Hair styling appliance

Abstract

A hair styling appliance for dual supply voltage operation is described comprising a body having at least one arm bearing a hair styling heater (560), wherein the hair styling heater comprises one or more heater electrodes (630,632,634,636) for heating the hair styling heater. A first power input is connectable to a battery power source (564) and a second power input is connectable to a mains powered source (561). The first power input and the second power input are each coupled to at least one of the one or more heater electrodes. Such a hair styling appliance is useable for styling when coupled to the mains powered source and when coupled to the battery power source increasing the versatility of the appliance.

Claims

1. A hair styling appliance comprising: a low voltage power supply to provide a voltage of less than 100V to power said hair styling heater; and a body having at least one arm bearing a hair styling heater, said hair styling heater comprising: a metal sheet or plate, an oxide layer comprising an oxide of said metal on a surface of said metal sheet or plate and a layer of plasma electrolytic oxide; and a heater electrode over said oxide layer, wherein said heater electrode of the heater is coupled to said low voltage power supply, wherein said heater electrode lies over glass which is at least partially merged into a surface of said oxide layer; and/or the appliance further comprises a planarization layer between said oxide layer and said heater electrode, and optionally said planarization layer comprises glass.

2. A hair styling appliance for dual supply voltage operation comprising: a body having at least one arm bearing a hair styling heater, a low voltage power supply to provide a voltage of less than 100V to power said hair styling heater, wherein said hair styling heater comprises: a metal sheet or plate, and an oxide layer comprising an oxide of said metal on a surface of said metal sheet or plate, two heater electrodes comprising a first low resistance electrode for said low voltage power supply and a second higher resistance electrode for mains voltage use, wherein said oxide layer comprises a layer of plasma electrolytic oxide.

3. A hair styling appliance configured for dual supply voltage operation and comprising: a body having at least one arm bearing a hear styling heater; a battery power supply to provide a DC voltage to power said hair styling heater; and an external power input connectable to a mains powered source to power said hair styling heater, wherein said hair styling heater comprises: a metal sheet or plate, an oxide layer comprising an oxide of said metal on a surface of said metal sheet or plate, said oxide layer comprising a layer of plasma electrolytic oxide, and at least two heater electrodes over said oxide layer, wherein one of said two heater electrodes is coupled to said DC battery power supply and the other of said two heater electrodes is coupled to said external power input.

4. The hair styling appliance as claimed in claim 3, wherein said heater electrode comprises a conductive ink electrode; and/or said conductive ink electrode is an inorganic conductive ink electrode.

5. The hair styling appliance as claimed in claim 3, further comprising at least one temperature sensor on said oxide layer, and wherein optionally said temperature sensor comprises a printed thermistor.

6. The hair styling appliance as claimed in claim 3, wherein said metal sheet or plate comprises a plurality of laterally-spaced zones, each with a respective said heater electrode.

7. The hair styling appliance as claimed in claim 3, further comprising: a circuit configured to sense a temperature of said metal sheet or plate from a resistance of said electrode; and/or a hardware electronic shutdown system connected to said electrode in parallel with said low voltage power supply; and/or a guard transistor connected between said low voltage power supply and said heater electrode and a hardware electronic shutdown system coupled to a heater sensor to control said guard transistor; and/or wherein a portion of a track of said heater electrode has a neck to provide an integral fuse.

8. The hair styling appliance as claimed in claim 3, wherein said one of said two heater electrodes coupled to said DC battery power supply has a resistance less than the other of said two heater electrodes coupled to said external power input.

9. The hair styling appliance as claimed in claim 3, further comprising said mains powered source, wherein said mains powered source is configured to convert an AC input to a DC voltage for powering said hair styling heater via said external power input, and said DC voltage from said mains powered source is greater than a voltage provided from said battery power supply.

10. The hair styling appliance as claimed in claim 6, wherein each of said laterally-spaced zones has a respective temperature sensor.

11. The hair styling appliance as claimed in claim 3, wherein said metal sheet or plate has a tubular configuration, with said oxide layer and heater electrode on an interior surface of the tubular configuration.

