incorporated into the composite lens as hereinbefore described. Suitable substrates for use in the TCF as hereinbefore described have properties such as optical transparency, mechanical dimensional stability, chemical and solvent resistance, stretchability, thermoformability, surface treatments (hydrophilic or hydrophobic), surface smoothness, and temperature stability. Suitable substrates may be inorganic and / or organic, including but not limited to glass, silicon wafer, plastic films of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), thermoplastic polyurethane (TPU), cyclic olefin polymer (COP), silicone, polyimide (CPI), polyarylate, polyether sulfone, polyolefin polyethylene, propylene (PP), copolymers of poly-1-butene (PB), methyl pentene (TPX), polytetrafluoroethylene (PTFE), polynorbornene. The substrate thickness may be in the range of from about 0.5 microns to about 20 microns. Plastic substrates may have a primer layer or have a surface treatment to improve surface tension (e.g., Corona Treatment, flame treatment, other plasma, etc.), and in some examples the film thickness is in the range of between about 12.5 microns and about 300 microns. An additional layer may be added to the substrate to improve adhesion of the metal-containing layer and / or the conductive layer to the substrate. Such a layer, where present, is referred to as a “tie layer”. The tie layer may comprise methylmethacrylate copolymer, ethylmethacrylate copolymer, iso-butyl / n-butyl methacrylate copolymer, n-butyl methacrylate polymer, mono, di-, and multifunctional acrylate monomers and oligomers, functional additives having phosphate or carboxylic acid groups, monomers having functional groups such as acids, amines, hydroxyls, multifunctional organosilanes. The tie layer may be coated to a thickness of in the range from about 5 microns to 15 microns. The tie layer dry thickness is preferably in the range of from about 0.01 microns to about 1 micron. The tie layer may also include an additive that is arranged to modify an optical property of the tie layer. The metal-containing layer can add a slight yellow hue to the transmitted light. A method commonly used to minimize the impact of a yellow tone from objects is to add an optical brightener into the material. As generally known, optical brightening agents (OBAs), fluorescent brightening agents (FBAs) or fluorescent whitening agents (FWAs) are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum, and reemit light in the blue region (typically 420-470 nm) by fluorescence. Such materials are soluble in solvents and the incorporation of an OBA in the tie layer with the associated addition of blue is expected to offset the yellow hue. A non-conductive (preferably electrically insulating) protective coating may be applied over the TCF to protect the heating layer. This protective coating functions to minimise (preferably prevent) damage to the heating layer, for example by scratching, impact, or abrasion, which could impair the functioning of the heated layer and hence the eye shield as a whole. Suitable substrates and / or tie layers for use in the present invention can be of the types disclosed in US Patent No. 9 / 777,167 and / or US Patent No. 9 / 777,168 and / or US Patent No. 11 / 393,607 and / or US Patent No. 11 / 943,865 and / or US Patent Application No. 2023 / 265,307 the entire contents and disclosures of which are incorporated herein by reference. In the eye shield according to a first aspect of the invention, the composite lens comprising a plurality of layers preferably further comprises: i) an outer layer; ii) a thermally insulating intermediate layer; and iii) an electrically insulating inner layer. The electrically insulating inner layer preferably has a first surface and a second surface, wherein the first surface is in thermal communication with the heating layer comprising a TCF, and the second surface is distal from the first surface. Preferably, the first surface of the electrically insulating inner layer is in direct physical contact with at least a portion of the heating layer comprising a TCF. One preferred material for the electrically insulating inner layer is glass. Preferably, therefore, the electrically insulating inner layer comprises glass. The thermally insulating intermediate layer preferably has a first surface and a second surface, wherein the first surface is in thermal communication with at least a portion of the heating layer comprising a TCF and the second surface is in thermal communication with the outer layer. Preferably the first surface of the electrically insulating inner layer is in direct physical contact with at least a portion of the heating layer comprising a TCF. The thermally insulating intermediate layer preferably comprises at least one polymer, preferably wherein the at least one polymer is a polyacrylate or a polycarbonate, more preferably a polycarbonate. The outer layer preferably has a first surface and a second surface, wherein the first surface is in thermal communication with at least a portion of the thermally insulating intermediate layer, and the second surface is distal from the first surface. One preferred material for the thermally insulating intermediate layer is glass. Preferably, therefore, the thermally insulating intermediate layer comprises glass. In one preferred embodiment of