Field of the Invention

The present invention relates to a haircare appliance.

Background of the Invention

A haircare appliance may utilise a pair of heated plates to style the hair of a user. In use, a tress of hair may be clamped between the heated plates, and the appliance drawn along the length of the tress. This process may then be repeated to style a full head of hair.

Summary of the Invention

The present invention provides a haircare appliance comprising a heater assembly comprising a contact member having a hair-contacting surface, and one or more heating elements for heating the contact member, wherein the heater assembly has a heat capacity per unit area of less than 0.002 J.K'fmm' ² .

As a result, a heater assembly having a relatively low heat capacity (i.e. low thermal mass) may be achieved. Thereby the heater assembly may be more responsive to heating demands. For example, the heater assembly may be more quickly heated to an operating temperature, and/or respond more quickly to temperature changes during use, e.g. as hair is brought into contact with and then subsequently removed from the heater assembly. In contrast, the heater assemblies of known haircare appliances may have a relatively high heat capacity (i.e. high thermal mass). A high heat capacity is purposefully chosen so that, once the heater assembly reaches an operating temperature, a relatively constant temperature may be maintained during use, which can be beneficial for styling hair. However, a heater assembly with a high heat capacity is slow to respond to changes in heating demand.

A heater assembly with a relatively low heat capacity may experience rapid or significant cooling upon coming into contact with wet hair. However, this may be managed by employing dynamic control of the power supplied to the heater assembly. For example, in response to sensing a change in the temperature of the heater assembly, the power supplied to the heater assembly may be controlled so as to maintain a substantially constant temperature. In another example, the power supplied to the heater assembly may be controlled so as to achieve dynamic or variable temperature control. For example, the haircare appliance may employ a lower temperature at the roots of the hair, gradually increase the temperature as the haircare appliance is moved towards the tips of the hair, and return to the lower temperature after passing the tips of the hair in readiness for the next pass. This root-to-tip heating may reduce damage to the hair by using a lower temperature at the roots where the hair is younger, and a higher temperature at the tips where the hair is older. A further advantage of having a relatively low thermal capacity is that the efficiency and/or safety of the haircare appliance may be improved. For example, when the haircare appliance is turned off, the heater assembly may cool more rapidly. There is therefore less wasted heat and less risk of harm to a user.

The hair-contacting surface may have an area of at least 1200 mm ² . The heater assembly therefore has a relatively large surface area for contacting the hair. The haircare appliance may therefore be used to style a relatively large or wide tress of hair with each pass. This may then reduce the time required to style a full head of hair.

The heater assembly may have a heat capacity of no more than 5 J.K' ¹ . The heater assembly therefore has a relatively low total heat capacity. As a result, the heater assembly may be heated and cooled relatively quick. As noted above, a faster thermal response has several benefits. For example, upon powering on the haircare appliance, the heater assembly may be heated to an operating temperature more quickly, and therefore the haircare appliance may be ready to use after a shorter period (cf. a conventional heater assembly having a relatively high heat capacity). Additionally, a heater assembly having a faster response enables dynamic or variable temperature control to be employed during each pass of the appliance. Furthermore, as already noted, the efficiency and/or safety of the haircare appliance may be improved.

The contact member may have a thickness of no greater than 0.5 mm. As a result, a relatively low heat capacity per unit area may be achieved whilst also allowing for a sufficiently large hair-contacting surface. Additionally, the relatively shallow thickness may provide sufficient flexibility for the contact member to be deformed when contacting hair. As a result, a corralling effect, where hair is gathered and shaped, may be provided, which may result in improved hair styling. The contact member may have a thickness of no less than 0.05 mm. As a result, the robustness and manufacturability of the heater assembly may be improved. Specifically, warping caused by thermal processes that may be used in the manufacture of the heater assembly, such as lamination or screen printing, may be reduced. Reducing warping and thereby improving the flatness of the contact member may be desirable to ensure good contact with hair to enable efficient heat transfer between the hair and the heater assembly. Moreover, improved flatness may aid the adhesion of other components of the heater assembly to the contact member and thereby may further improve the manufacturability and robustness of the heater assembly. Furthermore, the contact member having a thickness of no greater than 0.5 mm and no less than 0.015 mm may provide a good balance between the competing needs of providing sufficient flexibility, whilst also providing robustness.

The contact member may have a specific heat capacity of no greater than 1200 J.kg'fK' ¹ . As a result, the relatively low heat capacity per unit area may be achieved whilst also allowing for sufficient thickness for robustness and sufficient surface area for useful hair treatment. The contact member may comprise copper or steel.

Each of the heating elements may comprise a thin-film heater. The use of thin-film heaters may enable a relatively low heat capacity to be achieved. Additionally, thin-film heaters may be relatively flexible and thereby not prevent the corralling effect discussed above. Moreover, thin-film heaters may be designed to provide relatively evenly distributed heating over the hair-contacting surface. This may reduce potential damage to hair that might arise due to local hot spots. Alternatively, each of the heating elements may comprise a thickfilm heater.

