Patent Description:
Many conventional hair irons, such as flat irons, straightening irons, curling irons, crimping irons, etc., suffer from heat lag, which results in an inconvenient amount of time to heat the hair iron for use and to cool the hair iron after use. Prior to use, a user must wait for the device to heat to an effective temperature. After use, the user may need to wait for the device to cool to a safe temperature before storing the device. Because of the relatively long warmup and cooldown times, users often set hair irons on a countertop or the like during heating and cooling. This creates a safety risk to the user and to others, especially children, who may accidentally contact a hot device or who may not recognize that the device is powered on or not yet cooled. Additional safety risks arise when a hair iron is accidentally left powered on.

Prior art hair irons are divided into two main classes: wire heaters and ceramic heaters. Both classes of hair irons generate heat by passing an electrical current through a resistive element (either a wire resistor or a resistor positioned between layers of a ceramic substrate). Both classes of hair irons include, by necessity, substantial thermal mass leading to long warmup and cooldown times. For example, some wire heaters include nichrome wire potted with ceramic cement (for electrical insulation) and placed within cast aluminum. Other wire heaters include nichrome wire wound with an electrically insulative material that surrounds the inside and outside of the winding, and the insulated winding positioned within a steel or aluminum tube (or other formed metal piece), which forms the contact surface that contacts the user's hair during use. Both of these types of wire heater assemblies suffer from long warmup and cooldown times due to high thermal mass provided by the electrical insulation materials and the relatively large metal components.

Conventional ceramic heaters typically include electrically resistive and conductive traces printed on a "green state" (unfired) ceramic substrate. After printing, multiple sheets of the substrate are brought together with the printed resistive and conductive traces positioned internally (i.e., between ceramic substrate layers), and the combined materials are fired to form the ceramic heater. The ceramic substrate shrinks significantly during firing (as much as <NUM>-<NUM>%) resulting in a non-uniform pattern of resistive and conductive traces. The ceramic heater is then fitted with one or more coated pieces of metal, which form the contact surface that contacts the user's hair during use. The ceramic substrate surrounding the resistive and conductive traces and the additional metal piece combine to provide relatively high thermal mass and, as a result, long warmup and cooldown times.

Accordingly, a hair iron having a heater with improved thermal efficiency is desired.

Examples of known hair irons can be found in <CIT> or in <CIT>.

A hair iron according to the present invention comprises a first arm and a second arm movable relative to each other between an open position and a closed position. A distal segment of the first arm is spaced from a distal segment of the second arm in the open position. The distal segment of the first arm is positioned in close proximity to the distal segment of the second arm in the closed position. A contact surface is positioned on an exterior of the distal segment of the first arm for contacting hair during use. The first arm includes a heater having a ceramic substrate and an electrically resistive trace on an exterior face of the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to the contact surface. The hair iron further comprises a sleeve covering an outer face of the heater that faces toward the second arm in the closed position. A portion of the sleeve forms the contact surface. The sleeve is composed of a thin film of thermally conductive and electrically insulative material or the sleeve is composed of at least one of a filled or unfilled polyimide. In some embodiments, the electrically resistive trace includes the electrical resistor material thick film printed on the exterior face of the ceramic substrate after firing of the ceramic substrate.

In some embodiments, the electrically resistive trace is positioned on an inner face of the ceramic substrate that faces away from the second arm in the closed position.

Embodiments include those wherein the heater includes one or more glass layers on the exterior face of the ceramic substrate that cover the electrically resistive trace for electrically insulating the electrically resistive trace.

Embodiments include those wherein the heater includes a thermistor that is positioned on the ceramic substrate and in electrical communication with control circuitry of the heater for providing feedback regarding the temperature of the heater to the control circuitry of the heater. In some embodiments, the thermistor is positioned on an inner face of the ceramic substrate that faces away from the second arm in the closed position.

Embodiments include those wherein the heater is mounted to a heater housing that is positioned on the arm. The heater housing is composed of a plastic material having a maximum service temperature of at least <NUM> degrees Celsius.

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present disclosure and together with the description serve to explain the principles of the present disclosure.

In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present invention as long as these changes fall within the scope of protection defined by the appended claims. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present invention is defined only by the appended claims.

