Patent Application
20240276605
The present invention relates to an apparatus and method for styling hair. The hair may be human or non-human hair. The invention may be used to style dry hair or wet (or “towel-dry”) hair. Such styling of the hair may be performed by a user in respect of their own hair, for example, or by another user such as a hair stylist.
Conventional flat-plate hair stylers that incorporate a pair of heated plates are well known. In use, a tress of hair is placed between the plates, and heat transferred from the plates to the hair enables styling of the hair. For example, the user may achieve a straightening or curling effect.
As shown in the simplified schematic illustration of
An alternative, less bulky, configuration of a heater assembly for a hair styling device is described in GB2447750. The heater assembly comprises a thick film printed heating element for a battery powered device which is used to heat up the hair contacting surface. However, there is a need for further improvements to such heater assemblies. For example, a thick film printed heater is relatively delicate compared to conventional heating arrangements, increasing the difficulty of forming strong and reliable electrical connections to the heater. Moreover, there is a desire to further improve the thermal properties of such devices by further reducing the thermal lag, and by improving temperature distribution across the hair-contacting surface when the device is in operation.
According to a first aspect of the invention, there is provided a heater assembly for a hair styling device, the heater assembly comprising: a substrate; at least one conductor layer, the at least one conductor layer comprising at least one heater track through which current can flow to heat the substrate; and at least one electrically insulating layer between the at least one conductor layer and the substrate; wherein the at least one heater track is formed of a silver-based material; and wherein the at least one electrically insulating layer is configured to prevent electrical breakdown between the at least one conductor layer and the substrate.
The total thickness of the at least one electrically insulating layer may be between 0.02 mm and 0.05 mm.
A surface of the substrate facing the at least one electrically insulating layer may have a mean roughness of less than or equal to 0.2 μm. A surface of the substrate facing the at least one electrically insulating layer may have a mean roughness depth of less than or equal to 1.4 μm. According to a second aspect of the invention, there is provided a heater assembly for a hair styling device, the heater assembly comprising: a substrate; at least one conductor layer, the at least one conductor layer comprising at least one heater track through which current can flow to heat the substrate; and at least one electrically insulating layer between the at least one conductor layer and the substrate; wherein the at least one electrically insulating layer is configured to prevent electrical breakdown between the at least one conductor layer and the substrate; wherein the total thickness of the at least one electrically insulating layer is between 0.02 mm and 0.05 mm; and wherein a surface of the substrate facing the at least one electrically insulating layer has a mean roughness of less than or equal to 0.2 μm or has a mean roughness depth of less than or equal to 1.4 μm.
The at least one heater track may be formed of a silver-based material. The at least one heater track may be formed of a material comprising at least 90% silver.
The material preferably comprises 1% to 10% of a dielectric material that can bond with the dielectric layer on which the conductor layer is formed.
The resistance of a heater track of the at least one heater track may be between 0.3Ω and 0.9Ω.
The at least one electrically insulating layer may comprise two electrically insulating layers; wherein a first electrically insulating layer of the two electrically insulating layers has a thickness of between 0.010 mm and 0.025 mm; and wherein a second electrically insulating layer of the two electrically insulating layers has a thickness of between 0.010 mm and 0.025 mm. Typically, each insulating layer is a uniform layer of dielectric material.
The at least one electrically insulating layer may be screen printed or deposited using a physical vapour deposition, PVD, process. The at least one electrically insulating layer may be formed of a dielectric material. The dielectric material may be a silica based material.
The substrate may be elongate; and a heater track of the at least one heater tracks may extend longitudinally along the elongate substrate and have a non-constant width along the length of the substrate.
According to a third aspect of the invention, there is provided a heater assembly for a hair styling device, the heater assembly comprising: a substrate; at least one conductor layer mounted to the substrate, the at least one conductor layer comprising conductors that define at least one heater track through which current can flow to heat the substrate; and connection circuitry for connecting the at least one heater track to power control circuitry for causing current to flow through the at least one heater track; wherein the connection circuitry includes a conductive member that is ultrasonically bonded to the at least one heater track. Beneficially, the ultrasonic bond provides a strong and reliable electrical connection.
The heater assembly may further comprise: an intermediate connection member, wherein the conductive member is ultrasonically bonded to a first connection terminal of the intermediate connection member, to electrically connect the at least one heater track to the first connection terminal, wherein the intermediate connection member comprises a second connection terminal that is electrically connected to the first connection terminal, and wherein the power control circuitry is electrically connected to the second connection terminal for causing current to flow through the at least one heater track via the intermediate connection part.
The conductive member may be a ribbon of conductive material, and the conductive member may be ribbon bonded to the at least one heater track. The ribbon may be aluminium ribbon.
The ribbon may have a thickness of between 100 μm and 500 μm, preferably 400 μm. The ribbon may have a width of between 1 mm and 2 mm.
The ribbon between the ultrasonic bond to the heater track and the first connection terminal may have a loop portion. The length of the ribbon between the ultrasonic bond to the heater track and the first connection terminal may be substantially longer than the shortest connection path between the ultrasonic bond to the heater track and the first connection terminal. Beneficially, the loop portion reduces the strain on the electrical connection when there is relative movement between the heater track and the first connection terminal.
The conductive member may be ultrasonically bonded at a plurality of discrete connection points to a connection terminal of the at least one heater track. A plurality of the conductive members may be ultrasonically bonded to a single connection terminal of the at least one heater track. Beneficially, by bonding the conductive member at a plurality of discrete locations, and/or by bonding a plurality of conductive members to a single connection terminal, the risk of failure of the connection is reduced.
The heater assembly may further comprise at least one dielectric layer between the substrate and the at least one conductor layer. The at least one dielectric layer may have a total thickness of between 0.02 mm and 0.05 mm.
The at least one dielectric layer may comprise two dielectric layers; wherein a first dielectric layer of the two dielectric layers has a thickness of between 0.010 mm and 0.025 mm; and wherein a second dielectric layer of the two dielectric layers has a thickness of between 0.010 mm and 0.025 mm.
The at least one heater track may comprise: a power supply unit, PSU, heater track that is connected to the power control circuitry for flow of current derived from a mains power source; and a battery heater track that is connected to the power control circuitry for flow of current derived from a battery power source. The average width of the battery heater track may be greater than the average width of the PSU heater track.
The substrate may be elongate; the PSU heater track may extend longitudinally along the elongate substrate; and a width of the PSU track decreases away from an end of the substrate. The PSU heater track and the battery heater track may be interleaved with each other. The PSU heater track and the battery heater track may share a common ground terminal.
The substrate may be formed of an aluminium alloy. The substrate may have a thickness of between 1 mm and 2 mm. The substrate may have a mean roughness less than or equal to 0.2 μm. The substrate may have a mean roughness depth less than or equal to 1.4 μm.