The heating elements may cover an area of no less than 45% of the hair-contacting surface. Additionally or alternatively, the heating elements may span 90% of a length of the haircontacting surface. As a result, the heat generated by the heating elements may be distributed more evenly over the hair-contacting surface. This may be particularly important when the contact member is relatively thin, as the inventors have observed that, in this instance, the contact member alone may be insufficient to appropriately evenly distribute the heat from the heating elements. Each of the heating elements may extend adjacent and/or parallel to the hair-contacting surface and have a thickness of no greater than 0.2 mm. As a result, the relatively low heat capacity per unit area may be achieved whilst also allowing for a sufficiently large heating element coverage area to provide sufficient heat distribution. Additionally, this may reduce the stiffness contributed by the heating elements to a total stiffness of the heater assembly and thereby may aid in providing the flexibility required to provide the corralling effect discussed above.

The heating elements may have a specific heat capacity of no greater than 1200 J.kg'fK' ¹ . Thereby a heater assembly having a relatively low heat capacity per unit area may be achieved whilst ensuring that the heating elements cover a sufficiently large area of the contact member to provide even heat distribution.

The haircare appliance may comprise a controller configured to control a supply of power independently to each of the heating elements. Also, the haircare appliance may comprise a controller capable of controlling a supply of power independently to each of the heating elements. Thereby, more precise control of the temperature of the hair-contacting surface may be achieved. This may result in the reduction in occurrence of local hot spots on the hair-contacting surface which may reduce the occurrence of damage to hair due to overheating. Additionally, the functionality of the haircare appliance may be improved. For example, the controller may reduce the temperature of heating elements that are not required for hair heating, e.g. due to no hair being present on the zone of the hair-contacting member heated by that heating element, and maintain or increase the temperature of heating elements that are required for heating. This may result in the energy consumption of the heater assembly being reduced. In another example, the controller may control the amount of electrical power supplied to each heating element in response to the amount of hair present on the zone of the contact member heated by that heating element, to achieve a desired temperature across the hair-contacting surface.

The heater assembly may comprise an electrical insulation layer located between the heating elements and the contact member. As a result, the contact member may be electrically isolated from the heating elements, which may improve the safety of the haircare appliance. Specifically, the heater assembly may comprise an electrical insulation layer having a dielectric strength of less than 48 V.

The electrical insulation layer may comprise an adhesive for bonding the heating elements to the contact member. This may improve the thermal conduction between the contact member and the heating elements by reducing the occurrence of air gaps between the contact member and heating elements. Additionally, this may improve the manufacturability of the heater assembly by obviating the requirement for additional layers of adhesive or joining mechanism as the electrical insulation layer may serve a dual purpose as an electrical insulation and adhesive layer. The electrical insulation layer may comprise a pressure sensitive adhesive. As a result, the ease of manufacture of the heater assembly may be improved as the electrical insulation layer, contact member and heating elements may be joined at room temperature, which may reduce the time required for the joining operation and thereby may reduce the cost of the heater assembly.

The electrical insulation layer may have a thickness of no greater than 0.2 mm. As a result, the thermal insulation provided between the heating elements and the contact member may be reduced. This may improve the responsiveness of the heater assembly, for example, in responding to demands to increase the temperature of the hair-contacting surface or to compensate for temperature drops in the hair-contacting surface caused by conductive losses to hair in contact with the hair-contacting surface. Additionally, this may reduce the heat capacity contributed to the heater assembly by the electrical insulation layer, which may aid in achieving the low heat capacity per unit area. Moreover, this may reduce the thermal time constant of the electrical insulation layer, which may improve the accuracy and responsiveness of a sensor of the heater assembly (discussed below) to changes in the temperature of the heater assembly.

The thickness of the electrical insulation layer may be no less than 0.005 mm. As a result, sufficient electrostatic discharge protection may be provided between the heating elements and the contact member. Furthermore, providing an electrical insulation layer 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 protection and to reduce the thermal insulation provided by the electrical insulation layer. The heater assembly may comprise one or more sensors for sensing a temperature of the heater assembly at one or more locations. This may provide additional functionality to the heater assembly. For example, closed loop control of the temperature of the hair-contacting surface may be achieved, which may reduce the damage to hair caused by overheating. Additionally, this may enable the haircare appliance to detect the presence or absence of hair in contact with the hair-contacting surface. As a result, dynamic or variable temperature control discussed previously, such as the root-to-tip heating, may be achieved.