Referring now to the drawings and particularly to <FIG> and <FIG>, a hair iron <NUM> is shown according to one example embodiment. Hair iron <NUM> may include an appliance such as a flat iron, straightening iron, curling iron, crimping iron, or other similar device that applies heat and pressure to a user's hair in order to change the structure or appearance of the user's hair. Hair iron <NUM> includes a housing <NUM> that forms the overall support structure of hair iron <NUM>. Housing <NUM> may be composed of, for example, a plastic that is thermally insulative and electrically insulative and that possesses relatively high heat resistivity and dimensional stability and low thermal mass. Example plastics include polybutylene terephthalate (PBT) plastics, polycarbonate/acrylonitrile butadiene styrene (PC/ABS) plastics, polyethylene terephthalate (PET) plastics, including glass-filled versions of each. In addition to forming the overall support structure of hair iron <NUM>, housing <NUM> also provides electrical insulation and thermal insulation in order to provide a safe surface for the user to contact and hold during operation of hair iron <NUM>.

Hair iron <NUM> includes a pair of arms <NUM>, <NUM> that are movable between an open position shown in <FIG> where distal segments <NUM>, <NUM> of arms <NUM>, <NUM> are spaced apart from each other and a closed position shown in <FIG> where distal segments <NUM>, <NUM> of arms <NUM>, <NUM> are in contact, or close proximity (e.g., within a few millimeters or less, including in contact), with each other. For example, in the embodiment illustrated, arms <NUM>, <NUM> are pivotable relative to each other about a pivot axis <NUM> between the open position and the closed position. Hair iron <NUM> may include a bias member (not shown), such as one or more springs, that biases one or both of arms <NUM>, <NUM> toward the open position such that user actuation is required to overcome the bias applied to arms <NUM>, <NUM> to bring arms <NUM>, <NUM> together to the closed position.

Hair iron <NUM> includes a heater positioned on an inner side <NUM>, <NUM> of one or both of arms <NUM>, <NUM>. Inner sides <NUM>, <NUM> of arms <NUM>, <NUM> include the portions of arms <NUM>, <NUM> that face each other when arms <NUM>. <NUM> are in the closed position shown in <FIG>. In the example embodiment illustrated, each arm <NUM>, <NUM> includes a respective heater <NUM>, <NUM> positioned on or within the arm <NUM>, <NUM>. Heaters <NUM>, <NUM> supply heat to respective contact surfaces <NUM>, <NUM> on arms <NUM>, <NUM>. Each contact surface <NUM>, <NUM> is positioned on inner side <NUM>, <NUM> of distal segment <NUM>, <NUM> of the corresponding arm <NUM>, <NUM>. Contact surfaces <NUM>, <NUM> are positioned to directly contact and transfer heat to a user's hair upon the user positioning a portion of his or her hair between arms <NUM>, <NUM> and positioning arms <NUM>, <NUM> in the closed position. Contact surfaces <NUM>, <NUM> are positioned to mate against one another in a relatively flat orientation when arms <NUM>, <NUM> are in the closed position in order to maximize the surface area available for contacting the user's hair.

Hair iron <NUM> includes control circuitry <NUM> configured to control the temperature of each heater <NUM>, <NUM> by selectively opening or closing a circuit supplying electrical current to resistors of each heater <NUM>, <NUM> (shown schematically in <FIG>). Where hair iron <NUM> includes two heaters <NUM>. <NUM>, control circuitry <NUM> may be configured to control each heater <NUM>, <NUM> independently or to control both heaters <NUM>, <NUM> jointly. Open loop or, preferably, closed loop control may be utilized as desired. Control circuitry <NUM> may include a microprocessor, a microcontroller, an application-specific integrated circuit, and/or other form of integrated circuit. In the embodiment illustrated, hair iron <NUM> includes a power cord <NUM> for connecting hair iron <NUM> to an external voltage source <NUM>. In other embodiments, hair iron <NUM> may include an internal battery as desired.