12. The hair styling appliance as claimed in claim 3, wherein a thickness of said oxide layer is less than 200 μm and above 0 μm.

13. The hair styling appliance as claimed in claim 12, wherein said thickness of said oxide layer is less than 50 μm and above 0 μm.

14. The hair styling appliance as claimed in claim 13, wherein said thickness of said oxide layer is in the range from 5 μm to 15 μm.

15. The hair styling appliance as claimed in claim 3, wherein a thickness of said heater electrode is less than 200 μm and above 0 μm.

16. The hair styling appliance as claimed in claim 15, wherein said thickness of said heater electrode is less than 50 μm and above 0 μm.

17. The hair styling appliance as claimed in claim 16, wherein said thickness of said heater electrode is in the range from 2 μm to 20 μm.

18. The hair styling appliance as claimed in claim 3, wherein said battery power supply comprises a lithium ion battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:

(2) FIG. 1 shows a first example of a hair straightener in a context of which embodiments of the invention may be employed;

(3) FIG. 2 shows an example of a crimping iron in a context of which embodiments of the invention may be employed;

(4) FIGS. 3a and 3b show, respectfully, cross-sectional views of embodiments of a heater for a hair straightener and a hair curler according to the invention;

(5) FIG. 4 shows a plan view of an embodiment of a hair styling heater according to an aspect of the invention;

(6) FIG. 5 shows a schematic block diagram of a hair styling appliance incorporating a hair styling heater of the type illustrated in FIGS. 3 and 4;

(7) FIG. 6 shows a further schematic block diagram of a hair styling appliance incorporating a different power supply arrangement to that of FIG. 5;

(8) FIG. 7 shows one embodiment of the hair styling appliance capable of being powered by a mains powered source and battery power, with multiple heater electrodes and zones;

(9) FIG. 8 shows a further embodiment to that of FIG. 7 with a different arrangement of heater electrodes and zones;

(10) FIG. 9 shows a further embodiment of the hair styling appliance to that of FIGS. 7 and 8;

(11) FIG. 10 shows a further embodiment to that of FIGS. 7 to 9 using an external battery pack;

(12) FIG. 11 shows a plan view of an alternative embodiment of the hair styling heater of FIG. 4;

(13) FIG. 12 shows an example circuit for powering the dual drive heater at FIG. 7;

(14) FIGS. 13a and 13b show, respectfully, cross-sectional views of embodiments of a heater for a hair straightener and a hair curler according to the invention; and

(15) FIG. 14 shows a plan view of an alternative embodiment of the hair styling heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(16) Referring to FIG. 3a, this shows a hair styling heater 300 comprising an aluminium heater plate 310 of thickness of order 1 mm, bearing a plasma electrolytic oxide (PEO) coating of aluminium oxide 320 of thickness less than 100 μm, for example in the range 5-15 μm.

(17) In a suitable plasma electrolytic oxidation process the aluminium plate 310 is connected to a high voltage (in embodiments≥than 1 KV or ≥10 KV, for example approximately 25 KV) and immersed in a bath of electrolyte to grow an outside coating which is macroscopically smooth but microscopically rough. A suitable process is available from Keronite International Limited, Cambridge, UK.

(18) Although shown on just one surface of the heater, in embodiments the PEO coating is provided on both surfaces of the heater plate and, on the surface facing the hair (the lower surface in FIG. 3a) coloured with a lower silicon dioxide or similar material. In embodiments the coating comprises CeraSOL™) centrifuged with 6% silicone oil and provided to a spray head to coat the PEO, afterwards being baked hard. The inclusion of silicone oil helps to reduce friction with the hair.

(19) The various interstices, cracks and defects of the PEO layer at the microscopic level help to key in an electrode layer which is deposited on top of PEO layer 320. However alternatively, but less preferably, a polyamide planarisation layer is provided over layer 320 prior to applying the electrode.