The heater assembly may comprise a sensor for each respective heating element. As a result, closed loop control of each heating element may be achieved, which may improve the precision of the temperature control of the heating elements. As a result, the temperature of the heater assembly may be controlled such that good styling results are achieved without overheating the hair, which might otherwise damage the hair. Additionally, this may enable the presence or absence of hair in contact with the contact member to be detected at different zones on the hair-contacting surface. As a result, the temperature of heating elements that are not required for heating (owing to the absence of hair) may be lower. This may have two benefits. Firstly, this may reduce the energy consumption of the haircare appliance. Secondly, where a relatively small amount of hair covers a first zone of the hair contactingsurface, the heat generated at the first zone by the corresponding heating element 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 any hair in the second zone), part of the heat generated at the first zone may be transferred to the second zone (i.e. the second zone acts as heat sink to the first zone). Thereby, overheating and the associated hair damage may be reduced or avoided.

The heater assembly may comprise a plurality of layers and the sensors and the heating elements may be located on a same layer. This may improve the robustness of the heater assembly. Specifically, there may be a risk of layers becoming delaminated from one another. By locating the heating elements and the sensors on the same layer, the total number of layers may be reduced and thereby the number of delamination nucleation sites and associated risk of delamination may be reduced. Reducing the number of layers may also aid the manufacturability of the heater assembly. The heater assembly may comprise a plurality of layers, and the sensors and the heating elements may be located on different layers. Due to the minimum spacing achievable between conductive traces (e.g. 0.1 mm), each of the sensors may be placed closer to the zone of the respective heating element when located on a different layer, which may have a thickness (e.g. 0.015mm) significantly less than the minimum spacing. As a result, the sensors may be more responsive to changes in the temperatures of the heating elements.

The sensors may be located on a first layer. The heating elements may be located on a second layer, and the second layer may be located between the first layer and the contact member. Thereby the heating elements may be located between the sensors and the hair-contacting surface. As a result, the sensors do not act as a thermal insulation layer between the heating elements and the hair-contacting surface, which may improve the responsiveness of the heating elements.

The heater assembly may comprise conductive tracks connected to each of the sensors. Each of the heating elements may comprises a resistive track. The conductive tracks and the resistive tracks may be located on a same layer of the heater assembly, and the sensors may overlie the resistive tracks. Thereby, the previously articulated benefit of locating the sensors on a separate layer to the heating elements, improved sensor responsiveness, may be achieved whilst also potentially achieving the robustness benefits of locating the sensors and heating elements on the same layer.

Each sensor may comprise a conductive track configured to cover an area no less than 50 % of an area of each respective heating element. Thereby area average sensing may be achieved rather than point sensing, which may improve the accuracy and responsiveness of the sensors.

Each sensor may comprise a conductive track orientated in a first direction, and each heating element may comprise a resistive track orientated in a second direction. The first direction may be angularly offset from the second direction. Thereby inductive coupling between the sensors and the heating elements may be avoided. For example, the angular offset may be greater than 45°. The haircare appliance may comprise a housing and a support member for supporting the heater assembly within the housing. The support member may have a thermal conductivity of no greater than 1 W.m'fK' ¹ . Equivalently, the support member may have a thermal time constant of no greater than 1,450,000 s/m ² , wherein the thermal time constant is a measure of how long it takes thermal energy to move through a thermal mass. The support member may support the heater assembly such that in use the heater assembly may apply sufficient force to hair to style hair and prevent damage due to buckling of the heater assembly. By having a thermal conductivity of less than 1 W.m'fK' ¹ , heat conducted away from the heater assembly via the support member may be reduced. This may reduce the energy consumption of the heater assembly and improve the responsiveness of the heater assembly.

The support member may be over-moulded onto the heater assembly. This may ensure intimate contact between the support member and the heater assembly. Thereby the formation of air gaps between the support member and heater assembly may be reduced, which in turn may reduce the occurrence of air gap induced hot spots.

The power supplied to the heater assembly may have a voltage of no greater than 48 V. As a result, the thickness of the electrical insulation layer may be reduced. This may in turn reduce the thermal insulation provided by the electrical insulation layer and improve the flexibility of the electrical insulation layer to aid in achieving the corralling effect discussed above.

The present invention also provides a heater assembly for a haircare appliance comprising a contact member having a hair-contacting surface, and one or more heating elements for heating the contact member, wherein the heater assembly has a heat capacity per unit area of the hair-contacting surface of less than 0.002 J.K'fmm' ² .

Figure l is a side view of a haircare appliance with arms of the haircare appliance in an open position;

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 an exploded view of a heater assembly of the haircare appliance;

Figure 6 is a block diagram of electrical components of the haircare appliance;

Figure 7 is a plan view of an alternative example of a sensor and heating element layer of the heater assembly;

Figure 8 is a plan view of a further example of a sensor and heating element layer of the heater assembly;

Figure 9 is an exploded view of an alternative heater assembly;

Figure 10 is a plan view of a heating element layer of the alternative heater assembly; and Figure 11 is a plan view of a sensor layer of the alternative heater assembly.

Detailed Description of the Invention

The haircare appliance 10 of Figures 1 and 2 comprises a first arm 12 and a second arm 14 pivotably connected at one end by a hinge 16. The arms 12,14 are moveable about the hinge 16 between an open position (shown in Figure 1) and a closed position (shown in Figure 2). The haircare appliance 10 may take the general form of a hair straightener.

