Hair styling appliance, parts thereof and methods of manufacture

Abstract

Hair styling appliances are described as well as heaters and heater assemblies used in such hair styling appliances. Methods of manufacturing the heater assemblies are also described as are safety circuits used to protect the heater assemblies in the event of a fault or overheating situation.

Description

[0001] Hair Styling Appliance, Parts Thereof and Methods of Manufacture

[0002] Field of the Invention

[0003] The present invention relates to heaters and safety assemblies for heaters for use in hair styling appliances and to their methods of manufacture. The invention also relates to hair styling appliances having such heaters and safety assemblies and to manufacturing equipment for making the heaters and to new composite materials for use in the manufacture of such heaters.

[0004] Background to the Invention

[0005] There exist a variety of apparatus for styling hair, which use heat to effect a change in the shape of hair. Examples include hair straighteners, curling tongs and hair crimpers. The hair styling apparatus directly heats the hair to above its glass transition temperature, where the hair becomes mouldable. The hair is styled at a temperature above its glass transition temperature; and once cooled, the hair generally remains styled until it next becomes wet. Hair styling appliances, such as hair straighteners (as shown in Figures 1a and 1 b), typically comprise heating surfaces (typically defined by heating plates) which heat hair that comes into contact with the heating surfaces. Other styling devices, such as curling tongs, provide a curved heating surface, but the principle remains the same - the hair is heated above its glass transition temperature and styled by the user.

[0006] In its earlier application PCT / GB2024 / 052565, the applicant has described a heater that has very low thermal mass and which can heat up and cool down very quickly; as well as safety circuitry that can quickly remove power from the heater in the event of a fault or overheating situation.

[0007] This application describes a preferred method and apparatus for making the kind of low thermal mass heater described in the earlier application as well as a new safety assembly that helps to speed up the isolation of the heater from the power supply in the event of a fault or overheating situation. The safety assembly may be used with various kinds of heater and not just the low thermal mass heaters described in the earlier application.

[0008] Summary of the Invention

[0009] The present invention is set out in the appended independent claims. Optional features are set out in the appended dependent claims.

[0010] According to one aspect, the embodiments provide a method of manufacturing heater assemblies for hair stylers, the method comprising: forming a heater panel comprising a plurality of heater elements arranged over the heater panel, each heater element comprising one or more heater electrodes that heat up the heater element when current is applied; inserting a plurality of heater carriers within a press tool; providing a bonding film over the heater carriers; mounting the heater panel over the bonding film so that each heater element on the heater panel is positioned over a respective heater carrier within the press tool; and using a bonding machine to apply pressure to the press tool to bond each heater element to the respective heater carrier to create a plurality of heater assemblies.

[0011] The heater elements may be arranged in a regular array (two dimensional or a one dimensional array) on the heater panel and the heater carriers are arranged in a corresponding regular array within the press tool. Alternatively, the heater elements may not be arranged in a regular array, in order to maximise the packing density of the heater elements within the heater panel.

[0012] Typically, the bonding machine is configured to extract air from the press tool during the bonding process to ensure air bubbles are not trapped under the heater surface which could later expand under heating and cause delamination. The bonding machine may also heat the press tool during the bonding process.

[0013] Each heater element may comprise a laminate structure, with a first layer having a plurality of heater electrodes, a second dielectric layer and a third layer comprising safety circuitry for sensing, during use, overheat conditions with one or more of the heater electrodes. The third layer of the heater element is preferably bonded to an upper surface of the respective heater carrier.

[0014] The method may further comprise removing the heater assemblies from the press tool and separating the heater assemblies from the heater panel; connecting ends of the at least one heater electrode to drive and control circuitry mounted on a printed circuit board and attaching the printed circuit board to the heater assembly.

[0015] The heater carrier may comprise a plurality of windows each positioned adjacent fusing circuitry mounted on the heater element and the method further comprises placing a thermal fusing element through each window onto the respective fusing circuitry and providing means to press each fusing element onto the respective fusing circuitry. The means to press may comprise a bar of resilient material that is compressed within the heater assembly to provide a pressing force on each of the fusing elements. The bar of resilient material may be shaped to provide a respective guillotine structure for each fusing element that separates the fusing element from the fusing circuitry in the event of the fusing element melting.

[0016] The heater panel may be formed from a sheet of laminated material comprising a layer of stainless steel, a layer of electrical insulation and a layer of copper that are laminated together, which is etched and processed to form the one or more heater electrodes on the stainless-steel layer and etched to form fusing circuitry on the copper layer. The copper layer is preferably also etched and processed to form heat spreaders within the copper layer positionally aligned with a respective heater zone formed by a heater electrode on the stainless steel layer.

[0017] According to another aspect, the invention provides a heater assembly for a hair styler comprising: a heater stack having a first layer that includes at least one heater electrode for heating the heater stack upon the application of an electric current and a second layer comprising fusing circuitry that includes at least at least one pair of first and second connection pads; a heater carrier for supporting the heater stack, the heater carrier having an upper surface to which the second layer of the heater stack is bonded, wherein the heater carrier comprises at least one window that extends through the upper surface of the heater carrier and exposes the pair of first and second connection pads; at least one electrically conductive fusing element positioned within the window of the heater carrier and making an electrical connection between the pair of first and second connection pads; and means for applying a force on the at least one fusing element to hold the fusing element against the pair of first and second connection pads.

[0018] The means for applying force to the at least one fusing element may comprise resilient means that is compressed within the heater assembly to provide said force on the fusing element. The resilient means may be shaped to provide a guillotine structure that separates fusing material of the fusing element to prevent the fusing material from making an electrical connection between the pair of first and second connection pads in the event of the fusing element melting.

[0019] A printed circuit board may be provided to which the at least one heater electrode is attached and to which the at least one pair of first and second connection pads of the fusing circuitry are attached, and wherein the printed circuit board is mounted within the heater assembly to compress the resilient means to thereby provide said force on the fusing element.

[0020] The heater stack may include a plurality of heater electrodes for heating a plurality of heater zones of the heater. In this case, the fusing circuitry may comprise a plurality of pairs of first and second connection pads, wherein the heater carrier comprises a plurality of windows that each extends through the upper surface of the heater carrier and exposes a respective pair of first and second connection pads, wherein a respective fusing element is positioned within each window of the heater carrier to make an electrical connection between the respective pair of first and second connection pads and wherein the means for applying a force is configured to apply a force on each fusing element to hold the respective fusing element against the corresponding pair of first and second connection pads.

[0021] The means for applying a force may comprise a bar of resilient material that is compressed within the heater assembly to provide a respective pressing force on each of the fusing elements. The bar of resilient material may be shaped to provide a respective guillotine structure for each fusing element that helps to break the electrical connection between the corresponding pair of first and second connection pads in the event that the corresponding fusing element melts.

[0022] According to another aspect, the invention provides a roll of laminated material comprising a layer of stainless steel, a layer of electrical insulation and a layer of copper that are laminated together, wherein the layer of stainless steel has a thickness between 10 and 40 pm and the layer of copper has a thickness between 15 and 105 pm. The layer of electrical insulation may have a thickness between 5 and 50 pm. The layer of electrical insulation is preferably polyimide.

[0023] The layer of stainless steel is typically homogenous as is the layer of copper.

[0024] The roll preferably has a width of between 50mm and 600mm. The invention also provides a hair styling appliance comprising a heater assembly made according to the method of claim 1 , and / or a heater assembly according to claim 14 or has a heater formed using the roll of composite material of claim 22.

[0025] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0026] It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and / or supplied and / or used independently.

