Abstract:
Heat losses from electric heating pads, blankets and pillows are reduced by aligning heat reflective strips or coatings over the top of a heating wire arranged inside the pads, blankets and pillows. By reducing heat losses, lower wattage can be applied to the heating wire to transfer the same amount of heat to a user as equivalent higher wattage blankets which do not have the heat reflective strips. By lowering the applied wattage, a more efficient blanket results.

Description:
[0001]    This application claims the benefit of U.S. Provisional Serial No. 60/318,917 filed Sep. 11, 2001, and Provisional Application Serial No. 60/318,986 filed Sep. 11, 2001, and Provisional Application Serial No. 60/318,998 filed Sep. 11, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates in general to electric heating blankets, pads, pillows and the like and in particular to such heating products which include internal strips of heat reflective material.  
         DESCRIPTION OF PRIOR DEVELOPMENTS  
         [0003]    Present day warning blankets can draw as much as 180 watts of power during normal operation. Reducing this power is desirable for several reasons. First, reducing the power saves energy and makes the blanket more economical to operate. Second, reducing the wattage offers the possibility of reducing the size of the wire which lowers cost and improves comfort. Third, controlling a reduced wattage blanket allows the control electronics to dissipate less heat thereby allowing for the use of a smaller heat sink. Finally, by using less power, the operating voltage can be reduced to, say, about 33 volts AC which is less complicated to operate and poses fewer safety issues.  
           [0004]    Unfortunately, if one just decreases the wattage of a heating blanket, the blanket will not produce sufficient heat for a user. In order to allow the wattage to be decreased and yet provide the same amount of heat to a user, the heat losses from the blanket must also be decreased. Attempting to insulate the blanket to reduce heat losses doesn&#39;t solve the problem. By insulating the blanket, the heat losses are reduced, but then it is also more difficult for the heat to flow through the insulation from the wire to the user. Using a heat reflective sheet can help, but such sheets are bulky and prevent the blanket from breathing, i.e., from allowing water vapor to flow outwardly from a user&#39;s body through the blanket.  
           [0005]    What is required is some way to prevent heat losses without impeding the flow of heat from the wires to the user and without significantly affecting the passage of moisture or breatheability of the blanket. The solution, according to this invention, is to place strips of thermally reflective material on the top side of the blanket and aligned over the heating wires. In this manner substantially all of the available heat is directed downward towards the user, thereby increasing the amount of heat delivered to the user for a given input wattage, or allowing for the use of a lower wattage input with equivalent heating.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention has been developed to fulfill the needs noted above and therefore has as an object the provision of a heating blanket, pad, pillow or the like which provides (transfers) equivalent heat to a user as that provided by similar conventional heating products, yet which requires significantly less electrical power to achieve such equivalent warming.  
           [0007]    This result is achieved by providing a heat reflective layer of material in the form of thin heat reflecting strips or bands on only one side of the heating elements, which are typically resistance wires. The reflective layer can be provided as thin strips of heat reflective metal or plastic foil sewn or bonded onto the blanket or onto a substrate within the blanket. Aluminized coatings can also be used as well as titanium compounds such as found on ironing board covers. The thin strips are aligned directly over the top surface of the resistance wires to reflect heat downwardly to a user.  
           [0008]    The strips can also be applied as a spray or liquid coating to the blanket or to an internal substrate within the blanket. The spray can be applied by a moving nozzle in the manner of applying spray paint or applied over a stencil with a spray nozzle, brush or roller.  
           [0009]    Another approach is to apply a reflective coating directly to a portion, i.e., the upper half, of the resistance wire. The reflective coating or strips can also be applied as heat reflective adhesive tape. In each of the noted variations, substantially all of the heat produced by the resistance wire is transferred to a user, thereby increasing the amount of heat transferred to the user for a given input wattage to the heating wires or heating elements.  
           [0010]    By limiting the heat reflective material to thin bands, thin coatings or thin patches or strips located directly above the heating element (wires), most of the blanket remains “breathable,” i.e., capable of passing moisture, i.e., water vapor, outwardly to the ambient from a user. This greatly improves the comfort of the user and allows the blanket to remain lightweight, pliable and compliant.  
           [0011]    In order to construct the reduced wattage blanket, heating wire is first laid out on a thin pliable substrate. Then strips of the thermally reflective material are placed over the wires. The reflective material is then attached to the substrate, and can also secure the wire to the substrate. Finally, the complete substrate is placed inside a blanket shell. It is also possible to eliminate the substrate and apply the wire directly to an interior surface of the upper half of the shell, preferably before the two halves of the shell are completely sewn together. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic top plan view of a blanket constructed in accordance with the invention, with the top layer of the blanket cover or shell removed for clarity;  
         [0013]    [0013]FIG. 2 is a schematic top plan view of a blanket substrate having PTC wire provided thereon in accordance with the invention;  
         [0014]    [0014]FIG. 3 is a schematic top plan view of the blanket substrate of FIG. 2 having a pattern of reflective strips provided thereon in accordance with the invention;  
         [0015]    [0015]FIG. 4 is a view similar to FIG. 3 showing an alternate pattern of reflective strips; and  
         [0016]    [0016]FIG. 5 is an enlarged radial sectional view through a PTC heating wire constructed in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    The present invention will now be described in conjunction with the drawings, beginning with FIG. 1 which shows a heating blanket assembly  10  constructed in accordance with the invention. Although the invention is described using a blanket as an example, the invention is equally applicable to heating pads, pillows and wraps.  
