Abstract:
A therapeutic heating pad which is not hot to the touch provides substantial infrared radiation to a user. Accordingly it can be used for extended periods without feeling uncomfortable to the skin, while imparting deep therapeutic heat to the user. The heating pad is comprised of a radiant heat generating layer having a plane surface comprising means for radiating heat evenly from its surface, a pair of flexible electrically insulating and radiation permeable layers located adjacent and covering opposite sides of the layer, a thermal insulation layer disposed against and covering one of the electrically insulating layers, and a sealed radiation permeable envelope enclosing the entire heater. Preferably the flexible heat generating layer is comprised of a fiberglass material impregnated with a resistive material, which material provides a surface temperature, when current is conducted therethrough, which is no greater than about 54 degrees Celsius. Current limiting thermostats are provided to prevent energy and temperature spikes in the event that any of the electrical components are creased or bent.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to an improved heating pad which has been found to be useful for therapeutic applications, and more particularly to an improved radiant therapeutic heater.  
         [0003]     2. Description of the Prior Art  
         [0004]     Certain types of painful conditions of the muscles or joints such as arthritic pain often have the application of heat prescribed to relieve the pain. Heat is normally applied in a variety of ways, for instance by the use of irritant rubbing compounds which cause local stimulation of blood vessels thereby increasing body heat carried to the location, the use of infrared lamps, the use of radio frequency apparatus such as diathermy machines, the use of hot water bottles or electrically operated heating pads.  
         [0005]     While some or all of the aforenoted apparatus is alleged to work to some degree, all have certain disadvantages. For instance, the prolonged use of an infrared heating lamp can cause localized burning of the skin. Diathermy machines are specialized apparatus which require expensive skilled operators. Irritant rubs, while apparently generating local heat, sometimes irritate the skin. Hot water bottles maintain an uneven temperature with time, generally are applied too hot to the skin, and later cool to an ineffective temperature. They are thus uncomfortable for most of their time of application.  
         [0006]     Prior art heating pads are generally comprised of insulated electrical heating elements held within a sealed bag, covered with a washable removable cloth envelope. Such heating pads are resistance heated by the flow of electricity therethrough, which heat the surrounding insulated envelope. The pad is applied to an area of the body which is to be treated, and the hot pad provides fairly even heat to the skin.  
         [0007]     However the use of this form of heating pad must be carefully controlled. Since the pad heats the skin by conduction from the heating coils to the body of the user, it feels generally hot to the touch, and use must be limited or the skin can be burned, particularly if the user falls asleep on the pad. Due to the conduction of heat to the skin, the pad eventually begins feeling very uncomfortable. While such pads generally utilize thermostats to control the amount of heat generated, its use in a confined space, such as under the patient, generally causes the build up of heat on the skin which is conducted directly from the heating coils. The heat has been found to eventually become uncomfortable even at a generally low thermostatic setting.  