the first aspect of the invention, the eye shield comprises: a frame; a composite lens comprising a plurality of layers; a power supply in electrical communication with at least one of the plurality of layers of the composite lens; wherein at least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCP), the TCF comprising: a) a substrate having a surface; b) a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate; c) a conductive layer, comprising carbon nanotubes (CNTs); and the composite lens comprising a plurality of layers further comprises: i) an outer layer; ii) a thermally insulating intermediate layer; and ill) an electrically insulating inner layer. Preferably, the plurality of layers are arranged, sequentially, as i) an outer layer; ii) a thermally insulating intermediate layer; iii) a heating layer comprising a transparent conductive film (TCF); iv) an electrically insulating inner layer. The inventors have surprisingly found that a composite lens having this structure is suitable for minimising or preventing fogging of an eye shield, even in the challenging use case of an underwater diving mask. The synergy between the properties of the plurality of layers of the composite lens results in an eye shield having significantly improved defogging capability compared to known eye shields in the prior art. In Figure 4, a simplified schematic illustration of an eye shield 400 of the invention is shown. The eye shield 400 is, in use, secured to the face of a user, e.g. a diver. The eye shield 400 includes a composite lens 401 and a frame 402. In use, a skirt 403 is pressed against the face of the user (e.g. a diver). The skirt 403 is generically shaped to form a seal with the face of the user. The frame 402 and / or skirt 403 may include or have attached thereto a strap 404 that extends around the user's head to secure the eye shield 400 against the face of the user. The composite lens 401 is a composite lens comprising a plurality of layers as hereinbefore described. The composite lens 401 is supported by a frame 402. The frame 402 is attached to the skirt 403. The composite lens 401 has an outer surface 411 that is directly exposed to the ambient water surrounding the eye shield 400 when in use. While the composite lens 401 is illustrated as comprising multiple lenses secured to multiple frames (e.g. a pair of composite lens pieces, one for each eye), in other examples the eye shield of the invention may comprise a single lens extending across the entire width of the face of the user. An example of such an eye shield is shown in Figure 5. The eye shield 500 includes a single composite lens 501. The composite lens 501 is supported by a frame. The eye shield as hereinbefore described, wherein the frame supports the composite lens, is suitable for contacting against a user of the eye shield. In use, a skirt that is operably coupled with the frame is pressed against the face of the user (e.g. a diver). The skirt is generically shaped to form a seal with the face of the user. As a result, when in use by a user of the eye shield, the frame defines a compartment defined by an edge of the frame, a surface of the composite lens, and a surface of the user of the eye shield. The eye shield, when in use, therefore forms an air compartment between an inner surface of the composite lens and the user of the eye shield. In use, the air within the air compartment is in direct contact with the face of the user. Typically, the user’s nose and eyes will be in direct communication with the air with in the air compartment. As such, the relative humidity and temperature of the air within the air compartment is affected by the user, such as when the user equalizes pressure within the air compartment, and is typically raised above the temperature of the ambient water. The eye shield of the invention further comprises a power supply in electrical communication with at least one of the plurality of layers of the composite lens. The power supply is preferably configured to supply an electrical current to the heating layer comprising a transparent conductive film (TCF). The power supply may contain one or more electrochemical cells, or batteries. The one or more batteries may be primary batteries. In such cases, the power supply is configured such that the primary batteries may be replaced. The power supply is preferably a secondary, or rechargeable, electrochemical cell, battery, or battery arrangement. Suitable secondary electrochemical cells, batteries, and battery arrangements are known in the prior art, including lithium ion and sodium ion electrochemical cells, batteries, and battery arrangements. Such a power supply may be chargeable without removal from the eye shield. Alternatively, or additionally, the power supply may be reversibly removeable from the eye shield such that the power supply can be charged separately, or the user may carry more than one power supply and reversibly swap out a depleted power supply for a charged power supply to extend the useable time of the eye shield having anti-fogging capability. Preferably, the eye shield further comprises an electronic control system configured to control supply of the electrical current from the power supply to the heating layer comprising a transparent conductive film (TCF). The heating layer of the TCF is preferably operably connected to the power