<FIG> shows an example heater assembly <NUM> that includes heater <NUM> and a sleeve <NUM> for use on arm <NUM>. A substantially identical heater assembly including heater <NUM> and corresponding sleeve may be used on arm <NUM>. Heater assembly <NUM> includes heater <NUM>. sleeve <NUM> and a heater housing <NUM>. Heater <NUM> is mounted to heater housing <NUM> with heater housing <NUM> physically supporting heater <NUM>. Heater housing <NUM> is, in turn, mounted to a portion of housing <NUM> within arm <NUM>. In the embodiment illustrated, heater housing <NUM> includes a first housing portion 142a and a second housing portion 142b. Heater <NUM> is mounted to first housing portion 142a. Fasteners (not shown), such as screws, mount second housing portion 142b to first housing portion 142a and to housing <NUM>. Heater housing <NUM> may be composed of for example, a plastic that is thermally insulative and electrically insulative and that possesses relatively high heat resistivity and dimensional stability and low thermal mass. Due to the proximity to heater <NUM>, heater housing <NUM> is preferably composed of a plastic capable of resisting thermal degradation and maintaining sufficient strength and stiffness at high temperatures, including plastics having a maximum service temperature of <NUM> degrees Celsius or more. Example plastics include liquid crystal polymer (LCP) plastics, polyether ether ketone (PEEK) plastics and polyphenylene sulfide (PPS) plastics, including glass-filled versions of each.

Heater <NUM> includes an outer face <NUM> that is exposed from and faces away from heater housing <NUM> as shown in <FIG>. Heater <NUM> includes an inner face <NUM> that is positioned proximate to an interior portion of heater housing <NUM>, for example, between first housing portion 142a and second housing portion 142b as shown in <FIG>. When arms <NUM>. <NUM> are in the closed position, outer face <NUM> faces toward opposite arm <NUM> and inner face <NUM> faces away from opposite arm <NUM>. As shown in <FIG>, sleeve <NUM> is positioned against outer face <NUM> of heater <NUM> and forms contact surface <NUM>. In the embodiment illustrated, sleeve <NUM> wraps around heater housing <NUM> and covers outer face <NUM> of heater <NUM>. Sleeve <NUM> is positioned in contact with, or in close proximity to, outer face <NUM> of heater <NUM> in order to transfer heat from outer face <NUM> of heater <NUM> to the user's hair during use. Sleeve <NUM> is composed of a thin film (e.g., less than <NUM> thick) material. In one embodiment, sleeve <NUM> is composed of a thermally conductive and electrically insulative material, such as boron nitride filled polyimide. The thermal conductivity and relative thinness of sleeve <NUM> result in a relatively low thermal mass, which reduces the amount of time required to heat and cool sleeve <NUM>. In other embodiments, e.g., where decreased thermal conductivity is acceptable, sleeve <NUM> may be composed of unfilled polyimide. In other embodiments, e.g., where electrical conductivity is acceptable, sleeve <NUM> may be composed of graphite filled polyimide. Sleeve <NUM> aids in protecting heater <NUM> from damage and also provides a relatively low friction contact surface <NUM> during use.

<FIG> show heater <NUM> removed from heater housing <NUM>. <FIG> shows inner face <NUM> of heater <NUM>, and <FIG> shows outer face <NUM> of heater <NUM>. Heater <NUM> may be substantially identical to heater <NUM>. In the embodiment illustrated, outer face <NUM> and inner face <NUM> are bordered by four sides or edges <NUM>, <NUM>, <NUM>, <NUM> each having a smaller surface area than outer face <NUM> and inner face <NUM>. In this embodiment, heater <NUM> includes a longitudinal dimension <NUM> that extends from edge <NUM> to edge <NUM> and a lateral dimension <NUM> that extends from edge <NUM> to edge <NUM>. Heater <NUM> also includes an overall thickness <NUM> (<FIG>) measured from outer face <NUM> to inner face <NUM>.

