Heat mat with thermostatic control
A heat mat with thermostatic control having a reference voltage generating source that provide high voltage DC for a power controller and low voltage for a temperature sensor and hysteresis circuit. The sensor and hysteresis circuit establish a temperature threshold signal that is delivered to the resistance heating element. The resistance heating element is sandwiched between two layers of material with adhesive. Two layers of PVC protects the sandwich. In manufacturing the heat mat, the resistance heating element is placed with adhesive between two layers of material then cured and degassed under vacuum. The thermostatic control is sealed within an overmold housing or flat pack.
1. A method for manufacturing a heating pad comprising the steps of:
stringing a resistance heating wire out on a form in a pattern;
placing said patterned wires and form on to a first polyester film;
providing a self-crosslinking polymer liquid adhesive having a viscosity of between 2,000 and 5,000 cps and a density of between 6 and 8 lbs/gal.;
coating a second polyester film with said polymer liquid adhesive;
gluing the first and second polyester films together to encase the patterned wires therebetween;
removing the polyester encased wires from the form to create an intermediate mat;
sandwiching the mat between two larger polyvinyl chloride (PVC) sheets that extend beyond the mat's periphery to form an ensemble; and
degassing the ensemble under vacuum remove air and solvent from within the mat and heating to fuse the PVC sheets together around the periphery the mat.
2. The method of claim 1 , wherein the first and second polyester films are made from polyethylene terephthalate (PET).
3. The method of claim 2 , wherein the liquid adhesive is an acrylic polymer dissolved in a solvent.
4. The method of claim 3 , wherein the solvent is selected from the group consisting of toluene, heptane, isopropanol, acetone, ethanol and combinations thereof.
5. The method of claim 3 , wherein the solvent is a solvent blend including toluene, heptane, isopropanol, acetone, and ethanol.
6. The method of claim 5 , wherein a 1.0 mil thick layer of cured adhesive has a coating weight of about 16 lbs/3,000 ft 2 , a loop tack of about 4.4 lbs/in; a 180° peel adhesion of about 4.3 lbs/in utilizing a 15 minute dwell, a shear adhesion of 24+ hours utilizing ½ in×½ in×500 grams test conditions, and a plasticity of about 2.4 mm.
7. The method of claim 5 , wherein the intermediate mat comprises a fuse wherein the adhesive delaminates the PET film at high temperatures above about 300° F. causing the resistance heating wire to sever causing an open circuit that halts operation of the heating pad.