Each arm 12,14 comprises a heating section 22,24 located at an end of each arm 12,14 remote from the hinge 16, and a handle section 26,28 located at an opposite end of each arm 12,14 where the hinge 16 is located. In use, the user grips the handle sections 26,28 and inserts a section of hair between the two arms 12,14. The user then applies pressure to the handle sections 26,28 in order to close the arms 12,14. In closing the arms 12,14, the hair is gripped between the heating sections 22,24. The arms 12,14 are biased towards the open position such that when the user releases the pressure on the handle sections 26,28, the arms 12,14 return to the open position.

Referring now to Figures 3 and 4, the heating section 22,24 of each arm 12,14 comprises a casing 30, a heater assembly housing 32, a heater assembly 34 and a support member 38. The casing 30 defines a trough 31 within which the heater assembly housing 32 is located. The heater assembly housing 32 comprises a recess 33 within which the support member 38 and the heater assembly 34 are located. The support member 38 is located between the heater assembly housing 32 and the heater assembly 34 and supports the heater assembly 34 within the heater assembly housing 32. The heater assembly 34 is located on top of the support member 38.

Referring now to Figure 5, the heater assembly 34 comprises multiple layers of components arranged in a stack. The heater assembly 34 comprises, in order from the top to the bottom of the stack, a contact member 42, an electrical insulation layer 41 and a sensor and heating element layer 40.

The contact member 42 is located on top of the electrical insulation layer 41. The upper surface of the contact member 42 defines a hair-contacting surface 37. In use, the haircontacting surface 37 contacts hair and conducts heat generated by the sensor and heating element layer 40 to the hair in order to heat and thereby style the hair.

The contact member 42 is sized such that the hair-contacting surface 37 has an area of around 2250 mm ² . The heater assembly 34 therefore has a relatively large surface area for contacting the hair. The haircare appliance 10 may therefore be used to style a relatively large or wide tress of hair with each pass. This may then reduce the time required to style a full head of hair. Other sizes of contact member 42 may be used. For example, a smaller contact member 42 may be employed in order to achieve a more compact haircare appliance. However, as the area of the hair-contacting surface 37 decreases, the width of the tress of hair that may be styled with the haircare appliance decreases. Accordingly, the haircontacting surface 37 may have an area of no less than 1200 mm ² . As a result, a full head of hair may be styled in a relatively timely manner.

The contact member 42 has a thickness of 0.05 mm. A relatively thin contact member 42 has the advantage that a relatively low heat capacity may be achieved for the contact member 42 whilst also allowing for a sufficiently large hair-contacting surface 37. As a result, a lower heat capacity for the heater assembly 34 may be achieved, which may improve the responsiveness of the heater assembly 34 to heating demands, as will be discussed in more detail below. Additionally, the relatively shallow thickness may provide sufficient flexibility for the contact member 42 to be deformed when contacting hair. As a result, a corralling effect, where hair is gathered and shaped, may be provided, which may result in improved hair styling. A relatively thick contact member 42, on the other hand, has the advantage that the robustness and manufacturability of the heater assembly 34 may be improved. Specifically, warping caused by thermal processes that may be used in the manufacture of the heater assembly 34, such as lamination or screen printing, may be reduced. Reducing warping and thereby improving the flatness of the contact member 42, which may be desirable to ensure good contact with hair to provide efficient heat transfer between the hair and the heater assembly 34. A contact member 42 having a thickness of no greater than 0.5 mm and no less than 0.015 mm provides a good balance between the competing needs of providing sufficient flexibility, whilst also providing robustness.

The contact member 42 is formed of stainless steel. Stainless steel has a relatively low specific heat capacity (e.g., between 400 and 500 J.kg'fK' ¹ , depending on the type of steel). As a result, in spite of the relatively large surface area of the hair-contacting surface 37, the contact member 42 has a relatively low heat capacity. The contact member 42 may be formed of other materials having a different specific heat capacity. For example, the contact member may be formed of copper, which typically has a lower specific heat capacity than that of stainless steel. As the heat capacity of the contact member 42 increases, the responsiveness of the contact heater 42, and thus the heater assembly 34, to heating demands worsens. Accordingly, the contact member 42 may be formed of a material having a specific heat capacity of no greater than 1200 J.kg'fK' ¹ , for example copper.

The hair-contacting surface 37 of the contact member 42 may be coated with a coating. This may improve the robustness and/or the aesthetic appearance of the contact member 42. In examples, the coating may comprise titanium nitride or nickel.

The electrical insulation layer 41 is located between the contact member 42 and the sensor and heating element layer 40. The electrical insulation layer 41 has a similar shape and area to the contact member 42. By comprising the electrical insulation layer 41, the contact member 42 is electrically isolated from the sensor and heating element layer 40, which may improve the safety of the haircare appliance 10.

