Patent Publication Number: US-10773406-B2

Title: Heating member for a shaving razor

Description:
FIELD OF THE INVENTION 
     The present invention relates to shaving razors and more particularly to heated razors for wet shaving. 
     BACKGROUND OF THE INVENTION 
     Users of wet-shave razors generally appreciate a feeling of warmth against their skin during shaving. The warmth feels good, resulting in a more comfortable shaving experience. Various attempts have been made to provide a warm feeling during shaving. For example, shaving creams have been formulated to react exothermically upon release from the shaving canister, so that the shaving cream imparts warmth to the skin. Also, razor heads have been heated using hot air, heating elements, and linearly scanned laser beams, with power being supplied by a power source such as a battery. Razor blades within a razor cartridge have also been heated. The drawback with heated blades is they have minimal surface area in contact with the user&#39;s skin. This minimal skin contact area provides a relatively inefficient mechanism for heating the user&#39;s skin during shaving. However, the delivery of more heat to the skin generates safety concerns (e.g., burning or discomfort). 
     Accordingly, there is a need to provide a shaving razor capable of delivering safe and reliable heating that is noticeable to the consumer during a shaving stroke. 
     SUMMARY OF THE INVENTION 
     The invention features, in general, a simple, efficient heat delivery element for a shaving razor with a face plate having a skin contacting surface and an opposing inner surface. A heater having a heater track is positioned between an upper dielectric layer and a lower dielectric layer. A heat dispersion layer having a lower surface directly contacts the inner surface of the face plate. An upper surface of the heat dispersion layer directly contacts the lower dielectric layer of the heater. 
     In other embodiments, the invention features, in general, a simple, efficient heat delivery element for a shaving razor with a heater having a heater track positioned between an upper dielectric layer and a lower dielectric layer. The heater track is secured between the upper dielectric layer and the lower dielectric layer by an adhesive layer bonded to the upper dielectric layer and the lower dielectric layer. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. It is understood that certain embodiments may combine elements or components of the invention, which are disclosed in general, but not expressly exemplified or claimed in combination, unless otherwise stated herein. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present invention, it is believed that the invention will be more fully understood from the following description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a perspective view of one possible embodiment of a shaving razor system. 
         FIG. 2  is an assembly view of one possible embodiment of a heat delivery element that may be incorporated into the shaving razor system of  FIG. 1 . 
         FIG. 3  is a top view of one possible embodiment of a heater that may be incorporated into the heat delivery element of  FIG. 2 . 
         FIG. 4  is a cross section view of the heater, taken generally along line  4 - 4  of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , one possible embodiment of the present disclosure is shown illustrating a shaving razor system  10 . In certain embodiments, the shaving razor system  10  may include a shaving razor cartridge  12  mounted to a handle  14 . The shaving razor cartridge  12  may be fixedly or pivotably mounted to the handle  14  depending on the overall desired cost and performance. The handle  14  may hold a power source, such as one or more batteries (not shown) that supply power to a heat delivery element  16 . In certain embodiments, the heat delivery element  16  may comprise a metal, such as aluminum or steel. 
     The shaving razor cartridge  12  may be permanently attached or removably mounted from the handle  14 , thus allowing the shaving razor cartridge  12  to be replaced. The shaving razor cartridge  12  may have a housing  18  with a guard  20 , a cap  2 , 2  and one or more blades  24  mounted to the housing  18  between the cap  22  and the guard  20 . The guard  20  may be toward a front portion of the housing  18  and the cap  22  may be toward a rear portion of the housing  18  (i.e., the guard  20  is in front of the blades  24  and the cap is behind the blades  24 ). The guard  20  and the cap  22  may define a shaving plane that is tangent to the guard  20  and the cap  22 . The guard  20  may be a solid or segmented bar that extends generally parallel to the blades  24 . In certain embodiments, the heat delivery element  16  may be positioned in front of the guard  20 . 