Heater <NUM> includes one or more layers of a ceramic substrate <NUM>, such as aluminum oxide (e.g., commercially available <NUM>% aluminum oxide ceramic). Where heater <NUM> includes a single layer of ceramic substrate <NUM>. a thickness of ceramic substrate <NUM> may range from, for example, <NUM> to <NUM>, such as <NUM>. Where heater <NUM> includes multiple layers of ceramic substrate <NUM>, each layer may have a thickness ranging from, for example, <NUM> to <NUM>, such as <NUM>. In some embodiments, a length of ceramic substrate along longitudinal dimension <NUM> may range from, for example, <NUM> to <NUM>. In some embodiments, a width of ceramic substrate <NUM> along lateral dimension <NUM> may range from, for example, <NUM> to <NUM>, such as <NUM> or <NUM>. Ceramic substrate <NUM> includes an outer face <NUM> that is oriented toward outer face <NUM> of heater <NUM> and an inner face <NUM> that is oriented toward inner face <NUM> of heater <NUM>. Outer face <NUM> and inner face <NUM> of ceramic substrate <NUM> are positioned on exterior portions of ceramic substrate <NUM> such that if more than one layer of ceramic substrate <NUM> is used, outer face <NUM> and inner face <NUM> are positioned on opposed external faces of the ceramic substrate <NUM> rather than on interior or intermediate layers of ceramic substrate <NUM>.

In the example embodiment illustrated, outer face <NUM> of heater <NUM> is formed by outer face <NUM> of ceramic substrate <NUM> as shown in <FIG>. In this embodiment, inner face <NUM> of ceramic substrate <NUM> includes a series of one or more electrically resistive traces <NUM> and electrically conductive traces <NUM> positioned thereon. Resistive traces <NUM> include a suitable electrical resistor material such as, for example, silver palladium (e.g., blended <NUM>/<NUM> silver palladium). Conductive traces <NUM> include a suitable electrical conductor material such as, for example, silver platinum. In the embodiment illustrated, resistive traces <NUM> and conductive traces <NUM> are applied to ceramic substrate <NUM> by way of thick film printing. For example, resistive traces <NUM> may include a resistor paste having a thickness of <NUM>-<NUM> microns when applied to ceramic substrate <NUM>. and conductive traces <NUM> may include a conductor paste having a thickness of <NUM>-<NUM> microns when applied to ceramic substrate <NUM>. Resistive traces <NUM> form the heating element of heater <NUM> and conductive traces <NUM> provide electrical connections to and between resistive traces <NUM> in order to supply an electrical current to each resistive trace <NUM> to generate heat.

In the example embodiment illustrated, heater <NUM> includes a pair of resistive traces 164a, 164b that extend substantially parallel to each other (and substantially parallel to edges <NUM>, <NUM>) along longitudinal dimension <NUM> of heater <NUM>. Heater <NUM> also includes a pair of conductive traces 166a, 166b that each form a respective terminal 168a, 168b of heater <NUM>. Cables or wires 170a, 170b are connected to terminals 168a, 168b in order to electrically connect resistive traces <NUM> and conductive traces <NUM> to, for example, control circuitry <NUM> and voltage source <NUM> in order to selectively close the circuit formed by resistive traces <NUM> and conductive traces <NUM> to generate heat. Conductive trace 166a directly contacts resistive trace 164a, and conductive trace 166b directly contacts resistive trace 164b. Conductive traces 166a, 166b are both positioned adjacent to edge <NUM> in the example embodiment illustrated, but conductive traces 166a, 166b may be positioned in other suitable locations on ceramic substrate <NUM> as desired. In this embodiment, heater <NUM> includes a third conductive trace 166c that electrically connects resistive trace 164a to resistive trace 164b. Portions of resistive traces 164a, 164b obscured beneath conductive traces 166a, 166b, 166c in <FIG> are shown in dotted line. In this embodiment, current input to heater <NUM> at, for example, terminal 168a by way of conductive trace 166a passes through, in order, resistive trace 164a, conductive trace 166c, resistive trace 164b, and conductive trace 164b where it is output from heater <NUM> at terminal 168b. Current input to heater <NUM> at terminal 168b travels in reverse along the same path.