(20) Preferably conductive ink is screen printed onto the surface of PEO layer 320 in a desired electrode pattern 330. A preferred conductive ink is an inorganic ink comprising a dispersion of conducting, metallic for example silver, particles of sizes 100 μm down to 1 μm or less in combination with a glass or ceramic powder or frit, and a binder (which is typically organic). A curing process far such an ink might have 3 temperature stages, a thermostat, for example around 100° C. to drive off the solvent/binder a second at perhaps 350° C., and a third at, perhaps of order 500° C. (or more) for one to a few minutes. This latter stage softens the glass frit which it is believed settles into the cracks and other defects in the PEO layer, binding the printed electrodes to this layer. For a thin PEO layer the resistance to the layer may be of order of 10 s of kilohms and this layer can provide sufficient dielectric strength of voltages of less than 100v.

(21) A heater construction of this type has been found to be exceptionally durable and the heater may be bent in to a desired shape after printing (and clearing) of the ink: although the electrode resistance can change during such a process, it changes in a predictable manner. Thus this enables, for example, a ‘make, print, bend’ manufacturing process for a curved heater plate for a hair curler (FIG. 3b). The resistance to delamination is enhanced by using a relatively thin electrode layer, for example less than 100 μm, 50 μm or 20 μm.

(22) The heater may be provided with a thermistor 340 for temperature sensing. This may be a separate component but, preferably, the thermistor is a printed device, for example printed from carbon ink which has a relatively high change in resistance with temperature, then optionally laser trimmed to a desired resistance value. This provides a heater assembly which is integrally formed as a single unit, having many advantages in terms of cost, ease of manufacture and performance.

(23) Depending upon the thickness of heater plate 310, lateral conductivity within the plate may not be sufficient to reduce local cooling by hair to a desirable level. Thus in embodiments, as illustrated in FIG. 4, the heater plate 300 may be provided with a plurality of separately controllable heating zones 300a, b, each with a respective electrode 330a, b and thermistor 340a, b. Connections to these are brought out, for convenience, to one edge of the heater plate; a broadened track region 332 is provided for the electrode further from the connection point to reduce heating in the connection path. Each of the electrodes is provided with a separate control loop controlled by the temperature sensed by the respective thermistor. In embodiments more than 3 zones may be provided.

(24) FIG. 5 shows a block diagram of a power/control system 500 for a hair styling appliance incorporating heater 300. The system comprises a low voltage power supply 504 deriving power from a 12v lithium ion battery 505 and/or a mains power supply input 502, which is used to charge the battery 505. Power supply 504 may be configured to provide approximately 100 watts per heater; the heater resistance when hot may be selected accordingly—for example at 12v a current in the range 5-10 amps may be delivered to a heater with a resistance in the range 1-2 ohms. The resistance may be scaled accordingly as the design voltage increases or decreases (changing as the inverse square of the voltage).

(25) Power from power supply 504 is provided to a power control module 514, which in turn powers the one or more heaters 516. Power control module 514 may employ one or more power semiconductor switching devices to provide pulse with modulation control of the (DC) voltage from power supply 504 to heaters 516. Thus a high percentage on-time duty cycle may be employed during the initial, heating phase and afterwards the on-time duty cycle may be reduced and controlled to control the temperature(s) of the heaters 516.

(26) Power from power supply 504 is also provided to a microcontroller 506 coupled to non-volatile memory 508 storing processor control code for a temperature control algorithm, and to RAM 510. 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 appliance, for example to use the operation of the apparatus to improve the temperature control. An optional user interface 512 is also coupled to microcontroller 506, 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 heating plate has reached an operating temperature, for example in a region 140° C.-185° C.

(27) Microcontroller 506 is also coupled to one or more optional temperature sensors such as thermistors 340. However, as previously mentioned, the temperature of a heating element may be sensed from its resistance and thus embodiments of the system include a current sense input to microcontroller 506 sensing the current provided to a heater, for example via a current-sense resistor connected in series with the electrode. A predetermined calibration of resistance against temperature for an electrode may be stored in non-volatile memory 504 and in this way the printed track may be employed as a temperature sensor.

(28) FIG. 6 shows a variant of the power/control system 500 described and shown with reference to FIG. 5. In the embodiment in FIG. 6, an external AC to DC power supply adapter is used instead to provide a mains powered source.