     In certain embodiments, the guard  20  may comprise a skin-engaging member  26  (e.g., a plurality of fins) in front of the blades  24  for stretching the skin during a shaving stroke. In certain embodiments, the skin-engaging member  24  may be insert injection molded or co-injection molded to the housing  18 . However, other known assembly methods may also be used such as adhesives, ultrasonic welding, or mechanical fasteners. The skin engaging member  26  may be molded from a softer material (i.e., lower durometer hardness) than the housing  18 . For example, the skin engaging member  26  may have a Shore A hardness of about 20, 30, or 40 to about 50, 60, or 70. The skin engaging member  26  may be made from thermoplastic elastomers (TPEs) or rubbers; examples may include, but are not limited to silicones, natural rubber, butyl rubber, nitrile rubber, styrene butadiene rubber, styrene butadiene styrene (SBS) TPEs, styrene ethylene butadiene styrene (SEBS) TPEs (e.g., Kraton), polyester TPEs (e.g., Hytrel), polyamide TPEs (Pebax), polyurethane TPEs, polyolefin based TPEs, and blends of any of these TPEs (e.g., polyester/SEBS blend). In certain embodiments, skin engaging member  26  may comprise Kraiburg HTC 1028/96, HTC 8802/37, HTC 8802/34, or HTC 8802/11 (KRAIBURG TPE GmbH &amp; Co. KG of Waldkraiburg, Germany). A softer material may enhance skin stretching, as well as provide a more pleasant tactile feel against the skin of the user during shaving. A softer material may also aid in masking the less pleasant feel of the harder material of the housing  18  and/or the fins against the skin of the user during shaving. 
     In certain embodiments, the blades  24  may be mounted to the housing  18  and secured by one or more clips  28   a  and  28   b . Other assembly methods known to those skilled in the art may also be used to secure and/or mount the blades  24  to the housing  18  including, but not limited to, wire wrapping, cold forming, hot staking, insert molding, ultrasonic welding, and adhesives. The clips  28   a  and  28   b  may comprise a metal, such as aluminum for conducting heat and acting as a sacrificial anode to help prevent corrosion of the blades  24 . Although five blades  24  are shown, the housing  18  may have more or fewer blades depending on the desired performance and cost of the shaving razor cartridge  12 . 
     The cap  22  may be a separate molded (e.g., a shaving aid filled reservoir) or extruded component (e.g., an extruded lubrication strip) that is mounted to the housing  18 . In certain embodiments, the cap  22  may be a plastic or metal bar to support the skin and define the shaving plane. The cap  22  may be molded or extruded from the same material as the housing  18  or may be molded or extruded from a more lubricious shaving aid composite that has one or more water-leachable shaving aid materials to provide increased comfort during shaving. The shaving aid composite may comprise a water-insoluble polymer and a skin-lubricating water-soluble polymer. Suitable water-insoluble polymers which may be used include, but are not limited to, polyethylene, polypropylene, polystyrene, butadiene-styrene copolymer (e.g., medium and high impact polystyrene), polyacetal, acrylonitrile-butadiene-styrene copolymer, ethylene vinyl acetate copolymer and blends such as polypropylene/polystyrene blend, may have a high impact polystyrene (i.e., Polystyrene-butadiene), such as Mobil 4324 (Mobil Corporation). 
     Suitable skin lubricating water-soluble polymers may include polyethylene oxide, polyvinyl pyrrolidone, polyacrylamide, hydroxypropyl cellulose, polyvinyl imidazoline, and polyhydroxyethylmethacrylate. Other water-soluble polymers may include the polyethylene oxides generally known as POLYOX (available from Union Carbide Corporation) or ALKOX (available from Meisei Chemical Works, Kyota, Japan). These polyethylene oxides may have molecular weights of about 100,000 to 6 million, for example, about 300,000 to 5 million. The polyethylene oxide may comprise a blend of about 40 to 80% of polyethylene oxide having an average molecular weight of about 5 million (e.g., POLYOX COAGULANT) and about 60 to 20% of polyethylene oxide having an average molecular weight of about 300,000 (e.g., POLYOX WSR-N-750). The polyethylene oxide blend may also contain up to about 10% by weight of a low molecular weight (i.e., MW&lt;10,000) polyethylene glycol such as PEG-100. 
     The shaving aid composite may also optionally include an inclusion complex of a skin-soothing agent with a cylcodextrin, low molecular weight water-soluble release enhancing agents such as polyethylene glycol (e.g., 1-10% by weight), water-swellable release enhancing agents such as cross-linked polyacrylics (e.g., 2-7% by weight), colorants, antioxidants, preservatives, microbicidal agents, beard softeners, astringents, depilatories, medicinal agents, conditioning agents, moisturizers, cooling agents, etc. 
