Heater plate

Abstract

A heater plate 120 for a haircare appliance, such as a hair straightener, includes an electrically conductive substrate 128, such as a thermally conductive layer of copper, aluminium or graphite and a

Description

B ACKGROUND Some haircare appliances use a heated surface to style hair. For example, hair straighteners 5 and curlers employ one or more heater plates that are heated with a resistive heating element. The heat is transferred from a surface of the heater plate(s) to the hair while the appliance is in use. SUMMARY 10 The invention is defined in the attached independent claims to which reference should now be made. Further, optional features may be found in the sub-claims appended thereto. LO In accordance with an aspect, there is provided a heater plate for a haircare appliance, the C\J 15 heater plate comprising: an electrically conductive substrate; a recess extending into a face of the substrate; an electrically insulating layer disposed on a surface within the recess; and 1 a heating element disposed within the recess; 20 wherein the heating element is electrically insulated from the substrate by the electrically insulating layer. This arrangement may provide good thermal contact between the heating element and the electrically conductive substrate, and / or may distribute heat across the substrate, and / or may 25 be cost effective to produce. The heating element may comprise a resistive layer formed on the electrically insulating layer. 30 The electrically conductive substrate may comprise a thermally conductive layer, the recess being formed within the thermally conductive layer. The thermally conductive layer may comprise, for example, copper, aluminium, or graphite. The electrically conductive substrate may comprise at least one further layer on the thermally conductive layer. The further layer may offer one or more advantages, including better strength, impact protection, wear resistance or friction alteration. 5 The thermally conductive layer may be sandwiched between two further layers. This may help mitigate distortion of the heater plate as a result of the thermally conductive layer having a different of coefficient of thermal expansion compared to the other layer(s). 10 The or each further layer may comprise a material different to that comprising the thermally conductive layer. For example, the or each further layer may comprise stainless steel. The recess may extend through the further layer, or one of the further layers, into the LD thermally conductive layer. This may offer the character! stic(s) of the further layers while C\J 15 still ensuring good thermal contact between the heating element and the thermally conductive layer. The heater plate may comprise an encapsulant layer formed over a face of the heater plate 1 within which the heating element is disposed, so as to encapsulate the heating element. This 20 may help protect and / or electrically insulate the heating element and / or the face of the heater plate. The electrically insulating layer may extend over at least part of the face of the substrate in which the recess is formed. This may simplify a manufacturing process and / or may help 25 insulate and / or protect the part of the face over which the electrically insulating layer extends. According to a further aspect, there is provided a haircare appliance comprising the heater plate of preceding aspect. 30 According to a further aspect, there is provided a method of manufacturing a heater plate, comprising: disposing an electrically insulating layer on a surface within a recess formed in a face of an electrically conductive substrate; and disposing a heating element within the recess, such that the heating element is electrically insulated from the substrate by the electrically insulating layer. 5 This method may provide a heater plate having good thermal contact between the heating element and the electrically conductive substrate, and / or may distribute heat across the substrate, and / or may be a cost effective method of producing such a heater plate. The method may comprise forming a recess in a face of the electrically conductive substrate. 10 Disposing a heating element within the recess may comprise forming the heating element as a layer on the electrically insulating layer. LD Forming the heating element as a layer on the electrically insulating layer may comprise CM 15 printing the heating element onto the electrically insulating layer. Disposing the electrically insulating layer on the surface within the recess may comprise forming the electrically insulating layer onto the surface. I- 20 The electrically conductive substrate may comprise a thermally conductive layer and at least one further layer on the thermally conductive layer, and the method may comprise forming the recess through the at least one further layer into the thermally conductive layer. The method may comprise forming an encapsulant layer over a side of the heater plate within 25 which the heating element is disposed, so as to encapsulate the heating element. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa side view of a haircare appliance with arms of the haircare appliance in an open position; 30 Figure 2 is a perspective view of the haircare appliance with the arms in a closed position; Figure 3 is a partially exploded view of the haircare appliance; Figure 4 is an exploded view of part of a heating section of the haircare appliance; Figure 5 is a plan view of a heater plate of the haircare appliance of Figures 1 to 4; Figure 6 shows section VI-VI from Figure 5; Figure 7 is an electrical schematic of the haircare appliance of Figures 1 to 4; Figures 8 and 9 are sections of further heater plates; 5 Figures 10 and 11 are plan views of further heater plates; and Figure 12 is a flowchart showing a method of manufacturing a heater plate. DETAILED DESCRIPTION Figures 1 and 2 show a haircare appliance in the form of a hair straightener 100, comprising 10 a first arm 102 and a second arm 104 pivotably connected at one end by a hinge 106. The arms 102,104 are moveable about the hinge 106 between an open position (shown in Figure 1) and a closed position (shown in Figure 2). Each arm 102, 104 comprises a heating section 108, 110 located at an end distal to hinge 106, and a handle section 112, 114 located adjacent LD hinge 106. CM 15 In use, the user grips the handle sections 112, 114 and inserts a section of hair between the two arms 102, 104. The user applies pressure to the handle sections 112, 114 in order to close the arms 102, 104. In closing the arms 102, 104, the hair is gripped between the heating 1 sections 108, 110. The arms 102, 104 are biased towards the open position such that, when 20 the user releases the pressure on the handle sections 112, 114, the arms 102,104 return to the open position shown in Figure 1. Referring now to Figures 3 and 4, the heating section 108, 110 of each arm 102, 104 comprises a casing 116, a heater assembly housing 118, and a heater plate 120. The casing 25 116 defines a trough 122 within which the heater assembly housing 118 is located (for clarity, heater assembly 118 of second arm is shown removed from trough 122 of Figure 2). The heater assembly housing 118 comprises a recess 124 within which heater plate 120 is located. 30 In addition to arms 102, 104, haircare straightener 100 comprises a housing unit 146 that houses a power supply 148 and a control unit 150 (shown in Figure 7 and described in more detail below). In the present example, the housing unit 146 is attached to, and moves, with the first arm 102. Consequently, as the two arms 102, 104 move between the open and closed positions, the second arm 104 moves relative to the housing unit 146. The power supply 148 supplies electrical power to the other electrical components of the 5 hair straightener 100, such as the heater plate 120 of each of the two arms 102, 104 and the control unit 150. In the present example, the power supply 148 comprises a battery (not shown) supplying a DC voltage. In other examples, electrical power may be provided by a mains power supply, and the power supply 148 may comprise a rectifier and a DC-to-DC converter that outputs a DC voltage. 10 Heater plate 120 is supported within heater assembly housing 118 such that, in use, heater plate 120 may apply sufficient force to hair to style the hair and prevent damage to the heater plate 120 due to buckling of the heater plate 120. In some implementations, at least the base LD of recess 124 may be made from a flexible material, such as silicone. When heater plate 120 C\J 15 contacts hair, the heater plate 120 is resiliently deformed, with the flexible base of recess 124 flexing to conform with the deformed heater plate. As a result, a corralling effect (discussed in more detail below) may be provided. 1 In this example, the base of recess 124 comprises silicone and has a relatively low thermal 20 conductivity (i.e. no greater than 1 W m-l .K-l). As a result, base of recess 124 provides relatively good thermal insulation of the heater plate 120. This may reduce the energy consumption and improve the responsiveness of the heater plate 120. However, other materials may be used. 25 Referring now to Figures 5 and 6, heater plate 120 includes an electrically conductive substrate in the form of copper layer 128. Electric conductive substrate can alternatively be formed from any other suitable material or combination of materials, including alloys, and can include multiple layers. The electrically conductive substrate can comprise a thermally conductive layer (i.e., copper layer 128, in the implementation of Figures 5 and 6). Copper 30 layer 128 can be about 0.3 to 0.4 mm thick, but any other suitable thickness can be used in other implementations. Although the thermally conductive layer is copper layer 128 in the implementation of Figures 5 and 6, in other implementations, the thermally conductive layer can be formed from another material, such as aluminium or graphite, or any suitable material or combination of materials. 