         [0008]     An improvement over these types of heating pads can be found in Assignees prior U.S. Pat. No. 31,186,294 which issued on Jan. 29, 1980, which patent is incorporated herein by reference. Briefly, the &#39;294 patent discloses a therapeutic heating pad which operates using black body radiation of infrared heat, rather than conduction as in prior art pads. The surface temperature of the pad exceeds the temperature of the human body, somewhat, but because of its unique design the heat is dissipated and it does not feel uncomfortably hot to the touch. It can, as a result be used for extended periods of time. Yet the radiant heat generated by the pad has been found to penetrate the tissues relatively deeply, thus providing an enhanced therapeutic effect. This is accomplished without the previously encountered hot or burning feeling on the skin.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is directed to a novel form of electrically operated heating pad. The invention, in general, is a radiant therapeutic heater comprising a radiant heat generating layer having a plane surface comprising means for radiating heat evenly from its surface, a pair of flexible electrically insulating and radiation permeable layers located adjacent and covering opposite sides of the layer, a thermal insulation layer disposed against and covering one of the electrically insulating layers, and a sealed radiation permeable envelope enclosing the entire heater. The flexible heat generating layer is comprised of a foam insulation layer impregnated with a resistive material, which material provides a surface temperature, when current is conducted therethrough, which is in the range of about 54 degrees Celsius. The heating pad of the present invention may also include a stiffener to protect the heating element from damage due to bending or creasing of the pad. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     A better understanding of the invention and various other objects, features and advantages of the present invention will become readily apparent by reading the following description in conjunction with the drawings, which are shown by way of example only, wherein:  
         [0011]      FIG. 1  is a perspective view of the complete heating pad;  
         [0012]      FIG. 2  is a detailed view of a radiant heating element for the heating pad of the present invention;  
         [0013]      FIG. 3  is a plan view of the reverse side of the radiant heating element showing the heat generating layer; and  
         [0014]      FIG. 4  is a perspective view of a second embodiment of the heating pad according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring now to the drawings in detail, wherein like reference characters refer to like elements, there is shown in  FIG. 1 a  perspective view of a radiant heating pad  10  according to an embodiment of the present invention. The heating pad  10  preferably has a cloth cover  13  of cotton or other natural fiber, formed into an envelope and closed by a zipper, preferably a hook and loop fastener (Velcro)  16 . A power cord  19  extends from an opening which is closed, such as by a second Velcro zipper  22 , for carrying current to one or more heating elements  25  which is controlled by an inline cord on-off switch  28  with indicator light  31 . While a standard 117 volt AC main plug  34  is shown at the end of power cord  19 , it should be noted that upon appropriate design of the heating element  25 , other potentials can be used, for instance 12 volts AC or DC, 75 volts AC or DC. Also, the source of electrical power may be a re-chargeable battery pack (not shown) for enhanced portability of the heating pad  10 .  
         [0016]     Preferably, the surface temperature of the pad is no higher than about 54 degrees Celsius and in the most preferred embodiment on the order of about 49-54 degrees Celsius. As is common with conventional heating pads, the on-off switch  28  may incorporate a variable temperature control. Even at the 54 C degree temperature the heating pad  10  is safer for application to the skin of the user, while it has been found that the infrared radiation provided by the device of the present invention still penetrates deeply into the body and muscle of the user for the desired therapeutic benefit of the heating pad. Consequently the heating pad  10  can be used in place for even more extended periods of time with a comfortably warm feeling, and without causing surface skin bums.  
         [0017]      FIGS. 2 and 3  show the preferred embodiment of a heating element  25  which is used within the heating pad  10 . The heating element  25  includes of a fiberglass mat or layer  37 . The fiberglass layer  37  is preferably thoroughly impregnated and saturated with a chemical compound which is a mixture of low and high resistance carbon to provide the required resistance. Saturation is carried out in such manner as to insure that the fiberglass is throughly covered inside and out homogeneously. Following saturation the material is passed through a series of steel rollers which remove the excess wet chemical, after which it is passed through an oven drying process and is finally subjected to heat of about 425 degrees Celsius to extract any remaining moisture in the material, thus stabilizing the carbon-graphite impregnated material.  
         [0018]     The coating materials of the kind preferred to be used in the heating element of this invention are described in U.S. Pat. No. 3,865,626, issued Feb. 11, 1975.  
         [0019]     The quantity of the material impregnated in the fiberglass, which forms a resistive layer, ranges from about 0.1 grams per square meter to about 3 grams per square meter. After heat treatment, drawing and passing of the fiberglass through the rollers (the latter of which gauges the thickness of the particles of the impregnate adhering to the material) sets the resistivity of the material.  
         [0020]     It should be noted that materials other than fiberglass can be used as a base for the resistive material. For instance, as described in U.S. Pat. No. 3,865,626, a polyester film is treated with a solvent or swelling agent. Electroconductive particles, preferably carbon black is applied to the treated surface in a concentration corresponding to the desired resistance. The film is then subjected to heat treatment to solidify and retain the resistive material in the surface. It should be noted that since the resistance material is basically fabricated of carbon compound, the heating element  25  is a black body radiator, which has a high efficiency of radiant heat dispersion which, it is believed, contributes to the effectiveness of the invention.  