supply and the electronic control system for selectively powering the heating layer. The heating layer, in use, is selectively powered such that the inner surface (i.e. the surface facing the face of the user) of the electrically insulating inner layer is kept above the dew point for sufficient time to minimise (preferably prevent) or remove fogging of the eye shield. The selective supply of power is such that this defogging is achieved with intermittent, interrupted, or variable electrical current being supplied to the heating layer, to extend the lifetime of the power supply and to not overheat the heating layer or the eye shield as a whole. The eye shield may further comprise a monitoring system configured to measure at least one parameter associated with the eye shield. The parameter may be a temperature of a surface of the composite lens, a power supply charge status, or a power supply safety status. The monitoring system is configured to transmit a signal to the electronic control system, the electronic control system is configured to receive the signal from the monitoring system, and the electronic control system is configured to alter an output property of the power supply in response to the signal from the monitoring system. In one example, the monitoring system may comprise one or more temperature sensors which can communicate with the electronic control system. A temperature sensor may be configured to sense, or measure, the temperature of the air within the air compartment, or at a surface of the composite lens. The electronic control unit can regulate the heating layer based on the temperature measurement. This can be done by reducing power or altogether turning off power to the heating layer. Additionally, or alternatively, the monitoring system may comprise one or more water contacts that sense liquid water within the air compartment. The water contacts are connected to the electronic control unit. When a threshold value related to the measurement of liquid water is sensed by the water contacts, the electronic control unit can be configured to deactivate the heating layer and / or the power supply. In this way, the monitoring system may be configured to measure a power supply safety status, and, via the electronic control unit, alter the power output of the power supply in response to the signal from the monitoring system. The power supply and the electronic control unit may be a single component. Alternatively, these components may be separate. For instance, the electronic control unit could be located proximate the side of a user's head, while power supply may be remote from the electronic control unit, such as attached to a strap at the back of the user's head. Alternatively, the electronic control unit and the power supply could be on opposite sides of the user’s head so as to balance the weight of the eye shield. The power supply may be integral with the eye shield. When present, the electronic control system may be integral with the eye shield. When present, the monitoring system may be integral with the eye shield. Preferably, at least one of the power supply and the electronic control unit are integrated into the frame of the eye shield. More preferably, both the power supply and the electronic control unit are integrated into the frame of the eye shield. The eye shield of the invention may further comprise at least one bus bar for connecting the heating layer comprising a TCF with the power supply. The at least one bus bar is preferably located on a peripheral edge of the frame. In this way, the power supply may, when integral with the frame, provide electrical power to the heating layer via the at least one bus bar. EXAMPLES Materials A composite lens was formed from the following layers: 1. an electrically insulating inner layer (glass; 0.5 mm thickness) 2. a heating layer comprising a transparent conductive film (TCF) in the form of a foil (less than 0.5 mm thickness) 3. a thermally insulating intermediate layer (polycarbonate; 1 mm thickness) 4. an outer layer (glass; 2 mm thickness) The TCF used is commercially available as AgeNT (RTM) by CHASM Advanced Materials. To assess the suitability of the composite lens for use in an eye shield, particularly in underwater conditions, a calculation of the temperature of various nodes in the composite lens over time was conducted. The results are shown in Figure 6. The simulated underwater test conditions used were as follows: • inside air temperature: 10 °C • outside water temperature: 3 °C • internal starting temperature: 5 °C • No “waterspeed”; convection coefficient of water: 1000 r m2K • No “airspeed”; convection coefficient of air: 1000 K m2K • Heater power density: 1000 Figure 6a shows the nodes at which temperature of the composite lens was measured. Figure 6b shows a heatmap of the composite lens overtime. The graph in Figure 6c shows that the average temperature at the external surface of the outer layer was, on average, about 4 to about 5 °C. After an initial ramping period of about 60 seconds, the average temperature of the internal surface of the inner layer was about 13 to 14 °C. The composite lens was therefore capable of maintaining a temperature differential between the outer layer and the inner layer under the test conditions, and is therefore suitable for use in an eye shield with a defogging effect.

