GB2556066B

GB2556066B - A radiant emitter

Info

Publication number: GB2556066B
Application number: GB1619409.4A
Authority: GB
Inventors: Emily Phillips Rebecca; Walters Ian
Original assignee: Perpetuus Research & Development Ltd; Perpetuus Res & Development Ltd
Current assignee: Perpetuus Research & Development Ltd; Perpetuus Res & Development Ltd
Priority date: 2016-11-16
Filing date: 2016-11-16
Publication date: 2019-08-28
Anticipated expiration: 2036-11-16
Also published as: GB2556066A

Description

A radiant emitter

This invention relates to a radiant emitter and in particular a radiant emitter in the form of a heating panel comprising graphene for use in an interior zone of a building.

Conventional heating in the home primarily functions by warming the surrounding air; for example, a radiator provides most of its heating through convection currents. The radiator heats the air directly around it causing the air to expand and rise. As the hot air rises it creates a vacuum behind it, pulling colder air into contact with the radiator, causing the cold air to heat up and rise. As the hot air cools down it drops back to the floor level and is pulled back into close proximity to the radiator once again where the process is repeated. Such a convection method of heating is inefficient and it is preferable to heat only the surface areas within the targeted environment, rather than the atmospheric volume contained therein. Further, traditional convection warmed room environments are penalised when a window or door is opened since hot air escapes requiring greater energy consumption to reheat the new cold air in the room, which replaces the escaped warm air.

Infra red radiation travels through space and warms objects in its travel path. Infrared heats any object within the targeted environment providing thermal mass, for example ceilings, walls, floors, furniture and people. The objects within the target environment capture and emit heat therefore contributing significantly to energy cost reduction by effectively keeping the environment at a comfortable temperature. Since Infrared heats considerably less mass to provide the same amount of heat as conventional heaters, it is more efficient compared to conventional heaters.

Most conventional heating systems emit some form of infrared waves, however heat via infrared is usually limited.

Various solutions are known that attempt to improve the efficiency of heating a zone within a building at a reduced energy cost. For example, a recent addition to the domestic and commercial heating sector is infrared heaters, whereby infrared is emitted from a resistive heating element. The infrared radiation travels unimpeded through the air until it collides with an object in its path. The object absorbs the radiation, causing molecules within it to vibrate, and heat is generated. However such IR heaters have low efficiency characteristics and form hot spots on their surface and can malfunction and cause fires due to air enclosures in the heating substrate.

Embodiments of the present invention are derived from the realisation that there exists the need to provide a versatile radiant emitter that efficiently and economically heats and maintains the temperature of objects in a target environment reliably, efficiently and safely. Therefore, the present invention and its embodiments are intended to address at least some of the above described problems and desires.

According to a first aspect of the invention there is provided a radiant emitter for heating an area having a heat demand comprising a first carrier material; a second carrier material spaced apart from the first carrier material; a bonding layer configured to fix the spacing between the first carrier material and the second carrier material; a barrier layer comprising barrier material interposed between at least the bonding layer and the first carrier material; and an electrically conductive layer comprising a graphitic material being positioned on the surface of or within the first carrier material, wherein the graphitic material comprises a first graphitic material layer and a second graphitic material layer, the first graphitic material layer being spaced apart from the second graphitic material layer.

The carrier material may be glass and the carbon based electrically conducting material may be capable of adhering to the surface of the glass in a permanent manner. The strong relative adhesion between the carrier material and carbon based electrically conducting material is maintained even on applying an electrical current through the conducting material. Therefore the adhesive property is maintained across a predetermined temperature range experienced by the conducting layer and the first carrier layer.

The carbon based electrically conducting material comprises a graphitic material.

Use of the graphitic material offers good electron conductivity making the conductor suitable for use as a resistive element of the radiant emitter.

The graphitic material may be laminated to a surface of the first carrier material. This means that the conducting material is a coating applied to a surface of the carrier material, such that the carrier material can be considered to be a substrate for the conducting material.