         [0021]     Conductive tapes  40 , preferably of copper foil, are sewn into electrical contact with the resistive material along parallel edges of the fiberglass layer  37 . The tapes  40  can be made of either woven or non woven material. A pair of wires  43  are then electrically connected to the tapes  40 , such as by a clip  46 . The other ends of the electrical wires  43  are operatively connected to a quick connector  49 , which is connected to a complementary connector (not shown) to individually connect each heating element  25  to the main power cord  19 .  
         [0022]     It should be noted that as the resistivity of the material  37  is measurable in ohms per square units, the material can be made in large sheets or rolls, and then cut to the required resistance. In the preferred embodiment, the heat element dissipates 26.3 watts per square foot with an input voltage of 117 volts AC. Depending on the specific design, however, the dissipation can be made as low as thirteen (13) watts per square foot. The individual heating elements  25 , and thus the overall heating pad  10 , can be made a variety of desired dimensions in length or width depending on how and where the heating pad is to be used on a particular body art of the user. For example, “dedicated” heating pads can be designed for use on a users wrist, shoulders, knees or thighs and can be made so as to have securing straps for holding the heating pad in place for the best therapeutic effect. Moreover, although three (3) heating elements  25  are shown in  FIG. 1 , a larger, single heating element can be used, as well as one or more smaller units.  
         [0023]     As shown in  FIG. 2 , each wire  43  is individually connected to the quick connector  49  and one of the conductive tapes  40  in order to complete the electrical circuit. One of the wires is connected to the quick connector  49  via a second quick connector  52 . The other wire is connected to the quick connector  46  via one or more current limiting thermostats  55 . In the preferred embodiment, two (2) thermostats  55  are used, one acting as a back-up in the event of failure of the other. Connected in series with the heating element  25 , the thermostats  55  cut off power thereto in case the temperature becomes excessive. The thermostats  55  are preferably connected to the wire  43  and quick connector  49  via a pair of in-line quick connectors  58  for ease of replacement. Thus at least one current limiting control thermostat  55  is within the electrical circuit of the heating element  25  and distributed to sense whether any hot spots may be developing due to a fold, or the like in the heating pad  10 .  
         [0024]     In order to prevent the wires  43  and/or the thermostats  55  from being inadvertently creased or bent, which may cause a power surge within the heating element  25 , these components are attached to a stiffening member  61 . Preferably, the stiffening member  61  is a relatively thin layer of propylene material of about three-sixteenths ( 3/16) of an inch thick. Disposed against the surface of the stiffening member  61  against the thermostats  55  is an insulating layer  64  to more fully protect the individual components of the heating element  25 . The insulating layer  64  is preferably made of a foam insulation of between about one-quarter (¼) and one (1) inch in thickness, and most preferably the insulation is 1 inch thick.  
         [0025]     Additionally, each of the heating elements  25  is preferably encased within a vinyl envelope (not shown) so that only the quick connector  49  protrudes therefrom. In the event that a new heating element is required, the other cover  13  is opened and the quick connector is merely disconnected. A new heating element can then be connected, inserted into the cover  13 , and the Velcro zippers  16 , 22  resealed. This envelope holds all of the above described elements in a laminated position, and protects them against the intrusion of moisture or other contaminants. The pair of wires  43  which contact the conductive tapes  40  via the clips  43 , of course extend through a hole (not shown) in the vinyl envelope, which hole is preferably sealed against the wires  43 . Alternatively, the quick connector  49  itself can be a sealed connector projecting from the vinyl envelope, if desired. The area between the zippers  16 , 22  holds the various wires and connectors for the heating elements  25 .  