The at least one conductor layer may have a total thickness of between 0.01 mm and 0.03 mm. The at least one conductor layer may be screen printed or deposited using a physical vapour deposition, PVD, process.
The resistance of a heater track of the at least one heater track may be between 0.3 Q and 0.9 Q.
According to a fourth aspect of the invention, there is provided a heater assembly comprising: an elongate substrate; and at least one conductor layer mounted to a surface of the substrate, the at least one conductor layer comprising a plurality of conductors that define at least one heater track through which current can flow to heat said substrate; wherein said plurality of conductors includes one or more conductors that extend longitudinally along the elongate substrate and which have a non-constant width along the length of the substrate. Beneficially, the non-constant width of the conductors improves the heat distribution of the heater assembly.
The width of said one or more conductors may decrease in width away from an end of the elongate substrate.
The at least one conductor layer mounted to said surface of the substrate may comprise a plurality of conductors that define a first heater track and a second heater track through which current can flow to heat said substrate, wherein at least one conductor that defines the first heater track extends along the length of the substrate and has a larger width in a central part of the elongate substrate than its width in an end part of the elongate substrate, and wherein at least one conductor that defines the second heater track extends along the length of the substrate and has a larger width in the end part of the elongate substrate than its width in the central part of the elongate substrate.
The first heater track and the second heater track may be interleaved with each other. The second heater track may run substantially parallel to the first heater track.
The first heater track may be a power supply unit, PSU, heater track that is for receiving current derived from a mains power source, and the second heater track may be a battery heater track that is for receiving current derived from a battery power source. The average width of the second heater track may be greater than the average width of the first heater track.
The heater assembly may further comprise at least one dielectric layer between the substrate and the at least one conductor layer to electrically insulate the substrate from the at least one conductor layer.
The at least one conductor layer may have a total thickness of between 0.01 mm and 0.03 mm. The at least one conductor layer may be screen printed or deposited using a physical vapour deposition, PVD, process.
According to a fifth aspect of the invention, there is provided a hair styling device comprising: a housing; at least one heater assembly for heating hair to be styled; and a mounting clip that mounts the heater assembly to the housing; wherein, the heater assembly comprises: a substrate having a first surface that faces an inner surface of the housing and a second surface that faces away from the housing; and at least one heater track through which current can flow to heat said substrate; wherein the second surface comprises at least one channel extending along the substrate; wherein the mounting clip comprises: a first part that is configured to engage or couple with the housing to attach the mounting clip to the housing; and a second part that is configured to engage with the at least one channel to retain the heater assembly in the housing. Beneficially, the configuration of the mounting clip and heater assembly enables the heater assembly to be to be securely mounted to the hair styling device without obstructing the hair styling surface. Moreover, the configuration of the mounting clip and heater assembly enables a planar first surface of the substrate to be provided (the surface that faces the inner surface of the housing), which enables a screen printing process to be used to print the electrically insulating layer(s) and conductive layer(s) of the heater onto the substrate.
The second surface may comprise a central hair contacting surface and an edge portion; and the edge portion may be recessed relative to the central hair contacting surface so that the hair contacting surface protrudes beyond the second part of the clip when the mounting clip is engaged with the at least one channel.
The edge portion may be recessed relative to the central hair-contacting surface such that the second part of the mounting clip is below the hair contacting surface.
The substrate may include a coating that defines the hair contacting surface.
The second surface may comprise a pair of edge portions, each edge portion comprising a corresponding channel extending along the substrate, and each of the edge portions may be recessed relative to the central hair contacting surface so that the hair contacting surface protrudes beyond the second part of the clip when the mounting clip is engaged with the channels.
The substrate may be elongate. The thermal mass of the mounting clip may be less than 5 J/K.
According to a sixth aspect of the invention, there is provided a hair styling device comprising: a controller (such as a microprocessor or other control circuitry); and at least one heater assembly for heating hair that contacts a hair contacting surface of the heater assembly; wherein the heater assembly comprises a first heater track and a second heater track, and the controller is configured to be able to select either one of the first or second heater tracks to be operated to heat the heater assembly, and to select the other of the first or second heater tracks to be operated as a temperature sensor.
The first heater track may be a power supply unit, PSU, heater track that is connected to power control circuitry for flow of current derived from a mains power source, and the second heater track may be a battery heater track that is connected to power control circuitry for flow of current derived from a battery power source.
According to a seventh aspect of the invention, there is provided a hair styling device comprising one or more heating assemblies according to the first, second, third or fourth aspect of the invention.
The hair styling device may comprise a controller, wherein the at least one heater track comprises a first heater track and a second heater track, and the controller is configured to be able to select either one of the first or second heater tracks to be operated to heat the heater assembly, and to select the other of the first or second heater tracks to be operated as a temperature sensor.
The first heater track may be a power supply unit, PSU, heater track that is connected to power control circuitry for flow of current derived from a mains power source, and the second heater track may be a battery heater track that is connected to power control circuitry for flow of current derived from a battery power source.
According to an eighth aspect of the invention, there is provided a method of manufacturing a heater assembly for a hair styling device, the heater assembly comprising an elongate substrate, the method comprising: screen printing at least one dielectric layer onto the elongate substrate; screen printing a first layer of conductive material onto the at least one dielectric layer to form at least one heater track having a connection terminal for electrical connection to power control circuitry; firing the first layer of conductive material; and after firing the first layer of conductive material, screen printing a second layer of conductive material onto the connection terminal to increase the thickness of conductive material at the connection terminal.
The method may further comprise further screen printing a third layer of conductive material onto the second layer of conductive material to further increase the thickness of conductive material at the connection terminal.
The at least one dielectric layer may have a total thickness of between 0.02 mm and 0.05 mm. The at least one dielectric layer may comprise two dielectric layers; wherein a first dielectric layer of the two dielectric layers has a thickness of between 0.010 mm and 0.025 mm; and wherein a second first dielectric layer of the two dielectric layers has a thickness of between 0.010 mm and 0.025 mm. The first layer of conductive material may have a thickness of between 0.1 mm and 0.03 mm.
According to a ninth aspect of the invention, there is provided a method of manufacturing a heater assembly for a hair styling device, the heater assembly comprising an elongate substrate, the method comprising: screen printing a first dielectric layer onto the elongate substrate; firing the first dielectric layer; after firing the first dielectric layer, screen printing a second dielectric layer onto the first dielectric layer; firing the second dielectric layer; and after firing the second layer of dielectric layer, screen printing a layer of conductive material onto the second dielectric layer to form at least one heater track having a connection terminal for electrical connection to power control circuitry.
The method may further comprise ultrasonically bonding a conductive member to the connection terminal to connect the at least one heater track to the power control circuitry.