The radiant emitter comprises a second carrier material spaced apart from the first carrier material; a bonding layer configured to fix the spacing between the first carrier material and the second carrier material, and a barrier layer comprising barrier material interposed between at least the bonding layer and the first carrier material. The barrier layer is essentially arranged in this way so as to prevent migration of the bonding layer into the conducting layer during the autoclaving process. The autoclaving process is required to remove any air from between the layers of the radiant heater this not only provides improved adhesion, minimises the risk of hotspots on the surface, but also increases the safety performance of the radiant heater.

The graphitic material located on the first carrier material may be directed towards the second carrier material such that the barrier material is intermediate the graphitic material and the bonding layer. It is in fact paramount that the carrier material is the external layer of the front of the radiant emitter, therefore it is the conducting layer that comes into contact with the barrier layer. The conducting layer need not be applied to the entire rear surface of the carrier layer and in fact a peripheral edge (forming a frame shape) may be provided. Therefore, the bonding material may be in contact with the rear surface of the carrier layer at this peripheral edge.

The bonding layer may be interposed between a first and second conducting layer applied to the respective first and second carrier materials wherein the barrier layer is provided between the first conducting layer and the bonding layer and the second conducting layer and the bonding layer; and wherein the first conducting layer is the electrically conductive layer. This enables the first carrier layer and the second carrier layer to both provide the IR emission for a room. In this case the second carrier layer is also exposed towards objects in a room to be heated. The barrier layer therefore acts as an isolation layer between the bonding layer and the conducting layer.

The graphitic material and the barrier material may be the same material. This is a benefit since the conducting layer and the barrier layer are guaranteed to be compatible from a structural and electrical perspective.

The electrically conductive layer may have a resistance value that is less than the resistance value of the barrier material. This occurs since the bonding material (which is an insulator and thus has a very high resistance associated with it) migrates into the bonding layer during the autoclave process. Therefore the result is that the barrier material is actually formed of a combination of the manufactures graphitic material and the bonding material.

The radiant emitter may further comprise an electrode assembly in electrical communication with the electrically conductive layer and/or the barrier layer. The electrode may be a bus bar to enable the distribution of electricity through the conducting layer. This is suitable to 3-phase applications and can be formed of a metal e.g. copper, brass or aluminium or an alternative material that grounds and conducts electricity at the same time.

The graphitic material may be platelet-like.

The first graphitic material layer may have an undulating structure.

The graphitic material comprises a first graphitic material layer and a second graphitic material layer, the first graphitic material being spaced apart from the second graphitic material.

The first graphitic material layer may be slideable with respect to the second graphitic material layer. This aids the adhesion properties of the conducting layer and also allows for homogenous distribution on the carrier surface.

The first graphitic material layer may be a first sub-structure and the second graphitic material layer a second sub-structure, the first and second sub-structures including a stack of graphitic material layers, in which separation between successive stacked substructures is greater than the separation between successive graphitic material layers in each sub-structure

The separation between successive stacked substructures may be variable.

The separation between successive stacked substructures may increase the surface area of the graphitic material.

The separation between successive stacked sub-structures may be in a range 2 to 100 nm, preferably 5 to 50 nm, more preferably 10 to 30 nm, most preferably 10 to 20 nm.

The sub-structures may each have a thickness which is in the range of 1 to 15 nm, preferably 1 to 4 nm.

Each sub-structure may include a stack of between 2 and 12 graphitic material layers.

The sub-structures may each have a stack thickness, and the stack thicknesses of the sub structures may be less than the separation between successive stacked sub-structures.

The first and second graphitic material layers may have a net negative charge.

In use, the temperature of the graphitic material of the electrically conductive layer may be of a value in a range of 30 °C to 120 °C, more preferably 70 °C.

The graphitic material may be graphene or stacks of graphene.

The radiant emitter may further comprise an electricity source in electrical communication with the graphitic material of the electrically conductive layer. The electrical communication between the electricity source and the conducting layer is provided via the electrodes or bus bars. Alternatively the radiant emitter may be powered by mains electricity via a standard plug and socket arrangement.

The temperature distribution across the graphitic material may be substantially uniform. This is achieved due to the excellent dispersion properties of the graphene stacks in the ink that is applied to the surface of the carrier layer.

The carrier material may be flexible. This makes it application to use on a wide range of objects, for example seats in a car.