[0027] Brief Description of the Drawings

[0028] One or more embodiments will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which:

[0029] Figure 1 a illustrates a hair styler;

[0030] Figure 1 b illustrates a user using the hair styler on their hair;

[0031] Figure 2 is a partially exploded cross-sectional and perspective view of another heater assembly; Figure 3a is an exploded view from above of a flexible heater, a bonding layer and a heater carrier; Figure 3b is an exploded view from below of the flexible heater, a bonding layer and a heater carrier shown in Figure 3a;

[0032] Figure 4 illustrates a main heating electrode layer forming part of the heater shown in Figure 2;

[0033] Figure 5 illustrates a heat spreading and fuse layer forming part of the heater shown in Figure 2;

[0034] Figure 6 illustrates in more detail fuse circuitry shown in Figure 5;

[0035] Figure 7a is a cross-sectional view of part of the heater assembly shown in Figure 2 illustrating a fuse when intact;

[0036] Figure 7b is a cross-sectional view of part of the heater assembly shown in Figure 2 illustrating when the fuse has melted due to overheating;

[0037] Figure 8 is a simplified schematic diagram of drive and control circuitry that can be used to control the heating of the heater shown in Figure 2;

[0038] Figure 9 illustrates various manufacturing steps performed to manufacture heater assemblies that are mounted within a hair styler device;

[0039] Figure 10a illustrates a first side of a heater panel formed during the manufacturing steps illustrated in Figure 9;

[0040] Figure 10b illustrates an expanded view of one heater forming part of the heater panel shown in Figure 10a;

[0041] Figure 11a illustrates a second side of a heater panel formed during the manufacturing steps illustrated in Figure 9;

[0042] Figure 11 b illustrates an expanded view of one fusing circuitry forming part of the heater panel shown in Figure 11a; Figure 11 c illustrates a pair of first and second connection pads forming part of the fusing circuitry shown in Figure 11 b;

[0043] Figure 12a illustrates a press tool support plate;

[0044] Figure 12b illustrates the press tool support plate shown in Figure 12a with heater carriers mounted therein;

[0045] Figure 13a illustrates the form of a release panel used in a bonding process to form a heater assembly;

[0046] Figure 13b illustrates the release panel mounted within the press tool support plate shown in Figure 12b;

[0047] Figure 14a illustrates the form of a bonding film panel used in a bonding process to form a heater assembly;

[0048] Figure 14b illustrates the bonding film panel mounted within the press tool support plate shown in Figure 13b;

[0049] Figure 14c is an expanded view showing the bonding film for one heater within the heater panel;

[0050] Figure 15 illustrates the press tool support plate with the heater panel mounted thereon over the bonding film panel;

[0051] Figure 16a illustrates the press tool support plate shown in Figure 15 with a heater panel retention plate mounted thereon;

[0052] Figure 16b is an expanded view of Figure 16a showing the overlap between the heater panel and the heater panel retention plate;

[0053] Figure 17a shows the press tool support plate shown in Figure 16a with a heater panel forming plate mounted thereon;

[0054] Figure 17b is a cross-sectional view of the press tool shown in Figure 17a;

[0055] Figure 18 illustrates the way in which a bonding machine applies heat and mechanical pressure to the press tool during the bonding process;

[0056] Figures 19a, 19b and 19c illustrate the operation of the press tool during a bonding process;

[0057] Figure 20 illustrates the bonded heater assemblies being removed from the press tool after the bonding process;

[0058] Figure 21 illustrates the way in which the heater assemblies are separated from the heater panel after bonding;

[0059] Figure 22a illustrates an alternative form of heater carrier;

[0060] Figure 22b is a plan view of the heater carrier shown in Figure 22a;

[0061] Figure 22c is an expanded view of a window through an upper surface of the heater carrier shown in figure 22a;

[0062] Figure 23a is a rear view of the heater carrier shown in Figure 22 after bonding with a heater and placement of fusing elements within each of the windows of the heater carrier;

[0063] Figure 23b is an expanded view showing the positioning of the fusing element within a window;

[0064] Figure 24a illustrates a silicone bar that is mounted over the windows of the heater assembly shown in in Figure 23a;

[0065] Figure 24b is a longitudinal cross-section through the heater assembly shown in Figure 24a;

[0066] Figure 24c is a transverse cross-section through the heater assembly shown in Figure 24a;

[0067] Figure 25a is a view from the rear of the heater assembly shown in Figure 24a after mounting a printed circuit board and a retaining bar;

[0068] Figure 25b is a longitudinal cross-section through the heater assembly shown in Figure 25a; Figure 25c is a transverse cross-section through the heater assembly shown in Figure 25a;

[0069] Figure 26a is an expanded view of a guillotine feature within the silicone bar shown in Figure 24a when a fusing element is intact; and

[0070] Figure 26b is an expanded view of the guillotine feature within the silicone bar shown in Figure 24a when a fusing element has melted.

[0071] Detailed Description of Preferred Embodiments

[0072] The embodiments described below represent the best ways known to the inventors of putting the invention into practice. However, they are not the only ways in which this can be achieved.

[0073] Overview of hairstyler

[0074] Figure 1 a illustrates a hair styler 1. The hair styler 1 includes a first movable arm 4a and a second movable arm 4b, which are coupled at proximal ends thereof to a shoulder 2. The first arm 4a bears a first heater 6a at its distal end, and the second arm 4b bears a second heater 6b at its distal end. The first and second heaters 6a, 6b oppose one another and are brought together as the first and second arms 4a, 4b are moved from an open configuration to a closed configuration. Hair can be inserted between and in contact with a heating surface of the heaters 6a, 6b, in which position the heaters 6a, 6b impart conductive heat to the hair to facilitate styling.

[0075] The heaters 6a, 6b are low thermal mass heaters and can therefore heat up and cool down quickly. Figure 2 shows an exploded cross-sectional and perspective view of a preferred heater assembly 33 which may be used in the hair styling device 1 and which shows on the left hand side an exploded transverse cross-sectional view of a heater 6 and a heater carrier or support 68 and on the right hand side a perspective view of the heater 6 and heater carrier 68. This heater can be used with any of the safety circuits described in PCT / GB2024 / 052565, the contents of which are incorporated herein by reference. As shown, the heater 6 is formed from a number of discrete layers that are mechanically or chemically bonded together. These layers include:

[0076] Layer 81 is a low friction coating that also provides electrical insulation. This layer may be formed, for example, from a ceramic coating or wash and is directly applied on to the heater electrode layer 84. The layer 81 is designed to give 500 volts of dielectric breakdown strength and have thermal impedance between 9.35 x 10'4KW’cm2and to 0.8 KW'1cm2. This provides the required electrical insulation between the hair contacting surface of the heater (the upper surface of the layer 81) and the heater electrodes whilst minimising the temperature drop that will occur through this coating layer 81 . Minimising the temperature drop through the layer 81 is important when the heater electrodes are being used to sense temperature, as this will make the determined temperature closer to the actual temperature of the hair contacting surface. Ceramic based coatings, such as Cerasol with a thickness of about 30 to 45 pm, can provide this dielectric breakdown strength and have a thermal impedance of about 0.5 KW'1cm2to 0.6 KW'1cm2. Other materials such as Aluminium Nitride can provide the required dielectric breakdown strength whilst providing even lower thermal impedances. For example, a 30 pm layer of Aluminium Nitride can provide the require dielectric breakdown strength of 500 volts and has a thermal impedance of just 9.35 x 10'4KW'1cm2. However, for a mass-produced device such as a hair styler, the cost of an Aluminium Nitride layer may be too high in practice.

[0077] Layer 84 is the heater electrode layer that carries one or more heater electrodes for heating different parts or different heating zones of the heater. The electrodes may be formed from any suitable conducting material, although stainless steel is preferred. Further details of the heating zones that are formed by the heater electrodes can be found in the earlier application PCT / GB2024 / 052565, the contents of which are incorporated herein by reference.

[0078] Layer 87 is an insulation layer (made for example from polyimide) that provides electrical insulation between the electrode layer 84 and the heat spreading layer 88 underneath. Polyimide is a good option for this insulation layer 87.

[0079] Layer 88 is the heat spreading layer that carries the heat spreaders and fusing elements. Further details of the heat spreaders can be found in the earlier application PCT / GB2024 / 052565, the contents of which are incorporated herein by reference.

[0080] Layer 92 is an adhesive or bonding layer that is used to bond the flexible heater 6 (formed by layers 81 , 84, 87 and 88) to the heater carrier 68 which is typically rigid. In this example, the bonding layer 92 typically has a number of holes 57 along its length where fusing elements will be positioned on the heat spreading layer 88, so that the fusing elements are not covered with the bonding material.

[0081] The heater carrier 68 is typically made of a light weight but heat resistant plastics material, such as a Liquid Crystal Polymer like Vicryst, Vectra S135 or the like. Where the heater assembly 33 is desired to be rigid, it is the heater carrier 68 that will typically provide the rigidity to the flexible heater 6. As shown in Figure 2, in this example, the heater carrier 68 includes eight indents 59 along its length to receive the eight fusing elements on the heat spreading layer 88, so that when the heater 6 is bonded to the heat carrier 68, a smooth outer heating surface is presented.