The conductive member may be a ribbon of conductive material, and the method may further comprise ribbon bonding the conductive member to the connection terminal to connect the at least one heater track to the power control circuitry. The ribbon may be an aluminium ribbon. The ribbon may have a thickness of between 100 μm and 500 μm. The ribbon may have a width of between 1 mm and 2 mm.
The at least one heater track may include at least one conductor that extends longitudinally along the substrate and whose width varies along the length of the substrate. The resistance of a heater track of the at least one heater track may be between 0.3 Q and 0.9 Q. The at least one heater track may be formed of a material comprising at least 90% silver.
A surface of the substrate facing the at least one dielectric layer may have a mean roughness of less than or equal to 0.2 μm. A surface of the substrate facing the at least one dielectric layer may have a mean roughness depth of less than or equal to 1.4 μm.
According to a tenth aspect of the invention, there is provided a heater assembly comprising: an elongate substrate; and at least one conductor layer mounted to a surface of the substrate, the at least one conductor layer comprising a plurality of conductors that define a first heater track and a second heater track through which current can flow to heat said substrate; wherein at least one conductor that defines the first heater track extends longitudinally along the length of the substrate and has a larger width in a central part of the elongate substrate than its width in an end part of the elongate substrate, and wherein at least one conductor that defines the second heater track extends longitudinally along the length of the substrate and has a larger width in the end part of the elongate substrate than its width in the central part of the elongate substrate.
The first heater track and the second heater track may be interleaved with each other. The second heater track may run substantially parallel to the first heater track. The first heater track may be a power supply unit, PSU, heater track that is for receiving current derived from a mains power source, and the second heater track may be a battery heater track that is for receiving current derived from a battery power source. The average width of the second heater track may be greater than the average width of the first heater track. The heater assembly may further comprise at least one dielectric layer between the substrate and the at least one conductor layer to electrically insulate the substrate from the at least one conductor layer. The at least one conductor layer may have a total thickness of between 0.01 mm and 0.03 mm. The at least one conductor layer may be screen printed or deposited using a physical vapour deposition, PVD, process.
According to an eleventh aspect of the invention, there is provided a hair styling device comprising: a heater assembly for heating hair to be styled or dried; and power supply circuitry for providing electrical power to the heater assembly to heat the heater assembly; wherein the heater assembly comprises: a substrate for heating the hair; first and second elongate conductors mounted on the substrate either side of a heating area of the substrate; and a resistive heating element mounted over, and in thermal contact with, the heating area of the substrate and electrically coupled to the first and second elongate conductors; wherein the power supply circuitry is coupled to the first and second elongate conductors and is arranged to cause current to flow between the first and second elongate conductors through the resistive heating element, to cause the resistive heating element to be heated thereby heating the heating area of the substrate; and wherein the resistive heating element is formed using a physical vapour deposition, PVD, process.
The resistive heating element may comprise a generally planar layer of material arranged between the first elongate conductive element and the second elongate conductive element. The resistive heating element may at least partially overlap the first and second elongate conductors, and the resistive heating element may be formed before the first and second elongate conductors are mounted.
According to a twelfth aspect of the invention, there is provided a method of manufacturing a heater assembly for a hair styling device for heating hair to be styled or dried, the method comprising: forming, using a physical vapour deposition, PVD, process, a resistive heating element mounted over and in thermal contact with a heating area of a substrate; mounting first and second elongate conductors either side of the heating area, wherein the first and second elongate conductors are electrically coupled to the resistive heating element for, in use, current flow between the first and second elongate conductors through the resistive heating element to cause the resistive heating element to be heated, thereby heating the heating area of the substrate; wherein the resistive heating element is formed before the first and second elongate conductors are mounted.
Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:
In the figures, like elements are indicated by like reference numerals throughout.
The present embodiments represent the best ways known to the applicant of putting the invention into practice. However, they are not the only ways in which this can be achieved.
The device 20 comprises a pair of arms 22 connected by a hinge 21. The arms 22 are moveable between an open configuration, as illustrated in
The system comprises a low voltage power supply 171 deriving power from a battery 173 (for example, a 7.2 V battery comprising two 3.6 V cells, although 3 or more cells may alternatively be provided) and/or a mains power supply input 170, which can be used to charge the battery 173. Power from power supply 171 is provided to a power control module 174, which in turn powers one or more PSU tracks 62 and one or more battery tracks 61. The PSU tracks 62 and the battery tracks 61 (described in more detail below) are provided in heater assemblies of the device 20, for heating the hair contacting surface 52a and 52b. Power from power supply 171 is also provided to a microcontroller/control means 180 coupled to non-volatile memory 176 storing processor control code for a temperature control algorithm, and to RAM 177. The skilled person will appreciate that any of a wide range of different control algorithms may be employed including, but not limited to, on-off control and proportional control. Optionally the control loop may include a feed-forward element responsive to a further input parameter relating to the hair styling device 20, for example to use the operation of the device 20 to improve the temperature control. An optional user interface 178 is also coupled to microcontroller 180, for example to provide one or more user controls and/or output indications such as a light or audible alert. The output(s) may be employed to indicate, for example, when the temperature of the hair contacting surfaces 52 has reached a desired operating temperature, for example in a region between 140° C. and 190° C., typically about 185° C.
Microcontroller 180 is also coupled to one or more optional temperature sensors such as thermistors 179.
Each of the PSU track 62 and the battery track 61 may be provided with a separate control loop controlled by the temperature sensed by a respective thermistor 179.
A main PCB is provided within the housing of one of the arms 22 of the device (not shown in the figure). The main PCB includes the power control 174 circuitry.
When the device 20 is plugged in to the mains electricity, the device 20 may operate in a corded mode whilst simultaneously charging the battery 173. In this mode, only the PSU track 62 may be used to heat the hair contacting surfaces 52. Advantageously, therefore, the user need not wait for the battery 173 that powers the battery track 61 to recharge before the user can begin styling hair using the device 20. When the battery 173 is charged, it is also possible to power the PSU tracks 62 and the battery tracks 61 at the same time.
Beneficially, the heat transfer from the printed conductor layers 44 to 46 to the hair contacting surface of the aluminium substrate layer 41 is highly efficient due to the direct thermal contact between the printed layers and the substrate 41. Heat energy is transferred to the substrate 41 (the hair-contacting surface) almost immediately after the heat is generated by current flowing through the screen-printed conductor layers 44 to 46. Moreover, the direct thermal connection between the printed layers and the aluminium substrate 31 removes the need for any additional thermal interface material (for example, thermal paste) between the layers and the substrate 41. The improved thermal efficiency also increases the run-time of the device when the device operates on battery power. Beneficially, in use, the heater assembly 30 of the present disclosure requires approximately 5 W less power per hair styling surface (operating at approximately 60 W for a pair of hair styling surfaces) to maintain the hair styling surface 52 at the operating temperature, compared to a conventional heater assembly operating according to the same temperature profile. Moreover, the heater assembly 30 of the present disclosure only requires approximately 50% of the power required by conventional heater assemblies to heat the hair styling surface to the operating temperature in the same amount of time.