     The heat delivery element  16  may include a face plate  30  for delivering heat to the skin&#39;s surface during a shaving stroke for an improved shaving experience. In certain embodiments, the face plate  30  may have an outer skin contacting surface  32  comprising a hard coating (that is harder than the material of the face plate  30 ), such as titanium nitride to improve durability and scratch resistance of the face plate  30 . Similarly, if the face plate  30  is manufactured from aluminum, the face plate  30  may go through an anodizing process. The hard coating of the skin contact surface may also be used to change or enhance the color of the skin contacting surface  32  of the face plate  30 . The heat delivery element  16  may be mounted to either the shaving razor cartridge  12  or to a portion of the handle  14 . As will be described in greater detail below, the heat delivery element  16  may be mounted to the housing  18  and in communication with the power source (not shown). 
     Referring to  FIG. 2 , one possible embodiment of the heat delivery element  16  is shown that may be incorporated into the shaving razor system  10  of  FIG. 1 . The face plate  30  may be as thin as possible, but stable mechanically. For example, the face plate  30  may have a wall thickness of about 100 micrometers to about 200 micrometers. The face plate  30  may comprise a material having a thermal conductivity of about 10 to 30 W/mK, such as steel. The face plate  30  being manufactured from a thin piece of steel results in the face plate  30  having a low thermal conductivity thus helping minimize heat loss through a perimeter wall  44  and maximizes heat flow towards the skin contacting surface  32 . Although a thinner piece of steel is preferred for the above reasons, the face plate  30  may be constructed from a thicker piece of aluminum having a thermal conductivity ranging from about 160 to 200 W/mK. The heat delivery element  16  may include a heater (not shown) having a bridge  35  that is in electrical contact with micro-controller and a power source (not shown), e.g. a rechargeable battery, positioned within the handle  14 . 
     The heat delivery element  16  may include the face plate  30 , the heater  34 , a heat dispersion layer  36 , a compressible thermal insulation layer  38 , and a back cover  40 . The face plate  30  may have a recessed inner surface  42  opposite the skin contacting surface  32  (see  FIG. 1 ) configured to receive the heater  34 , the heat dispersion layer  36  and the compressible thermal insulation layer  38 . The perimeter wall  44  may define the inner surface  42 . The perimeter wall  44  may have one or more legs  46   a ,  46   b ,  46   c  and  46   d  extending from the perimeter wall  44 , transverse to and away from the inner surface  42 . For example,  FIG. 2  illustrates four legs  46   a ,  46   b ,  46   c  and  46   d  extending from the perimeter wall  44 . As will be explained in greater detail below, the heater  34  may include heater tracks and electrical tracks, not shown. 
     The heat dispersion layer  36  may be positioned on and in direct contact with the inner surface  42  of the face plate  30 . The heat dispersion layer  36  may have a lower surface  37  directly contacting the inner surface  42  of the face plate  30  and an upper surface  39  (opposite lower surface  37 ) directly contacting the heater  34  (for example, the lower dielectric layer shown in  FIGS. 3 and 4 ). The heat dispersion layer  36  is defined as a layer of material having a high thermal conductivity, and is compressible. For example, the heat dispersion layer  36  may comprise graphite foil. Potential advantages of the heat dispersion layer  36  include improving lateral heat flow (spreading the heat delivery from the heater  34  across the inner surface  42  of the face plate  30 , which is transferred to the skin contacting surface  32 ) resulting in more even heat distribution and minimization of hot and cold spots. The heat dispersion layer  36  may have an anisotropic coefficient of thermal conductivity in the plane parallel to the face plate  30  of about 200 to about 1700 W/mK (preferably 400 to 700 W/mK) and vertical to the face plate  30  of about 10 to 50 W/mK and preferably 15 to 25 W/mK to facilitate sufficient heat conduction or transfer. In addition, the compressibility of the heat dispersion layer  36  allows the heat dispersion layer  36  adapt to non-uniform surfaces of the inner surface  42  of the face plate  30  and non-uniform surfaces of the heater  34 , thus providing better contact and heat transfer. The compressibility of the heat dispersion layer  36  also minimizes stray particulates from pushing into the heater  34  (because the heat dispersion layer  36  may be softer than the heater), thus preventing damage to the heater  34 . In certain embodiments, the heat dispersion layer  36  may comprise a graphite foil that is compressed by about 20% to about 50% of its original thickness. For example, the heat dispersion layer  36  may have a compressed thickness of about 50 micrometers to about 300 micrometers more preferably 80 to 200 micrometers. 