The electrical insulation layer 41 has a thickness of 0.05 mm. A relatively thin electrical insulation layer 41 has the advantage that the thermal insulation provided between the sensor and heating element layer 40 and the contact member 42 may be reduced. Additionally, this may reduce the heat capacity contributed to the heater assembly 34 by the electrical insulation layer 41. A relatively thick electrical insulation layer 41, on the other hand, has the advantage that sufficient electrostatic discharge protection may be provided between the heating element 50 and the contact member 42. An electrical insulation layer 41 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 protection and to reduce the thermal insulation provided by the electrical insulation layer 41.

The electrical insulation layer 41 is formed of an adhesive layer that bonds the contact member 42 to the sensor and heating element layer 40. This may improve the thermal conduction between the contact member 42 and the sensor and heating element layer 40 by reducing the occurrence of air gaps. In this example, the electrical insulation layer 41 is formed of a polyimide adhesive. However, other materials, including other polymers, glass or enamel, may be used that provide sufficient electrical insulation and thermal stability to operate at the operating temperatures of the heating element, e.g. 200 °C. In some examples, the electrical insulation layer 41 may be formed of a pressure sensitive adhesive. As a result, the heater assembly 34 may be assembled at room temperature, thereby simplifying the manufacture of the heater assembly 34. In other examples, the electrical insulation layer 41 may comprise a layer of electrical insulation material between two layers of adhesive.

The sensor and heating element layer 40 is located beneath the electrical insulation layer 41. The sensor and heating element layer 40 comprises a substrate 49, a heating element 50 and a sensor 48.

The substrate 49 supports and locates the sensor 48 and heating element 50 within the heater assembly 34. In this example, the substrate 49 has the same shape and area as the electrical insulation layer 41 and contact member 42. In this example, the substrate comprises two sheets of silicone between which the sensor 48 and heating element 50 are located. However, other materials may be used such as polyimide. Moreover, in other examples, the substrate 49 may comprise only a single sheet on which the sensor 48 and heating element 50 are located. The heating element 50 provides heat to the contact member 37 to heat hair in contact with the hair-contacting surface 37. In this example, the heating element 50 comprises a resistive track and a pair of conductive pads. The resistive track comprises a material such as copper, silver, constantan or stainless steel, and extends in a serpentine shape over the substrate 49. The resistive track may be formed by processes such as etching or printing. However, in other examples, the heating element 50 may be formed from a length of wire. The conductive pads are located at either end of the resistive track.

In this example, the heating element 50 has the form of a thin-film heater. The use of a thin- film heater may enable a relatively low heat capacity to be achieved. Additionally, thin-film heaters may be relatively flexible and thereby not prevent the corralling effect discussed above. Moreover, thin-film heaters may be designed to provide relatively evenly distributed heating over the hair-contacting surface 37. 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.

The heating element 50 extends over the substrate 49 such that the heating element 50 covers an area of about 50% of the hair contacting-contact surface 37 and spans about 95% of a length of the hair-contacting surface 37. As a result, the heat generated by the heating element 50 may be distributed more evenly over the hair-contacting surface 37. This may be particularly important when the contact member 42 is relatively thin, as the contact member 42 alone may be insufficient to appropriately evenly distribute the heat from the heating element 50. The heating element 50 may cover a smaller area and/or span a shorter length of the hair-contacting surface 37. Relatively even heat distribution may be provided by a heating element 50 covering an area of no less than 45% of the hair-contacting surface 37 and/or spanning no less than 90% of the hair-contacting surface 37. In the example of Figure 5, the resistive track has a width of 0.1 mm and a spacing between parallel portions of the track of 0.1 mm. However, in other examples, different widths and spacings may be used to achieve the desired coverage.

As described above, the heating element 50 may be formed of copper, silver, constantan or stainless steel. As a result, the heating element 50 is formed of a material having a specific heat capacity of no greater than 1200 J.kg'fK' ¹ . Thereby a heater assembly 34 having a relatively low heat capacity may be achieved whilst ensuring that the heating element 50 covers a sufficiently large area of the contact member 42 to provide even heat distribution.

The sensor 48 senses a temperature of the heater assembly 34. In this example, the sensor 48 comprises a thermistor connected to a pair of wires. In other examples, the sensor may comprise a thermocouple. In this example, the sensor 48 senses a temperature of the contact member 42. However, in other examples, the sensor 48 may sense a temperature of the heating element 50. The sensor 48 is located between (and spaced from) parallel portions of the resistive track on the centre of the substrate 49. As a result, the sensor 48 is located beneath the centre of the contact member 42 and senses the temperature at the centre of the hair-contacting surface 37. In the present example, the layer 40 comprises a single sensor. In other examples, the layer 40 may comprise multiple sensors placed at different locations on the substrate 49 such that a multiple temperature measurements at different locations on the hair-contacting surface 37 may be achieved.