Advantageously, because the thermal efficiency of the heater assembly 30 is much greater than the prior art heater assemblies used in commercial flat plate stylers and because the thermal mass of the heater assembly 30 is relatively low, the hair styling device 20 may be configured to operate at safe-extra-low voltages (for example, less than 42 V). That is the mains derived voltage generated by the low voltage PSU 171 can be kept below 42 Volts. Whilst in practice this limits the operating power to about 150 W, the inventors have found that because of the thermal efficiency of the heater assembly 30, this can be enough power to heat the user's hair sufficiently to allow styling. If additional heat is required, the power control unit 174 can simultaneously connect the AC derived supply voltage to the PSU track(s) 62 and the battery voltage to the battery track(s)—so that both heater elements heat the aluminium substrate 41 at the same time which can provide over 200 W of heating power. The use of such safe-extra-low voltages also enables the use of contact temperature measurement sensors and the use of metal surfaces on the styler housing, which could otherwise not be used due to the possibility of user electric shock (and high voltage safety regulations). The use of metal surfaces on the styler housing can also improve the hair-styling performance and overall thermal properties of the device 20, due to improved heat dissipation properties compared to, for example, a plastic casing.
Advantageously, the heater assembly 30 of the present disclosure is particularly compact. The heater assembly 30 can therefore be more easily packaged into the housing of the device 20, reducing the design constraints on the housing and reducing the overall size of the hair styling device 20. The reduced size of the hair styling device 20 enables the user to more easily hold the device and more easily style hair. Alternatively, or additionally, the additional space created by the compact heater assembly 30 may be used to provide additional insulation between the heater assembly 30 and the main housing of the hair styling device 20. This reduces the thermal transfer to the housing, increasing the efficiency of the device and the comfort of the user.
As described above and as illustrated in
The heater assembly 30 may also comprise one or more additional dielectric layer(s) on the upper surface of the heater assembly 30 illustrated in
A detailed description will now be given of these different layers of the heater assembly 30 that is used in this exemplary embodiment. Clearly, the dimensions given are exemplary only and other dimensions could of course be used.
As illustrated in
As illustrated in
The first dielectric layer 42 and second dielectric layer 43 are electrically insulating layers that are provided between the conductive heater track layers (the PSU track layer 44, the battery track layer 45 and the connection pad reinforcement layer 46) and the aluminium substrate 41, providing electrical insulation between these current carrying heater tracks and the aluminium substrate 41 which comes into contact with the user's hair. Typically, the dielectric layers are not patterned and each form a substantially uniform layer of material. The dielectric material used to form the dielectric layers may be a silica (SiO2) based material. The length of the first dielectric layer 42 is 78 mm and the width of the first dielectric layer 42 is 18.3 mm. The thickness of the first dielectric layer 42 is between 0.01 mm and 0.025 mm, for example 0.023 mm. The length of the second dielectric layer 43 is 77.9 mm and the width of the second dielectric layer 43 is 18.2 mm. The thickness of the second dielectric layer 43 is also between 0.01 mm and 0.025 mm, for example 0.023 mm.
The first dielectric layer 42 is printed directly onto the aluminium substrate 41, which results in highly efficient thermal transfer between the first dielectric layer 42 and the aluminium substrate layer 41. The second dielectric layer 43 is printed directly onto the first dielectric layer 43 to increase the electrical insulation between the heater tracks and the aluminium substrate 41.
It will be appreciated that the electrically insulating properties of the dielectric layers depends on both the material composition of the layers and on the thickness of the layers. The composition and thickness of the layers in the present example is described in detail below. However, it will be appreciated that any other suitable material or thickness may be used to form the dielectric layers. For example, an anodic oxide layer (up to 50 microns in thickness) could be fabricated directly onto the aluminium substrate 41. Plasma electrolytic oxidation (PEO), also known as micro arc oxidation (MAO), can be used to fabricate an oxide layer which can provide the necessary dielectric properties. This type of coating has several advantages. For example, there is no adhesion or CTE mismatch issue, good consistency in layer thickness, a robust coating process with good control, excellent repeatability, and excellent dielectric properties. Other high temperature and electrically insulating materials such as polyimide could also be used.
In the heater assembly 30 illustrated in
Increasing the number of dielectric layers may increase the propensity for undesirable warping of the heater assembly 30. Therefore, in the heater assembly 30 illustrated in
As illustrated in
A presently preferred configuration of the PSU track layer 44 and battery track layer 45 will now be described with reference to
In the present example, the PSU track layer 44 has a thickness of 0.015 mm and the battery track layer 45 also has a thickness of 0.015 mm. Whilst the thickness of the tracks is an important parameter when considering the electrical conductivity and hence resistance of the tracks, there is a limit on the thickness of track that can be reliably and efficiently formed using a screen printing process. Therefore, the material composition of the PSU track 62 and the battery track 61 is important for achieving the desired electrical conductivity/resistance. In the present example, the PSU track 62 is formed from a conductive material comprising a relatively large fraction of silver. The battery track 61 is similarly formed from a conductive material comprising a relatively large fraction of silver (in this example, at least 90% silver). More specifically, the battery track 61 and the PSU track 62 are formed from materials comprising glass and large fraction of silver, enabling particularly low resistances of the heater tracks to be achieved (for example, a 0.4Ω resistance for the battery track, that enables operation using a 2 cell battery of approximately 8 V—the use of 2 cells enables a particularly compact and low weight hair styling device). Whilst the resistance of the tracks could also be reduced by increasing the track thickness, this would require printing additional track material (possibly in the form of additional layers), increasing the manufacturing cost and complexity.
Alternatively, the PSU track 62 and battery track 61 may be formed of any other suitable conductive material (for example, copper, gold, platinum, titanium graphite, or a silver-palladium alloy) that can be deposited onto the insulating dielectric layer(s) to form the heater tracks. However, whilst use of a silver-palladium alloy may provide improved stability (reduced migration of free silver ions towards the substrate through the dielectric layers), the use of palladium results in an undesirable increase in the unit resistance of the material.
In the present example, the migration of the silver-based material through the dielectric layers towards the substrate (which may cause short circuits over time) is mitigated by providing sufficient dielectric insulation between the heater tracks and the aluminium substrate (and by providing a sufficiently smooth surface of the aluminium substrate) to prevent electrical breakdown. However, increasing the thickness of the dielectric layers increases the propensity for warping of the heater assembly (and also undesirably increases the thermal mass of the heater assembly). Therefore, the particularly advantageous thickness of the dielectric layers in the present example has been selected to provide a balance between providing sufficient electrical insulation to allow the use of the silver-based material to form the heater tracks, whilst also reducing the risk of warping.
