A heater assembly

Abstract

A heater assembly for a haircare appliance is described. The heater assembly comprises a contact member that defines a hair-contacting surface. The heater assembly comprises one or more heating elements configured to heat the contact member. The heater assembly comprises a support member in thermal contact with the one or more heating elements and the contact member. The support member has a thermal diffusivity of at least 1.0 mm2 / s.

Description

[0001] A HEATER ASSEMBLY

[0002] BACKGROUND

[0003] A haircare appliance may utilise a pair of heated clamping plates to style the hair of a user. In use, a tress of hair is clamped between the heated clamping plates, and the haircare appliance is drawn along the length of the tress. This process may then be repeated to style a full head of hair.

[0004] In a ‘root-to-tip’ mode, the target temperature of the clamping plates varies as the haircare appliance is pulled from the root of a clamped tress of hair to the tip of a clamped tress of hair during a root-to-tip hair pass. For example, the target temperature of the clamping plates may be set to increase over a predefined time window that corresponds to the duration of a root-to-tip hair pass. Achieving such increase in clamping plate temperature during a root-to-tip hair pass may be beneficial as older hair at the tip of a tress of hair usually requires a higher styling temperature than newer hair at the root of a tress of hair to achieve the same styling effect and to retain hair health.

[0005] Although the duration of a root-to-tip hair pass will vary depending on a number of factors such as the length of the user’s hair and the speed with which the haircare appliance is pulled along the tress of hair, it generally falls within a range of around 0.5 to 20 seconds. When operating in a root-to-tip mode, heat must therefore be supplied to the clamping plates at a rate that is sufficient to achieve an increase in temperature on the required timescale of the duration of a hair pass.

[0006] It is an object of the present invention to provide an improved heater assembly for a haircare appliance. SUMMARY

[0007] In a first aspect of the invention there is provided a heater assembly for a haircare appliance. The heater assembly comprises a contact member that defines a hair-contacting surface. The heater assembly comprises one or more heating elements configured to heat the contact member. The heater assembly comprises a support member in thermal contact with the one or more heating elements and the contact member, wherein the support member has a thermal diffusivity of at least 1.0 mm2 / s. In some embodiments, the support member may have a thermal diffusivity of at least 1.4 mm2 / s.

[0008] In this way, the invention provides a support member that acts as a heat store that absorbs and stores heat from the heating elements during a heating phase of the haircare appliance, and that can subsequently deliver that stored heat to the contact member and haircontacting surface to assist in maintaining or increasing the temperature of the haircontacting surface during styling of a tress of hair.

[0009] For example, when operating in a root-to-tip mode, the support member can assist in increasing the temperature of the hair-contacting surface as the haircare appliance is pulled along a tress of hair to be styled, such that older hair at the tip of the tress of hair is styled using a higher temperature than newer hair at the root of the tress of hair for improved styling.

[0010] Utilising a support member having a thermal diffusivity that exceeds a predetermined lower threshold of 1.0 mm2 / s enables transfer of heat energy from the support member to the contact member on a timescale that is sufficiently fast to enable the heat energy from the support member to effectively contribute to heating of the hair-contacting surface during a root-to-tip hair pass. The one or more heating elements may be located between the contact member and the support member. The support member may comprise polymer foam, which in some embodiments may be silicone foam.

[0011] The contact member may comprise a heat spreading layer for distributing heat across the hair-contacting surface. The heat spreading layer may have a lateral thermal resistance of no greater than 22 Kelvin / W att.

[0012] Utilising a heat spreading layer having a lateral thermal resistance of no greater than 22 Kelvin / Watt in the haircare appliance advantageously improves the distribution of heat across the hair-contacting surface, thereby reducing the likelihood of hot-spots forming across the hair-contacting surface. In this way, the risk of damage to hair caused by excessive heating is reduced. Furthermore, safety of a haircare appliance including the heater assembly is improved.

[0013] The heating elements may together cover an area of no less than 50% of the haircontacting surface of the contact member. The heating elements together may extend across no less than 95% of a length of the hair-contacting surface of the contact member. This coverage of the heating elements across the hair-contacting surface assists in providing a more uniform heat distribution across the hair-contacting surface.

[0014] In a second aspect the invention provides a haircare appliance comprising a heater assembly according to any preceding paragraph.

[0015] The haircare appliance may comprise one or more temperature sensors for indicating a temperature at one or more positions of the hair-contacting surface.

[0016] The controller may be configured to control the power supplied to each of the heating elements to increase the temperature indicated by the one or more sensors from a root temperature corresponding to a temperature of the hair-contacting surface when at a root portion of a tress of hair to a tip temperature corresponding to a temperature of the haircontacting surface when at a tip portion of the tress of hair. In this way, the haircare appliance may operate in a root-to-tip mode, in which the temperature of the haircontacting surface is dynamically varied as the haircare appliance is pulled from the root of the hair to the tip of the hair.

[0017] The tip temperature may be at least 1°C higher than the root temperature. It is known that older hair at the tip requires styling at a higher temperature than newer hair at the root to achieve the same styling effect. Thus, increasing the temperature of the hair-contacting surface during a root-to-tip hair pass in this way is beneficial to achieve more uniform styling across a length of hair. Furthermore, it will be appreciated that a greater difference between the tip temperature and the root temperature may be desirable when the haircare appliance is in use on longer hair compared to shorter hair. For example, for longer hair, it may be desirable for the tip temperature to be at least 5°C higher than the root temperature. For shorter hair, e.g. when in use on a fringe, it may be desirable for the difference between the tip temperature and the root temperature to be closer to 1°C.