         [0018]    The assembly  10  includes a blanket or outer cover  12 , typically formed of a pliable fabric material known and referred to as a “shell”. The blanket cover or shell  12  is generally formed as a two-layered laminate which forms a pocket which receives and encloses a substrate  14 , heating element  16  and reflective strips  18 . An electrical connector  20  is provided on the substrate  14  in a known manner to connect the heating element  16  to a source of electrical power.  
         [0019]    Only the bottom half layer of the outer cover or shell  12  is shown in FIG. 1. Substrate  14  is formed of a thin sheet of breathable material such as a non-woven natural or synthetic material such as a non-woven polyester fabric. This material preferably has a light, breathable gauze-like consistency. A perforated breathable plastic or elastomeric sheet of material may also be used for substrate  14 . The substrate is needed only for facilitating manufacture, and may be omitted.  
         [0020]    The heating element  16  in FIG. 1 is shown arranged in a closed serpentine loop on top of the substrate  14 , with each end connected to the electrical connector  20 . The heating element  16  may be attached directly to substrate  14  by adhesive bonding, stitching, ultrasonic welding, or other mechanical or chemical means.  
         [0021]    Alternatively, the heating element  16  may be held on substrate  14  by the heat reflective strips  18 . In this case, the heat reflective strips can have an adhesive underside which can be applied over the heating element  16  in the manner of a strip of adhesive tape and thereby tape and hold the heating element against the substrate.  
         [0022]    Another alternative is to sew the strips  18  over the heating element  16  and to the substrate  14  so as to capture the heating element between the strips and substrate. Gluing, ultrasonic welding and direct spray painting can also be used to hold the resistance wire in place. The heat reflective strips can be applied to the wires and substrate as strips of heat reflective metal foil, metallized plastic or fabric, adhesive tape, or as a thin coating such as heat reflective paint.  
         [0023]    As seen in FIGS. 2 and 3, the present invention is particularly well adapted for use with heating elements formed of positive temperature coefficient (PTC) heating wire  24 . In this example, the wire  24  is first applied to a substrate  14  in a serpentine pattern. An electrical connector  20  is secured to the edge of the substrate and connected to one end of the wire  24 . The other end of the wire is free and if a current sensor is used externally of the substrate, the wire need not loop back to the connector  20  when PTC wire is used. The current sensor provides a signal to a safety circuit which terminates power to the heating wire in the event an electrical fault is detected.  
         [0024]    The substrate  14  shown in FIG. 2 is provided with longitudinally-extending strips  18  of heat-reflective material as shown in FIG. 3. The strips  18  are spaced apart so as to overlie a pair of adjacent longitudinally-extending wires when the strips are superimposed over the wires and subsequently connected to the substrate. The resulting semi-laminated substrate is then placed within a blanket cover  12 . The spaces between the reflective strips define moisture escape passages to allow moisture to escape to the ambient and allow the blanket assembly  10  to breathe.  
         [0025]    If additional heat insulation is desired, additional heat reflective transverse strips or portions  28  shown in FIG. 4 may be provided between the longitudinally-extending strips  18 . In this embodiment, parallelogram or diamond-shaped openings  30  are defined between the longitudinally-extending strips  18  and the transverse strip portions  28  to allow for the passage of moisture and water vapor through the assembly  10 , while maintaining a pliable breathable blanket construction.  
         [0026]    It should be noted that it is possible to apply the heat reflective strips directly to the inside surface of one side of the blanket cover  12  and avoid the use of one or two substrate sheets. The wire can be attached to the blanket cover  12  in a manner similar to that described above regarding the connection of the wire to the substrate  14 .  
         [0027]    It is also possible to apply heat reflective material  34  as a coating or film or tape applied directly to one side or half of the heating wire  16 , as shown in FIG. 5. In this case, conventional blanket manufacturing techniques and constructions are enabled without any special consideration for the use of the reflective material  34 , other than the option to provide much lower wattage to the blanket assembly  10  than with prior blanket assemblies.  
         [0028]    The wire  24  shown in FIG. 5 is a PTC wire having a pair of parallel current carrying wires  36  embedded in a dog bone or dumbbell-shaped matrix of carbon-particle containing plastic material  38 . Current flows from one wire  36  to the other through the plastic material  38 . In this manner, heat is generated along the entire length of the wire. The heat reflective material  34  reduces the amount of heat escaping upwardly away from a user by reflecting heat toward the user that would otherwise be lost to the ambient.  
         [0029]    An advantage of the present invention is the ability to manufacture and inventory a large quantity of substrate subassemblies having heating element  16  or heating wire  24  mounted thereon along with reflective strips  18 . These subassemblies can be later inserted into various colors and sizes and fabrics of blanket shells  12  as market needs demand. This eliminates the need to stockpile and inventory the entire blanket assembly  10 . The shells  12  can be fabricated on demand as needed, and the subassemblies can be taken from inventory and quickly be assembled into a complete assembly  10 .