As will be described in more detail below, the configuration of the PSU track 62 and the battery track 61 provide a particularly uniform power output across the surface of the heater assembly 30 (which generates a corresponding uniform temperature distribution on the hair contacting surface 52), whilst maximising the width of the battery track 61 to make efficient use of the available space. Moreover, the arrangement of the tracks results in a relatively uniform power output across the surface of the heater assembly even when one of the heater tracks is powered alone (i.e. when only one of the PSU track 62 or the battery track 61 is in operation). As can be seen from
As can be seen from
As the PSU track 62 and the battery track 61 are packed tightly together with a minimum spacing between the tracks, as the PSU track gets thicker the battery track preferably gets thinner in order to maintain the desired minimum spacing between the tracks.
Due to the lower power output from the battery track 61 compared to the PSU track 62, there is less need for the width of the battery track 61 to be configured to reduce excessive heat build-up at the connection pad end of the heater assembly 30. Therefore, the battery track 61 can instead be configured primarily to make more efficient use of the available space, by maintaining a minimum spacing between the battery track 61 and the PSU track 62. In the present example a minimum separation of approximately 0.7 mm is maintained between the battery track 61 and the PSU track 62 due to electrical operation requirements (e.g. to ensure adequate electrical isolation between the battery track 61 and the PSU track 62).
In the heater assembly 30 illustrated in
The heater assembly 30 generates heat by passing an electrical current along the PSU track 62, the battery track 61, or both tracks simultaneously. The resistance of each track is an important property for achieving the desired level of heat output from the heater for the given operating voltages. The resistance of a heater track is determined by the material composition of the heater track (in this example, the material of each heater track comprises a relatively large fraction of silver) and the physical dimensions of the heater track. Beneficially, the resistance of the battery track 61 of the present example is particularly low, reducing the number of cells of the battery 173 required to power the battery track 61 whilst achieving a given heating power output. In this example the battery track 61 has a resistance of approximately 0.42. When a pair of heater assemblies 30 are provided in the device, this allows a total heating power of up to approximately 274 W (approximately 137 W per heater) to be provided using a total battery voltage of 7.4 Volts.
As mentioned above, the thickness of an individual layer of heater track material that can be formed is restricted due to limitations of the screen printing process. Whilst additional layers of track material could be printed to increase the track thickness (and therefore decrease the resistance of the track), this results in increased manufacturing complexity and cost, and may increase the propensity for undesirable warping or failure of the heater assembly 30. Therefore, the width of the tracks is an important parameter in determining the resistance at a particular point along the track. The spatial configurations of the tracks of the present example have been carefully configured to achieve more uniform heat distribution across the hair contacting surface 52. As described above, the width of the tracks varies along the length of the heater assembly to provide a more uniform heat distribution.
A method of manufacturing the heater assembly 30 illustrated in
The heater assembly 30 is formed by screen printing thick film layers of material onto the aluminium substrate layer 41. Once each layer is printed, the assembly is heated (fired) to approximately 500 degrees C. to bond the printed layer to the substrate or the layer below. Therefore, the properties of the surface of the aluminium substrate layer 41 are important for reliably printing the other layers of the heater assembly 30, and for providing efficient thermal transfer between the aluminium substrate layer 41 and the fist dielectric layer 42.
Due to the different thermal properties of the layers that form the heater assembly 30, the heater assembly 30 has a propensity for warping when undergoing changes in temperature during the firing process discussed above. Therefore, it is desirable that the particular alloy used for the substrate layer 41 reduces the propensity for warping. Moreover, when the alloy has a reduced propensity for warping, this allows the thickness of the aluminium substrate layer 41 to be decreased, which beneficially further reduces the thermal mass of the heater assembly 30. As discussed above, a reduction in the thermal mass of the heater assembly 30 advantageously reduces the thermal lag between the user switching on the device 20 and the hair contacting surface 52 reaching the operating temperature for styling hair.
In a preferred embodiment the aluminium alloy 6063-T5 is used to form the aluminium substrate layer 41. A 1.5 mm thick layer of this alloy was found to remain particularly flat (i.e. this alloy has a low propensity for warping) when fired to a temperature of 580° C.—a temperature similar to those used to fire the printed layers during the construction of the heater assembly.
The aluminium alloy 6063-T5 may comprise, for example, 0.440 wt. % Si, 0.480 wt. % Mg, 0.170 wt. % Fe, 0.030 wt. % Mn, <0.01 wt. % Cu and 0.01 wt. % Ti. Alternatively, for example, the aluminium alloy 6063-T5 may comprise 0.441 wt. % Si, 0.443 wt. % Mg, 0.198 wt. % Fe, 0.037 wt. % Mn, 0.009 wt. % Cu, and 0.032 wt. % Ti.
The surface roughness of the aluminium substrate layer 41 is an important property of the heater assembly 30. When the aluminium substrate layer 41 is sufficiently smooth, the number of layers of dielectric material and their thickness can be reduced whilst maintaining sufficient electrical insulation between the PSU track 62 and the aluminium substrate 41 (and between the battery track 61 and the aluminium substrate 41). Reducing the number of dielectric layers reduces the manufacturing costs and reduces the propensity of the heater assembly 30 to warp. In a preferred embodiment, the roughness parameters for the surface of the aluminium substrate 41 that contacts the first dielectric layer 42 are given by: Ra≤0.2 μm; Rz≤1.4 μm; and Rmax≤1.4 μm, where Ra is the mean roughness (the arithmetic average of the absolute values of the roughness profile ordinates), Rz is the mean roughness depth (the arithmetic mean value of the single roughness depths of consecutive sampling lengths), and Rmax is the maximum roughness depth (the largest single roughness depth within the evaluation length).
Whilst in this example an aluminium substrate formed of the aluminium alloy 6063-T5 is used, it will be appreciated that any other suitable aluminium alloy may be used. Moreover, it will be appreciated that the substrate need not necessarily be formed of aluminium. For example, magnesium or a suitable magnesium-aluminium alloy may be used to form the substrate. Alternatively, for example, copper (or a suitable copper alloy) may be used to form the substrate. In a further alternative, described in more detail later, the substrate may be formed from an electrically insulating, but thermally conductive, material such as aluminium nitride or beryllium oxide.
In the following description, the term ‘total heating time’ is used. The ‘total heating time’ is the total time taken to heat the material from room temperature to the peak temperature, and then to cool back to room temperature.
Before the material of the first dielectric layer 42 is deposited, the aluminium substrate 41 is heated to a temperature of 580° C. using a total heating time of between 35 to 40 minutes, including 5 to 7 minutes at the peak temperature.