[0082] Figure 3a is a perspective view from above showing the flexible heater 6 (with the layers 81 , 84, 87 and 88 bonded together), the bonding layer 92 and the rigid heater carrier 68. Figure 3b is a view from below of the flexible heater 6, bonding layer 92 and the rigid heater carrier 68. As shown in Figure 3b, in this example, the rigid heater carrier 68 has honeycomb struts 53 to provide rigidity whilst keeping the weight down. The rigid heater carrier 68 includes eight holes 55 arranged along its length corresponding to the locations of thermal fuses used to protect the heating zones. In this embodiment, there are sixteen heating zones (heater electrodes) and each thermal fuse provides overheat protection for two neighbouring heating zones. Figure 3b also shows that the bonding layer 92 has eight holes 57 arranged along its length corresponding to the locations of the thermal fuses.

[0083] Figure 4 is a plan view of the independently controllable heater electrodes 64-1 to 64-16 on the heater electrode layer 84 that define the corresponding sixteen heating zones (one of which is labelled 67 in Figure 4) provided in this example. Each heater electrode 64 is formed of a track of resistive material, whose geometry (track width, thickness, length) and material is specified in order to achieve the desired resistance for a specific power source voltage, therefore providing a desired peak power for a given heating zone. Each heater electrode 64 may be formed into a serpentine pattern using chemical etching as a manufacturing process (although, other manufacturing processes can be used to form the heater electrodes 64). In more detail, a solid layer of conductive material is provided and then etched to form the different heater electrodes 64. The dark regions shown in Figure 4 are the boundaries between the etched parts of the electrode layer between the white serpentine parts of the figure that are the serpentine conductor paths that form the heater electrodes 64. In this illustrated example, each heater electrode 64 serpentines from an edge of the heater 6 to a centre line of the heater 6 before returning in a serpentine path back to the starting edge of the heater 6.

[0084] Adjacent heater electrodes 64 share a common positive terminal 65-1 to 65-8 (although in other embodiments the common terminal may be a common ground terminal) to reduce the number of electrical connections needed to be made between the drive and control circuitry (not shown) and the heater 6. The common positive terminal 65 for pairs of adjacent heater electrodes 64 are connected back from the edge of the heater 6 to the drive and control circuitry. The other end of each heater electrode 64 connects to a ground terminal 66-1 to 66-16 which connects to ground through a respective switch forming part of the drive and control circuit to allow for independent control of current flow through each heater electrode 64. As those skilled in the art will appreciate, it is not essential to have such a common positive (or ground) terminal, each heater electrode 64 may be physically separate from all other heater electrodes 64 in which case, each end of each heater electrode 64 would be connected separately back to the drive and control circuitry. As illustrated in Figure 4, both lengthways edges of this electrode layer 84 have twelve tabs extending outward from it that, when assembled, bend round the upper surface of the rigid heater carrier substrate 68 to connect to the drive and control circuitry. Sixteen of the twenty-four total tabs each contain the ground terminal 66 for a heater electrode 64 and eight contain the common positive terminal 65 for a pair of adjacent heater electrodes 64.

[0085] The conductive material used in the layer 84 (to form the heater electrodes 64) is preferably a PTC or an NTC material (such as stainless steel or copper) so that the resistance of the heater electrode 64 depends upon its temperature - and so the temperature of the heating zone 67 can be determined by measuring a parameter that varies with the resistance of the corresponding heater electrode 64.

[0086] Figure 5 shows in more detail the form of the heat spreading layer 88 used in this example (as viewed from below the heater 6). As shown, this heat spreading layer 88 includes sixteen heat spreaders 91-1 to 91-16 that are positionally aligned with the corresponding heater electrodes 64- 1 to 64-16. The heat spreaders 91 are formed of a thermally and electrically conducting material like copper. Each heat spreader 91 (except for heat spreaders 91-1 and 91-16) is electrically connected to a neighbouring heat spreader at a corner portion thereof. Each heat spreader 91 is also electrically connected to at least one neighbouring heat spreader 91 by a fuse that sits between the neighbouring heat spreaders. A dashed circle 34 shows one of the locations where a fuse is installed to electrically connect neighbouring heat spreaders 91-3 and 91-4. The heat spreaders 91 are arranged so that when the fuses are in place, there is an electrical connection (and therefore a current path represented by the dashed arrows) from a positive fuse connection 36 that is coupled to heat spreader 91-1 , through the heat spreaders 91-1 to 91-16 and back to a negative fuse connection 38 that is coupled to heat spreader 91-16. If one of the heating zones overheats and the corresponding fuse connection breaks, then that current path breaks and the controller or control circuitry (to which the positive and negative fuse connections 36, 38 are coupled) can detect this break in the current path (for example by applying a voltage across the two fuse connections 36 and 38 and detecting the presence of a current (fuse circuit working correctly) or the absence of a current (meaning that one or more fuses have blown)) and can take the appropriate control action - such as stopping or preventing power being applied to the heater electrodes. The operation of preferred control circuitry to detect a fuse melting and to take a control action will be described in more detail later.

[0087] Figure 6a and 6b are zoomed perspective views of a fuse 34 used in this example to connect adjacent heat spreaders 91-3 and 91-4. In this example, the fuse 34 is formed of an electrically conductive solder material that electrically connects the adjacent heat spreaders 91 -3 and 91-4. The fuse material sits on and electrically bridges across a layer of solder resist 41. Figure 6a shows the fuse when intact, such that current can flow between adjacent heat spreaders 91-3 and 91-4; and Figure 6b shows what happens if a heating zone next to the fuse overheats and melts the solder material of the fuse 34. In particular, when the solder material melts, it is repelled off the solder resist 41 and beads up to the side where it will cool (once power is removed from the heaters) and solidify again. The solder resist 41 is not electrically conductive, and so when the solder material melts and moves off the solder resist 41 (as shown in Figure 6b), the adjacent heat spreaders 91-3 and 91-4 are electrically separated from one another thereby breaking the electrical connection between the two fuse connections 36 and 38. As discussed above, this break in the electrical connection is detected by the control circuitry and used to control (typically stop) the power delivery to the heater electrodes 64.

[0088] Figure 7a and 7b are cross-sectional views through the heater 6 (showing the electrode layer 84, the insulation layer 87 and the heat spreader and fuse layer 88) and the support 68, showing the placement of a fuse 34 discussed above. In particular, Figure 7a is a cross-sectional view when the fuse 34 is intact and Figure 7b is a cross-sectional view when the fuse 34 has melted and moved off the solder resist 41. As shown in Figure 7, an air pocket 44 is provided within the support 68 to house the fuse 34.

[0089] Preferred Drive & Control Circuitry

[0090] Figure 8 is a schematic diagram of the way in which the heater electrodes 64 may be connected together and to the drive circuitry 23 and the power supply 21 and illustrating the preferred safety circuitry that can remove power from the heater electrodes 64 if any of them overheat. As shown in Figure 8, each heater electrode 64-1 to 64-16 is connected at one end to the power supply 21 through a master switch 51 and at the other end to a respective switch (in this case a MOSFET switch) 95-1 to 95-16. The switches 95 are controlled by the microprocessor 29. When a heater electrode 64 is to provide heat, the corresponding switch 95 is closed thereby connecting the heater electrode 64 to ground through the resistor R. As a result, current flows from the power supply 21 to ground causing the heater electrode 64 to heat up (provided the master switch 51 is closed). The microprocessor 29 can control the position of each switch 95 independently thereby allowing each heater electrode 64 to be powered independently to attain its own desired set point temperature. Typically, the set point temperatures for the different heater electrodes 64 will be the same.