The carrier material may comprise paint, wood, fire brick, rubber or steel or a combination thereof.

Preferably, the carrier material may comprise glass.

According to a second aspect of the invention there is provided a heating system comprising at least one radiant emitter as hereinbefore described, an electricity source and a control unit for selectively controlling the at least one radiant emitter and/or the electricity source.

In an alternative embodiment of the invention there is provided a method of manufacturing a radiant emitter as hereinbefore described, wherein a conducting paste, ink or slurry is applied to the surface of the first carrier material and the surface of the first carrier material is subsequently heated. Alternatively, a conducting paste, ink or slurry may be applied to the surfaces of the first and second carrier materials and the surfaces of the first and second carrier materials may be subsequently heated. The carrier material may be glass and the conducting ink may comprise the graphene stacks dispersed uniformly in the ink. An initial bonding process may be applied, for example to ensure that the initial positioning of the layers is achieved.

The first and second carrier materials may be subsequently placed into an autoclave. This ensures that the quality of adhesion is achieved by removing the air from between the layers and to improve the contact area between each of the layers. During this process the bonding layer migrates into the barrier layer. If the barrier layer was not included then the bonding layer would disrupt the graphene film by interacting with the conducting layer on lamination thereby undesirably increasing the resistivity of the conducting layer and decreasing the efficiency of the IR emission.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic cross sectional view of the radiant emitter according to the invention;

Figure 2 is an exploded schematic perspective view of the radiant emitter of Figure 1;

Figure 3a shows a front view of the radiant emitter of Figure 1;

Figure 3b shows a view of the front face of the radiant emitter according to the invention;

Figure 4 shows an IR image of the radiant emitter in use;

Figure 5a shows the graphene stacks;

Figure 5b shows the graphite starter material;

Figure 6 shows the gap between a first graphitic layer and the second graphitic layer of a graphene stack;

Figure 7 shows the results of a steel ball test on the toughened glass radiant emitter; and

Figure 8 shows a cross sectional schematic view of an alternative embodiment of the radiant emitter of the invention.

Referring firstly to Figure 1, there is shown a radiant emitter 1 comprising a front face carrier layer 2 and a rear face carrier layer 3 spaced apart from each other. The front face carrier layer 2 is the layer that is presented towards the room in use whereas the rear face carrier layer 3 is located remote from the room during use. The front surface 2a of the first carrier layer 2 faces outwardly towards the objects to be heated. The front face carrier layer 2 supports a conducting material layer 4 on its rear side 2b. The conducting layer 4 is made from a carbon based material, for example a graphitic material. The rear carrier layer 3 is in contact with a bonding layer 5 formed of bonding material. A shielding barrier layer 6 is provided between the bonding layer 5 and the conducting layer 4 for preventing the bonding material from migrating into the graphitic conducting material layer 4. Electrodes 7a, 7b are located in electrical communication with the conducting layer 4. The electrodes 7a, 7b can alternatively be located in the barrier material which is still in electrical communication with the electrically conducting layer.

The electrically conducting layer 4 is of a thickness of 25 pm and has a resistivity value of 7 Ω/sq. The barrier layer can be of a thickness of between 25pm to 125 pm. Migration of the bonding agent into the conductive layer can elevate the resistivity of the conductive layer, which results in a dilution of the efficiency of the heating system. The bonding layer is Polyvinyl butyral (PVB) adhesive which is a well known resin used in the formation of toughened glass i.e. laminated safety glass. PVB is prepared from polyvinyl alcohol by reaction with butyraldehyde.

The barrier layer 6 can be formed of the same material as the conducting layer 4 which obviously ensures that the conducting layer and the barrier layer are compatible, however due to the migration of the bonding layer into the barrier layer 6 the resistivity of the barrier layer 6 differs to the resistivity of the conducting layer 4 since the resistivity of the barrier layer is dependent on a combination of the bonding layer and the graphitic material of the barrier layer 6. The barrier layer 6 is therefore a sacrificial layer that is included to ensure that the resistivity of the conducting layer remains at the predetermined value to provide the predetermined temperature at the front surface of the carrier layer 2. Since the laminated glass bonding layer 5 is an electrical insulator, the resistivity value of the barrier layer 6 is greater than the resistivity value of the conducting layer 4.