[0018] The tip temperature of the hair-contacting surface may be between 100°C and 230°C, and the root temperature of the hair-contacting surface may be between 100°C and 230°C.

[0019] The controller may be configured to control the power supplied to each of the heating elements in a time period based on a length of the tress of hair and a hair pass speed. The time period may be in the range of 0.5 to 20 seconds.

[0020] The time period, being dependent on both the length of the tress of hair and the speed with which the haircare appliance is pulled along the length of hair during the hair pass (i.e. the hair pass speed), corresponds to the duration of a hair pass. With that in mind, it will be appreciated that shorter tresses of hair and faster hair pass speeds result in shorter hair pass durations and shorter time periods. The haircare appliance may comprise a motion detection unit configured to detect movement of the haircare appliance. The motion detection unit may be configured to output signals containing information relating to movement of the haircare appliance to the controller.

[0021] The hair-contacting surface may be substantially planar in a first position. The support member of the heater assembly may be flexible to allow deflection of the hair-contacting surface from its first position during styling of a tress of hair by the haircare appliance. In this respect, the desired flexibility is such that the support member is generally planar when not acted upon by an external force, but when the appliance is used to corral hair between the hair-contacting surfaces, the reaction force of the hair due to the clamping force on the device from the user’s hand is sufficient to bend the support member into a curved form.

[0022] In this way, a tress of hair can be gathered or corralled for increased comfort in use and superior hair styling. This flexibility also improves clamp-force and tension on the hair gripped by the haircare appliance, as well as reduced snagging of hair for better comfort and glide of the haircare appliance in use.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a side view of a haircare appliance with arms of the haircare appliance in an open position;

[0025] Figure 2 is a perspective view of the haircare appliance of Figure 1 with the arms in a closed position;

[0026] Figure 3 shows a haircare appliance in use by a user during a root-to-tip hair pass in which the haircare appliance is pulled along the length of a tress of hair, from its root to its tip; Figure 4 is a partially exploded view of the haircare appliance of Figure 1;

[0027] Figure 5 is an exploded view of part of a heating section of the haircare appliance of Figure 1; Figure 6 is an exploded view of a heater assembly of the haircare appliance of Figure 1; Figure 7 is a cross-sectional view a heater assembly of the haircare appliance of Figure 1; Figure 8 is a perspective view of a heat spreading layer of the heater assembly of Figure 7;

[0028] Figure 9a is a graph showing measured temperature of a tress of hair during five root-to- tip hair passes using a hair straightener comprising heated ceramic plates;

[0029] Figure 9b is a graph showing measured temperature of a tress of hair during five root-to- tip hair passes using a hair straightener in accordance with the invention, comprising support members having a thermal diffusivity of 1.4 mm2 / s;

[0030] Figure 10a shows output from a computer simulation of a root-to-tip hair pass with a hair straightener that includes support members having a thermal diffusivity of 0.1 mm2 / s;

[0031] Figure 10b shows output from a computer simulation of a root-to-tip hair pass with a hair straightener in accordance with the invention that includes support members having a thermal diffusivity of 1.4 mm2 / s; and

[0032] Figure 11 illustrates a tress of hair in contact with a hair-contacting surface of a hair straightener.

[0033] DETAILED DESCRIPTION

[0034] 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.

[0035] 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 positioned. In use, the user grips the handle sections 26,28 and inserts a section or tress of hair 29 between the two arms 12, 14. The user applies pressure to the handle sections 26,28 to close the arms 12, 14 and grip the hair 29 between the heating sections 22,24, and pulls the haircare appliance 10 along the length of the hair 29 to be styled. 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 and the tress of hair 29 is released. When the haircare appliance 10 is pulled from a root portion 35 to a tip portion 39 of the tress of hair 29 along its length, as shown in Figure 3, this may be referred to as a root-to-tip hair pass.

[0036] Referring now to Figures 4 and 5, 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. That is, the heater assembly 34 is located on the side of the support member 38 that is distal from the heater assembly housing 32.

[0037] The heater assembly 34 will now be described with reference to Figures 6 and 7 in particular.

[0038] The heater assembly 34 comprises multiple layers of components arranged in a stack. Specifically, the heater assembly 34 comprises a sensor and heating element layer 40, an electrical insulation layer 41, a dielectric cover 52, a support member 54 and a contact member 42.

[0039] The sensor and heating element layer 40 comprises a substrate 49, multiple heating elements 50 and a sensor 48. The sensor and heating element layer 40 has a thickness of 0.05 mm in this example, but in other examples the thickness of the sensor and heating element layer 40 may vary. However, in general a thinner sensor and heating element layer 40 is preferable for increased flexibility. The substrate 49 supports and locates the sensor 48 and the heating elements 50 within the heater assembly 34, and further provides electrical insulation to insulate the heating elements 50 from one another and from the sensor 48. In this example, the substrate 49 has the same shape and area as the electrical insulation layer 41 and the contact member 42, and comprises a layer of glass based dielectric material that supports the sensor 48 and the heating elements 50. However, other materials such as pre-preg, which is a partially cured fibre resin composite sheet material that can be used for electrical insulation and bonding, or polyimide may be used. Moreover, in other examples, the substrate 49 may comprise more than one layer or sheet on or between which the sensor 48 and heating elements 50 are located. Furthermore, it would be possible for the sensor 48 and heating elements 50 to be provided on different layers from one another, so as to define a distinct sensor layer and a distinct heating element layer. In that case, the sensor layer and the heating element layer may be separated by a layer of insulation. It should be noted that in other examples additional sensors 48 may be included, such that the sensor and heating element layer 40 may generally include one or more sensors 48. In some cases, the sensor and heating element layer 40 may include equal numbers of sensors 48 and heating elements 50, such that each heating element 50 has an associated sensor 48. In examples where the sensor and heating element layer 40 includes multiple sensors 48, said sensors may, for example, be equally spaced along the length of the sensor and heating element layer 40.