[0091] When the temperature of a selected heating zone 67 is to be determined, the switch 95 of the corresponding heater electrode 64 is closed and all other switches 95 are opened. In this way, the selected heater electrode 64 is provided in series with the resistor R. Since the heater electrodes 64 are formed of a PTC or an NTC material whose resistance changes with the temperature of the heater electrode 64, by measuring the voltage dropped across the resistor R (using the operational amplifier 97), the microprocessor 29 can determine the resistance of the selected heater electrode 64 and hence can determine the temperature of the corresponding heater electrode 64. If the determined temperature is above the desired temperature for that heating zone 67, then the microprocessor 29 can reduce the power applied to that heater electrode 64; or if the heating zone 67 is at a lower temperature than that desired, then the microprocessor 29 can increase the power applied to the corresponding heater electrode 64. Any suitable ON / OFF control or PWM (pulse width modulation) control can be used to vary the power applied to the different heater electrodes 64. The microprocessor 29 can select each heater electrode 64 in turn in order to determine the temperature of each heater electrode 64. Figure 8 also shows that the voltage supplied to the heater electrodes 64 may also be provided to the microprocessor 29 (through suitable scaling or conversion circuitry (not shown) if at a voltage greater than can be accepted by the microprocessor 29). This voltage input allows the microprocessor 29 to adjust the driving of the heater electrodes 64 in the event that, for example, the power is supplied by batteries and the batteries are becoming depleted. The voltage applied across the heater electrodes may drop for other reasons, including voltage drops along cables during high loads, tolerances in the outputs of the power supply etc. By measuring the applied voltage, the microprocessor 29 can use this information to calculate more accurately the resistance of each heater electrode (and hence the temperature of that heater electrode) given the present circuit conditions. For example, the microprocessor 29 can use the measured voltage across resistor R to work out the current flowing through the heater electrode 64 (by dividing the measured voltage across resistor R by the known resistance of resistor R). The microprocessor 29 can then determine the resistance of the heater electrode 64 by subtracting the voltage across resistor R from the sensed voltage applied to the heater electrode 64 and dividing that by the determined current. The calculated resistance can then be equated, if desired, to the temperature of the heater electrode 64 through an appropriate look up table.

[0092] Figure 8 also shows how the eight thermal fuses 34-1 to 34-8 used in the preferred heater 6 are connected to the control circuitry and can automatically remove power from the heater electrodes 64. In particular, as shown in Figure 8, the gate of the master switch 51 is connected to the power supply through a potential divider circuit 56 that connects to ground through the fuses 34 and an optional test switch 58. In normal operation, when the fuses 34 are intact, the voltage at the gate of the master switch 51 will be at a lower voltage than at the source terminal of the master switch 51 . This means that the master switch 51 is closed and current can flow from the power supply 21 through the master switch 51 to the heater electrodes 64. However, in the event that one or more of the fuses 34 melts and breaks the electrical connection between the potential divider circuit 56 and ground, then the voltage on the gate of the master switch 51 will become the same as the voltage on the source of the master switch 51 , and this will cause the master switch 51 to open, thereby isolating the heater electrodes 64 from the power supply 21 .

[0093] The optional test switch 58 is provided to allow the microprocessor 29 to test the circuitry for faults. Specifically, it is possible for the master switch 51 to fault into a permanently closed position, in which case, in the event one or more of the fuses 34 melts and breaks the connection to ground, the master switch 51 will not break the connection between the power supply 21 and the heater electrodes 64. However, by providing the test switch 58, which can be opened and closed by the microprocessor 29, the microprocessor 29 can check that the master switch 51 has not failed into a permanently closed state. In more detail, when the microprocessor 29 opens the test switch 58, this simulates a break in one of the fuses 34, which should open the master switch 51. The microprocessor 29 can then monitor the temperature of one or more of the heater electrodes 64 (using the op-amp 97) in the manner discussed above. If the master switch 51 is operating correctly, then the temperature of the or each monitored heater electrode 64 should drop (rapidly because the heater has a low thermal mass). If the temperature of any of the monitored heater electrodes 64 remains above a threshold temperature after the test switch has been opened, then the microprocessor 29 can assume the master switch 51 has faulted in its closed state) and as a result can open all the switches 95 to prevent further heating of the heater electrodes 64.

[0094] As shown in Figure 8, the test switch 58 and the switches 95 are n-channel MOSFETs and the master switch 51 is a p-channel MOSFET. The advantage of using n-channel switches is that they will go into an open state in the event of power being removed from the control circuit, which should remove all power to the heater electrodes 64.

[0095] Heater Manufacture

[0096] A preferred method of manufacturing the heater assembly 33 will now be described. An overview of the manufacturing method will be described with reference to Figure 9. The preferred heater stack uses stainless steel for the heater electrode layer 84, polyimide for the insulation layer 87 and copper for the heat spreading layer 88. A roll of stainless steel 101 , a roll of polyimide 103 and a roll of copper 105 are provided. The material on these rolls will have a thickness between about 1 pm and 150 pm and a common width between about 50mm and 600mm, although wider rolls are possible. The stainless steel will typically have a thickness within the range of 10 to 40 pm (preferably between 20 and 30 pm); the insulating layer will typically have a thickness within the range of 5 to 50 pm (preferably about 25 pm); and the copper will typically have a thickness within the range of 15 to 105 pm (preferably between 35 and 70 pm). Material from these rolls is fed into a roll-to-roll vacuum laminator 107 which bonds the three layers together to form a roll of laminated composite (stainless steel-polyimide-copper) material 109. At this stage in the process, the stainless steel layer, the polyimide layer and the copper layer are all uniform or homogenous layers. That is, at this stage the stainless steel layer does not define the heater electrodes 64 and the copper layer does not define the heat spreaders 91 . Once the roll of composite material 109 has been formed to the required length (which can be 10s or 100s of meters long), material from the roll 109 is passed through a sheet cutter 111 which cuts the roll of composite material 109 into sheets or panels for subsequent processing. The panels can be any desired size. In this example, the panels are cut to about 305mm wide and 500mm long. Preferably, the roll of composite material 109 is 500mm wide, so that one panel is formed by cutting the length of the roll 109 every 305mm. Each cut panel is then passed through various PCB manufacturing processes 113 that etch the stainless steel layer (using a ferric chloride etching process) to form the heater electrodes 64 and that etch the copper layer to form the heat spreaders 91. These PCB manufacturing processes are well known and will not be described in further detail here.

[0097] The resulting heater panel 115 is shown in Figure 10a. As can be seen from Figure 10a, each heater panel 115 carries the heater stack for twenty heaters 6 in a regular array. Figure 10b is an expanded view showing the heater electrode layer 84 for one of the heaters 6. As can be seen by comparing the track patterns shown in Figure 10b with the track pattern shown in Figure 4, the heater tracks in this example are slightly different to those described above - but the same process can be used to manufacture either layout. The twelve dashed circles (two of which are labelled 117 in Figure 10b) indicate tabs which connect the heater 6 to the rest of the heater panel 115. Three tabs 117 are provided along each of the curved ends and three tabs 117 are provided along each long edge of the heater 6. Each heater 6 has an associated hole 119-1 and 119-2 at either end thereof which are used to secure the heater panel 115 within a press tool in a subsequent manufacturing step. The rectangular periphery around each heater 6 is also etched into the heater panel 115 to provide the panel 115 with some flexibility when securing the heater panel 115 within the press tool.

[0098] Once the heater panel 115 has been formed, thermal fuses 34 are mounted 121 to the heat spreading layer 88 formed from the copper side of the composite roll 109. The copper side of each heater panel 115 is shown in Figure 11 a. Figure 11 b is an expanded view showing the heat spreading layer 88 for one of the twenty heaters 6 formed on the heater panel 115. There are eight thermal fuses 34 per heater 6, so, with twenty heaters 6 per heater panel 115, there are one hundred and sixty (160) thermal fuses 34 to be mounted in this step. As before, each thermal fuse 34 connects two adjacent heat spreaders 91 . A solder resist material 123 is formed between and around the pair of connection pads 125-1 and 125-2 across which the fuse 34 is connected. The fuses 34 may be mounted to the heat spreading layer 88 by soldering the fuses 34 onto the connection pads 125. To provide a reliable electrical connection to the thermal fuse 34, the pair of connection pads 125 for each fuse are preferably formed from ENIG (electroless nickel immersion gold) which is a two-layer metallic surface finish that comprises a very thin layer of gold over a layer of nickel. The rest of the copper layer forming the heat spreaders 91 will preferably have a brown oxide surface finish as this facilitates subsequent bonding of the heater 6 to the heater carrier 68. These surface finishes are made during the various PCB manufacturing processes 113 discussed above. As discussed above, the heater carriers 68 may include indents 59 on their upper surface (as shown in Figure 2) for receiving the fuses 34 that are surface mounted onto the copper side of the heater panel 115 when the heater panel 115 is bonded onto the upper surface of the heater carriers 68.