     The heater  34  may be positioned between two compressible layers. For example, the heater  34  may be positioned between the heat dispersion layer  36  and the compressible thermal insulation layer  38 . The two compressible layers may facilitate clamping the heater  34  in place without damaging the heater  34 , thus improving securement and assembly of the heat delivery element  16 . The compressible thermal insulation layer  38  may help direct the heat flow toward the face plate  30  and away from the back cover  40 . Accordingly, less heat is wasted and more heat may be able to reach the skin during shaving. The compressible thermal insulation layer  38  may have low thermal conductivity, for example, less than 0.30 W/mK and preferably less than 0.1 W/mK. In certain embodiments, the compressible thermal insulation layer  38  may comprise an open cell or closed cellular compressible foam. The compressible thermal insulation layer  38  may be compressed 20-50% from its original thickness. For example, the compressible thermal insulation layer  38  may have a compressed thickness of about 400 μm to about 800 μm. 
     The back cover  40  may be mounted on top of the compressible thermal insulation layer  38  and secured to the face plate  30 . Accordingly, the heater  34 , the heat dispersion layer  36  and the compressible thermal insulation layer  38  may be pressed together between the face plate  30  and the back cover  40 . The heat dispersion layer  36 , the heater  34 , and the compressible thermal insulation layer  38  may fit snugly within the perimeter wall  44 . The pressing of the various layers together may result in more efficient heat transfer across the interfaces of the different layers in the heat delivery element  16 . In absence of this compression force the thermal transfer across the interfaces is insufficient. Furthermore, the pressing of the layers together may also eliminate secondary assembly processes, such as the use of adhesives between the various layers. The compressible thermal insulation layer  38  may fit snugly within the perimeter wall  44 . 
     Referring to  FIG. 3 , a top view of the heater  34  is shown. The heater  34  may have a heater track  48  laid over a lower dielectric layer  50 . One or more electrical tracks  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  and  66  may also be laid over the lower dielectric layer  50  such that they are all spaced apart from the heater track  48 . The one or more electrical tracks  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  and  66  may be positioned within a loop (e.g., perimeter) formed by the heater track  48 . The electrical tracks  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  and  66  may connect a plurality of thermal sensors  70 ,  76 ,  80  and  86  to a micro controller  75 . The microcontroller may process information from the thermal sensors  70 ,  76 ,  80  and  86  and adjust power to the heater track  48  to regulate temperature accordingly. The thermal sensor  70  may be thermally connected to a sensor pad  68 . Similarly, the thermal sensor  76  may be thermally connected to a sensor pad  74 . The thermal sensors  70  and  76  and respective sensor pads  68  and  74  may facilitate temperature control on one side of the heater  34 . A thermal sensor pad  84  may be thermally connected to the thermal sensor  86 . Similarly, a sensor pad  78  may be thermally connected to the thermal sensor  80 . The thermal sensors  80  and  86  and respective sensor pads  78  and  84  may facilitate temperature control on another side of the heater  34 . The thermal sensors  70  and  76  may be positioned laterally between the sensor pads  68  and  74 . The thermal sensors  80  and  86  may be positioned laterally between the sensor pads  78  and  84 . The spacing of the thermal sensors  70 ,  76 ,  80  and  86  and the sensor pads  68 ,  74 ,  78  and  84  may optimize spacing for more efficient heating of the heater  34 . 
     One or more of the thermal sensors  70 ,  76 ,  80  and  86  may be independently connected to the circuit board  75  to provide for redundant safety measure if one or more of the thermal sensors  70 ,  76 ,  80  and  86  has a failure. At least one of the thermal sensors  70 ,  76 ,  80  and  86  may be spaced apart from the heater track  48  by a distance of about 0.05 mm to about 0.10 mm, which may help prevent direct heating of the thermal sensors  70 ,  76 ,  80  and  86  from the heater tracks. In addition, the sensor pads  68 ,  74 ,  78  and  84  may also be spaced apart from the heater track  48  to provide an accurate temperature reading of the graphite foil layer shown in  FIG. 2 . The sensor pads  68 ,  74 ,  78  and  84  may improve thermal connection to graphite foil layer to measure temperature quickly and accurately. The sensor pads  68 ,  74 ,  78  and  84  may be spaced apart from a lateral edge  92  and  94  of the dielectric layer  50 . For example, the sensor pads may be spaced apart from a center line “CL” of the dielectric layer by about 10-30% and from the closest lateral edge  92  and  94  of the dielectric layer  50  by about 10-30%. The spacing and positioning of the sensor pads  68 ,  74 ,  78  and  84  may facilitate accurate temperature reading by the thermal sensors  70 ,  76 ,  80  and  86 . The sensor pads may comprise a layer of copper. In certain embodiments, the sensor pads  68 ,  74 ,  78  and  84  may each have a minimum surface area greater than 0.3 mm 2 , for example, about 0.3 mm 2  to about 0.45 mm 2 . If the surface area of one or more of the sensor pads  68 ,  74 ,  78  and  84  is too small, the thermal sensors  70 ,  76 ,  80  and  86  may not be able to read small fluctuations in temperature and/or the response time may be longer. 