Claims

1. An eye shield comprising:a frame;5 a composite lens comprising a plurality of layers;a power supply in electrical communication with at least one of the plurality of layers of the composite lens;wherein at least one of the plurality of layers is a heating layer comprising a transparent conductive film (TCF), the TCF comprising:10 a) a substrate having a surface;b) a metal-containing layer, comprising an electrically conductive arrangement comprising at least one metal M on at least a portion of the surface of the substrate;c) a conductive layer, comprising carbon nanotubes (CNTs); andwherein the composite lens comprising a plurality of layers further comprises:15 i) an outer layer;ii) a thermally insulating intermediate layer; andiii) an electrically insulating inner layer.

2. The eye shield according to claim 1, wherein the electrically conductive arrangement is a metal nanowire layer or metal mesh layer comprising the at least one metal M.

203. The eye shield according to claim 1 or claim 2, wherein the metal M is copper (Cu), aluminium (Al), gold (Au), silver (Ag), or mixtures or alloys thereof.

4. The eye shield according to any preceding claim, wherein the metal M is copper (Cu).

255. The eye shield according to any preceding claim, wherein the conductive layer comprises CNTs in an amount of from 1 mg CNT / m2to 10 mg CNT / m2.

6. The eye shield according to any preceding claim, wherein the conductive layer further 30 comprises a conductivity aid, preferably wherein the conductivity aid is selected from conductive nanoparticles and graphene.

7. The eye shield according to any preceding claim, wherein the conductive layer further comprises a binder, preferably wherein the binder comprises a polymer.3526 0.3 258. The eye shield according to any preceding claim, wherein the electrically conductive layer further comprises a layer on the substrate that promotes adhesion between the surface of the substrate and the metal-containing layer, the conductive layer, or both the metal-containing layer and the conductive layer.

59. The eye shield according to any preceding claim, wherein the at least one of the plurality of layers comprising a transparent conductive film (TCF) has a visible light transmission of from about 95% to about 100%.10 10. The eye shield according to claim 9, wherein the electrically insulating inner layer has afirst surface and a second surface, wherein the first surface is in thermal communication with the heating layer comprising a TCF, and the second surface is distal from the first surface.

11. The eye shield according to claim 10, wherein the first surface of the electrically insulating 15 inner layer is in direct physical contact with at least a portion of the heating layer comprising a TCF.

12. The eye shield according to any of claims 9 to 11, wherein the thermally insulating intermediate layer has a first surface and a second surface, wherein the first surface is in thermal 20 communication with at least a portion of the heating layer comprising a TCF and the second surface is in thermal communication with the outer layer.

13. The eye shield according to claim 12, wherein the first surface of the electrically insulating inner layer is in direct physical contact with at least a portion of the heating layer comprising a 25 TCF.

14. The eye shield according to any of claims 9 to 13, wherein the outer layer has a first surface and a second surface, wherein the first surface is in thermal communication with at least a portion of the thermally insulating intermediate layer, and the second surface is distal from the 30 first surface.

15. The eye shield according to any of claims 9 to 14, wherein the outer layer comprises glass.

16. The eye shield according to any of claims 9 to 15, wherein the electrically insulating inner35 layer comprises glass.26 0.3 2517. The eye shield according to any of claims 9 to 16, wherein the thermally insulating intermediate layer comprises at least one polymer, preferably wherein the at least one polymer is a polyacrylate or a polycarbonate, more preferably a polycarbonate.5 18. The eye shield according to any preceding claim, wherein the frame supports thecomposite lens, and is suitable for contacting against a user of the eye shield.

19. The eye shield according to any preceding claim, wherein, when in use by a user of the eye shield, the frame defines a compartment defined by an edge of the frame, a surface of the 10 composite lens, and a surface of the user of the eye shield.

20. The eye shield according to any preceding claim, wherein the power supply is configured to supply an electrical current to the heating layer comprising a transparent conductive film (TCF).15 21. The eye shield according to claim 20, further comprising an electronic control systemconfigured to control supply of the electrical current from the power supply to the heating layer comprising a transparent conductive film (TCF).

22. The eye shield according to any preceding claim, further comprising a monitoring system 20 configured to measure at least one parameter associated with the eye shield, wherein the at least one parameter is a temperature of a surface of the composite lens, a power supply charge status, or a power supply safety status.

23. The eye shield according to claim 22, wherein the monitoring system is configured to 25 transmit a signal to the electronic control system, the electronic control system is configured to receive the signal from the monitoring system; andwherein the electronic control system is configured to alter an output property of the power supply in response to the signal from the monitoring system.30 24. The eye shield according to any preceding claim, wherein the power supply is integral withthe eye shield, preferably wherein, when present, the electronic control system is integral with the eye shield and, when present, the monitoring system is integral with the eye shield.24

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