Method for heat treating PTC devices
AssigneeLittelfuse, Inc.
InventorsTom J. Hall, Michael J. Weber
Life of this patent
Estimating the term…
Abstract
The present invention provides a method for heat treating a polymer PTC composition to increase the peak resistivity of the composition making it especially well suited for high voltage applications. A polymer PTC composition having a melting point temperature Tmp is provided. The temperature of the polymer PTC composition is increased at a rate, r1, to a temperature greater than Tmp. The temperature of polymer PTC composition is held at the temperature greater than Tmp for a predetermined period of time. Then the temperature of the polymer PTC composition is decreased to a temperature less than Tmp at a rate, r2, wherein r2 is greater than r1.
Claims16
A method for heat treating a polymer PTC composition, the method comprising the steps of:
- providing a polymer PTC composition having a melting point temperature Tmp;
- increasing the temperature of the polymer PTC composition at a first rate, r1, to a temperature greater than Tmp;
- holding the polymer PTC composition at the temperature greater than Tmp for a predetermined period of time;
- decreasing the temperature of the polymer PTC composition to a temperature less than Tmp at a second rate, r2, wherein r2 is greater than r1.
A method for heat treating a polymer PTC composition having an initial peak resistivity, Rpi, and a melting point temperature, Tmp, the method comprising the steps of:
- increasing the temperature of the polymer PTC composition at a first rate, r1, to a temperature greater than Tmp;
- holding the polymer PTC composition at the temperature greater than Tmp for a predetermined period of time;
- decreasing the temperature of the polymer PTC composition to a temperature less than Tmp at a second rate, r2, wherein r2 is greater than r1;
- and
- after decreasing the temperature of the polymer PTC composition, the composition has a new peak resistivity, Rpn, which is at least 1.5×Rpi.
A method for heat treating an electrical circuit protection device having a PTC element and two electrodes, the PTC element being composed of a polymer PTC composition having a melting point temperature, Tmp, and an initial peak resistivity, Rpi, the method comprising the steps of:
- increasing the temperature of the polymer PTC composition at a first rate, r1, to a temperature greater than Tmp;
- holding the polymer PTC composition at the temperature greater than Tmp for a predetermined period of time;
- decreasing the temperature of the polymer PTC composition to a temperature less than Tmp at a second rate, r2, wherein r2 is greater than r1 such that the polymer PTC composition has a new peak resistivity, Rpn, which is at least 1.5×Rpi.
Dependencies are inferred from the claim text.