The first dielectric layer 42 is then formed by screen printing the dielectric material directly onto the aluminium substrate 41 using a 200 mesh stainless steel screen to form a layer that is 78 mm long, 18 mm wide and 0.023 mm thick. After the material has been deposited, the heater assembly 30 is dried in a ventilated box furnace at 150° C. for 15 minutes. The heater assembly 30 is then fired in a ventilated box furnace at 570° C. for a total time of 35 minutes, including 5 to 7 minutes at the peak temperature.
After the first dielectric layer 42 has been formed, the second dielectric layer 43 is deposited. The second dielectric layer 43 is formed by screen printing the dielectric material directly onto the first dielectric layer 42 using a 200 mesh stainless steel screen to form a layer that is 77.9 mm long, 18.2 mm wide and 0.023 mm thick. The screen-printed dielectric material is then dried in a ventilated box furnace at 150° C. for 15 minutes, before being fired in a ventilated box furnace at 570° C. for a total time of 35 minutes, including 5 to 7 minutes at the peak temperature.
As described above, additional layers of dielectric material may be deposited at this stage, depending on the specific insulation requirements. However, each time a new layer is screen printed and fired, the chances that the heater assembly will fail increases. Therefore, minimizing the number of dielectric layers is desirable.
After the second dielectric layer 43 has been formed, the PSU track layer 44 is deposited. The PSU track layer 44 is formed by screen-printing the PSU track material directly onto the second dielectric layer 33 to form a layer that is 0.015 mm thick.
The screen-printed material of the PSU track layer 44 is then dried in a ventilated box furnace at 150° C. for 15 minutes, before being fired in a ventilated box furnace at 550° C. for a total time of 35 minutes, including 5 to 7 minutes at the peak temperature.
After the PSU track layer 44 has been formed, the battery track layer 45 is deposited. The battery track layer 45 is formed by screen-printing the battery track material directly onto the PSU track layer 44 (and where there are gaps in the PSU track layer, the material of the battery track layer 45 is printed onto the surface of the second dielectric layer 43) to form a layer that is 0.015 mm thick.
The screen-printed material of the battery track layer 45 is then dried in a ventilated box furnace at 150° C. for 15 minutes, before being fired in a ventilated box furnace at 550° C. for a total time of 35 minutes, including 5 to 7 minutes at the peak temperature.
In a preferred embodiment, the material of the battery track 61 comprises a higher percentage of silver material than that of the PSU track 62. As a result, per unit volume, the battery track 61 material has a lower resistance compared to the PSU track 62 material, and enables a particularly low resistance (of approximately 0.4 Q) to be achieved for the path between the battery connection pad 33 and the common ground pad 34.
After the battery track layer 45 has been formed, the connection pad reinforcement layer 46 is deposited. The connection pad reinforcement layer 46 is formed by screen printing battery track material directly onto the connection pads of the battery track layer 45 to form a layer that is between 0.010 mm and 0.020 mm thick (for example, 0.015 mm thick).
The screen-printed material of the connection pad reinforcement layer 46 is then dried in a ventilated box furnace at 150° C. for 15 minutes, before being fired in a ventilated box furnace at 550° C. for a total time of 35 minutes, including 5 to 7 minutes at the peak temperature.
The screen printed layers of dielectric material and heater track material are relatively fragile, compared to the surfaces of a conventional heater assembly. Therefore, it is relatively difficult to form strong and reliable electrical connections to the heater tracks, since standard joining methods that damage the delicate layers of the heater assembly 30 cannot be used. Therefore, there is a need for an improved bonding method to form electrical connections to the heater tracks of a thick film printed heater that allow the power control circuitry 174 to connect to the heater tracks 61 and 62.
The inventors have found that conventional joining methods (such as soldering, resistance welding, and conductive adhesives) that are commonly used by the consumer electronics industry to make electrical connections, do not provide a reliable and repeatable solution for joining the connection pads of the heater tracks to the power control circuitry.
In the device of the present disclosure, a technique known as ribbon-bonding was used to form strong and reliable electrical connections to the PSU connection pad 72, battery connection pad 73 and the common ground pad 74. Beneficially, the resultant electrical connections were found to be repeatable, reliable and can be mass manufactured.
Ribbon-bonding is a type of ultrasonic bonding. Ultrasonic bonding involves the use of force, time and ultrasonics to join two materials. The ribbon or wire is pressed against the surface (both at ambient temperature) at low force and vibrated for a limited period of time to achieve the bond. Ultrasonic energy, when applied to the metal to be bonded, renders it temporarily soft and plastic. This causes the metal to flow under pressure. The acoustic energy frees molecules and dislocates them from their pinned positions and that allows the metal to flow under the low compressive forces of the bond. Thus heat at the bond site becomes a bi-product of the bonding process and so external heat is not necessary. Such ultrasonic bonding is also called a “cold weld”. There are two types of ultrasonic bonding: wedge bonding and tape automated bonding (TAB). Wedge bonding (which includes ribbon bonding) is preferred as there is more control over the placement of the wires (in TAB bonding, the wire is already pre-aligned over the pad to which it is to be bonded).
The bonding parameters used to form the ribbon bonds are important for forming strong and reliable connections. The ultrasonic voltage used to form the ribbon bonds may be, for example, between 40 V and 110 V, preferably between 50 V and 80 V. The bond force used to form the ribbon bonds may be, for example, between 1500 cN and 5000 cN, preferably between 4500 cN and 5000 cN. The phase duration used to form the ribbon bonds may be, for example, between 200 ms and 500 ms, preferably between 300 ms and 500 ms.
The ‘ribbon leave out angle’ is the angle at which the ribbon extends away from the joining surface. The ribbon leave out angle may be, for example, between 10 degrees and 80 degrees. A ribbon leave out angle of between 20 degrees and 50 degrees was found to be particularly beneficial for reducing the stress on the ribbon bonds.
In one example, the PCB stackup may comprise a layer of FR4 (a glass-reinforced epoxy laminate material) of between 0.8 mm and 3.2 mm thickness. A first copper layer of approximately 0.035 mm thickness is arranged on top of the FR4 layer. Two or more ‘PrePreg 1080’ layers of approximately 0.140 mm thickness are arranged on top of the copper layer. A second copper layer of approximately 0.035 mm thickness is arranged on top of the PrePreg 1080 layer. An electroless Ni layer of approximately 0.0025 mm to 0.008 mm thickness is arranged on top of the second copper layer. A layer of immersion gold of approximately 0.05 μm to 0.15 μm thickness is arranged on top of the electroless Ni layer. However, it will be appreciated that any other suitable configuration of the PCB stackup may be used.
Advantageously, the ribbon bonds 134 to 136 form strong and reliable connections to the pads 32 to 34 of the heater assembly 30, and the bonding process does not damage the relatively delicate thick film printed layers of the heater assembly 30. A first ribbon bond 134 connects the PSU connection pad 32 to a first intermediate connection pad 147 on the ribbon side of the bridge 137. A second ribbon bond 135 connects the battery connection pad 33 to a second intermediate connection pad 148 on the ribbon side of the bridge 137. A third ribbon bond 136 connects the common ground pad 34 to a third intermediate connection pad 149 on the ribbon side of the bridge 137.