The graphitic conducting material layer 4 is laminated to the rear surface of the front facing carrier material 2 and as shown in Figure 1 and Figure 2 the electrodes 7a, 7b are placed on the underside of the front facing carrier layer and are spaced apart from each other to permit the electric current to conduct through the conducting material so that it behaves as a resistive element.

The barrier layer 6 which provides the shielding effect from migration of the bonding layer to the conducting layer is laminated to the graphitic conducting layer 4.

The forwardly and rearwardly facing carrier materials 2, 3 are formed of a flexible substrate. The radiant emitter is shown as a glass panel heater or glass radiator in Figure 3a and Figure 3b and is sized to be 900mm by 300mm so as to provide IR radiation for an average sized room.

The graphitic material used to form the conductive layer contains stacks of graphene material layers and are formed of a first and second graphitic layer so as to form a graphitic stack 8.

The graphitic layers are platelet like, or flake like and have an undulating structure, which means the distance between the successive stacked substructures is variable.

Without wishing to be bound by any particular theory or conjecture, it is believed that the graphitic stacks 8 and the graphenes within the stacks have a net negative charge which acts to keep the first and second material (or substructures) apart and aids the dispersal of material within the vehicle employed as a means of printing a surface with a conductive membrane. Defects are provided, within the graphenes contained in the graphitic stacks 8 e.g. Stone Wales defects that gives rise to the relatively large separations between substructures. It is believed that the relatively large major gaps (or spaces) between sub-structures or layers improve friability of the material, whereby application of a small force will overcome the force that holds the first and second material, in a predetermined spaced arrangement. This therefore means that the first graphitic material is slideable with respect to the second graphitic material providing high expansion and contraction tolerances. This gives rise to improved packaging, handling and incorporation of the material into a liquid media. In contrast, prior art nanoparticles such as CNTs, GNPs and single flakes of graphene are notoriously difficult to handle and disperse, and commonly exhibit a high degree of entanglement and poor friability. This is ultimately because the prior art exhibits relatively flat stacked structures that have sized gaps 9 between the layers that are unable to host intercalate, since the spacing is too small.

The sliding nature of the stacks 8 enables good adhesion properties to be realised when the stacks are applied to a glass surface. The excellent dispersive properties of the graphene stacks 8 in a solvent to form an ink to be applied to the carrier layer also ensures that a homogenous conducting element is produced whereby the IR emission is uniform i.e. does not possess hot spot regions as shown in Figure 4. Figure 4 also shows that the radiation does not pass through the side edges of the heater surface. This is because the bonding layer extends to the region above and below the conducting layer 4 and barrier layer 6 (not shown) so as to be located between the first carrier material 2 and second carrier material 3.

The temperature of the exposed face of the first carrier material 2 can be predetermined and depends on the intended use of the radiant emitter 1, for example when the radiant emitter 1 is to be used in a conventional dwelling in an accessible location the surface temperature of the exposed surface of the radiant emitter 1 is configured to not exceed 70 °C so as to meet regulations. However in a care home or a health institution the temperature is configured not to exceed 60 °C, again so as to meet regulations. Similarly if the radiant emitter 1 is to be installed in a position not easily accessible by a person, the temperature of the front surface may be increased to emit at far IR rather than low to mid IR and as such a surface temperature of 120 °C can feasibly be implemented. Alternatively, a lesser surface temperature is required where a radiant emitter of a large surface area is applied, for example applying the radiant emitter 1 to the entire ceiling of a room would beneficially require a reduced resistivity of the conducting layer 4.

For the avoidance of doubt, the exposed face of the first carrier material 2 is that which is remote from, and not in contact with the conducting layer 4. A further advantage associated with the relatively large gaps 9 of the graphene stacks 8 is that a decorate material can be intercalated into the gap or space between the first and second graphitic material. To enable this, the space between the first and second material, is a minimum of 2 nm. The graphitic material as shown in Figure 5a has an undulating morphology, whereby the layers of a starting material, for example graphite as shown in 5b, have been twisted and buckled so as to provide graphene flakes that have a random waved morphology with the gaps or spaces being provided between the undulating graphene layers. Electro-active materials, for example polyethylenedioxythiophene, are used as the intercalate which are inserted into the gaps subsequent to the gaps being formed.