     The heater  34  may include a feeder track  88  and  90  that are part of the bridge  35  and connect the micro-controller to the heater track  48 . A width of the feeder tracks  88  and  90  may be more than 5 times a maximum width of the heater track  48  positioned within the faceplate  30  of  FIG. 2 . The large width of the feeder tracks  88  and  90  supplies energy to the heater track  48  and helps prevent the bridge  35  from becoming too hot to the touch by minimizing the electrical resistance and hence the amount of heat generated. The bridge  35  may be exposed to the consumer during shaving in order to facilitate pivoting of the shaving razor cartridge  12  (see  FIG. 1 ). Accordingly, if the bridge  35  becomes too hot, a consumer may be accidentally burned. Furthermore, the bridge  35  may not be insulated to prevent heat loss. Thus, it may be advantageous for the bridge  35  to generate as little heat as possible. 
     The lower dielectric layer  50  may comprise polyimide or polytetrafluoroethylene, polyvinylchloride, polyester, or polyethylene terephthalate. The heater track  48  may include copper tracks having a meander pattern forming a loop along a perimeter of the lower dielectric layer  50 . The heater track  48  may have varying widths. For example, the heater track  48  may have a width of about 0.05 mm to about 0.09 mm in a first area  96   a  and  96   b  of the heater  34  and a width of about 0.07 mm to about 0.12 mm in a second area  98   a  and  98   b  of the heater  34 . In certain embodiments, the heater track  48  may have a third area  100   a  and  100   b  having a width of about 0.10 mm to about 0.2 mm. Space may be limited on the lower dielectric layer  50  due to the electrical tracks  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  and  66 , the sensor pads  68 ,  74 ,  78  and  84  and the thermal sensors  70 ,  76 ,  80  and  84 . Accordingly, the heat generation should be maximized and uniform as possible. In certain embodiments, the layout of the heater track  48  may be symmetrical. For example, the heater track  48  may have the same layout on a first side  72  of the centerline “CL” as on a second side  82  of the centerline “CL”. 
     The varying width of the heater track  48  allows for lower resistance in areas with more space and higher resistance in area of little space to achieve more uniform heat generation. Accordingly, more an equivalent amount of heat may be generated by the heater track  48  in a smaller space, for example in the first area  96   a  and  96   b , compared to a larger space, for example, in the second area  98   a  and  98   b . The second area  98   a  and  98   b  may be positioned toward a center line “CL” of the heater  34 . The first area  96   a  may be associated with the thermal sensors  80  and  86  and/or sensor pads  78  and  84  toward one end  94  of the dielectric layer  50 . Similarly, the first area  96   b  may be associated with the thermal sensors  70  and  76  and/or sensor pads  68  and  74  on an opposing end of the dielectric layer  50 . For example, the sensor pads  78  and  84  and/or the thermal sensors  80  and  86  may be positioned between a pair of lengths  85   a  and  87   a  of the heater track  48  having a smaller width than a width for a length  89   a  and  91   a  of the heater track  48  located in the second area  98   a . The second area  98   a  and  98   b  may have only the electrical tracks positioned between the length  89   a  and  91   a  of the heater track  48  (e.g., no sensors or sensor pads). 
     The first area  96   b  may be associated with the thermal sensors  70  and  76  and/or sensor pads  68  and  74  toward one end  92  of the dielectric layer  50 . Similarly, the first area  96   b  may be associated with the thermal sensors  70  and  76  and/or sensor pads  68  and  74  on an opposing end of the dielectric layer  50 . For example, the sensor pads  68  and  74  and/or the thermal sensors  70  and  76  may be positioned between a pair of lengths  85   b  and  87   b  of the heater track  48  having a smaller width than a width for a length  89   b  and  91   b  of the heater track  48  located in the second area  98   b . The second area  98   a  and  98   b  on each side of the heater  34  may not have any sensor pads or thermal sensors positioned between the lengths of the heater track  48 . For example, in the second area  98   b , only the electrical tracks  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  and  66  may positioned between the length  89   b  and  91   b  of the heater track  48 . 