In some embodiments, heater <NUM> includes a thermistor <NUM> positioned in close proximity to a surface of heater <NUM> in order to provide feedback regarding the temperature of heater <NUM> to control circuitry <NUM>. In some embodiments, thermistor <NUM> is positioned on inner face <NUM> of ceramic substrate <NUM>. In the example embodiment illustrated, thermistor <NUM> is welded directly to inner face <NUM> of ceramic substrate <NUM>. In this embodiment, heater <NUM> also includes a pair of conductive traces 174a. 174b that are each electrically connected to a respective terminal of thermistor <NUM> and that each form a respective terminal 176a, 176b. Cables or wires 178a, 178b are connected to terminals 176a, 176b in order to electrically connect thermistor <NUM> to, for example, control circuitry <NUM> in order to provide closed loop control of heater <NUM>. In the embodiment illustrated, thermistor <NUM> is positioned at a central location of inner face <NUM> of ceramic substrate <NUM>, between resistive traces 164a, 164b and midway from edge <NUM> to edge <NUM>. In this embodiment, conductive traces 174a, 174b are also positioned between resistive traces 164a. 164b with conductive trace 174a positioned toward edge <NUM> from thermistor <NUM> and conductive trace 174b positioned toward edge <NUM> from thermistor <NUM>. However, thermistor <NUM> and its corresponding conductive traces 174a, 174b may be positioned in other suitable locations on ceramic substrate <NUM> so long as they do not interfere with the positioning of resistive traces <NUM> and conductive traces <NUM>.

<FIG> is a cross-sectional view of heater <NUM> taken along line <NUM>-<NUM> in <FIG>. With reference to <FIG> and <FIG>, in the embodiment illustrated, heater <NUM> includes one or more layers of printed glass <NUM> on inner face <NUM> of ceramic substrate <NUM>. In the embodiment illustrated, glass <NUM> covers resistive traces 164a, 164b, conductive trace 166c, and portions of conductive traces 166a, 166b in order to electrically insulate such features to prevent electric shock or arcing. The borders of glass layer <NUM> are shown in dashed line in <FIG>. In this embodiment, glass <NUM> does not cover thermistor <NUM> or conductive traces 174a, 174b because the relatively low voltage applied to such features presents a lower risk of electric shock or arcing. An overall thickness of glass <NUM> may range from, for example, <NUM>-<NUM> microns. <FIG> shows glass <NUM> covering resistive traces 164a. 164b and adjacent portions of ceramic substrate <NUM> such that glass <NUM> forms the majority of inner face <NUM> of heater <NUM>. Outer face <NUM> of ceramic substrate <NUM> is shown forming outer face <NUM> of heater <NUM> as discussed above. Conductive trace 166c, which is obscured from view in <FIG> by portions of glass <NUM>, is shown in dotted line. <FIG> depicts a single layer of ceramic substrate <NUM>. However, ceramic substrate <NUM> may include multiple layers as depicted by dashed line <NUM> in <FIG>.

Heater <NUM> may be constructed by way of thick film printing. For example, in one embodiment, resistive traces <NUM> are printed on fired (not green state) ceramic substrate <NUM>, which includes selectively applying a paste containing resistor material to ceramic substrate <NUM> through a patterned mesh screen with a squeegee or the like. The printed resistor is then allowed to settle on ceramic substrate <NUM> at room temperature. The ceramic substrate <NUM> having the printed resistor is then heated at, for example, approximately <NUM>-<NUM> degrees Celsius for a total of approximately <NUM> minutes, including approximately <NUM>-<NUM> minutes at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to dry the resistor paste and to temporarily fix resistive traces <NUM> in position. The ceramic substrate <NUM> having temporary resistive traces <NUM> is then heated at, for example, approximately <NUM> degrees Celsius for a total of approximately one hour, including approximately <NUM> minutes at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to permanently fix resistive traces <NUM> in position. Conductive traces <NUM> and 174a, 174b are then printed on ceramic substrate <NUM>, which includes selectively applying a paste containing conductor material in the same manner as the resistor material. The ceramic substrate <NUM> having the printed resistor and conductor is then allowed to settle, dried and fired in the same manner as discussed above with respect to resistive traces <NUM> in order to permanently fix conductive traces <NUM> and 174a, 174b in position Glass layer(s) <NUM> are then printed in substantially the same manner as the resistors and conductors, including allowing the glass layer(s) <NUM> to settle as well as drying and firing the glass layer(s) <NUM>. In one embodiment, glass layer(s) <NUM> are fired at a peak temperature of approximately <NUM> degrees Celsius, slightly lower than the resistors and conductors. Thermistor <NUM> is then mounted to ceramic substrate <NUM> in a finishing operation with the terminals of thermistor <NUM> directly welded to conductive traces 174a, 174b.