The sensor and heating element layer 40 has a thickness of 0.05 mm. As a result, a relatively low heat capacity may be achieved for the heater assembly 34 whilst also allowing for a sufficiently large coverage area to provide sufficient heat distribution. Additionally, this may reduce the stiffness contributed by this layer 40 to the total stiffness of the heater assembly 34 and thereby may aid in providing the flexibility required to provide the corralling effect discussed above. In other examples, the sensor and heating element layer 40 may be thinner or thicker. As the thickness increases, the heat capacity and/or the stiffness of the layer are likely to increase. Accordingly, the layer 40 may have a thickness of no greater than 0.2 mm, so as to preserve the aforementioned benefits.

As a result of the construction of the heater assembly 34, the heater assembly 34 has a relatively low heat capacity, i.e., a relatively low thermal mass. In the present example, the heater assembly 34 has a heat capacity of 1 J.K' ¹ . The heater assembly 34 therefore has a relatively quick response time to changes in heating demands. For example, the heater assembly 34 may be more quickly heated to an operating temperature, and/or respond more quickly to temperature changes during use, e.g. as hair is brought into contact with and then subsequently removed from the heater assembly 34. In contrast, the heater assemblies of known haircare appliances may have a relatively high heat capacity (i.e. high thermal mass). A high heat capacity is purposefully chosen so that, once the heater assembly reaches an operating temperature, a relatively constant temperature may be maintained during use, which can be beneficial for styling hair. However, a heater assembly with a high heat capacity is slow to respond to changes in heating demand. A heater assembly with a relatively low heat capacity may experience rapid or significant cooling upon coming into contact with wet hair. However, this may be managed by employing dynamic control of the power supplied to the heater assembly. For example, in response to sensing a change in the temperature of the heater assembly, the power supplied to the heater assembly may be controlled so as to maintain a substantially constant temperature. In another example, the power supplied to the heater assembly 34 may be controlled so as to achieve dynamic or variable temperature control. For example, the haircare appliance may employ a lower temperature at the roots of the hair and gradually increase the temperature as the haircare appliance is moved towards the tips of the hair. This root-to-tip heating may reduce damage to the hair by using a lower temperature at the roots where the hair is younger, and a higher temperature at the tips where the hair is older. A further advantage of having a relatively low thermal capacity is that the efficiency and/or safety of the haircare appliance 10 may be improved. For example, when the haircare appliance 10 is turned off, the heater assembly 34 may cool more rapidly. There is therefore less wasted heat and less risk of harm to a user.

Although the heater assembly 34 of the present example has a heat capacity of 1 J.K' ¹ , the heater assembly 34 may have a different heat capacity. This may be achieved, for example, by employing different materials and/or thickness for each of the layers. However, as the heat capacity of the heater assembly 34 is increased, the thermal responsiveness of the heater assembly 34 worsens. Accordingly, the heater assembly 34 may have a heat capacity of no more than 5 J.K' ¹ so as to preserve the aforementioned benefits associated with a relatively low heat capacity.

The heater assembly 34 has a relatively low heat capacity in spite of the relatively large area of the hair-contacting surface 37. As noted above, hair-contacting surface 37 of the heater assembly 34 may be larger or smaller. Nevertheless, with the construction of heater assembly 34 described herein, a relatively low heat capacity may be achieved. Indeed, the heater assembly 34 may be said to have a relatively low heat capacity per unit area of the hair-contacting surface 37. In the example described above, the heater assembly 34 has a heat capacity per unit area of the hair-contacting surface 37 of 0.0005 J.K'fmm' ² . The heater assembly 34 may have a different heat capacity per unit area of the hair-contacting surface 37. As the heat capacity per unit area increases, the thermal responsiveness of the heater assembly 34 decreases. Accordingly, the heater assembly may have a heat capacity per unit area of the hair-contacting surface 37 of no more than 0.002 J.K'fmm' ² so as to preserve the aforementioned benefits.

The support member 38 supports the heater assembly 34 within the heater assembly housing 32 such that, in use, the heater assembly 34 may apply sufficient force to hair to style the hair and prevent damage to the heater assembly 34 due to buckling of the heater assembly 34. In some examples, the support member 38 may be made from a flexible material, such as silicone, such that when the heater assembly 34 contacts hair, the support member 38 and the heater assembly 34 are resiliently deformed. As a result, the corralling effect discussed previously may be provided. In this example, the support member 38 comprises silicone and has a relatively low thermal conductivity (i.e. no greater than 1 W.m'kK' ¹ ). As a result, the support member 38 provides relatively good thermal insulation of the heater assembly 34. This may reduce the energy consumption and improve the responsiveness of the heater assembly 34. However, other materials may be used which also have a relatively low thermal conductivity. Specifically, the thermal time constant of the support member is less than 1,450,000 s/ m ² .