5 An upper surface of heater plate 120 defines a hair-contacting surface 160. In use, the haircontacting surface 160 contacts hair and conducts heat generated by heater plate 120 to the hair in order to heat and thereby style the hair, as described in more detail below. While haircontacting surface 160 can be the upper face of copper layer 128, hair-contacting surface 10 160 more usually takes the form of a tough non-corrosive and / or non-stick surface that is better adapted for contact with hair. For example, a ceramic, titanium nitride, or nickel coating (not shown) may be applied to hair-contacting surface 160, which may reduce friction, and / or improve robustness and / or the aesthetic appearance of the hair-contacting LD surface. CM 15 As shown in Figure 6, a recess 130 extends into a face 132 of copper layer 128 opposite that of hair-contacting surface 160. As shown in Figure 5, recess 130 is generally serpentine in plan, but as described in more detail below, can take any other suitable shape or form in 1 other implementations. Recess 130 is about 0.1 mm deep, but can be deeper or shallower to 20 suit implementation requirements. For example, recess 130 can be around 0.05 - 0.2 mm deep, assuming a 0.3 mm thick copper layer 128. Alternatively, or in addition, the recess depth can be about 25% to 75% of the electrically conductive substrate (e.g., copper layer 128). Recess 130 is about 1 mm wide, but can be wider or narrower to suit implementation requirements. Both the width and depth of recess 130 can vary along its length, which can 25 provide different thermal characteristics across different regions of copper layer 128. An electrically insulating layer 134 is disposed on a surface 136 within recess 130. In the implementation of Figures 5 and 6, electrically insulating layer 134 coats the walls and floor of recess 130. Electrically insulating layer 134 is formed from colourless ceramic ink and 30 can be applied by spraying, dipping, printing, or any other suitable technique. Optionally, techniques used in the PCB industry for what is termed “silkscreen printing” on similar scales and resolutions can be used. In other implementations, electrically insulating layer 134 can be formed from one or more other materials, including polymers, glass or enamel, which provide sufficient electrical insulation and thermal stability to operate at the operating temperatures of the heating 5 element, e.g. 200 °C. Electrical insulation layer 134, once cured, is around 0.01 - 0.05 mm thick. An electrical insulation layer 134 with a thickness of no greater than 0.2 mm and no less than 0.005 mm may provide a good balance between the competing needs to provide electrostatic discharge 10 protection and to reduce the thermal insulation provided by the electrical insulation layer 134. A heating element 138 is disposed within recess 130. In the implementation of Figure 6, LD heating element 138 comprises a resistive layer formed on electrically insulating layer 134. CM 15 Heating element 138 can be formed from any suitable material, such as copper, silver, constantan or stainless steel or from a conductive non-solid that is later processed to become solid (e.g., a conductive ceramic ink that is fired to create a conductive ceramic solid. Heating element 138 is applied onto electrically insulating layer 134. However, in other 1 implementations, heating element 138 can take the form of a track or a length of wire. 20 Although heating element 138 is shown as filling all of recess 130, in other implementations, heating element 130 may either under-fill or overfill recess 103. Under-filling has the advantage of burying the heating element more deeply into copper layer 128, which may improve heat transfer and / or help protect heating element from damage during manufacture 25 of hair straightener 100 or during use. Overfilling has the advantage of potentially providing a greater cross sectional area of heating element for a given depth of recess 130. In this example, the heating element 138 takes the form of a thin-film heater, which is about 0.2 - 0.5 mm. Thin-film heaters (in conjunction with the width and plan layout of recess 30 130) may be designed to provide relatively evenly distributed heating over the hair contacting surface 160. This may reduce potential damage to hair that might arise due to local hot spots. However, other forms of heating element may be used such as foil heaters, thick-film heaters, tubular heating elements or coiled heating elements. Such heating elements can be adhered to the electrically insulating layer 134 by way of an adhesive. Optionally, such an adhesive may form some or all of the electrically insulating layer 134. 