The provision of the gaps prior to introducing the electro-active material increases the surface area of the graphitic material enabling more infrared emissions to be generated. In fact the stacked arrangement has a massive surface area, approximately 800 meters per gram. Further the gaps allow electro-active material to be accommodated in the stacked material compared to other known structures.

The stacked material used in the radiant emitter is a flexible yet highly crystalline structure which has been revealed by XRD analysis whereby both the alpha graphitic form (hexagonal) and beta graphitic form (rhombohedral) have been observed. This high level crystallinity facilitates conductivity through the material. This therefore provides a conductive framework for electron transport making it suitable for use as a resistor.

The stacked material is highly stable and durable making it particularly appropriate for use in domestic and commercial buildings.

In plane defects or vacancies (not shown) are also included in the morphology of the graphene layers providing a shortcut for free ion travel where appropriate. The graphitic material comprises several layers. Commonly, there are observed a first plurality of successive sub-structures having edges that are substantially in alignment, followed by a second group of successive substructures having edges which are substantially in alignment, but which are not necessarily aligned with the first plurality of sub-structures, and so on. It has been shown that each sub-structure comprises a number of layers of graphene. Typically there are about ten layers of graphene in each sub-structure. Often, sub-structures are observed to have about three graphene layers with a substructure thickness of about 2.1 nm. The minor gaps between successive layers in the sub-structures 5 are about 0.5-0.8 nm.

Apparatus suitable for producing the stacked material used in the radiant emitter of the invention has been described in our International patent application number PCT/GB2015/050935. The graphitic material forms a resistive element capable of emitting Infrared radiation. The substrate and the graphitic material combined form a 600W infrared heat panel which is used to heat a room in the same way as a radiator. The resistor 4 is connected in a closed electric circuit which also includes an electricity supply, or alternatively is connected to the mains electricity.

The radiant emitter 1 has multiple layers that provide a structure where the bonding layer 5 keeps the first and second carrier layers in the same location when broken, thereby preventing the glass from breaking up into large sharp pieces. This is especially important where the first and second carrier layers 2, 3 are formed of glass. This produces a characteristic "spider web" cracking pattern when the impact is not enough to completely pierce the glass as shown in Figure 7. This glass is known as toughened glass.

The radiant emitter 1 can be used in an infrared heating system (not shown) in which the heater panel is connected in a circuit having a power source and the resistance of the conducting layer can be controlled via a control panel, whereby the temperature is monitored by electrical sensors and a feedback mechanism is implemented accordingly. Multiple radiant emitters can be configured to operate in zones whereby the temperature of one zone, for example the bedrooms, may be controlled independently from that of another, for example the living quarters.

Figure 8 shows an alternative embodiment of the invention, where the external surface of the first carrier layer 2 and the second carrier layer 3 are both presented to a zone containing objects to be heated. For example such a configuration could be used on a staircase or the like. In this embodiment the bonding material is located at the centre of the radiant emitter and the carrier material with a conducting layer is provided either side of the bonding layer. A first barrier layer 6 is interposed between the first conducting layer 4 and the bonding layer 5 and a second barrier layer 6’ is provided between the second conducting layer 4’ and the bonding layer 5.

The first and second graphitic material is applied to the substrate in the form of a particle dispersion. To produce the particle dispersion a binder material (not shown), for example PTFE, is mixed with an organic solvent and the powder is added to the solution (which is a liquid medium) and is milled for 3 hours, to obtain a slurry. The resulting particle dispersion is used as a surface transferable material.

Production of a radiant emitter

To form a radiant emitter 1 as shown in Figure 1, the graphene enabled coating layer provides a robust bond to the carrier material which is, for example glass.