[0099] The heater panel 115 (with the mounted fuses) is then assembled in a press tool together with twenty heater carriers in an assembly process 127.

[0100] Press Tool Assembly Process

[0101] More detail of this press tool assembly process 127 will now be given with reference to Figures 12 to 18.

[0102] Figure 12a shows a press tool support plate 161 that forms the base of the press tool 160. The press tool support plate 161 is formed of a metal such as an aluminium alloy. The press tool support plate 161 includes two dowel pins 163-1 and 163-2 located at either end of the press tool support plate 161 that are used to align the press tool support plate 161 with other plates of the press tool 160 (to be described below). The press tool support plate 161 has twenty supports (some of which are labelled 164 in Figure 12a) that each receive and support a heater carrier 68 within the press tool 160. The press tool support plate 161 also has two tapered pins 165-1 and 165-2 for aligning each heater carrier 68 with the corresponding heater 6 on the heater panel 115. As the press support plate 161 can support twenty heater carriers, the press support plate 161 has forty tapered pins 165.

[0103] The first step in the assembly process is to load twenty heater carriers 68 into the press tool support plate 161 , as shown in Figure 12b. The heater carriers are made of a lightweight but heat resistant plastics material, such as a Liquid Crystal Polymer like Vicryst, Vectra S135 or the like. The next step is to insert a profiled release liner 167 (shown in Figure 13a) onto the upper surface of the press tool support plate 161 (as illustrated in Figure 13b). The release liner 167 prevents excess bonding film from sticking to the press tool support plate 161 in a later step. The release liner 167 has holes (some of which are labelled 169) located to receive the tapered pins 164 of the press tool support plate 161. The release liner 167 also has cut-outs 171 to allow the bonding film (described below) to touch the heater carriers 68 and to allow the forming tool to pass through. The release liner 167 may be made from various different non-stick materials but a PTFE based material (such as ACC-3 provided by Ventec International Group) is often used.

[0104] The next step is to insert a profiled bonding film panel 173 (shown in Figure 14a) on top of the release liner 167, as shown in Figure 14b. The bonding film panel 173 has holes (some of which are labelled 175) located to receive the tapered pins 164 of the press tool support plate 161. Figure 14c is an expanded view of an area of the bonding film panel 173 around one of the heater carriers 68. The central portion 177 of the bonding film panel 173 is the desired bonding area - on the upper surface of the heater carrier 68. The other portions of the bonding film panel 173 are undesired excess bonding areas, but these will stick to the sacrificial release liner 167. The bonding film panel is preferably a polyimide prepreg material such as VT-901 available from Ventec International Group, although other bonding materials can be used. The next step is to insert the heater panel 115 on top of the bonding film panel 173, as shown in Figure 15. The tapered pins 165 of the press tool support plate 161 receive the holes 119 on the heater panel 115 - which positionally aligns each heater 6 on the heater panel 115 over a corresponding heater carrier 68. The etched channels between adjacent heaters 6 on the heater panel 115 provide some “play” in the heater panel 115 making it easier to install the heater panel 115 onto the tapered pins 165.

[0105] The next step is to mount a heater panel retention plate 181 on top of the heater panel 115, which constrains all the heaters 6 on the heater panel 115 during the forming step (to be discussed below). The heater panel retention plate 181 is formed of a metal such as an aluminium alloy and has a hole at each end to receive the two dowel pins 163 of the press tool support plate 161 . The heater panel retention plate 181 also has holes to receive the tapered pins 165 of the press tool support plate 161. As shown in Figure 16a, this retention plate 181 is secured to the press tool support plate 161 by four screws 183, although other fixing means could be used. As shown in the expanded view of Figure 16b, the heater panel retention plate 181 has twenty cut-outs 185 that are shaped around each heater 6 on the heater panel 115, which allows parts of the heater panel forming plate (to be described next) through. The six tabs 117 holding the long edges of each heater 6 to the rest of the heater panel 115 are visible through the cut-out 185, which allows them to be cut by the heater panel forming plate. The other six tabs 117 around the two curved ends of the heater 6 are covered by the heater panel retention plate 181 , which means that the forming plate cannot cut these tabs 117 which ensures that the heater 6 is held in position during the bonding process.

[0106] The next step is to insert the heater panel forming plate 187 on top of the heater plate retention plate 181 - as shown in Figure 17a. The heater panel forming plate 187 is formed of a metal such as an aluminium alloy. The heater panel forming plate 187 is aligned with respect to the press tool support plate 161 by holes that engage with the two dowel pins 163 and with the tapered pins 165. Figure 17b is a cross-sectional view through the assembled press tool 160 along the line X— X shown in Figure 17a, which shows in more detail the heater panel forming plate 187. As shown, the forming tool has an inner wall that has twenty indentations 189 that are shaped to press down against the upper surface of the heater 6 that is positioned over the corresponding heater carrier 68. The walls 191-1 and 191-2 extending away from these indentations 189 are sloped and end at a sharp edge 193-1 and 193-2. These sharp edges 193 act to cut the tabs 117 along the long edges of the heater 6 before the sloped walls 191 bend the long edges of the heater 6 around the long edges of the heater carrier 68. Figure 17b also illustrates a channel 195 above each heater carrier 68 into which a temperature sensor (not shown) can be mounted to sense the temperature within the press tool 160 during the bonding process, which measurements can be used to control the heating applied to the press tool 160 during the bonding process.

[0107] Heater Bonding Process

[0108] Returning to Figure 9, the assembled press tool 160 is inserted into a vacuum lamination press machine 129 which removes all the air from the press tool 160 and applies heat and pressure to the press tool 160 to bond the heaters 6 to the heater carriers 68. The overall thickness of the assembled press tool is about 35mm which makes it suitable for most vacuum press machines 129. The operation of the vacuum lamination press machine 129 is illustrated in Figure 18. As shown, the press machine 129 removes the air from the press tool 160, applies mechanical pressure to the press tool 160 (represented by the larger arrows) and applies heat to both sides of the press tool 160 (represented by the smaller arrows).

[0109] The effect of the mechanical pressure applied by the vacuum lamination press machine 129 on the press tool 160 is illustrated in more detail in Figures 19a, 19b and 19c. Figure 19a is a perspective cut-away view showing part of the heater panel forming plate 187, the heater carrier 68, the heater panel 115, the retention plate 181 and the support plate 161 before any mechanical pressure is applied to the press tool 160; Figure 19b is a cross-sectional view of the perspective view shown in Figure 19a; and Figure 19c is an expanded view of the sharp edge 193-2 used to break the tabs 117 along the long edge of the heaters 6. When pressure is applied to the press tool 160 and there is relative movement between the heater panel forming plate 187 and the support plate 161 (as represented by the arrow 197), the sharp edges 193-1 and 193-2 will break through the tabs 117 along the long edge of the heater 6; and the sloped walls 191-1 and 191-2 will bend the edges of the heater 6 around the curved edges of the heater carrier 68. The plates 161 , 187 of the press tool 160 are designed so that when the indentations 189 press down on the heater 6, the press portions of the heater panel forming plate 187 do not come down and touch the retention plate 181 or the support plate 161. This ensures that the pressing force applied by the press tool 160 is applied to the heater 6 and the heater carrier 68. Figure 19 also illustrates ejector pin holes 199 through which ejector pins can be pushed to eject the heaters from the press tool 160 after the bonding process has completed.

[0110] With a vacuum lamination press machine 129, it is customary to input the panel area to be pressed. However, since the press tool 160 described above is designed to apply all the pressure just to the areas corresponding to the upper surface of the heater carriers 68 (the dark regions shown in Figure 10a), the overall area of the upper surfaces of the heater carriers 68 needs to be defined instead. The example heater carriers 68 illustrated in this embodiment have a surface area of approximately 2670mm2. As there are twenty heater carriers within the press tool 160, the total applied pressure area is 20 x 2670mm2or 53400mm2. This requires a clamping force of 13350kg or 130kN to achieve 25kgcnr2, which is a typical desired clamping force for bonding using VT-901 bonding film. Other clamping forces may be required with other bonding films.