5 As best shown in Figure 5, heating element 138 is recessed into copper layer 128. This offers a number of potential advantages. For example, heat generated within heating element 138 in use is thermally coupled with copper layer 128 through the walls and base of recess 130. This improves heat transfer. Further, recessing heating element 138 into copper layer 128 protects heating element from damage during assembly and / or use. 10 Heating element 138 includes a first terminal 142 at one end, and a second terminal 144 at the other end. First terminal 142 and second terminal 144 are connected to a heater-driving circuit, allowing heating element 138 to be driven by a drive current, as described in more LD detail below with reference to Figure 7. CM 15 An optional encapsulant layer in the form of a conformal coating 140 coats face 132 and the exposed portions of electrically insulating layer 134 and heating element 138, to provide physical protection and electrical insulation. Conformal coating 140 is silicone in the 1 implementation of Figures 5 and 6, but where used, can be formed from any other suitable 20 material or materials. Figures 5 and 6 show electrically insulating layer 134 within recess 130 and also covering face 132 into which recess 130 extends. In other implementations, electrically insulating layer 134 may be restricted to just the interior surface(s) of recess 130 allowing layer 140 to 25 bond directly to the core material. Electrically insulating layer 134 only needs to cover enough of the interior surface(s) of recess 130 to provide electric insulation between the heating element and the electrically conductive substrate. A thermal sensor in the form of a thermistor 162 is positioned on the same side of copper 30 layer 128 as recess 130, and can optionally be recessed into copper layer 128. Thermistor 162 is located between (and spaced from) parallel portions of copper layer 128 near its centre. As a result, thermistor 162 senses the temperature near the centre (in plan) of heater plate 120. The temperature signal from thermistor 162 can be used as feedback to allow control of heating element 138. Although thermistor 162 is positioned to sense a temperature of copper layer 128, in other 5 implementations, thermistor 162 can be positioned to sense a temperature of heating element 138, hair-contacting surface 160, or any other suitable part of hair straightener 100. In other implementations, multiple thermal sensors can be placed at different locations such that temperature measurements are taken across different regions of hair-contacting surface 10 160 (or heating element, etc.). Other thermal sensor types, such as thermocouples, may be used in other implementations. Turning now to Figure 7, the control unit 150 comprises a pair of switches 152, 154, a user LD interface 156 and a controller 158. CM 15 Each of the switches 152, 154 is connected between the power supply 148 and a heating element 138 of a respective arm 102, 104. Accordingly, when one of the switches 152, 154 is closed, electrical power is supplied to the heating element 138 of the corresponding arm 1 102, 104 and the temperature of the heater plate 120 increases. Conversely, when switch 20 152, 154 is open, the supply of electrical power to heating element 138 is halted and the temperature of the heater plate 120 decreases. Accordingly, the switches 152, 154 may be controlled in order to control the temperature of the heater plate 120 of each of the arms 102, 104. 25 User interface 156 may be used to power on and off the hair straightener 100. Additionally, the user interface 156 may also be used to select a particular heat setting (e.g., low, medium, high) and / or to select a particular mode of operation (e.g., constant temperature or root-to-tip heating). 30 Controller 158 is connected to switches 152, 154 and user interface 156. Additionally, controller 158 is connected to thermistor 162 of the heater plate 120 of each arm. As a result, the controller 158 is provided with a measure of the temperatures of the two heater assemblies 120. Controller 158 is responsible for controlling the operation of hair straightener 100. In particular, the controller 158 controls the opening and closing of the switches 152, 154, and thus the electrical power supplied to the heating elements 138, in response to input data received from the user interface 156 and thermistors 162. For 5 example, controller 158 may control switches 152, 154 such that the temperature of each heater plate 120, as sensed by thermistor 162, is maintained at a particular setpoint. The controller 158 can, for example, control the duty cycle of switches 152, 154, optionally using closed loop control, such as PI or PID control. 10 In other implementations, the electrically conductive substrate comprises at least one further layer on the thermally conductive layer. For example, the further layer can take the form of a stainless steel layer formed on one or the other of face 132 or hair-contacting surface 160. In the latter case, the further layer is disposed underneath any low-friction or aesthetic outer LD coating, such as those described above. CM 15 Optionally, the further layer is formed from a material that is stiffer than that of the thermally conductive layer. For example, where the thermally conductive layer is copper (such as copper layer 128), the further layer can take the form of a stainless steel layer. I- 20 Figure 8 shows a cross section of an alternative heater plate 120, in which features that are similar to those of the heater plate 120 in Figures 5 and 6 are indicated with the same reference signs. Heater plate 120 in Figure 8 includes a stainless steel layer 