[0040] The heating elements 50 provide heat to the contact member 42, which in turn provides heat to hair 29 in contact with a hair-contacting surface 37 of the contact member 42 in use. In this example, with reference to Figure 6, the sensor and heating element layer 40 includes six heating elements 50 that each comprise a resistive track 51 and a pair of conductive pads (not shown). The resistive track 51 of each heating element 50 comprises a material such as copper, silver, stainless steel, or an appropriate alloy such as Constantan (copper-nickel alloy), and extends over the substrate 49 to define a generally U-shaped resistive track 51, with the conductive pads located at either end of the resistive track 51. The resistive tracks 51 may be formed by processes such as etching or printing. However, in other examples, one or more of the heating elements 50 may be formed from a length of wire. Furthermore, the sensor and heating element layer 40 may comprise more or fewer heating elements 50 in other examples.

[0041] In this example, the heating elements 50 take the form of thick film printed heater traces, but other forms of heating element may be used, such as foil heaters, thin-film heaters, tubular heating elements, etched heaters or coiled heating elements.

[0042] The heating elements 50 together extend over the substrate 49 such that the heating elements 50 together cover about 25% of an area, Ac, defined by the hair-contacting surface 37 of the contact member 42, and span about 80% of a length, Lc, defined by the hair-contacting surface 37 of the contact member 42. In other examples these percentage values may vary, and in fact the heating elements 50 together may preferably cover no less than 50% of the area, Ac, defined by the hair-contacting surface 37 and span no less than 95% of the length, Lc, defined by the hair-contacting surface 37. In this way, a more even distribution of heat across the contact member 42 and hair-contacting surface 37 may be provided.

[0043] Each of the resistive tracks 51 is located beneath a different heating zone 55 of the contact member 42 such that each heating element 50 heats a respective heating zone 55 of the contact member 42 and thus of the hair-contacting surface 37. Thus, in this example of Figure 6 having six heating elements 50 equally spaced along the length Lcof the contact member 42, the contact member 42 is divided into six heating zones 55 of equal length, and the heater assembly 34 is a six-zone heater. In use, the power supplied to each heating element 50 may be controlled independently. Specifically, the haircare appliance 10 may comprise a controller (not shown) configured to independently control the power supplied to each of the heating elements 50, such that different amounts of power may be supplied to each heating element 50. This allows for more precise control of the temperature across the hair-contacting surface 37 to be achieved. Furthermore, the controller may be configured to control and adjust the power supplied to each of the heating elements 50 in a given time period corresponding to the duration of a hair pass. This allows the power supplied to the heating elements 50, and thus the temperature of the hair-contacting surface 37, to be adjusted during a hair pass. In this way, the temperature of the hair-contacting surface 37 may be increased from a lower root temperature when the haircare appliance 10 is in use on a root portion of the tress of hair 29, to a higher tip temperature when the haircare appliance 10 is in use on a tip portion of the tress of hair 29. This enables higher temperatures to be applied to older hair at the tip than to newer hair at the root for more uniform styling across the length of hair.

[0044] It will be appreciated that the duration of a hair pass depends on the length of the tress of hair 29 and the speed with which the haircare appliance 10 is pulled along the length of hair 29 (referred to as the hair pass speed). In some embodiments, the haircare appliance 10 comprises a motion detection unit (not shown) that may include an accelerometer. The motion detection unit is configured to detect movement of the haircare appliance 10, and to transmit signals containing information in respect of movement of the haircare appliance 10 to the controller for use in determining the duration of the hair pass.

[0045] In some embodiments, an expected hair pass speed is used for the determination of the hair pass duration. The expected hair pass speed represents the expected speed with which a user is likely to pull the haircare appliance 10 along a length of hair 29 in use. One or more expected hair pass speed values may be stored on a storage device (not shown) of the haircare appliance 10, and the storage device may be accessible by the controller such that stored expected hair pass speed values can be utilised in determination of the hair pass duration when desired.

[0046] The sensor 48 senses or measures a temperature of the heater assembly 34, and provides an indication of the temperature of the hair-contacting surface 37 of the contact member 42. That is, although the sensor 48 does not directly measure the temperature of the hair- contacting surface 37 in this example, the temperature sensed or measured by the sensor 48 provides a good approximation of the temperature at the hair-contacting surface 37.

[0047] In this example, the sensor 48 comprises a thermistor connected to a pair of wires, but in other examples the sensor 48 may take a different form, for example a thermocouple. In some examples the sensor 48 may be a printed film sensor.