The ribbon bonding process is a relatively clean joining method that does not require epoxy. Each ribbon bond may be formed by first connecting an end of the ribbon to a connection pad of the heater assembly 30, and then connecting the other end of the ribbon to the corresponding pad on the bridge 137. Alternatively, each ribbon bond may be formed by first connecting an end of the ribbon to a connection pad of the bridge 137, and then connecting the other end of the ribbon to the corresponding pad of the heater assembly 30.
The ribbons form ‘step-up’ connections from the connection pads of the heater assembly 30 to the corresponding connection pads on the PCB of the bridge 137. As illustrated in
As illustrated in
As illustrated in
By providing the bridge 137, the ribbons can be terminated at the intermediate PCB of the bridge 137, rather than being connected directly a main PCB of the device 20. Beneficially, the provision of the bridge 137 between the ribbons and the wires to the main PCB of the device 20 reduces the strain on the ribbon bonds to the heater tracks, reducing the risk of failure of the connection. In particular, when the heater plates are configured to ‘float’ within the corresponding arm of the hair styling device 20, the bridge 137 reduces the strain on the ribbon bonds as the heater assembly moves, since the bridge 137 does not move relative to the heater assembly (i.e. the bridge 137 is in a fixed position relative to the heater assembly 30). Instead, the strain is applied at the general connection pads of the bridge 137. However, since a wide range of bonding techniques can be used to bond to the general connection pads, a stronger and more robust bonding method can be used to mitigate against such movement-induced strain, without risk of damaging the relatively delicate layers of the heater assembly 30. Moreover, the provision of the bridge 137 shortens the lengths of the ribbons required to form the connections from the heater assembly 30, compared to if the ribbons instead connected the connection pads of the heater assembly 30 directly to the main PCB of the hair styling device 20.
Multiple ribbons may be used to form a connection between one of the connection pads of the heater assembly and the corresponding pad of the bridge 137. Advantageously, this configuration maintains an electrical connection between a connection pad of the heater assembly 30 and the corresponding connection pad of the bridge 137, even when one of the ribbon bonds fails.
In a presently preferred embodiment, the ribbons are formed of aluminium. Beneficially, aluminium was found to form particularly strong and reliable bonds to the silver based material of the connection pads. However, the ribbons need not necessarily be formed of aluminium. For example, the ribbons could instead be formed of copper, silver, gold, aluminium cladded copper, or platinum.
Whilst the aluminium ribbons form particularly strong and reliable connections to the connection pads of the heater assembly 30, the aluminium material has a relatively low conductivity compared to commonly used metals for electrical connections (for example, copper). Therefore, in this example, the ribbon bonds have a relatively large thickness of approximately 400 μm. This particularly thick ribbon allows sufficient current to be carried to the tracks of the heater assembly 30. However, it will be appreciated that the ribbons need not necessarily be 400 μm thick. For example, thicknesses of between 100 μm and 500 μm could be used. Advantageously, the use of relatively thick ribbons also increases the mechanical strength of the ribbon bonds, reducing the risk of failure of the electrical connections. The ribbons used to form the ribbon bonds may be, for example, between 1 mm and 2 mm wide. A ribbon thickness of 400 μm and a ribbon width of 2 mm was found to be particularly beneficial when aluminium ribbon is used, since this allows sufficient current to be carried, and enables strong and reliable electrical connections to be formed.
Conventional hair styler plate geometries typically contain non-flat edge features for facilitating mounting of the heater plate to the casing. However, with a screen printing process for manufacturing the heater assembly 30 it is desirable that the aluminium substrate 41 is flat on the side on which the thick film layers are printed, so that the printer rollers of the screen printing process are not obstructed. It is also desirable for the hair contacting surface 52 on the other side of the aluminium substrate 41 to be flat, so that the heater plate can effectively engage with the hair to be styled. Therefore, there is a need for an improved mounting assembly for mounting the heater assembly 30 to an arm 22 of the hair styling device 20, that does not obstruct the screen printing process.
The central hair contacting surface 52 may be provided with an additional coating (e.g. to increase the smoothness or visual appeal of the hair contacting surface), which need not necessarily also be provided in the edge portions (although may also be provided in the edge portions).
The mounting clip 151 retains the heater assembly 30 (and the corresponding electrical connection assembly 130) inside the arm 22 of the device 20. Advantageously, the mounting clip 151 has relatively low thermal contact with the heater assembly 30, which increases the efficiency of the device 20 by reducing the amount of heat that is wasted by transfer to the mounting clip 151 and from the mounting clip to the housing of the arm 22. Moreover, the mounting clip 151 has a relatively low thermal mass (for example, less than 5 J/K) compared to a conventional heater carrier, further increasing the efficiency of the device.
As illustrated in
As shown in the Figure, the mounting clip 151 comprises a curved portion 55 at each side of the clip 155 that engages with the respective longitudinal groove 53 in the upper surface 52 of the substrate 41, to grip the substrate 41 and hold the substrate 41 (and therefore the heater assembly 30) to the housing of the arm 22. The radius of curvature of the curved portion 55 may be configured to reduce a crimping effect on the hair being styled, as the hair is pulled through the device 20. The mounting clip 151 is attached to the housing at the rear wall 152. This may be achieved by using a suitable fastener such as a screw. Alternatively, the mounting clip 151 can be shaped so that it is held in place by suitable friction fit between the mounting clip 151 and the housing of the arm 22.
Advantageously, the configuration of the mounting assembly 140 and the heater assembly 30 is such that the heater assembly 30 can be mounted to an arm 22 of the device 20, whilst providing smooth surfaces of aluminium substrate for compatibility with the screen printing process.
A further example of a heater assembly that could be used as part of the device 20 will now be described with reference to
The heating element may be deposited (e.g. using the PVD process) before the bus bars are mounted. This enables a particularly uniform layer to be formed for the heating element 184, resulting in more uniform heating of the substrate 186. As shown in
Detailed embodiments and some possible alternatives have been described above. As those skilled in the art will appreciate, a number of modifications and further alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. It will therefore be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.
Whilst the layers of the heater assembly 30 have been described in some examples as being formed using a thick film printing process, it will be appreciated that some of the benefits of the disclosure do not require the layers to have been thick film printed. For example, the benefits of the non-constant widths of the PSU track and the battery track to improve the heat distribution across the hair contact surface to not require the tracks to have been formed using a thick film printing process. Alternatively, the tracks could be formed, for example, by depositing silver (or another suitable conductive material) using a method such as electroplating (also known as electrodeposition), electroless plating, physical vapour deposition, ion assisted deposition or atomic layer deposition.