(29) As previously mentioned a heater may incorporate a thermal fuse, for example a bimetallic strip or similar on the rear of the heater, to automatically disconnect a power supply to an electrode if the heater temperature increases above a threshold for greater than a permitted duration. Additionally or alternatively, however, the system incorporates one or more safety shut down circuits 520 coupled to the one or more heater electrodes and/or temperature sensors 340 to monitor the heater temperature and electronically shut down the power supply to the heater should overheating be detected. Overheating may comprise exceeding a threshold temperature or exceeding a threshold temperature for greater than a permitted duration or some more complex function such as integral of temperature over time. Preferably the safety shut down circuit is implemented in hardware rather than in software on the microcontroller, to reduce possible failure modes. In embodiments safety shut down circuit 520 controls a guard transistor 522, as illustrated a power MOSFET, which removes power from the power control block on detection of a potential fault. Guards transistor 522 may be provided either before or after power control block 514. In normal operation this device is always on; the device may be selected such that when power is removed from the transistor it switches off, thus failing safe, for example by employing an enhancement—mode device. Such control and safety shut down is applicable to all the embodiments described herein.

(30) In embodiments low voltage power supply 504 may support both 110v and 230v mains input and may be a switch mode power supply. As described with reference to FIG. 6, other embodiments may use an external power supply which may itself support 110V or 230V mains input. This external power supply may be used to provide galvanic isolation, step down the AC voltage and/or provide a DC voltage, such as 24V to the hair styling appliance.

(31) In variants of the above described appliances the heater may be configured for both low voltage and mains voltage operation, by increasing the thickness of the oxide layer. The option of a mains powered heater can provide some advantages for the user even if reducing some of the benefits of the low voltage heater construction. In another variant rather than employing the electrode itself for temperature sensing, a separate electrode track or spur from an electrode may be employed for this purpose, thus using the printed ink as the temperature sensing element.

(32) FIGS. 7 to 10 show alternative embodiments of the hair styling appliance with varying power supply, heater electrode and zone configurations. These variants may also be applied the heater embodiments shown in the previously described embodiments. Such features may include, but are not limited to, use of a metal sheet or plate, an oxide layer, the use of conductive ink electrodes.

(33) Generally speaking, the different embodiments 560, 570, 580, 590 each have an external power supply 561, 571, 581, 591 respectively to deliver 24V DC (for example) to the hair styling apparatus. The embodiments may also use differing numbers of cells in the battery packs. Selecting the number of cells to use is a trade-off between the weight and size of the styling appliance and the styling performance and battery life.

(34) In the embodiments shown in FIGS. 7 to 10 the charge control 1 power path block 562, 572, 582, 592 controls delivery of power from the battery and external supply, and charging of the battery 564, 574, 584, 594. System control block 563, 673, 583, 593 generally includes many of the blocks of FIG. 5 or 6 such as power control and the processor electrodes including microcontroller and memory.

(35) Referring to FIG. 7, this embodiment shows a variant of the hair styling apparatus in a ‘dual drive’ configuration, further details of which are shown in FIG. 12. In this embodiment each heater has two electrodes 630, 634, and 632, 636. Electrode one 630 is powered by the battery pack 564 and electrode two 634 by external 24V supply 561. In this configuration, a two or three cell battery pack is used, using cells with a nominal voltage of, for example, 3.7V, supplying a total voltage of between 7.4V and 11.1V. Lithium Ion or Lithium Polymer batteries are particularly useful due to their high power density.

(36) Such a battery pack may be removeable or not removeable. In this embodiment and by way of example only, the battery pack may not be removable reducing design constraints and allowing a more compact and/or aesthetically pleasing design to be used.