[0048] As shown in Figure 6, the sensor 48 is located between (and spaced from) parallel portions of the resistive track 51 of neighbouring heating elements 50 on a central portion of the substrate 49, so as to be located centrally along a length, Lc, defined by the haircontacting surface 37 of the contact member 42. As a result, the sensor 48 is arranged to sense the temperature of the hair-contacting surface 37 at a position centrally along its length, Lc. However, in other examples the sensor 48 may be provided at a different position on the substrate 49, so as to sense the temperature at a different position on the hair-contacting surface 37. Furthermore, the sensor and heating element layer 40 may comprise multiple sensors 48 provided at different locations on the substrate 49 to allow for multiple temperature measurements to be taken, at different locations on the haircontacting surface 37. In examples in which the sensor and heating element layer 40 includes multiple sensors 48, these sensors 48 may be positioned across the sensor and heating element layer 40 so as to be equally spaced from one another, as noted already. This arrangement advantageously allows the temperature of the hair-contacting surface 37 to be measured at multiple positions across the length of the contact member 42. This temperature information can be used to determine whether the heat supplied to the contact member 42 from one or more of the heating elements 50 should be adjusted. For example, if one of the sensors 48 measures a temperature that is below the desired temperature of the hair-contacting surface 37, the power supplied to an associated heating element 50 may be adjusted to supply more heat to its associated heating zone 55, so as to raise the temperature of its associated heating zone 55 accordingly. Now turning back to Figure 7, the electrical insulation layer 41 of the heater assembly 34 comprises a first layer 56 and a second layer 58. The electrical insulation layer 41 is provided between the sensor and heating element layer 40 and the contact member 42, so as to electrically isolate the contact member 42 from the heating elements 50 (not shown in Figure 7) of the sensor and heating element layer 40 for safety. With the heater assembly 34 orientated as shown in Figures 6 and 7, the first layer 56 is positioned directly above the sensor and heating element layer 40, and the second layer 58 is positioned directly above the first layer 56 and directly beneath the contact member 42. In this example, the first layer 56 and the second layer 58 are each formed of a glass based dielectric material, and each have a thickness of 0.0175 mm. However, it will be understood that other materials and thicknesses of the electrical insulation layer 41 and any constituent layers of the electrical insulation layer 41 are possible to electrically isolate the contact member 42 from the heating element 50. For example, in some cases materials such as pre-preg or polyimide may be utilised in the electrical insulation layer 41.

[0049] Both the thickness of the electrical insulation layer 41 and the material(s) of the electrical insulation layer 41 affects the thermal resistance of the electrical insulation layer 41. In general, for a given material, a thicker electrical insulation layer 41 has a higher thermal resistance. An electrical insulation layer 41 having a higher thermal resistance is more resistant to the transfer of heat across it. Thus, a thicker electrical insulation layer 41 may reduce the amount of heat that reaches the contact member 41 and hair-contacting surface 37. The thickness and material(s) of the electrical insulation layer 41 are chosen with this in mind.

[0050] The contact member 42 is provided on top of the electrical insulation layer 41, so as to be positioned above the electrical insulation layer 41 in the orientation shown in Figures 6 and 7. In this way, the hair-contacting surface 37 defines an outer surface of the heater assembly 34 and is arranged to contact and heat a tress of hair 29 received between the arms 12,14 of the haircare appliance 10 for styling in use. In some embodiments, the contact member 42 comprises a heat spreading layer 60. Such a heat spreading layer 60 is represented in isolation in Figure 8. In this example the contact member 42 is defined in its entirety by the heat spreading layer 60, but in other examples the heat spreading layer 60 may form only a part of the contact member 42. The heat spreading layer 60 comprises six heating zones 55 of equal length, Lhz. As explained already, each heating zone 55 is associated with a corresponding heating element 50 located beneath that heating zone 55. It should be noted that boundary lines 57 between the heating zones 55 are shown on the heat spreading layer 60 for illustrative purposes only, and do not indicate distinct segments of the heat spreading layer 60 which in this case is defined by a continuous layer of material.

[0051] The heat spreading layer 60 is arranged and configured to spread heat provided by the heating element 50 of the sensor and heating element layer 40 through the contact member 42 and across the hair-contacting surface 37 of the contact member 42, so as to provide a more uniform temperature distribution across the hair-contacting surface 37. The heat spreading layer 60 is configured in particular to provide a more uniform distribution of heat from the sensor and heating element layer 40 across the length, Lc, of the haircontacting surface 37.

[0052] Achieving a more uniform temperature distribution across the length, Lc, of the haircontacting surface 37 is advantageous as this allows for hair engaged at different locations along the length, Lc, of the hair-contacting surface 37 to be styled more consistently as the haircare appliance 10 is pulled along the length of the hair in use. Furthermore, improving temperature uniformity across the hair-contacting surface 37 advantageously reduces the temperature of any hot-spots that may develop across the hair-contacting surface 37 in use. This reduces the likelihood of damage to hair caused by excessive temperature in hot-spot regions of the hair-contacting surface 37, and improves the safety of the haircare appliance 10. To achieve a more uniform temperature distribution across the hair-contacting surface 37, the heat spreading layer 60 has a lateral thermal resistance, R, of no greater than 22 Kelvin / W att.

[0053] The thermal resistance of a material is a measure of how resistant the material is to the transfer of heat across it. The lateral thermal resistance of the heat spreading layer, Rhsi, is the thermal resistance experienced by heat propagating through the heat spreading layer in a lateral direction, x, and is defined as:

[0054] Rhsi = Lhsi / (khsi * Ahsi) Equation 1

[0055] In equation 1, LH is the length travelled by heat from the heating elements 50 in the heat spreading layer 60 in the lateral direction, x, and is defined as half the length Lhz of a heating zone 55, i.e. Lhsi = Lhz / 2. With this definition in mind, it will be understood that the length, Lhsi, is dependent on the total length of the heat spreading layer, Lt, and the number of heating elements 50 and corresponding heating zones 55.