164, which is about [thickness to be confirmed] mm thick. In this implementation, stainless steel layer 164 was joined to copper layer 128 prior to the process of forming recess 130 into copper layer 25 128. The layers can be joined by any suitable method, such as bonding, forging, hot-rolling, welding, etc. As a result, recess 130 was formed through both stainless steel layer 164 and copper layer 128. Stainless steel is considerably stiffer than copper and more resistant to corrosion. As a result, 30 stainless steel layer 164 adds considerable stiffness and corrosion resistance to heater plate 120. Optionally, the thermally conductive layer is sandwiched between two further layers. Figure 9 shows a cross section of an alternative heater plate 120, in which features that are similar to those of the heater plate 120 in Figures 5, 6, and 8 are indicated with the same 5 reference signs. Heater plate 120 in Figure 9 includes a further stainless steel layer 166, which is about 0.03 - 0.2 mm thick. The total thickness of heater plate 120 in Figure 9, including copper layer 128 and stainless steel layers 164, 166, is about 0.1 mm - 0.4mm. The outer surface of further stainless steel layer 166 defines the hair-contacting surface 160 (optionally including a low-friction or protective coating, for example as described above). 10 As with stainless steel layer 164, further stainless steel layer 166 was joined to copper layer 128 prior to the process of forming recess 130 into copper layer 128. Both stainless steel layer 164 and further stainless steel layer 166 can be joined to copper layer 128 using the LD same process, optionally simultaneously. C\J 15 The use of further stainless steel layer 166 offers a number of additional advantages. Copper and stainless steel have different coefficients of thermal expansion. Where only a single stainless steel layer (i.e., stainless steel layer 164) is used, heater plate 120 effectively 1 becomes a type of bimetallic strip. As such, as it heats up, there is a tendency for it to bend. 20 While this can be managed by careful selection of materials and layer thicknesses, optional further stainless steel layer 166 means that the forces generated as a result of differential coefficient of thermal expansion are largely cancelled out. There may be some small residual net force on one side as a result of the removal of part of stainless steel layer 164 as part of forming recess 130, but this is generally manageable. 25 Optionally, and in relation to any described implementation (and alternatives whether specifically described or not), copper layer 128 (and stainless steel layers 164, 166, where provided) can be made sufficiently thin that the heater plate 120 as a whole is flexible, allowing heater plate 120 to be deformed when contacting hair. As a result, a corralling 30 effect, where hair is gathered and shaped, may be provided, which may result in improved hair styling. Alternatively, a relatively thick copper layer 128 (and stainless steel layers 164, 166, where provided) may provide additional robustness, and manufacturability of the heater plate 120 may be improved. For example, warping, caused by thermal processes that may be used in the manufacture of the heater plate 120, such as laser processing, lamination or screen 5 printing, may be reduced. Reduced warping and corresponding improved flatness of heater plate 120 may be desirable to ensure good contact with hair to provide efficient heat transfer between the hair and the heater plate 120. A heater plate 120 optionally having a thickness of no greater than 0.5 mm and no less than 10 0.015 mm may provide a good balance between the competing needs of providing sufficient flexibility, whilst also providing robustness. Figures 10 and 11 show further recess / heating element configurations for heater plates. In LD each case, the recess configuration can be applied to any type of heater plate, including those CM 15 described in relation to Figures 5, 6, 8, and 9. Figure 10 shows a heater plate 120 having several recesses 130, each having a heating element 138. Each recess 130 is disposed within a generally rectangular (in plan) region, 1 each of which defines a different zone along hair-contacting surface 160. In this way, each 20 of heating elements 138 heats a respective zone of hair contacting surface 160. In this implementation, control unit 150 comprises additional switches, one for each of heating elements 138, and controller 158 is configured to control a supply of power independently to each of the heating elements 138. In this way, more precise control of the temperature of the hair-contacting surface 160 can be achieved. This may result in the reduction in 25 occurrence of local hot spots on the hair-contacting surface 160, which may reduce the occurrence of damage to hair due to overheating. Each heating element 138 has an associated thermistor 162, allowing the temperature of each of the zones of the hair-contacting surface 160 to be sensed. The temperature of the heater 30 plate 120 may therefore be better controlled such that improved styling results and / or