(37) Heater one and two in FIG. 7 refer to two different thermally regulated zones and may be two different zones on the same heater plate as shown in FIG. 11, or two different heater plates, one on each arm of a styling appliance. FIG. 11 adapts the heater plate of FIG. 4 to include two further heater electrodes. Heater electrodes 630 and 634 provide a first heating zone with thermal sensing provided by thermistor 64a. In this first heating zone, heater electrode 630 is powered by the battery pack 564 of FIG. 7 and heater electrode 634 is powered by the external supply 561. Heater electrodes 632 and 636 provide a second heating zone with thermal sensing provided by thermistor 640b. In this second heating zone, heater electrode 632 is powered by battery pack 564 of FIG. 7 and heater electrode 646 is powered by the external supply 561. It will be appreciated that the arrangement of FIGS. 7 and 11 may be readily adapted to provide a styling apparatus with more than two thermally regulated zones, for example with dual zones on each heating plate.

(38) Further details of the heater electrode are shown in FIG. 12. In this arrangement, the heater plate 700 includes two heater electrodes formed by resistive electrodes R1 (730) and R2 (734). R1 provides heater electrode one 630 of the dual drive arrangement and is powered by the battery source. R2 provides heater electrode two 634 of the dual drive arrangement and is powered by the external power supply. As previously explained with reference to FIG. 5, the electrode resistances R1 and R2 may be scaled accordingly as the design voltage increases or decreases (changing as the inverse square of the voltage). In FIG. 12, one or both of the heater electrodes may be enabled and shutdown by a control/safety shutdown circuits 763, 765.

(39) Returning now to FIG. 7, in a first mode of operation, the styling appliance may operate on battery power only, being powered by the battery pack 564. When running from battery power, system control block 563 enables electrode one (630, 632, 730) to be powered on each heater. In the example in FIG. 12, the battery power source is a 3-cell battery pack providing 11.1V (each cell provides 3.7V) and resistive electrode R1 is 2.25 Ohms yielding a power dissipation of around 50W. It will be appreciated that these values are approximate and other values are possible.

(40) In a second mode of operation, the styling appliance is powered by external power supply 561. In this mode, system control block 563 enables electrode two (634, 636, 734) to be driven on each heater. The battery pack 564 may also charged. It will be appreciated however that in variants the battery may only be charged when no electrodes are being heated. In the example in FIG. 12, a mains AC to DC power supply delivers 24V DC to the hair styling apparatus and resistive electrode R2 is 11.65 Ohms yielding a power dissipation of around 50W. It will be appreciated that these values are approximate and other values are possible.

(41) From the above it will be appreciated that in this embodiment the electrode resistances are set such that the power output from each electrode is generally similar given a similar heating effect from either power source. Each different heater electrode may have a resistance matched to the supply voltage such that the electrical power dissipated is in the range 50-200 watts. Matching the power outputs of each electrode is however non-essential, and an appliance may be implemented to provide a lower power output from battery, or a higher power output when mains powered. It will be appreciated however that providing a generally similar power output from both power sources provides the user with a consistent styling experience whether running from batter or mains power.

(42) In a third mode of operation, the styling appliance is again connected to external power supply 561, but both heater electrodes may be turned on simultaneously. This ‘dual drive’ mode boosts the power available and improves the heating of the heater plate the electrode is mounted on. This is particularly useful for reducing the time to heat up the heater plate from cold and may also be useful to provide a ‘power boost’ to increase the plate temperature if a section of hair is proving particularly challenging to straighten. In some embodiments this power boost may be limited to a short duration of time or be dependent on the charge level in the battery pack. Such dual drive and power/heating boost may be controlled by the system control and charge control blocks.

(43) FIG. 8 shows a further embodiment to that of FIG. 7 with a different arrangement of heater electrodes and zones. In this configuration the battery pack 574 is increased to include four cells providing more energy and a higher supply voltage. In this variant a single heater electrode 630, 632 is provided for each heater/thermal zone. In a first mode of operation, the styling appliance may operate on battery power only, being powered by the battery pack 574. In a second mode of operation, the styling appliance operates on the external power supply 571. In this second mode the battery pack may also be charged, either simultaneously with powering the heater electrode or separately, when no power is delivered to the heater electrode. In both modes, the same heater electrode is powered.