[0056] Ahsi is a cross-sectional area of the heat spreading layer, and khsi is the thermal conductivity of the heat spreading layer. In the example of Figure 8 in which the heat spreading layer 60 has a rectangular cross-section, the cross-sectional area, Ahsi, is defined as the thickness of the heat spreading layer, thsi, multiplied by the width of the heat spreading layer, whsi, i.e. Ahsi = whsi * thsi. However, the specific definition of the cross- sectional area, Ahsi, will of course vary depending on the shape of the cross-sectional area, which is not limited to square or rectangular.

[0057] It will be understood from Equation 1 that for a given number of heating elements 50 and associated heating zones 55, and a given -length, Lt, and width, whsi, of the heat spreading layer 60, a material having an appropriate thermal conductivity and thickness can be chosen to provide a lateral thermal resistance of no more than 22 Kelvin / Watt. Referring now again to Figure 7, in this example the heat spreading layer 60 defines the contact member 42 in its entirety, and itself comprises a lower layer 62, a middle layer 64 and an upper layer 66. The lower layer 62, middle layer 64 and upper layer 66 are joined together so as to define a single self-supporting layer, i.e. the heat spreading layer 60. The lower layer 62 and the upper layer 66 are each formed of stainless steel and the middle layer 64 is formed of copper, such that the heat spreading layer 60 is defined by a stainless steel and copper trimetallic material, which is a sandwich of stainless steel, copper and stainless steel, in this example. The thermal conductivity, khsi, of the stainless steel and copper trimetallic material of this example is 180 W / mK. The lower layer 62, the middle layer 64 and the upper layer 66 each have a thickness of 0.0333 mm, such that the heat spreading layer 60 of this example has a total thickness, thsi, of approximately 0.100 mm. Thus, in this example in which the total length of the heat spreading layer, Lt, is 90mm, the width of the heat spreading layer, whsi, is 25mm, and the heat spreading layer 60 includes six heating zones 55 of equal length, the heat spreading layer has a lateral thermal resistance, Rhsi, of approximately 17 Kelvin / Watt.

[0058] In other examples, the heat spreading layer 60 may be formed entirely of copper or entirely of pyrolytic graphite.

[0059] Turning now to the remaining elements of the heater assembly 34, the dielectric cover 52 is positioned beneath the sensor and heating element layer 40 and is overmoulded with a flexible backing that defines the support member 54.

[0060] The support member 54 is flexible, and in particular is more flexible than the surrounding heater assembly housing 32 in which it is housed. This flexibility of the support member 54 enables flexing of other elements of the layered heater assembly 34, which in turn enables deflection of the hair-contacting surface 37 away from a first resting position in which it is substantially planar. Thus, the flexible support member 54 enables corralling of a tress of hair 29 in use. The support member 54 has a thermal diffusivity of at least 1.0 mm2 / s, and is arranged and configured so as to be in thermal contact with both the contact member 42 and the heating elements 50 of the sensor and heating element layer 40.

[0061] This arrangement and configuration of the support member 54 advantageously enables heat energy from the heating elements 50 to be absorbed and stored in the support member 54, and subsequently supplied to the contact member 42 to assist in maintaining or increasing the temperature of the hair-contacting surface 37 in use. In particular, the support member 54 assists in increasing the temperature of the hair-contacting surface 37 during a root-to-tip hair pass, when the haircare appliance 10 is operating in a root-to-tip mode. This enables more heating to be applied to older hair at the tip portion 39 of the tress of hair 29 than to newer hair at the root portion 35 of the tress of hair 29, which is known to result in improved styling.

[0062] As a haircare appliance 10 is pulled along a length of hair 29, heat energy is lost from the hair-contacting surface 37 to heat the tress of hair 29. To maintain or increase the temperature of the hair-contacting surface 37 during a hair pass, it will be appreciated that sufficient heat energy must be supplied to the contact member 42 on a suitably fast timescale. For a root-to-tip hair pass in which the haircare appliance 10 is pulled along the length of hair 29 from its root to its tip, the relevant timescale may be in the range of around 0.5 to 20 seconds, depending on the speed with which the haircare appliance is pulled along the length of hair 29 (i.e. the hair pass speed) and the length of the hair tress 29.

[0063] Haircare appliances 10 according to the invention include a support member 54 having a thermal diffusivity that exceeds a predetermined lower threshold of 1.0 mm2 / s, so as to enable transfer of heat energy from the support member 54 to the contact member 42 on a timescale that is sufficient to increase the temperature of the hair-contacting surface 37 during a root-to-tip hair pass. The thermal diffusivity, a, of a material is defined as the thermal conductivity, k, divided by density, p, and specific heat capacity, CP, as follows: k a = — Equation 2 pcP1

[0064] The thermal diffusivity of a material is a measure of how quickly heat transfers through that material. In other words, the thermal diffusivity indicates the rate at which heat diffuses through a material. Materials having a higher thermal diffusivity are able to transfer heat more rapidly than materials having a lower thermal diffusivity, and as such enable a higher rate of heat transfer than materials having a lower thermal diffusivity.

[0065] With that in mind, the support member 54, having a pre-defined minimum value of thermal diffusivity of at least 1.0 mm2 / s, ensures that heat stored within the support member 54 can be transferred to the contact member 42 at a rate that is sufficient to contribute to heating of the hair-contacting member 37 during a root-to-tip hair pass, which may for example have a duration of around 0.5 to 20 seconds. Thus, the support member 54 assists with maintenance and increase of the temperature of the haircontacting surface 37 during a root-to-tip hair pass.