The support member 38 may be over-moulded onto the heater assembly 34. This may ensure intimate contact between the support member 38 and the heater assembly 34. Thereby the formation of air gaps between the support member 38 and heater assembly 34 may be reduced, which in turn may reduce the occurrence of hot spots. However, other methods for joining the support member 38 to the heater assembly 34 may be used, such as an adhesive layer located between the support member 38 and heater assembly 34.

In addition to the two arms 12, 14, the haircare appliance 10 comprises a housing unit 20 that houses a power supply 60 and a control unit 62. In the present example, the housing unit 20 is attached to and moves with the first arm 12. Consequently, as the two arms 12,14 move between the open and closed positions, the second arm 14 moves relative to the housing unit 20.

The power supply 60 supplies electrical power to the other electrical components of the haircare appliance 10, such as the heater assembly 34 of each of the two arms 12,14 and the control unit 62. In the present example, the power supply 60 comprises a battery supplying a DC voltage. In other examples, electrical power may be provided by a mains power supply, and the power supply 60 may comprise a rectifier and a DC-to-DC converter that outputs a DC voltage. The electrical power supplied by the power supply 60 to each of the heater assemblies 34 may have a voltage of no more than 48 V. As a result, a thinner electrical insulation layer 41 may be employed.

Turning now to Figure 6, the control unit 62 comprises a pair of switches 66,68, a user interface 70 and a controller 72.

Each of the switches 66,68 is connected between the power supply 60 and the heating element 50 of a respective arm 12,14. Accordingly, when one of the switches 66,68 is closed, electrical power is supplied to the heating element 50 of the corresponding arm 12, 14 and the temperature of the heater assembly 34 increases. Conversely, when the switch 66,68 is open, the supply of electrical power to the heating element 50 is halted and the temperature of the heater assembly 34 decreases. Accordingly, the switches 66,68 may be controlled in order to control the temperature of the heater assembly 34 of each of the arms 12,14.

The user interface 70 may be used to power on and off the haircare appliance 10. Additionally, the user interface 70 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).

The controller 72 is connected to the switches 66,68 and the user interface 70. Additionally, the controller 72 is connected to the sensor 48 of the heater assembly 34 of each arm. As a result, the controller 72 is provided with a measure of the temperatures of the two heater assemblies 34. The controller 72 is responsible for controlling the operation of haircare appliance 10. In particular, the controller 72 controls the opening and closing of the switches 66,68, and thus the electrical power supplied to the heating elements 50, in response to input data received from the user interface 70 and the sensors 48. For example, the controller 72 may control the switches 66,68 such that the temperature of each heater assembly 34, as sensed by the sensor 48, is maintained at a particular setpoint. In examples, the controller 72 may control the duty cycle of the switches 66,68, perhaps using closed loop control, such as PI or PID control.

Figure 7 shows an alternative example of a sensor and heating element layer 200. The sensor and heating element layer 200 differs from that described previous in two major ways.

Firstly, instead of comprising a single heating element 50, the layer 200 comprise a plurality of heating elements 202. Specifically, in this particular example, the sensor and heating element layer 200 comprises three heating elements 202. Each of the heating elements 202 comprises a resistive track 204 in a concentric rectangular shape and a pair of conductive pads 206 for supplying power to each of the resistive tracks 204 independently. Each of the resistive tracks 204 is located beneath a different zone of the contact member 42 such that each of heating elements 202 heats a respective zone of the contact member 42 and thus the heat-contacting surface 37. In this example, the control unit 62 comprises additional switches, one for each of the heating elements 202, and the controller 72 is configured to control a supply of power independently to each of the heating elements 202. Thereby, more precise control of the temperature of the hair-contacting surface 37 may be achieved. This may result in the reduction in occurrence of local hot spots on the hair-contacting surface 37 which may reduce the occurrence of damage to hair due to overheating.

Secondly, the sensor and heating element layer 200 comprises a sensor 208 for each of the heating elements 202. As a result, the temperature of each of the zones of the contact member 42 and/or each of the heating elements 202 may be sensed. The temperature of the heater assembly 34 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 contact member 42 to be detected at different zones on the hair-contacting surface 37. 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 have two benefits. Firstly, this may reduce the energy consumption of the haircare appliance 10. Secondly, where a relatively small amount of hair covers a first zone of the hair contactingsurface 37, 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 reduced or avoided.

Figure 8 shows a further example of a sensor and heating element layer 300 which differs from the layer 200 of Figure 7 in two major ways.

Firstly, the heating elements 302 have different geometries. The layer 300 again comprises three heating elements 302, and each of the heating elements 302 comprises a resistive track 304. However, in contrast to the example of Figure 7, the resistive tracks 304 are not concentric. Additionally, the width of the resistive tracks 304 is greater than those of Figure 7 so that a similar area of the contact member 42 is covered by the heating elements 302.