The slurry (not shown) is spread on a substrate i.e. the carrier material, using a slot die coating technique, or alternatively the slurry may be applied to a non-conducting substrate previously treated with a conductive material. The coating on the radiant emitter is dried under a vacuum at 125°C for 5 minutes. This produces a coherent film or layer on the substrate 2. The coating process can be repeated until a coating of the desired thickness is achieved. Suitable coating thicknesses range from 0.3 microns to 250 microns.

The formation of a slurry incorporating the graphitic material enables current printing or coating technology to be utilised which allows rapid and easily reproducible production of the heat panel of the radiant emitter.Toughened laminated glass with the graphene enabled heating element printed or coated onto the inner surface of the front glass panel and laminated to the inner surface of the rear glass panel is also a preferred safety option for a glass graphene enabled radiant heater.

Laminated glass is produced by bonding two or more layers of tempered glass together with a polymer adhesive interlayer, typically polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA). The PVB or EVA laminating layers are inserted in between the glass layers, and bonded by pressure through a series of rollers, or vacuum bagging systems, and ovens, or autoclaves, to expel any air pockets.

Once the layers of the radiant emitter are brought together, the multilayer structure is heated to form the initial melt bond. The multilayer structure is subsequently heated under pressure in an autoclave or oven, to achieve the final product. This ensures that there are no air pockets in the final product and ensures a stronger more reliable bond is achieved. Colored P.E.T. films can be combined within the thermoset material, during the laminating process, in order to obtain a colored glass.

The laminated glass radiant heater may use two or more pieces of graphene coated glass of equal or unequal thickness bonded between one or more adhesives layers; such as PVB or EVA, preferably by means of laminating with heat and pressure. Alternatively two or more pieces of glass and or polycarbonate may be coated with a graphene layer, bonded together with an aliphatic urethane or EVA interlayer under heat and pressure. This may be interlaid with a cured resin or EVA.

Without wishing to be bound by any particular theory or conjecture, it is the essential autoclave step that causes the migration of the bonding layer 5 into the conducting layer 4.

Use of the first and second graphitic material applied to a glass substrate to form a heat panel provides a more targeted heating system which rapidly provides the optimum desired heating temperatures after a few minutes of being turned on and which is efficient and economic for the user, substantially eliminates convection currents which is a benefit to those who suffer from asthma and dust allergies and comprises no moving parts, which as a result provides a system with zero noise.

The panels are suitable for a wide range of applications, particularly in the home, office, healthcare and educational sectors, and can help to reduce energy consumption and hence carbon emissions. The output from the radiant panel will be predominantly radiant, but there will also be some convective heat output from the panel’s surface due to air movement in the room.

Radiant heat transfer is determined by the panel emissivity i.e. the ability of the panel to radiate heat. Radiant heating panels can be surface mounted, freely suspended or integrated within a wall suspended ceiling, or other architectural structures and features. Panels may be grouped to provide zone control (for energy efficiency and comfort); directly controlled by thermostatic valves; or linked into a central control system. The panels may be curved and profiled to fulfill aesthetic requirements, and can be positioned with drop rods, wires or chains.

By mounting the heating system at elevated levels, the flexibility of the use of the occupied space is improved, whilst at the same time reducing potential damage and tampering thereby hence reducing maintenance requirements and associated costs. The elimination of heating surfaces from the reach of occupants also reduces the potential for injury.

Since the heat transfer mode is predominantly radiant rather than via convection, there is fewer undesirable air movement in the space, for example especially in controlled environments, such as laboratories and clean rooms, where air and dust movement must be kept to a minimum, also where specific air movement management is required for infection control.

Radiant panels create virtually no noise and are therefore advantageous in areas such as health care establishments, theatrical, educational and sound recording studios.

The invention relates to radiant electric heaters, such as wall type ceiling and floor type heaters in which a laminated glass graphene-heating element is incorporated within the laminated glass, preferably coated on the underside 2b of the forwardly facing glass panel. This construction ensures an efficient intimate contact between the graphene enabled heating element and the radiating surface, thus efficiently extending the thermal transfer to the face of the panel.

Various modifications to the principles described above would suggest themselves to the skilled person. For example, the substrate need not be rigid and may instead be a flexible structure. Other suitable materials for the substrate include: ceramics, wood plastics and fibres reinforced with carbon fibre or other textiles.