[0066] In the embodiment of Figure 7, the support member 54 is formed of silicone foam having a thermal conductivity, k, of 0.4 W / m.k, a density, p, of 290 kg / m3, and a specific heat capacity, Cp, of 1000 J / kg.K. Thus, the silicone foam of the support member 54 of this embodiment has a thermal diffusivity, a, of 1.4 mm2 / s. It should be understood that the support member 54 may comprise materials other than silicone foam, including but not limited to other polymer foams, so long as the thermal diffusivity, a, of the support member 54 is at least 1.0 mm2 / s.

[0067] Turning now to Figure 9a, this illustrates experimental data of measured hair temperature 68 during five consecutive hair passes 70a-e using a ceramic hair straightener arrangement (not shown) that does not include a support member 54 of the invention. The ceramic hair straightener arrangement comprises heating sections 22,24 that include heated ceramic plates that define hair-contacting surfaces 37 between which a tress of hair 29 is clamped for styling, as is known in the art.

[0068] In a first step of the experimental method for obtaining the data of Figure 9a, the first root-to-tip hair pass 70a was initiated by gripping a root portion 35 of a tress of hair 29 between the heating sections 22,24 of the hair straightener operating at a set temperature of 175°C. The set temperature defines the desired or target temperature of the haircontacting surfaces 37 of the hair straightener.

[0069] In a second step, the hair straightener was pulled along the length of the tress of hair 29 at a constant speed towards the tip portion 39 of the tress of hair 29 using a robotic arm. In a third step, once the hair straightener reached the tip portion 39, the tress of hair 29 was released from the hair straightener to terminate the first hair pass 70a.

[0070] In a fourth step, no portion of the tress of hair 29 was engaged with the hair straightener, such that no heat was applied to the tress of hair 29 from the hair straightener during a resting window 72.

[0071] Steps one to four were repeated to obtain a second root-to-tip hair pass 70b, a third root- to-tip hair pass 70c, a fourth root-to-tip hair pass 70d and a fifth root-to-tip hair pass 70e.

[0072] The temperature across the portion of hair 29 engaged with the hair-contacting surfaces 37 of the hair straightener was measured using an infra-red (IR) camera (not shown) throughout each hair pass 70a-e. The average temperature (in °C) of the hair 29 engaged with the hair-contacting surface 37 was determined from the IR camera measurements, and is plotted against time (in seconds) on the graph of Figure 9a. Each hair pass of Figure 9a has a duration of around 8 seconds, and the resting window 72 between consecutive hair passes has a duration of around 10-15 seconds. It should be noted that although the measured hair temperature 68 is represented as falling to 0°C between consecutive hair passes 70a-e in Figure 9a, this is simply for clear illustration of the temperature data during the hair passes 70a-e, and is not a true representation of the hair temperature during the resting windows 72. In other words, the measured hair temperature 68 during the resting windows 72 is not illustrated in Figure 9a.

[0073] It will be appreciated that the measured hair temperature 68 at the start 74 of each hair pass 70a-e corresponds to the hair temperature at the root portion 35 of the tress of hair 29, and the measured hair temperature 68 at the end 76 of each hair pass 70a-e corresponds to the hair temperature at the tip portion 39 of the tress of hair 29.

[0074] It can be seen from Figure 9a that the measured hair temperature 68 decreases during each hair pass 70a-e, even though the hair-contacting surfaces 37 are intended to maintain a constant set temperature of 175°C throughout each hair pass 70a-e, so as to apply even heating across the length of the tress of hair 29 during each hair pass 70a-e.

[0075] A decrease in measured hair temperature 68 during a root-to-tip hair pass is undesirable, as this implies reduced styling of the tip portion 39 of the tress of hair 29 compared to the root portion 35 of the tress of hair 29.

[0076] Turning now to Figure 9b, this illustrates experimental data of measured hair temperature 68 during five consecutive hair passes 80a-e using a haircare appliance 10 according to the invention, in the form of a hair straightener 10 comprising in each arm 12, 14 the heater assembly 34 of Figure 7 that includes a support member 54 of silicone foam having a thermal diffusivity, a, of 1.4 mm2 / s.

[0077] The method followed to obtain the data of Figure 9b is the same as that used to obtain the data of Figure 9a, except that for Figure 9b the hair straightener 10 was operated in a root- to-tip mode, in which the heating elements 50 of each arm 12,14 were controlled so as to increase the target temperature of their respective hair-contacting surfaces 37 from 150°C to 210°C in a predetermined root-to-tip time window of 8 seconds.

[0078] As shown in Figure 9b, the measured hair temperature 68 increases during each hair pass 80a-e when using a hair straightener 10 in accordance with the invention. In this way, a higher temperature is applied to older hair at the tip portion 39 of the tress of hair 29 than to newer hair at the root portion 35 for improved styling.

[0079] Figures 10a and 10b illustrate data obtained through computer simulation of a root-to-tip hair pass of a tress of hair 29 using two different hair straighteners 10, each having two hair-contacting surfaces 37 that engage and heat a tress of hair 29 clamped between them as shown in Figure 11 (which only illustrates one of the hair-contacting surfaces 37 for clarity).

[0080] Turning first to Figure 10a, this simulated data relates to a hair straightener 10 comprising a heater assembly 34 similar to that of Figure 7 associated with each hair-contacting surface 37, but each including a support member 54 of silicone having a thermal diffusivity, a, of 0.1 mm2 / s.

[0081] Figure 10a illustrates two simulated power curves 82a, 82b and four simulated temperature curves 84a, 84b, 84c and 84d.