Thick film printing resistive traces <NUM> and conductive traces <NUM> on fired ceramic substrate <NUM> provides more uniform resistive and conductive traces in comparison with conventional ceramic heaters, which include resistive and conductive traces printed on green state ceramic. The improved uniformity of resistive traces <NUM> and conductive traces <NUM> provides more uniform heating across contact surface <NUM> as well as more predictable heating of heater <NUM>.

Preferably, heaters <NUM> are produced in an array for cost efficiency. Heaters <NUM> are separated into individual heaters <NUM> after the construction of all heaters <NUM> is completed, including firing of all components and any applicable finishing operations. In some embodiments, individual heaters <NUM> are separated from the array by way of fiber laser scribing. Fiber laser scribing tends to provide a more uniform singulation surface having fewer microcracks along the separated edge in comparison with conventional carbon dioxide laser scribing.

While the example embodiment illustrated in <FIG> includes resistive traces <NUM> and thermistor <NUM> positioned on inner face <NUM> of ceramic substrate <NUM>. in other embodiments, resistive traces <NUM> and/or thermistor <NUM> may be positioned on outer face <NUM> of ceramic substrate <NUM> along with corresponding conductive traces as needed to establish electrical connections thereto. Glass <NUM> may cover the resistive traces and conductive traces on outer face <NUM> and/or inner face <NUM> of ceramic substrate <NUM> as desired in order to electrically insulate such features.

<FIG> and <FIG> show a heater assembly <NUM> suitable for use with hair iron <NUM> according to another example embodiment. With reference to <FIG>, heater assembly <NUM> includes a heater <NUM> mounted to a heater housing <NUM> similar to heater <NUM> and heater housing <NUM> discussed above. Heater <NUM> includes an outer face <NUM> that is exposed from and faces away from heater housing <NUM> and an inner face <NUM> that is positioned proximate to an interior portion of heater housing <NUM> as discussed above. Heater assembly <NUM> also includes a sleeve <NUM>, similar to sleeve <NUM> discussed above, that covers heater <NUM>.

Heater <NUM> includes one or more layers of ceramic substrate <NUM> as discussed above. Ceramic substrate <NUM> includes an outer face <NUM> that is oriented toward outer face <NUM> of heater <NUM> and an inner face <NUM> that is oriented toward inner face <NUM> of heater <NUM>. In contrast with the embodiment shown in <FIG>, in the example embodiment illustrated in <FIG> and <FIG>, electrically resistive traces <NUM> and electrically conductive traces <NUM> are positioned on outer face <NUM> of ceramic substrate <NUM>, rather than inner face <NUM>. Resistive traces <NUM> and conductive traces <NUM> may be applied by way of thick film printing as discussed above.

As shown in <FIG>, in the example embodiment illustrated, heater <NUM> includes a pair of resistive traces 1164a, 1164b on outer face <NUM> of a ceramic substrate <NUM>. Resistive traces 1164a, 1164b extend substantially parallel to each other along a longitudinal dimension <NUM> of heater <NUM>. Heater <NUM> also includes three conductive traces 1166a, 1166b, 1166c positioned on outer face <NUM> of ceramic substrate <NUM>. Conductive trace 1166a directly contacts resistive trace 1164a. and conductive trace 1166b directly contacts resistive trace 1164b. Conductive traces 1166a, 1166b are both positioned adjacent to a common edge of ceramic substrate <NUM><NUM> in the example embodiment illustrated. Conductive trace 1166c is positioned adjacent to an opposite edge of ceramic substrate <NUM> (relative to conductive traces 1166a, 1166b) and electrically connects resistive trace 1164a to resistive trace 1164b. Portions of resistive traces 1164a, 1164b obscured beneath conductive traces 1166a, 1166b, 1166c in <FIG> are shown in dotted line.

In the embodiment illustrated, heater <NUM> includes a pair of vias 1190a, 1190b that are formed as through-holes substantially filled with conductive material extending through ceramic substrate <NUM> from outer face <NUM> to inner face <NUM>. Vias 1190a, 1190b electrically connect conductive traces 1166a, 1166b to corresponding conductive traces on inner face <NUM> of ceramic substrate <NUM> as discussed below.