[0111] Typically, the press will be heated until the material being bonded (the heaters 6, the bonding film 173 and the heater carriers 68 reach a temperature above 200°C. Depending on the materials used, the vacuum lamination press machine 129 may apply this pressure, heat and vacuum conditions for between 1 hr and 3hrs to ensure a good bond is achieved between the heater 6 and the heater carrier 68. The exact press conditions used will depend on the materials used and are typically specified by the manufacturer.

[0112] The particular press conditions used when VT-901 is used as the bonding film panel 173 are set out below by way of example only: 1 . The press is heated at a heat up rate of between 1 ,5°C / min and 6°C / min until it reaches a temperature of about 230 °C.

[0113] 2. The press is then maintained at this temperature in order to increase the temperature of the material in the press (the heater panel 115, the heater carriers 68 and the bonding film panel 173) to a temperature greater than 218 °C. The temperature of the material in the press is then maintained above 218 °C for between 120 and 150 minutes, depending on the thickness of the material in the press.

[0114] 3. During the heating process, a mechanical pressure greater than 25Kg / cm2 is applied to the plates of the press and a vacuum is maintained at about 4 kPa at least until the material in the press has reached a temperature above 200 °C and preferably during the full heating process.

[0115] Once the bonding process has been completed, the press tool 160 is removed from the vacuum lamination press machine 129 and the plates 161 , 181 and 187 of the press tool 160 are separated to allow the heater panel 115 (nowwith the bonded heater carriers 68 attached to it) to be removed from the press tool 160 - as shown in Figure 20.

[0116] Returning to Figure 9, after the heater panel 115 with the bonded heater carriers have been removed from the vacuum lamination press machine 129, the individual heaters 6 and heater carriers 68 are separated 131 from the rest of the heater panel 115 (as shown in Figure 21) - by breaking the remaining tabs 117 that are still intact around the curved ends of the heater 6. This can be done by hand or by another machine if desired. The heater drive and control circuitry is then connected to the ends or tails of the heater 6 and installed 133 into the heater assembly 33.

[0117] A low friction coating that also provides electrical insulation is then applied 135 to the upper surface of the heater assembly 33. This layer may be formed, for example, from a ceramic coating or wash such as Cerasol with a thickness of about 30 to 45 pm. The heater assembly 33 is then mounted 137 into the hair styler 1 , such that the coated surface provides the hair contacting surface of the hair styler. Where the hair styler 1 has two arms, one heater assembly 33 is typically installed in each arm of the hair styler.

[0118] Alternative Heater Manufacture

[0119] In the manufacturing method described above, the thermal fuses 34 were soldered onto the heat spreading layer 88. The inventor has found that such soldering of the fuses 34 onto the heat spreading layer 88 can lead to failure of the fuses 34 due to cracking caused by the thermal cycling that the heater 6 goes through during normal use, and this cracking can ultimately lead to premature breaking of the fuse circuit. An embodiment will now be described which doesn’t require the thermal fuses 34 to be soldered to the heater 6, meaning that they are free to expand and contract as the heater 6 thermally cycles during the normal use of the hair styler.

[0120] Figure 22 illustrates the heater carrier 68 used in this alternative embodiment. As before the heater carrier 68 is made of a light weight but heat resistant plastics material, such as a Liquid Crystal Polymer like Vicryst or Vectra S135. Figure 22a is a perspective view of the upper surface 201 of the heater carrier 68, Figure 22b is a plan view of the lower surface 203 of the heater carrier 68, and Figure 22c is an expanded view showing one of the shaped holes or windows 205 that extend through from the lower surface 203 to the upper surface 201 of the heater carrier 68. As shown in Figure 22, there are eight shaped holes 205 that extend through the heater carrier 68. The same manufacturing process as described above can be used to bond the heaters 6 to the heater carriers 68, except that the thermal fuses 34 are not mounted on the heat spreading layer 88 before the heater panel 115 is bonded onto the heater carriers 68 within the vacuum lamination bonding process. However, in this embodiment, the bonding film panel 173 should be shaped to include cut-outs where these shaped holes 205 are located on the heater carriers 68, to prevent bonding material blocking these holes 205 during the manufacturing process.

[0121] After the heater panel 115 has been bonded onto the heater carriers 68, the thermal fuses 34 can then be mounted into the holes 205 from the lower surface 203 of the heater carriers 68, as shown in Figure 23. Specifically, Figure 23a shows the lower surface 203 of the heater carrier 68 and Figure 23b is an expanded view showing the thermal fuse 34 that is mounted within the hole 205. The fuse 34 extends across and is in electrical contact with the pair of connection pads 125-1 and 125-2. The holes 205 are sized relative to the size of the thermal fuse 34 so that no matter where the thermal fuse 34 is within the hole 205, one part of the fuse 34 is in physical contact with the connection pad 125-1 and another part of the fuse 34 is in physical contact with the other connection pad 125-2. However, importantly, in this embodiment, each thermal fuse 34 is not soldered onto the connection pads 125, it is just placed into contact with the connection pads 125. To ensure a reliable electrical connection between the electrically conductive thermal fuses 34 and the corresponding connection pads 125, a mechanism is provided to apply pressure onto the thermal fuses 34 to push the thermal fuse 34 down onto the corresponding connection pads 125. This may be achieved in many different ways, but in this embodiment, it is achieved by using a silicone bar 207 (or a bar made of other compressible resilient material) which is mounted over the fuses 34, as shown in Figure 24. In particular, Figure 24a shows the lower surface of the heater carrier 68 with a silicone bar 207 mounted along the longitudinal axis of the lower surface 203. Figure 24b is a cross-sectional view of the heater carrier 68 shown in Figure 24a taken along the line X — X and Figure 24c is a transverse sectional view of the heater carrier shown in Figure 24a through the line Y — Y. Figures 24a and 24b also show three screw holes 209-1 , 209-2 and 209-3 which are used to secure a printed circuit board having the drive and sensor electronics for powering the heater 6.

[0122] Figure 25 illustrates the final assembled heater assembly 33. In particular, Figure 25a is a view of the rear of the heater assembly 33; Figure 25b is a cross-sectional view of the heater assembly 33 shown in Figure 25a taken along the line X — X; and Figure 25c is a transverse sectional view of the heater assembly 33 shown in Figure 25a through the line Y — Y. Figure 25c shows most clearly the printed circuit board (PCB) 211 to which the ends (or tails) of the fuse circuitry and the ends (or tails) of the heater electrodes 64 connect. In this embodiment, the screws 211-1 , 211-2 and 211-3 cause the PCB 213 to compresses the silicone bar 207 which helps causes the silicone bar 207 to push down and hold the fuses 34 in place against the corresponding pair of connection pads 125, which helps to maintain a reliable electrical connection between the thermal fuses 34 and the corresponding connection pads 125. Silicone Guillotine

[0123] As shown in Figure 26, in this embodiment, the lower surface of the silicone bar 207 is shaped and cut to define a silicone guillotine 215 over each fuse 34 which pushes down on the corresponding fuse 34. The amount of force that the guillotine 215 applies to the fuse 34 depends on the depth 217 of the cuts 219-1 and 219-2. Making the cuts 219 deeper in the silicone bar 207 reduces the force that the guillotine 215 applies to the fuse 34; and making the cuts shallower increases the force that the guillotine 215 applies to the fuse 34. Figure 26a shows the guillotine 215 when the fuse 34 is intact; and Figure 26b shows what happens to the guillotine 215 if the thermal fuse 34 melts. As can be seen in Figure 26b, in the event that the thermal fuse 34 melts, the compressive force stored in the guillotine 215 causes the guillotine 215 to expand and push downwards (in the figure) which helps to separate the fuse material into two parts 34-1 and 34-2 to ensure that the electrical connection between the corresponding pair of connection pads 125- 1 and 125-2 is broken (and remains broken once the fuse material cools and resolidifies).

[0124] Although this silicone guillotine 215 is not essential to the operation of the thermal fuse (as the fuse material should flow away from the solder resist material between the two connection pads 125 if the fuse melts), it helps to prevent the fuse material flowing back between the connection pads and resolidifying in a way that electrically connects the connection pads together again. The silicone guillotine 215 helps to ensure that the fuse material is pushed away to the sides and held away from the middle area that separates the pair of connection pads 125, thereby making a more reliable and permanent break in the fusing circuit in the event that any of the thermal fuses 34 melt.