[0082] The power curves 82a, 82b show the total power supplied to heat the two opposing haircontacting surfaces 37 of the hair straightener 10 before and during the simulated root-to- tip hair pass 90, across a simulation time window 91 of around 8 seconds. Specifically, the first power curve 82a illustrates the change in total instantaneous power (in Watts) supplied to heat the two hair-contacting surfaces 37, and the second power curve 82b illustrates the change in total average power (in Watts) supplied to heat the two haircontacting surfaces 37. The temperature curves 84a-d represent the change in temperature of each hair-contacting surface 37 at different positions across its length before and during the simulated hair pass 90, across the simulation time window 91. Specifically, and with reference to Figure 11, the temperature curves 84a-d represent the change in the average temperature across respective regions 86a-d of the hair-contacting surfaces 37 that are in contact with the tress of hair 29.

[0083] During a heating window 92, a generally constant power is supplied to the hair-contacting surfaces 37 to increase the average temperature of each region 86a-d of each haircontacting surface 37 to a set temperature of 195°C. Once the set temperature is reached, each region 86a-d of each hair-contacting surface 37 is maintained at the set temperature during an interim time window 94 between the heating window 92 and the hair pass window 90. The power supplied to heat the hair-contacting surfaces 37 is reduced during the interim time window 94 to prevent the temperature of the hair-contacting surfaces 37 from overshooting the set temperature.

[0084] The hair pass window 90 illustrates the simulated root-to-tip hair pass during which the tress of hair 29 is in contact with the hair-contacting surfaces 37 as shown in Figure 11. The start 90a of the hair pass window 90 corresponds to the time at which the root portion 35 of the tress of hair 29 is clamped between and in contact with the hair-contacting surfaces 37 for heating, and the end 90b of the hair pass window 90 corresponds to the time at which the tip portion 39 of the tress of hair 29 is clamped between and in contact with the hair-contacting surfaces 37 for heating.

[0085] During the hair pass window 90, the total power supplied to the hair-contacting surfaces 37 is adjusted with the aim of achieving an increase in the temperature of each region 86a-d of each hair-contacting surface 37 from the initial set temperature of 195°C to a target temperature of 205°C, for a root-to-tip mode of operation. The duration of the hair pass window is 4.2 seconds. As can be seen in Figure 10a, regions 86a, 86b and 86c of each hair-contacting surface 37 experience a drop in temperature at the start 90a of the hair pass window 90, and do not recover to the initial temperature set point of 195°C by the end 90b of the hair pass window 90. Thus, in the simulation of Figure 10a the average temperature across each of regions 86a, 86b and 86c of the hair-contacting surfaces 37 is higher during heating of the root portion 35 of the tress of hair 29 than during heating of the tip portion 39 of the tress of hair 29. Thus, the intended temperature increase across the root-to-tip hair pass 90 is not achieved in regions 86a, 86b and 86c. The average temperature in region 86d of the hair-contacting surfaces 37 increases from the set temperature of 195°C at the start 90a of the hair pass window 90 to 204°C at the end of the hair pass window 90b, and thus falls short of the intended temperature increase by 1°C.

[0086] Turning now to Figure 10b, this simulated data relates to a haircare appliance 10 in accordance with the invention, in the form of a hair straightener comprising, in each arm 12,14, the heater assembly 34 of Figure 7 that includes a support member 54 of silicone foam having a thermal diffusivity, a, of 1.4 mm2 / s.

[0087] Similarly to Figure 10a, Figure 10b illustrates two simulated power curves 96a, 96b and four simulated temperature curves 98a, 98b, 98c and 98d.

[0088] The power curves 96a, 96b show the total power supplied to heat the two opposing haircontacting surfaces 37 of the hair straightener 10 before and during the simulated root-to- tip hair pass 100, across a simulation time window 101 of around 7.5 seconds. Specifically, the first power curve 96a illustrates the change in total instantaneous power (in Watts) supplied to heat the two hair-contacting surfaces 37, and the second power curve 96b illustrates the change in total average power (in Watts) supplied to heat the two hair-contacting surfaces 37. The temperature curves 98a-d represent the change in temperature of each hair-contacting surface 37 in respective regions 86a-d of the hair-contacting surfaces 37 that are in contact with the tress of hair 29 before and during the simulated hair pass window 100, across the simulation time window 101.

[0089] As in Figure 10a, Figure 10b illustrates a heating window 102 during which a generally constant power is supplied to the hair-contacting surfaces 37 to increase the temperature of each region 86a-d of each hair-contacting surface 37 to a set temperature of 195°C. Once the set temperature is reached, each region 86a-d of each hair-contacting surface 37 is maintained at the set temperature during an interim time window 104 between the heating window 102 and the hair pass window 100. The power supplied to heat the haircontacting surfaces 37 is reduced during the interim time window 104 to prevent the temperature of the hair-contacting surfaces 37 from overshooting the set temperature.

[0090] The hair pass window 100 illustrates the simulated root-to-tip hair pass during which the tress of hair 29 is in contact with the hair-contacting surfaces 37 as shown in Figure 11. The start 100a of the hair pass window 100 corresponds to the time at which the root portion 35 of the tress of hair 29 is clamped between and in contact with the haircontacting surfaces 37 for heating, and the end 100b of the hair pass window 100 corresponds to the time at which the tip portion 39 of the tress of hair 29 is clamped between and in contact with the hair-contacting surfaces 37 for heating.

[0091] During the hair pass window 100, the total power supplied to the hair-contacting surfaces 37 is adjusted with the aim of achieving an increase in the temperature of each region 86a-d of each hair-contacting surface 37 from the initial set temperature of 195°C to a target temperature of 200°C, for a root-to-tip mode of operation. The duration of the hair pass window is 4.2 seconds.