In the embodiment illustrated, heater <NUM> includes one or more layers of printed glass <NUM> on outer face <NUM> of ceramic substrate <NUM>. In the embodiment illustrated, glass <NUM> covers resistive traces 1164a. 1164b and conductive traces 1166a. 1116b, 1166c in order to electrically insulate these features. The borders of glass layer <NUM> are shown in dashed line in <FIG>.

<FIG> shows inner face <NUM> of heater <NUM> according to one example embodiment. In this embodiment, heater <NUM> includes a pair of conductive traces 1192a, 1192b positioned on inner face <NUM> of ceramic substrate <NUM> that that each form a respective terminal 1168a. 1168b of heater <NUM>. Each conductive trace 1192a, 1192b on inner face <NUM> of ceramic substrate <NUM> is electrically connected to a respective conductive trace 1166a. 1166b on outer face <NUM> of ceramic substrate <NUM> by a respective via 1190a, 1190b. Cables or wires 1170a, 1170b are connected to (e.g., directly welded to) terminals 1168a, 1168b in order to supply current to resistive traces 1164a, 1164b to generate heat. In this embodiment, current input to heater <NUM> at, for example, terminal 1168a by way of conductive trace 1192a passes through, in order, via 1190a, conductive trace 1166a, resistive trace 1164a, conductive trace 1166c, resistive trace 1164b, conductive trace 1164b, via 1190b and conductive trace 1192b where it is output from heater <NUM> at terminal 1168b. Current input to heater <NUM> at terminal 1168b travels in reverse along the same path.

In the example embodiment illustrated, heater <NUM> includes a thermistor <NUM> positioned in close proximity to inner face <NUM> of ceramic substrate <NUM> in order to provide feedback regarding the temperature of heater <NUM> to control circuitry <NUM>. In this embodiment, thermistor <NUM> is not directly attached to ceramic substrate <NUM> but is instead held against inner face <NUM> of ceramic substrate <NUM> by a mounting clip (not shown) or other form of fixture or attachment mechanism Cables or wires 1178a, 1178b are connected to (e.g., directly welded to) respective terminals of thermistor <NUM> in order to electrically connect thermistor <NUM> to, for example, control circuitry <NUM>. Of course, thermistor <NUM> of heater <NUM> may alternatively be directly welded to ceramic substrate <NUM> as discussed above with respect to thermistor <NUM> of heater <NUM>. Similarly, thermistor <NUM> of heater <NUM> may be held against ceramic substrate <NUM> by a fixture instead of directly welded to ceramic substrate <NUM>.

In the example embodiment illustrated, heater <NUM> also includes a thermal cutoff <NUM>. such as a bi-metal thermal cutoff, positioned on inner face <NUM> of ceramic substrate <NUM>. Cables or wires 1196a, 1196b are connected to respective terminals of thermal cutoff <NUM> in order to provide electrical connections to thermal cutoff <NUM>. Thermal cutoff <NUM> is electrically connected in series with the heating circuit formed by resistive traces <NUM> and conductive traces <NUM> permitting thermal cutoff <NUM> to open the heating circuit formed by resistive traces <NUM> and conductive traces <NUM> upon detection by thermal cutoff <NUM> of a temperature that exceeds a predetermined amount. In this manner, thermal cutoff <NUM> provides additional safety by preventing overheating of heater <NUM>. Of course, heater <NUM> discussed above may also include a thermal cutoff as desired.

While not illustrated, it will be appreciated that inner face <NUM> of ceramic substrate <NUM> may include one or more glass layers in order to electrically insulate portions of inner face <NUM> of heater <NUM> as desired.

<FIG> shows a heater <NUM> suitable for use with hair iron <NUM> according to another example embodiment. <FIG> shows an outer face <NUM> of heater <NUM>. In one embodiment, an inner face of heater <NUM> is substantially the same as inner face <NUM> of heater <NUM> shown in <FIG>. Heater <NUM> includes one or more layers of a ceramic substrate <NUM> as discussed above. <FIG> shows an outer face <NUM> of ceramic substrate <NUM>.