(44) FIG. 9 shows a further embodiment of the hair styling appliance to that of FIGS. 7 and 8. In this variant, termed “charge through” a single heater electrode 630, 632 is provided for each heater/thermal zone as used in FIG. 8. In this variant, the heater electrode is powered only from the battery pack 584 and the external power supply used to charge the battery pack only. This means that the external power supply is indirectly coupled to the heater electrodes via the battery pack. The charge control block 582 may allow the battery back to be charged during styling to allow for extended use of the styling appliance.

(45) FIG. 10 shows a further embodiment to that of FIGS. 7 to 9 using an external/removeable battery pack in addition to operating from an external power supply. In this variant the battery pack is provided as a removeable module 594. The battery pack may be an interchangeable unit that can slot in or clip onto the styling appliance, allowing a user to carry spares. Using a removeable battery pack may further allow for different capacity modules to be used, depending on the user's preference for portability versus available styling time.

(46) In the variant of FIG. 10, three modes of operation are again possible as described with reference to FIG. 7.

(47) Referring now to FIG. 11, this shows an example of a heater plate with two heating zones 600a and 600b, and dual drive electrodes for each heating zone. In the first zone 600a, heater electrodes 630 and 634 provide a battery driven heater electrode and external power supply driven electrode respectively. In the second zone 600b heater electrodes 632 and 636 provide a further battery driven heater electrode and external power supply driven electrode respectively. Thus, in a variant of the embodiment illustrated in FIG. 4, a heater plate may be provided with a plurality of separately controllable heating zones. Connections to these heating zones are also brought out, for convenience, to one edge of the heater plate. As with FIG. 4 a broadened track region 638, 640 may be provided for the electrode further from the connection point to reduce heating in the connection path. In variants that do not provide multiple heating zones such broadening may not be necessary.

(48) Referring now to FIGS. 13a and 13b, these show a hair styling heater 600a and 600b comprising an aluminium heater plate 610 of thickness of the order 1 mm, bearing a plasma electrolytic oxide (PEO) coating of aluminium oxide 620a, 621a, 620b and 621b. The thickness of each oxide layer may be less than 100 μm, for example in the range 5-15 μm. Further details of plasma electrolytic oxidation process are set out with reference to FIG. 3a.

(49) In the embodiment in FIG. 13a, two electrodes 630 and 634 are separated from the metal plate by oxide regions 620a, 621a. Electrode 630 is powered by the battery supply and electrode 634 by the mains powered source and at a higher voltage. Both regions of oxide 620a, 621a have the same thickness meaning that only a single uniform oxide layer can be used. This simplifies the manufacturing process. It will be appreciated that the lower voltage provided by the battery supply means that the oxide region 620a under electrode 630 may be thinner that that actually used as shown in FIG. 13b.

(50) In the embodiment in FIG. 13b, the oxide thickness 620b of the lower voltage electrode is less the oxide layer 621b under the electrode powered by an external mains powered source.

(51) FIG. 14 shows a variant of the heater of FIG. 11 and a further electrode arrangement for powering from both a battery source and mains powered external source. In this arrangement, electrode 660 is tapped off at point 662 to form a lower resistance electrode by only using a portion of the full electrode length. In this way, the battery power source then only powers this portion of the electrode 660. When a higher resistance is needed, the full electrode length may be used. This may be useful when a dual drive arrangement is not required and may mean that the layout of electrodes on the heater can be simplified. Selection of a particular resistance/length of electrode may be dependent on which power source is connected and may be controlled by the controller.

(52) Many forms of hair styling heater include a ceramic substrate thermally coupled to a heater plate (such as the aluminium heater plate). To form an aluminium heater, unbaked (‘green’) ceramic, such as aluminium oxide, may be shaped and then placed on the aluminium heater plate/aluminium substrate and baked (typically at up to 600 degrees C.). By baking the green ceramic on the aluminium plate a molecular bond is formed, providing a thermally and mechanically strong bond. Such a process may be used to form conventional flat hair styling heaters or other shapes, such as curved, cylindrical heaters and the like.

(53) The skilled person will appreciate that the techniques we have described above may be employed for a range of hair styling appliances including, but not limited to, a hair straightener, a hair crimping device, and a hair curler. The skilled person would also appreciate that features from many of the embodiments are interchangeable and not limited to the specific embodiment they are described in relation to.

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