     A third area  100   a  and  100   b  may be located toward a lateral edge  92  and  94  of the dielectric layer  50 . For example, the third area  100   a  may be positioned between the thermal sensor  86  and the lateral edge  94 . Similarly, the third area  100   b  may be positioned on the other side of the dielectric layer  50 , between the thermal sensor  70  and the lateral edge  92 . The third area  100   a  and  100   b  may lack thermal sensors, thermal pads, and electrical tracks. Accordingly, the heater track  48  in the third area  100   a  and  100   b  may have the widest section of the heater track  48  because the space is not limited by other electrical components. The layout of the first area  96   a  and  96   b , the second area  98   a  and  98   b  and the third area  100   a  and  100   b  allow for more uniform distribution of heat by having varying widths to account for space that may be needed by other electrical components. 
     In certain embodiments, the heater track  48  may have a total resistance of about 1.5 to about 3 Ohms. The heater track  48  may have a meander pattern forming a loop along a perimeter of the lower polyamide layer  50 . For example, the heater track  48  may extend around the electrical tracks (i.e., the electrical tracks are positioned within a loop formed by the heater track  48 ), the thermal sensors and the sensor pads. The meander pattern forming a perimeter or loop and the lower resistance in the area of the thermal sensors  70 ,  76 ,  80 ,  86  and the sensor pads  68 ,  74 ,  78  and  84  may facilitate delivery of sufficient heat in the area of the sensors because the thermal sensors and sensor pads generate no heat. The meander pattern of the heater track  48  may have the form of a zigzag; veering to right and left alternately. In certain embodiments, meander pattern of the heater track  48  may have a line or course with abrupt substantially 90 degree turns (e.g., train wave or square wave shape), to provide even more heater track  48  within a given area of the heater  34 . 
     Referring to  FIG. 4 , a cross section view of the heater  34  is shown, taken generally along the line  4 - 4  of  FIG. 3 . The heater  34  may include the lower dielectric layer  50 , a conductive layer  102  (that comprises the electrical tracks  52 ,  54 ,  56  and  58  and the heater track  48 ) an adhesive layer  104  and an upper dielectric layer  110 . The conductive layer  102  may have a thickness of about 10 μm to about 40 μm (i.e., the electrical tracks  52 ,  54 ,  56 ,  58  and the heater tracks  48  have a thickness of about 10 μm to about 40 μm). The lower dielectric layer  50  may have a thickness of about 10 μm to about 30 μm. The upper dielectric layer  110  may have a thickness of about 10 μm to about 30 μm. The conductive layer  102  (comprising the electrical tracks  52 ,  54 ,  56  and  58  and the heater track  48 ) may be laid down on top of the lower dielectric layer  50 . Since there are spaces between the electrical tracks  52 ,  54 ,  56  and  58  and the heater track  48 , the adhesive layer  104  may flow between the electrical tracks  52 ,  54 ,  56  and  58  and the heater track  48  to improve integrity of the fragile conductive layer  102 . The adhesive layer  104  may form a strong bond between the upper dielectric layer  110  and the lower dielectric layer  50 . The adhesive layers  104  may also cover the conductive layer  102  (i.e., the heater track  48  and electrical tracks) creating a water proof seal. The various materials and thickness that make up the heater  34  allow it to bend under its own weight, thus making the heater  34  more malleable and less susceptible to breaking during handling and assembly. In addition, the heater  34  takes up less space due to its thin profile. In certain embodiments, the upper dielectric layer  110  and/or the adhesive layer  104  may be transparent. For example, the heater track  48  may be visible through the upper dielectric layer  110  and the adhesive layer  104 , but may be colored, if desired. 
     The heater  34  may be sufficiently thin to provide flexibility and sufficient heat transfer. If the heater  34  (e.g., the lower dielectric layer  50 ) is too thick, poor heat transfer may result. The heater  34  may also provide sufficient mechanical stability to allow it to conform during assembly within the face plate  30  of  FIG. 2 . The lower dielectric layer may prevent electrical contact with other layers of the heat delivery element  16 , but yet allow sufficient heat transfer. For example, the lower polyimide dielectric layer may prevent the heater track and the electrical tracks from directly contacting the graphite layer or the inner surface of the face plate  30 . 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”. 
     Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.