reduced hair damaged may be achieved. For example, the temperatures of the different zones may be controlled so as to avoid overheating, which might otherwise damage the hair. Additionally, having multiple sensors may enable the presence or absence of hair in contact with the hair-contacting surface 160 to be detected at different zones. Zones in contact with hair may then be heated to a higher temperature, and zones not in contact with hair may be heated to a lower temperature or not heated at all. This may help reduce energy consumption 5 of the hair straightener 100. Also, where a relatively small amount of hair covers a first zone of the hair contacting-surface 160, the heat generated at the first zone may overheat and damage the hair. However, by having an adjacent second zone that is at a lower temperature (i.e. owing to the absence of hair), part of the heat generated at the first zone may be transferred to the second zone. Thereby, overheating and the associated hair damage may be 10 reduced or avoided. Figure 11 shows a heating element 138 that extends alternately up and down the length of heater plate 120. In this implementation, no thermistor 162 is shown, but this can be added LD if desired. CM 15 Turning to Figure 12, there is shown a method 200 of manufacturing a heater plate, for use in a haircare appliance. Method 200 can be used, for example, in the manufacture of a heater plate such as heater plate 120. I- 20 Method 200 comprises forming 202 a recess in a face of an electrically conductive substrate. The electrically conductive substrate can be formed from, for example, copper, graphite, or any other suitable material or combination of materials. The recess can be formed in any suitable way, which may depend upon the particular 25 material(s) involved. For example, the recess can be formed into the face of electrically conductive substate by any suitable combination of chemical etching, machining, ablation, laser etching, stamping, or any other suitable recess-forming technology. Alternatively, the conductive substrate can be formed by an additive manufacturing process such as 3D printing, or by a process such as forging, moulding or sintering, the recess being formed as 30 part of the process. Where the recess extends through multiple layers (e.g., through an outer stainless teel layer into a copper layer), different processes may be required for the different layers. For example, laser etching can be used to remove a portion of a stainless steel outer later, and then an etching process can be used to form the recess into the copper layer (the patterned stainless steel acting as a mask for the etchant). Next, an electrically insulating layer is disposed 204 on a surface within the recess. For 5 example, the electrically insulating layer can be printed, flowed, sprayed, or otherwise applied to a surface within the recess. If necessary, the insulating layer is allowed to set, dry, or cure. Alternatively, a solid insulating layer can be positioned within the recess, and can optionally be held in place by an adhesive or heated to partly melt and adhere to the recess. 10 As described above, the insulating layer can optionally extend outside of the recess, for example to cover at least some of the face into which the recess extends. A heating element is disposed within the recess, such that the heating element is electrically LD insulated from the substrate by the electrically insulating layer. For example, the heating C\J 15 element can be printed, flowed, sprayed, or otherwise applied as a layer to a surface of the electrically insulating layer within the recess. Alternatively, a solid heating element in, for example in the form of a foil heater, thick-film heater, tubular heating element or coiled heating elements, can be positioned within the recess, and can optionally be held in place by 1 an adhesive. Optionally, the electrically insulating layer can act as an adhesive. 20 The electrically conductive substrate can comprise a thermally conductive layer (such as copper layer 128) and at least one further layer on the thermally conductive layer (such as stainless steel layer(s) 164, 166). In that case, forming the recess can optionally comprise forming the recess through the at least one further layer into the thermally conductive layer. 25 Optionally, an encapsulant layer (such as conformal coating 140) is formed over a side of the heater plate within which the heating element is disposed, so as to encapsulate the heating element. 30 While various heater plates for a hair straightener have been described, it will be appreciated that various other forms of heater plate can be used in different haircare appliances, such as hair curlers, hair crimpers, and hair curling wands. The skilled person will appreciate how the heater plate may need to be modified to suit any particular haircare application. Although various implementations have been described, it should be understood that these 5 are illustrative only, and that various modifications may be made without departing from the scope of the invention as defined by the claims. LD CM