Whilst in the above examples the first and second dielectric layers have been described as being rectangular, this need not necessarily be the case. The first and second dielectric layers may have any other suitable geometry.
Whilst the reinforcing pads of the connection pad reinforcement layer 46 have been described above as being formed of the same material used to form the battery track layer 45, it will be appreciated that this need not necessarily be the case. Any other suitable conductive material may be used to form the connection pad reinforcement layer 46.
It will be appreciated that when two hair contacting plates are provided (for example, as shown by the two hair contacting plates of the device illustrated in
Any or all of the main body of the device 20 illustrated in
Whilst in this particularly advantageous example a PSU track and a battery track are provided, it will be appreciated that the heater assembly may alternatively be configured with only a PSU track (for a device powered directly by mains power without a cordless mode of operation) or with only a battery track. It will be appreciated, therefore, that the number of heater tracks (and corresponding heater track layers) need not necessarily be two. Alternatively, three or more stacked heater tracks, possibly separated by additional dielectric layers, could be provided.
In the above-described examples, the PSU track 62 and/or the battery track 61 may be configured to operate as a temperature sensor. As the temperature of the heater track changes, the resistance of the heater track also changes according to a predetermined relationship (which may be determined in a calibration routine). Therefore, by measuring the resistance of the heater track, the temperature (or change in temperature) of the heater track can be determined and used by the controller for controlling the temperature of the heater assembly. The controller can measure the resistance of the relevant track in various different ways. For example, the controller can apply, or cause to be applied, a known voltage to the track and measure the current flowing through (or voltage drop across) a resistance of known value that is connected to the track. Beneficially, the provision of two (or more) independently operable heater tracks allows one of the tracks to be operated as a temperature sensor when the other heater track is operated to heat the heater assembly. For example, when the device 20 is operating in a mode in which the PSU track 62 is used for heating, the battery track 61 may be operated as a temperature sensor. When the device 20 is operating in a mode in which the battery track 61 is used for heating, the PSU track 62 may be operated as a temperature sensor. The controller then selects which of the heater tracks is to be used to heat the substrate (heater assembly) and selects which of the heater tracks is to be operated as a temperature sensor. The controller may be configured to select between a first mode in which both the battery track 61 and the PSU track 62 are used for heating, a second mode in which the battery track 61 is used for heating and the PSU track 62 is operated as a temperature sensor, and a third mode in which the PSU track 62 is used for heating and the battery track 61 is operated as a temperature sensor. Alternatively, one or both of the heater tracks 61, 62 may be operated simultaneously for heating and as a temperature sensor.
The device 20 may be provided with auxiliary sensors, for example hair sensors for detecting the presence of hair on one of the hair contacting surfaces. The device 20 may comprise one or more moisture sensors for determining a moisture content of the hair on a hair contacting surface of the device 20. The operation of the heater tracks may then be controlled based on the measurements of the one or more moisture sensors. Alternatively, the moisture content of the hair may be inferred from a change in temperature of at least one of the heater tracks or the hair contacting surfaces.
In the above description the configuration of the layers of the heater assembly 30 have been described as reducing the propensity for warping of the device. Alternatively, the layers may be configured (for example, by increasing the number of layers of dielectric material) to achieve controlled warping of the heater assembly during a curing process, resulting in the hair contacting surface having a bowed shape. Alternatively, a heater assembly having a bowed shape may be obtained by bending the heater assembly after the screen printing process, by applying a force to the heater assembly. In a further alternative, the electrically insulating material and heater tracks may be printed onto a curved substrate (for example, using a pad/tampon printing method). In a further alternative, as described above, the electrically insulating material and/or heater electrode may be deposited onto a curved substrate using PVD. A bowed (concave or convex) or curved hair contacting surface may be desirable for some types of hair styling device, for example to corral the hair into a central region of the hair styling surface when the surface is concave.
Whilst in the preferred embodiment illustrated in
Whilst in the preferred embodiment illustrated in
Whilst in some of the examples above electrical insulation between a heater electrode and a substrate has been described as being provided by a separate electrically insulating layer (e.g. screen printed dielectric material, or dielectric material deposited using PVD) arranged between the heater electrode and the substrate, this need not necessarily be the case. The electrical insulation could alternatively, or additionally, be provided by applying a surface treatment to the substrate in order to form an electrically insulating barrier from the substrate material. For example, when the substrate is metallic (e.g. aluminium), the surface of the substrate could be treated using a plasma electrolytic oxidation (PEO) process, or a NANOCERAMIC Electro Chemical Oxidation (ECO) process to form an electrically insulating oxide layer. The PEO process may comprise, for example, applying a voltage of approximately 300 V and using an alkaline solution at approximately 15 to 20° C. to form a layer of micro-crystalline aluminium oxide. The micro-crystalline aluminium oxide may have a thermal conductivity of approximately 1 to 2 W/mK, and a dielectric strength of approximately 10 to 30 KV/mm. The thickness of the surface treatment in the PEO process may be, for example, between 0.01 and 0.4 mm. The ECO process may comprise applying a voltage of approximately 400 V using controlled shape bipolar pulses, and a room temperature colloidal alkaline solution, to form a layer of nanocrystalline aluminium oxide. The layer of nanocrystalline aluminium oxide may have a thermal conductivity of approximately 7 W/mk and a dielectric strength of approximately 50 KV/mm. The thickness of the surface treatment in the ECO process may be, for example, between 0.005 and 0.3 mm. In a further alternative, a hard anodising technique could be used to form the electrically insulating layer. The hard anodising technique may comprise applying a relatively low voltage (e.g. below 300 V), and using a concentrated acidic electrolyte at approximately 0° C., to form Al Hydroxide Amorphous and Al Oxide in a column-like structure. The thickness of the surface treatment in the hard anodising process may be, for example, between 0.05 and 0.6 mm. Advantageously, the oxide layer formed in the hard anodising, PEO and ECO methods increases the electrical insulation between the heater element and the conductive part of the substrate, without compromising the thermal conductivity that is needed to transfer heat from the heater element to the substrate for heating the user's hair.
In the above-described examples the electrically insulating layers have been described as being formed, for example, of a silica (SiO2) based material. However, this need not necessarily be the case, and any other suitable material could be used to form the electrically insulating layers. For example, a polymer dielectric material (e.g. polyimide membrane or varnish) may be used, or a solvent-based silicone resin comprising inorganic fillers could be used.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2115266.5 | Oct 2021 | GB | national |
This application is a Continuation of PCT/GB2022/052597, filed Oct. 12, 2022, which claims benefit of Great Britain Application No. 2115266.5, filed Oct. 22, 2021, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/GB2022/052597 | Oct 2022 | WO |
| Child | 18641014 | US |
