Blanket wire utilizing positive temperature coefficient resistance heater
First Claim
1. A self-limiting electric heating element adapted for use in flexible heated products such as heating pads, electric blankets and the like comprising an elongated conductor including a flexible insulating core supporting a pair of conductor wires disposed helically around said core, an envelope of positive temperature coefficient material positioned in direct engagement with said spaced conductors providing a conducting path between said conductor wires through said material, a first coating of insulating material enclosing said positive temperature coefficient material, said coating having a melting point above the melting point of said positive temperature coefficient material to maintain the shape during the annealing operation at a temperature above the melting point of said positive temperature coefficient material and below the melting point of said coating, an insulating spacer positioned between said conductors to prevent electrical contact and maintain substantial spacing between said wires during annealing of said positive temperature coefficient material, and a second coating of insulating material surrounding said first coating.
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Abstract
A heating element for use in an electric blanket or the like including conductors spaced apart in a positive temperature coefficient (PTC) material which serves as a self-limiting heater. The conductors are separated by a spacer which prevents the conductors from engaging each other when the PTC material softens or melts during annealing thereof. A coating of material having a higher melting point than the PTC material is placed over the PTC material to maintain its shape during the annealing process.
57 Citations
4 Claims
- 1. A self-limiting electric heating element adapted for use in flexible heated products such as heating pads, electric blankets and the like comprising an elongated conductor including a flexible insulating core supporting a pair of conductor wires disposed helically around said core, an envelope of positive temperature coefficient material positioned in direct engagement with said spaced conductors providing a conducting path between said conductor wires through said material, a first coating of insulating material enclosing said positive temperature coefficient material, said coating having a melting point above the melting point of said positive temperature coefficient material to maintain the shape during the annealing operation at a temperature above the melting point of said positive temperature coefficient material and below the melting point of said coating, an insulating spacer positioned between said conductors to prevent electrical contact and maintain substantial spacing between said wires during annealing of said positive temperature coefficient material, and a second coating of insulating material surrounding said first coating.
Specification