Alternatively, referring to the paint embodiment, the wet binder (not shown) may be polyurethane, polyethylene, polypropylene, polyvinylidene difluoride, styrene-butadiene rubber, carboxymethyl cellulose or organic polymers that conduct electricity such as polyaniline or a binder may not be applied at all. In fact it is preferable not to use a binder since they tend to be insulating. The choice of the binder system will ultimately depend on the thermoplastic or cross-linkable polymer species to be implemented.

Instead of an organic material the binder and composite material mix may be added to water.

Instead of a slurry, the powder may be mixed to form a paste or an ink, depending on the desired rheology. The ink is of particular interest since it can be printed onto a desired substrate with ease.

Additional volumes of electro-active materials may be added to the slurry if desired in addition to the electro-active material already applied to the wavy graphene stack.

The coating method, be it using static bed or reel to reel techniques, may be implemented and may include flexographic printing, screen-printing or stencil printing as alternatives to slot die printing.

In the case of use of cross-linkable binders the coating must be cured instead of dried (which is the technique used for thermoplastic binders).

As an alternative to bead milling, the coating may be formed by roll milling or high speed dispersing techniques.

Instead of using a wet method of forming the heat panel (using a slurry or ink), a dry method (not part of the claimed invention) may be implemented, whereby a treatment may be performed on the stacks to decorate the surface of the substrate by means of a binding material. A suitable binding material is Polyethylene, Polypropylene or a rubber (such as Nitrile Butadiene or Styrene Butadiene rubber). The resulting material is then compression moulded or casted to form the heat panel. This dry method provides a solvent free process forming a heat panel having a higher specific surface area, higher energy storage capacity and an improved or higher packing density compared to the wet method.

The surface of the stack may be doped with a species that may promote conductivity such as nitrogen or amines.

The stacked material may be a nano-material, whereby at least one dimension of the material is less than 1000nm.

The electrode placements need not be included in the material and as such they are an optional feature.

Instead of being placed on the underside of the front face layer, the electrodes can instead be provided within the graphitic conducting layer 4 or on the rear of the shielding barrier layer 6. Regardless of the location the electrodes are still in electrical communication with the conducting layer 4. The electrodes may be bus bars or an alternative conducting element attached in electrical communication with the conducting layer 4.

The barrier material need not be formed of the same material as the conducting material and may instead be formed of a dielectric for example titanium dioxide, epoxy-resin, polyester or acrylic.

Whilst the above embodiments have considered a planar set up for the radiant emitter, in an alternative embodiment of the invention, the radiant emitter may be cylindrical in form whereby the second carrier would be a central core portion and the layers will be arranged concentrically with the central core. This arrangement offers a free standing radiant emitter that may be positioned at a central location of a room rather than at a peripheral region. This offers a radiant heater that is portable. To enable this embodiment the carrier is a rigid structure that has been formed into a predetermined shape. In this example the shape is cylindrical, but alternative shapes may be considered. This embodiment may provide a modern ornament with the capability of providing IR radiation to heat up objects located within the vicinity.

In an alternative embodiment of the invention the surface temperature of the external surface 2a of the first carrier layer 2 may exceed regulatory values to be applied in a building, it is then therefore necessary to configure a thermally insulating layer as a protective measure at the external surface 2a, which reduces the surface temperature of the heater panel to an acceptable 70°C or less (or 60 °C in a care home). The insulating material is a double glazing unit type arrangement formed of a first and second thermally insulating panel, the first panel being configured in parallel relationship with the second panel with a space defined there-between. The panels are made from glass, but other suitable thermally insulating materials may be applied. A suitable thermally insulating material is provided within the space between the first and second panel, for example air, is capable of transmitting IR waves there-through. A spacer is provided between the first and second panel and around their peripheral edge. It may comprise a single panel or more than two panels without or with multiple air gaps.

In an alternative embodiment that bonding material may be solvent based. Therefore instead of a melt bond, the initial step may be provided by a solvent bond.

The dimensions of the radiant emitter can be varied dependent upon the space in which it is to be applied.