Secondly, in the example of Figure 7, each sensor 208 comprises a thermistor which provides a single point temperature sensing capability. Each sensor of the layer 300 of Figure 8, on the other hand, comprises a thermistor which provides area average sensing. This may then improve the accuracy and responsiveness of the sensors. The layer 300 of Figure 8 comprises three sensors, each having a conductive track 306 and a pair of conductive pads 308. Each conductive track 306 has a known resistance at room temperature, for example 100 , and is constructed from a material which undergoes a detectable and predictable change in resistance over the operating temperature range of the heater assembly 34, for example nickel, such that a temperature change in the heater assembly 34 may be detected. The conductive tracks 306 are interspersed between the resistive tracks 304 of the heating elements 302 such that an average temperature for the zone of the contact member 42 heated by the respective heating element 304 may be sensed.

In the above examples, the sensors and heating elements are located on the same layer (i.e. the sensor and heating element layer 40). This may improve the robustness of the heater assembly 34. Specifically, there may be a risk of layers becoming delaminated. By locating the heating elements and the sensors on the same layer, the total number of layers may be reduced and thereby the number of delamination nucleation sites and associated risk of delamination may be reduced. Reducing the number of layers may also aid the manufacturability of the heater assembly. However, in other examples, the sensors and the heating elements may be located on different layers.

Figure 9 shows an example heater assembly 400 in which the sensor and heating element layer is replaced by a heating element layer 402 and a sensor layer 404. The heater assembly 400 further comprises a contact member 418, a first electrical insulation layer 408, and a second electrical insulation layer 406.

The contact member 418 is unchanged from that described previously.

The first electrical insulation layer 408 is located between the contact member 418 and the heating element layer 402, and the second electrical insulation layer 406 is located between the heating element layer 402 and the sensor layer 404. Each of the insulation layers 406,408 is unchanged from that described previously.

Turning to Figure 10, the heating element layer 402 is similar to the layer 200 of Figure 7, except that the resistive tracks 412 of the heating elements 411 have different shapes (sinuous rather than concentric) and the sensors are omitted.

Turning now to Figure 11, the sensor layer 404 comprises three sensors 413 and three pairs of conductive pads 416. The sensors 413 each comprising a conductive track 414, one for each of the heating elements 411, which operate similarly to those described in relation to Figure 8. However, in this example, each of the conductive tracks 414 extends over an area which is directly beneath the area covered by the respective heating element 411. Due to the minimum spacing achievable between conductive traces (e.g. 0.1 mm), each of the sensors 413 may be placed closer to the respective heating element 411 when located on a different layer, which may have a thickness (e.g. 0.005 mm) significantly less than the minimum spacing. As a result, the sensors 413 may be more responsive to changes in the temperatures of the heating elements 411. The conductive tracks 414 each cover an area of 60% of an area of each respective heating element 411. By covering an area of no less than 50% of the area of each respective heating element 411, the accuracy and responsiveness of the sensors 413 to changes in temperature of the heating elements 411 may be improved. The pairs of conductive pads 416 are located at the ends of each of the tracks 414 and have similar function to the conductive pads of Figure 8.

In the example of Figure 9, the heating element layer 402 is located closer to the contact member 418 than the sensor layer 404. As a result, the sensor layer 404 does not act as a thermal insulation layer between the heating element layer 402 and the contact member 418, which may improve the responsiveness of the heater assembly. However, it is conceivable that the sensor layer 404 may be located closer to the contact member 418 than the heating element layer 402.

In the examples of Figures 10 and 11, the conductive tracks 414 of the sensors 413 and the resistive tracks 412 of the heating elements 411 are orientated in the same direction (that is to say, that the majority of the conductive tracks 414 are orientated in a first direction and the majority of the resistive tracks 412 are orientated in a second direction which is parallel to the first direction). However, in other examples, the first direction may be angularly offset (for example by angles greater than 45°) from the second direction. Thereby inductive coupling between the sensors 413 and the heating elements 411 may be avoided.

In other examples, the heater assembly may comprise, from the top to the bottom of the stack, a contact member, a first electrical insulation layer, a heating element layer, and a second electrical insulation layer. The sensor layer is omitted. Instead, the sensors may be located on the second electrical insulation layer. The heating element layer may comprise resistive tracks and conductive tracks. The resistive tracks form the heating elements, and the conductive tracks provide electrical connections to the sensors via holes in the second electrical insulation layer. The previously articulated benefit of locating the sensors on a separate layer to the heating elements, i.e., improved sensor responsiveness, may therefore be achieved whilst also potentially achieving the robustness benefits of locating the sensors and heating elements on the same layer.

In an exemplary embodiment, each electrical insulation layer may have a thickness of between 0.001mm and 0.1mm. In the examples described above the contact member comprises a single material. However, embodiments are envisaged in which the contact member comprises multiple materials, for example multiple materials arranged in a sandwich construction.

Whilst particular examples and embodiments have thus far been described, it should be understood that these are illustrative only and that various modifications may be made without departing from the scope of the invention as defined by the claims.