In the example embodiment illustrated, heater <NUM> includes a single resistive trace <NUM> on outer face <NUM> of ceramic substrate <NUM>. Resistive trace <NUM> extends along a longitudinal dimension <NUM> of heater <NUM>. Heater <NUM> also includes a pair of conductive traces 2166a, 2166b positioned on outer face <NUM> of ceramic substrate <NUM>. Each conductive trace 2166a, 2166b directly contacts a respective end of resistive trace <NUM>. Conductive trace 2166a contacts resistive trace <NUM> near a first longitudinal edge <NUM> of heater <NUM>. Conductive trace 2166b contacts resistive trace <NUM> near a second longitudinal edge <NUM> of heater <NUM> and extends from the point of contact with resistive trace <NUM> to a position next to conductive trace 2166a. Portions of resistive trace <NUM> obscured beneath conductive traces 2166a, 2166b in <FIG> are shown in dotted line.

In the embodiment illustrated, heater <NUM> includes a pair of vias 2190a, 2190b that are formed as through-holes substantially filled with conductive material extending through ceramic substrate <NUM> as discussed above with respect to heater <NUM>. Vias 2190a, 2190b electrically connect conductive traces 2166a. 2166b to corresponding conductive traces on the inner face of ceramic substrate <NUM> as discussed above.

In the embodiment illustrated, heater <NUM> includes one or more layers of printed glass <NUM> on outer face <NUM> of ceramic substrate <NUM>. Glass <NUM> covers resistive trace <NUM> and conductive traces 2166a, 2166b in order to electrically insulate these features as discussed above. The borders of glass layer <NUM> are shown in dashed line in <FIG>.

It will appreciated that the example embodiments illustrated and discussed above are not exhaustive and that the heater of the present disclosure may include resistive and conductive traces in many different geometries, including resistive traces on the outer face and/or the inner face of the heater, as desired, as long as these geometries fall within the scope of invention as defined by the appended claims. Other components (e.g., a thermistor) may be positioned on either the outer face or the inner face of the heater as desired.

The present disclosure provides a ceramic heater having a low thermal mass in comparison with the heaters of conventional hair irons. In particular, thick film printed resistive traces on an exterior face (outer or inner) of the ceramic substrate provides reduced thermal mass in comparison with resistive traces positioned internally between multiple sheets of ceramic. The use of a thin film, thermally conductive sleeve, such as a polyimide sleeve) also provides reduced thermal mass in comparison with metal holders, guides, etc. The low thermal mass of the ceramic heater of the present disclosure allows the heater, in some embodiments, to heat to an effective temperature for use in a matter of seconds (e.g., less than <NUM> seconds), significantly faster than conventional hair irons. The low thermal mass of the ceramic heater of the present disclosure also allows the heater, in some embodiments, to cool to a safe temperature after use in a matter of seconds (e.g., less than <NUM> seconds), again, significantly faster than conventional hair irons.

Further, embodiments of the hair iron of the present disclosure operate at a more precise and more uniform temperature than conventional hair irons because of the closed loop temperature control provided by the thermistor in combination with the relatively uniform thick film printed resistive and conductive traces. The low thermal mass of the ceramic heater and improved temperature control permit greater energy efficiency in comparison with conventional hair irons. The rapid warmup and cooldown times of the ceramic heater of the present disclosure also provide increased safety by reducing the amount of time the hair iron is hot but unused. The improved temperature control and temperature uniformity further increase safety by reducing the occurrence of overheating. The improved temperature control and temperature uniformity also improve the performance of the hair iron of the present disclosure.

Claim 1:
A hair iron (<NUM>), comprising:
a first arm (<NUM>) and a second arm (<NUM>) movable relative to each other between an open position and a closed position, a distal segment (<NUM>) of the first arm is spaced from a distal segment (<NUM>) of the second arm in the open position, the distal segment of the first arm is positioned in close proximity to the distal segment of the second arm in the closed position;
a contact surface (<NUM>) positioned on an exterior of the distal segment of the first arm for contacting hair during use; and
the first arm includes a heater (<NUM>) having a ceramic substrate (<NUM>) and an electrically resistive trace (<NUM>) on an exterior face of the ceramic substrate, the heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to the contact surface,
characterised in that
the hair iron further comprises a sleeve (<NUM>) covering an outer face (<NUM>) of the heater that faces toward the second arm in the closed position, wherein a portion of the sleeve forms the contact surface,
wherein the sleeve is composed of a thin film of thermally conductive and electrically insulative material or wherein the sleeve is composed of at least one of a filled or unfilled polyimide.