Claims

1. A radiant emitter for heating an area having a heat demand comprising a first carrier material; a second carrier material spaced apart from the first carrier material; a bonding layer configured to fix the spacing between the first carrier material and the second carrier material; a barrier layer comprising barrier material interposed between at least the bonding layer and the first carrier material; and an electrically conductive layer comprising a graphitic material being positioned on the surface of or within the first carrier material, wherein the graphitic material comprises a first graphitic material layer and a second graphitic material layer, the first graphitic material layer being spaced apart from the second graphitic material layer.

2. A radiant emitter according to claim 1, wherein the graphitic material is laminated to a surface of the first carrier material.

3. A radiant emitter according to claim 1, wherein the graphitic material located on the first carrier material is directed towards the second carrier material such that the barrier material is intermediate the graphitic material and the bonding layer.

4. A radiant emitter according to claim 3 wherein the bonding layer is interposed between a first and second conducting layer applied to the respective first and second carrier materials wherein the barrier layer is provided between the first conducting layer and the bonding layer and the second conducting layer and the bonding layer; and wherein the first conducting layer is the electrically conductive layer.

5. A radiant emitter according to any of claims 1 to 4, wherein the graphitic material and the barrier material are the same material.

6. A radiant emitter according to claim 5, wherein the electrically conductive layer has a resistance value that is less than the resistance value of the barrier material.

7. A radiant emitter according to any of claims 1 to 6 further comprising an electrode assembly in electrical communication with the electrically conductive layer and/or the barrier layer.

8. A radiant emitter according to any of claims 1 to 7, wherein the first graphitic material layer has an undulating structure.

9. A radiant emitter according to any preceding claim, wherein the first graphitic material layer is slideable with respect to the second graphitic material layer.

10. A radiant emitter according to any preceding claim, wherein the first graphitic material layer is a first sub-structure and the second graphitic material layer is a second sub-structure, the first and second substructures including a stack of graphitic material layers, in which separation between successive stacked substructures is greater than the separation between successive graphitic material layers in each substructure.

11. A radiant emitter according to claim 10, wherein the separation between successive stacked substructures is variable.

12. A radiant emitter according to claim 10 or claim 11, wherein the separation between successive stacked substructures increases the surface area of the graphitic material.

13. A radiant emitter according to any of claims 10 to 12, in which the separation between successive stacked sub-structures is in a range 2 to 100 nm.

14. A radiant emitter according to claims 10 to 13, in which the sub-structures each have a thickness which is in the range of 1 to

15 nm. 15. A radiant emitter according to claims 10 to 14, in which each substructure includes a stack of between 2 and 12 graphitic material layers.

16. A radiant emitter according to claims 10 to 15, in which the sub-structures each have a stack thickness, and the stack thicknesses of the sub structures are less than the separation between successive stacked substructures.

17. A radiant emitter according to any preceding claim, in which the first and second graphitic material layers have a net negative charge.

18. A radiant emitter according to any preceding claim, wherein in use, the temperature of the graphitic material of the electrically conductive layer is of a value in a range of 30 °C to 120 °C.

19. A radiant emitter according to any preceding claim, wherein the graphitic material is graphene or stacks of graphene.

20. A radiant emitter according to any preceding claim, wherein the carrier material comprises paint, wood, fire brick, rubber or steel or a combination thereof.

21. A radiant emitter, according to any of claims 1 to 20 wherein the carrier material comprises glass.

22. A radiant emitter according to any preceding claim, further comprising an electricity source in electrical communication with the graphitic material of the electrically conductive layer.

23. A heating system comprising at least one radiant emitter according to any of claims 1-21; an electricity source and a control unit for selectively controlling the at least one radiant emitter and/or the electricity source.

24. A method of manufacturing a radiant emitter according to any of claims 1-22, wherein a conducting paste, ink or slurry is applied to the surface of the first carrier material and the surface of the first carrier material is subsequently heated.

25. A method of manufacturing a radiant emitter according to claim 24, wherein a conducting paste, ink or slurry is applied to the surfaces of the first and second carrier materials and the surfaces of the first and second carrier materials are subsequently heated.

26. A method of manufacturing a radiant emitter according to claim 24 or 25, wherein the first and second carrier materials are subsequently placed into an autoclave.