         [0026]     As shown in  FIG. 1 , the outer cloth bag or cover  13  encloses each vinyl envelope and hence each heating element  25 . Preferably the cloth cover  13  is fabricated of terry towel, or other cotton or natural fiber material, which has been found to be most comfortable to the user. As noted above, the cloth cover  13  can be closed by one or more fastening devices, such as by a hook and loop closure zippers (generally referred to as Velcro) or the like. The cover  13  may thus be removed and washed as desired. In a preferred embodiment each half of the cover  13  is stitched  67  together so as to create one or more individual pockets  70  into which each heating element  25  is inserted. This also allows the heating pad  10  to be bent along the area of the stitching  67  to conform to the body part of the user, while each heating element  25  is prevented from being creased by the stiffener  61 . The thermostats  55  further prevent temperature spikes in the event that any of the electrical wires or cords are creased or bent.  
         [0027]     In operation, the heating pad  10  is plugged in or otherwise connected to a source of electrical current. The heating pad  10  is placed over a region to be therapeutically warmed with deep heat. Current passes through the resistance material of the fiberglass layer  37 , creating a source of black body infrared radiation. The radiation is received by the body of the user, and penetrates deeply beneath the skin to the users underlying muscle. Yet the heating pad  10  does not feel uncomfortably hot to the touch as it does not exceed 54 degrees Celsius (140° F.), and preferably about 49-54 degrees Celsius (120-130° F.).  
         [0028]      FIG. 4  shows an alternate embodiment of vibrating heating pad  110  according to the present invention. In this embodiment the cover  113  includes one or more pockets  116  which house vibrating elements  119  for providing this added therapeutic benefit to the user. Similar to that of the heating elements  125 , each vibrating element  119  is connected to a switch  128  which preferably has separate a control  131  for each of the heating elements  125  and vibrating elements  119 . As with the heating pad  10 , the control  131  for the vibrating elements  119  may include variable speeds.  
         [0029]     In the event the heating pad  10  is heated before being applied to the user&#39;s body, should the heating pad have a resistivity which raises its temperature higher than that of the temperature of the human body, the pad may feel warm for an instant when it is first applied to the body of the user. However it has been found that this warmth is almost instantly dissipated by the skin of the user, and further contact with the pad does not impart an uncomfortably hot sensation to the touch. Accordingly there is a very little heat conduction from the inventive structure, but there is substantial radiated heat. The radiated heat is received by receptive bodies opposite the side of the pad. Yet the air which is in contact with the heating pad does not heat, since it is transparent to infrared radiated heat.  
         [0030]     It has been found that the described structure radiates heat in the wave length band of between 9 and 12 microns, while the entire infrared bandwidth extends between 0.72 and 3100 microns. It is believed that the particular bandwidth of the radiation which is emitted by this invention contributes to the apparent deep penetration and therapeutic effect obtained.  
         [0031]     As noted earlier, the heating pad can be made of various sizes, such as the size given by example herein, blanket size, or of particular shape to match the shape of a portion of a user&#39;s body.  
         [0032]     Accordingly a heating pad has been invented which has significant advantages over prior art therapeutic heat applying devices. Since the pad gives its deep heat penetration by radiation, with a relatively low surface temperature, skin surface bums do not result from prolonged use. The pad is useable by the patient, and no specialist is required for its application. Nonconductive and virtually entire radiative infrared heat in the range of 9 to 12 microns is imparted to the user, which has been found to result in a penetrating deep heat, which patients have found to be highly successful in relief of symptoms of arthritic pain, etc.  
         [0033]     It may now become evident to a person skilled in the art understanding this invention that other materials than the ones described can be substituted for the ones described, and that other embodiments and configurations may now be designed. All are considered within the scope and sphere of the invention, as defined in the appended claims. While specific embodiments of the invention have been shown in the drawings and described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives would be developed in light of the overall teachings of the disclosure. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. Accordingly, the particular arrangements disclosed herein are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and in any and all equivalents thereof.