Claims

1. A heater plate for a haircare appliance, the heater plate comprising:an electrically conductive substrate;a recess extending into a face of the substrate;5 an electrically insulating layer disposed on a surface within the recess; anda heating element disposed within the recess;wherein the heating element is electrically insulated from the substrate by the electrically insulating layer;wherein the electrically conductive substrate comprises a thermally conductive layer,10 the recess being formed within the thermally conductive layer; andwherein the electrically conductive substrate comprises at least one further layer on the thermally conductive layer.LO 2. The heater plate of claim 1, wherein the heating element comprises a resistive layer C\J 15 formed on the electrically insulating layer.

3. The heater plate of claim 1 or 2, wherein the thermally conductive layer comprises copper, aluminium, or graphite.I-20 4. The heater plate of any preceding claim, wherein the thermally conductive layer issandwiched between two further layers.

5. The heater plate of any preceding claim, wherein the or each further layer comprises stainless steel.

256. The heater plate of any preceding claim, wherein the recess extends through the further layer, or one of the further layers, into the thermally conductive layer.

7. The heater plate of any preceding claim, comprising an encapsulant layer formed 30 over a face of the heater plate within which the heating element is disposed, so as to encapsulate the heating element.

8. The heater plate of any preceding claim, wherein the electrically insulating layer extends over at least part of the face of the substrate in which the recess is formed.

9. A haircare appliance comprising the heater plate of any preceding claim.

510. A method of manufacturing a heater plate, comprising:disposing an electrically insulating layer on a surface within a recess formed in a face of an electrically conductive substrate; anddisposing a heating element within the recess, such that the heating element is10 electrically insulated from the substrate by the electrically insulating layer;wherein the electrically conductive substrate comprises a thermally conductive layer and at least one further layer on the thermally conductive layer, the method comprising forming the recess through the at least one further layer into the thermally conductive layer.LOCM 15 11. The method of claim 10, comprising forming the recess into the face of theelectrically conductive substrate.

12. The method of claim 10 or 11, wherein disposing a heating element within the recess 1 comprises forming the heating element as a layer on the electrically insulating layer.2013. The method of claim 12, wherein forming the heating element as a layer on the electrically insulating layer comprises printing the heating element onto the electrically insulating layer.25 14. The method of any one of claims 10 to 13, wherein disposing the electricallyinsulating layer on the surface within the recess comprises forming the electrically insulating layer onto the surface.30 15. The method of any one of claims 10 to 14, comprising forming an encapsulant layerover a side of the heater plate within which the heating element is disposed, so as to encapsulate the heating element.

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