[0125] Alternatives and modifications

[0126] Various embodiments have been described above by way of example. As those skilled in the art will appreciate, various alternatives and modifications may be made to the above embodiments. Some of those alternatives and modifications will now be described.

[0127] The invention has been described above by way of implementation in a hair styling device for straightening hair (‘hair straighteners’) which employ flat hair styling heaters 6. However, it could alternatively be implemented in any form of hair styling device, such as (but not limited to) crimpers, curlers or heated brushes. The heaters 6 may define a heating surface that is flat, curved, ridged or in the shape of a barrel. The hair styling device may have two arms like the device illustrated in Figure 1 or it may be a single armed device. The hair styling device may be a hair dryer type of device, in which case, the heaters may be used for heating air, which is then used to heat and style the hair. That is there may be no direct convective heating between the heater and the hair.

[0128] In the embodiment described above that uses a silicone bar to hold the fuses 34 in place against the respective connection pads 125, a separate mechanism may be provided to hold each thermal fuse 34 against the corresponding connection pads 125. For example, a separate piece of silicone may be provided for each fuse 34. Alternatively, a spring mechanism (such as a helical spring) may be provided to provide the required retaining force on the thermal fuse 34 to retain the fuse 34 in position during use. However, the use of a resilient bar 207 is preferred due to its simplicity and ease of manufacture and assembly.

[0129] In the above embodiments, MOSFET switches were used to control powering and sensing of the heater electrodes. As those skilled in the art will appreciate, other switches could be used instead. For example, Field Effect Transistors (FETs) could be used, such as Gallium Nitride FETs or bipolar junction transistors (BJTs).

[0130] The switching device can be placed in the high or low side of the power supply to the heaters.

[0131] In Embodiments described above, the heater electrodes 64 were used for heating and temperature sensing. In alternative embodiments, separate temperature sensors may be provided for sensing the temperature of each heating zone defined by the individual heater electrodes 64. For example, referring to Figure 2, a separate layer of temperature sensors and an additional dielectric layer may be provided under dielectric layer 78 or on top of the adhesive layer 92.

[0132] In the above embodiments, a DC power source was used to provide electrical power for heating the heater electrodes 64. This DC power source will typically be a battery, although DC supplies that derive their power from a mains power AC signal may be used. In embodiments where separate temperature sensors are provided, then AC mains power may be used to heat the heater electrodes. Thicker dielectric layers may be provided in this case between the heater electrodes 64 and the hair contacting surface of the hair styler.

[0133] It should be understood that the permitted response time for the fuse to melt is dependent on the heat-up rate, maximum permitted temperature, Tmax, and trigger temperature, Tigger. By way of example, for a heat up rate of 410°Cs'1, a Tmaxof 250 °C and a Tigger set at 240 °C, a (maximum) response time of 0.024 seconds is required. By way of a further example, for up rate of 400 °Cs_1, a Tmaxof 300 °C and a Tigger set at 240 °C, a (maximum) response time of 0.15 seconds is required.

[0134] It should also be noted that the solder link (fuse) may be defined by its thickness rather than weight. For example, the required thickness of the solder link can be determined from the equation:

[0135] Where Az is the solder film thickness; Q is the energy flux; t is the permitted response time; L is the latent heat of fusion; and p is the density. In an example, the available heater flux is 20 W / cm2, and the permitted response time is 0.3 s (as discussed above). If a tin-based solder is used, the latent heat of fusion is 60 kJ / kg and the density is 7,300 kg / m3. Accordingly, for this example, a solder film thickness, Az, of less than 0.011 mm might be required to achieve the required response time. In order to account for the possibility that not all of the available heater flux passes into the solder link, an even smaller thickness of solder link is preferably implemented. By way of a further example, dimensions of the solder link may be 1 mm x 0.5mm x 0.25mm, with a mass of around 0.002 g. The fuse may comprise a solder link formed of a tin-based alloy such as SN95SB5, which is tin alloyed with antimony, and which has a specific heat capacity of 0.23 kJ / kg K. A fuse such as this would be expected to blow in around 0.2 s, in other words has a response time of approximately 0.2 s (for example, when starting at 185 °C and blowing at 240 °C).

[0136] In the preferred control circuitry described above, the fuses were coupled between the master switch and a reference potential (ground). As those skilled in the art of circuit design will appreciate, the fuses may be coupled to the master switch in many different ways. For example, the fuses could be coupled between a supply reference potential (e.g. 5V) and the control gate of a control switch, the output of which is connected to the control gate of the master switch. In this case, when one of the fuses melts, this breaks the connection between the control switch and the reference potential causing the control switch to change state, which change of state causes the master switch to also change state, thereby preventing power from being supplied to one or more of the heater electrodes. Other arrangements are of course possible.

[0137] In the preferred heater arrangement described above, eight fuses were provided to protect sixteen heating zones. As those skilled in the art will appreciate, one fuse may be provided for each heating zone or indeed, one fuse may be provided for three or more heating zones. With heating zones arranged along the length and the width of the heater, one fuse for four heating zones works well.

[0138] As those skilled in the art will appreciate, the manufacturing method described above and the use of the silicone bar to press and hold the fuses against the connection pads of the fusing circuitry can be used with any kind of heater electrodes. The heater electrodes described above are preferred, but other heater electrode structures can of course be used, including, for example, those described in the applicant’s earlier patent application W02023 / 067308 which are formed of thick film or thin film conductor tracks, the contents of which are incorporated herein by reference. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

[0139] Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

[0140] No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

[0141] Throughout the description and claims of this specification, the words “comprise” and "contain" and variations of the words, for example "comprising" and "containing", means "including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps. Many of the embodiments described above can be summarized by the following numbered clauses:

[0142] 1 . A hair drying and / or styling device comprising: a heater for providing heat for drying and / or styling hair, the heater having a heat up rate greater than 30 °C per second; a power source for providing power to the heater; and safety circuitry for disconnecting the power source from the heater in response to an overheat trigger event or a fault detection event; wherein the safety circuitry is configured to disconnect the power source from the heater within a period between 0.02 and 2 seconds of the overheat trigger event or the fault detection event.

[0143] 2. The hair drying and / or styling device of clause 1 , wherein the heater comprises independently operable heater zones, and wherein each heater zone comprises at least one independently operable heater electrode.

[0144] 3. The hair drying and / or styling device of clause 2, wherein the safety circuitry is configured to disconnect power from the heater in dependence on detection of the overheat trigger event or the fault detection event in any one (or more) of the heater zones, preferably to disconnect power to all heater electrodes in dependence on detection of the overheat trigger event or the fault detection event in any one (or more) of the heater zones.

[0145] 4. The hair drying and / or styling device of any of clauses 1 to 3, wherein the safety circuitry comprises an array of temperature sensors, and a means for detecting if any one (or more) of the temperature sensors indicates an overheat trigger event.

[0146] 5. The hair drying and / or styling device of clause 4, wherein at least one of the array of temperature sensors is provided in thermal connection to one or more heater zones of the heater, or wherein at least one of the array of temperature sensors is provided in thermal connection to each heater electrode of the heater.

[0147] 6. The hair drying and / or styling device of any preceding clause, wherein the safety circuitry comprises at least one weak link configured to melt at a predetermined temperature indicative of an overheat trigger event, thereby breaking the circuit.

[0148] 7. The hair drying and / or styling device of clause 6, wherein at least one weak link is provided in thermal connection with one or more heater zones of the heater such that the weak link is configured to melt if any of the corresponding heater zones exceeds the predetermined temperature, or wherein at least one weak link is provided in thermal connection with each heater electrode of the heater such that the weak link is configured to melt if the corresponding heater electrode exceeds the predetermined temperature. 8. The hair drying and / or styling device of clause 7, wherein the safety circuitry is configured to disconnect the power only to the corresponding heater zone and / or heater electrode in dependence on at least one weak link melting.

[0149] 9. The hair drying and / or styling device of any of clauses 6 to 8, wherein the at least one weak link is configured to melt within a period between 0.02 and 2 seconds of the overheat trigger event, preferably between 0.025 and 1 seconds, and more preferably between 0.05 and 0.6 seconds.

[0150] 10. The hair drying and / or styling device of any of clauses 6 to 9, wherein the at least one weak link has a mass less than or equal to 0.1 gram, and preferably greater than or equal to 0.5 milligrams.