[0092] The average temperature of all four regions 86a, 86b, 86c and 86d of each hair-contacting surface 37 is higher at the end 100b of the hair pass window 100 than at the start 100a of the hair pass window 100 in Figure 10b. Specifically, region 86a of each hair-contacting surface 37 increases from 195°C at the start 100a of the hair pass window 100 to 198°C at the end of the hair pass window 100, region 86c increases from 195°C at the start 100a of the hair pass window 100 to 196°C at the end of the hair pass window 100, and both region 86b and region 86d increase from 195°C at the start 100a of the hair pass window 100 to the target temperature of 200°C at the end of the hair pass window 100. Furthermore, it will also be appreciated that the initial fall in temperature of regions 86a, 86b and 86c is less pronounced in Figure 10b than in Figure 10a.

[0093] The simulations of Figures 10a and 10b illustrate the improvement in temperature control of the hair-contacting surfaces 37 during a root-to-tip hair pass that may be obtained through use of support members 54 having a higher thermal diffusivity, a.

[0094] T o heat the hair-contacting surface 37 of a hair straightener 10 to a desired set temperature for use, power is supplied to heating elements 50 of the hair straightener 10, and heat generated by the heating elements 50 is supplied to the hair-contacting surface 37. However, heat generated by the heating elements 50 will also act to heat other elements of the hair straightener 10 in which they are in thermal contact. In particular, the support member 54, which is in thermal contact with the heating elements 50, will absorb heat from the heating elements 50 during the heating phase.

[0095] During a hair pass, when heat is lost from the hair-contacting surface 37 to heat the tress of hair 29 to be styled, additional power can be supplied to the heating elements 50 to attempt to maintain or increase the temperature of the hair-contacting surface 37 as desired. However, as illustrated in Figures 9a and 10a, in some arrangements this may not be sufficient, and the temperature of the hair-contacting surface 37 may decrease during a root-to-tip hair pass.

[0096] The support member 54 provides a thermal store that is able to absorb and store heat from the heating elements 50 during the heating phase, and supply that stored heat to the hair- contacting surface 37 during a hair pass. By defining a lower threshold of 1.0 mm2 / s for the thermal diffusivity of the support member 54, this ensures that the support member 54 is able to supply the heat stored within at a rate that is sufficient to usefully contribute to heating of the hair-contacting surface 37 during the duration of a hair pass, and in particular a root-to-tip hair pass, which may be on the order of 0.5 to 20 seconds depending on the length of a user’s hair and the speed with which the hair straightener 10 is pulled along the hair length.

[0097] 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.

Claims

CLAIMS1. A heater assembly for a haircare appliance, the heater assembly comprising: a contact member that defines a hair-contacting surface; one or more heating elements configured to heat the contact member; and a support member in thermal contact with the one or more heating elements and the contact member, wherein the support member has a thermal diffusivity of at least 1.0 mm2 / s.

2. A heater assembly as claimed in Claim 1, wherein the support member has a thermal diffusivity of at least 1.4 mm2 / s.

3. A heater assembly as claimed in Claim 1 or Claim 2, wherein the one or more heating elements are located between the contact member and the support member.

4. A heater assembly as claimed in any preceding claim, wherein the support member comprises polymer foam.

5. A heater assembly as claimed in Claim 4, wherein the support member comprises silicone foam.

6. A heater assembly as claimed in any preceding claim, wherein the contact member comprises a heat spreading layer for distributing heat across the hair-contacting surface.

7. A heater assembly as claimed in Claim 6, wherein the heat spreading layer has a lateral thermal resistance of no greater than 22 Kelvin / Watt.

8. A heater assembly according to any preceding claim, wherein the heating elements together cover an area of no less than 50% of the hair-contacting surface of the contact member.

9. A heater assembly according to any preceding claim, wherein the heating elements together extend across no less than 95% of a length of the hair-contacting surface of the contact member.

10. A haircare appliance comprising a heater assembly according to any preceding claim.

11. A haircare appliance as claimed in Claim 10, comprising one or more temperature sensors for indicating a temperature at one or more positions of the hair-contacting surface.

12. A haircare appliance according to Claim 11, comprising a controller configured to control the power supplied to each of the heating elements to increase the temperature indicated by the one or more sensors from a root temperature corresponding to a temperature of the hair-contacting surface when at a root portion of a tress of hair to a tip temperature corresponding to a temperature of the hair-contacting surface when at a tip portion of the tress of hair.

13. A haircare appliance as claimed in Claim 12, wherein the tip temperature is at least 1°C higher than the root temperature.

14. A haircare appliance as claimed in Claim 12 or Claim 13, wherein the tip temperature is between 100°C and 230°C, and the root temperature is between 100°C and 230°C.

15. A haircare appliance as claimed in any of Claims 12 to 14, wherein the controller is configured to control the power supplied to each of the heating elements in a time period based on a length of the tress of hair and a hair pass speed.

16. A haircare appliance as claimed in Claim 15, wherein the time period is in the range of 0.5 to 20 seconds.

17. A haircare appliance as claimed in any of Claims 12 to 16, comprising a motion detection unit configured to detect movement of the haircare appliance, and output signals containing information relating to movement of the haircare appliance to the controller.

18. A haircare appliance as claimed in any of Claims 10 to 17, wherein the haircontacting surface is substantially planar in a first position, and wherein the support member of the heater assembly is flexible to allow deflection of the hair-contacting surface from its first position during styling of a tress of hair by the haircare appliance.

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