[0151] 11 . The hair drying and / or styling device of any of clauses 6 to 10, wherein a substrate on which the weak link is provided has a coating of solder resist to facilitate removal of melted solder to ensure a break in electrical connection.

[0152] 12. The hair drying and / or styling device of any of clauses 6 to 11 , wherein the at least one weak link is connected to a switch, preferably wherein the switch is configured to disconnect power from the heater in dependence on the at least one weak link melting.

[0153] 13. The hair drying and / or styling device of any of clauses 6 to 12, wherein the safety circuitry comprises an array of weak links, wherein the weak links are connected in series to a switch, preferably wherein the switch is configured to disconnect power from the heater in dependence on at least one weak link of the array of weak links melting.

[0154] 14. The hair drying and / or styling device of any of clauses 6 to 13, wherein the at least one weak link is coupled to a switch whereby in the event that one or more of the at least one weak link melts, the switch is configured to change state and prevent power being provided to at least one heater electrode of the heater.

[0155] 15. The hair drying and / or styling device of clause 14, wherein the heater comprises a plurality of heater electrodes and wherein the change of state of the switch prevents power being provided to each of the heater electrodes.

[0156] 16. The hair drying and / or styling device of clause 14, wherein the at least one link is coupled between a control gate of the switch and a reference potential such that the melting of the at least one link decouples the control gate of the switch from the reference potential thereby causing the switch to change state.

[0157] 17. The hair drying and / or styling device of clause 16, wherein the switch is a first switch, wherein a second switch is coupled between the control gate of the first switch and the reference potential, and wherein a controller is configured to operate the second switch to simulate a melting of the at least one link to test the operation of the first switch. 18. The hair drying and / or styling device of any preceding clause, wherein the safety circuitry is configured to disconnect the power source from the heater within a period between 0.025 and 1 seconds, and more preferably between 0.05 and 0.6 seconds. 19. Safety circuitry for a hair styling appliance comprising a heater with a heat up rate greater than 30 °C per second, wherein the safety circuitry is configured to disconnect (or cut) power supply to the heater within a period between 0.02 and 2 seconds of an overheat trigger event or a fault detection event.

Claims

ClaimsMethod of manufacture1 . A method of manufacturing heater assemblies for hair stylers, the method comprising: forming a heater panel comprising a plurality of heater elements arranged over the heater panel, each heater element comprising one or more heater electrodes that heat up the heater element when current is applied; inserting a plurality of heater carriers within a press tool; providing a bonding film over the heater carriers; mounting the heater panel over the bonding film so that each heater element on the heater panel is positioned over a respective heater carrier within the press tool; and using a bonding machine to apply pressure to the press tool to bond each heater element to the respective heater carrier to create a plurality of heater assemblies.

2. The method of claim 1 , wherein the heater elements are arranged in a regular array on the heater panel and the heater carriers are arranged in a corresponding regular array within the press tool.

3. The method according to claim 1 or 2, wherein the bonding machine is configured to extract air from the press tool during the bonding process.

4. The method according to claim 1 , 2 or 3, wherein the bonding machine is configured to heat the press tool during the bonding process.

5. The method according to any of claims 1 to 4, wherein each heater element comprises a laminate structure, with a first layer having a plurality of heater electrodes, a second dielectric layer and a third layer comprising safety circuitry for sensing, during use, overheat conditions with one or more of the heater electrodes.

6. The method according to claim 5, wherein the third layer is bonded to an upper surface of the respective heater carrier.

7. The method according to any of claims 1 to 6, further comprising removing the heater assemblies from the press tool and separating the heater assemblies from the heater panel.

8. The method according to claim 7, further comprising connecting ends of the at least one heater electrode to drive and control circuitry mounted on a printed circuit board and attaching the printed circuit board to the heater assembly.

9. The method according to any of claims 1 to 8, wherein the heater carrier comprises a plurality of windows each positioned adjacent fusing circuitry mounted on the heater element and further comprising placing a fusing element through each window onto the respective fusing circuitry and providing means to press each fusing element onto the respective fusing circuitry.

10. The method according to claim 9, wherein the means to press comprises a bar of resilient material that is compressed within the heater assembly to provide a pressing force on each of the fusing elements.11 . The method of claim 10, further comprising shaping the bar of resilient material to provide a respective guillotine structure for each fusing element that separates the fusing element from the fusing circuitry in the event of the fusing element melting.

12. The method according to any of claims 1 to 11 , wherein the heater panel is formed from a sheet of laminated material comprising a layer of stainless steel, a layer of electrical insulation and a layer of copper that are laminated together, which is etched and processed to form the one or more heater electrodes on the stainless-steel layer and etched to form fusing circuitry on the copper layer.

13. The method of claim 12, wherein the copper layer is etched and processed to form heat spreaders within the copper layer positionally aligned with a respective heater zone formed by a heater electrode on the stainless steel layer.Heater assembly14. A heater assembly for a hair styler comprising: a heater stack having a first layer that includes at least one heater electrode for heating the heater stack upon the application of an electric current and a second layer comprising fusing circuitry that includes at least at least one pair of first and second connection pads; a heater carrier for supporting the heater stack, the heater carrier having an upper surface to which the second layer of the heater stack is bonded, wherein the heater carrier comprises at least one window that extends through the upper surface of the heater carrier and exposes the pair of first and second connection pads; at least one electrically conductive fusing element positioned within the window of the heater carrier and making an electrical connection between the pair of firstand second connection pads; and means for applying a force on the at least one fusing element to hold the fusing element against the pair of first and second connection pads.

15. The heater assembly according to claim 14, wherein the means for applying force to the at least one fusing element comprises resilient means that is compressed within the heater assembly to provide said force on the fusing element.

16. The heater assembly according to claim 15, wherein the resilient means is shaped to provide a guillotine structure that separates the fusing element from making an electrical connection between the pair of first and second connection pads in the event of the fusing element melting.

17. The heater assembly according to claim 15 or 16, further comprising a printed circuit board to which the at least one heater electrode is attached and to which the at least one pair of firstand second connection pads of the fusing circuitry are attached, and wherein the printed circuit board is mounted within the heater assembly to compress the resilient means to thereby provide said force on the fusing element.

18. The heater assembly according to any of claims 14 to 17, wherein the heater stack includes a plurality of heater electrodes for heating a plurality of heater zones of the heater.

19. The heater assembly according to claim 18, wherein the fusing circuitry comprises a plurality of pairs of first and second connection pads, wherein the heater carrier comprises a plurality of windows that each extends through the upper surface of the heater carrier and exposes a respective pair of first and second connection pads, wherein a respective fusing element is positioned within each window of the heater carrier to make an electrical connection between the respective pair of first and second connection pads and wherein the means for applying a force is configured to apply a force on each fusing element to hold the respective fusing element against the corresponding pair of first and second connection pads.

20. The heater assembly according to claim 19, wherein the means for applying a force comprises a bar of resilient material that is compressed within the heater assembly to provide a respective pressing force on each of the fusing elements.21 . The heater assembly of claim 20, wherein the bar of resilient material is shaped to provide a respective guillotine structure for each fusing element that breaks the electrical connection between the corresponding pair of first and second connection pads in the event that the corresponding fusing element melts.Roll of Composite material22. A roll of laminated material comprising a layer of stainless steel, a layer of electrical insulation and a layer of copper that are laminated together, wherein the layer of stainless steel has a thickness between 10 and 40 pm and the layer of copper has a thickness between 15 and 105 pm.

23. The roll of laminated material according to claim 22, wherein the layer of electrical insulation has a thickness between 5 and 50 pm.

24. The roll of laminated material according to claim 22 or 23, wherein the layer of electrical insulation is polyimide.

25. The roll of laminated material according to claim 22, 23 or 24, wherein the layer of stainless steel is homogenous.

26. The roll of laminated material according to any of claims 22 to 25, wherein the layer of copper is homogenous.

27. The roll of laminated material according to any of claims 22 to 26, wherein the roll has a width of between 50mm and 600mm.

28. A hair styling appliance comprising a heater assembly made using the method of any of claims 1 to 13, and / or a heater assembly according to any of claims 14 to 21 and / or has a heater formed using the roll of composite material according to any of claims 22 to 27.

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