PPTC Polymer Composition for Low Thermal Derating
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Solution Overview
Problem
Polymer positive temperature coefficient (PPTC) devices exhibit significant thermal derating at low temperatures, leading to increased electrical resistance and reduced performance as a resettable fuse, due to the expansion of the polymer matrix and separation of conductive filler particles with temperature increases, which is undesirable for overcurrent or over-temperature protection applications.
Innovation Solution
Incorporating a high temperature polymer filler with a melting temperature at least 20°C higher than the polymer matrix, and/or a low thermal expansion polymer filler, into the PPTC material to minimize resistance changes and maintain low thermal derating characteristics below the trip temperature, achieved through a process involving hot melt extrusion and foil lamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional PPTC device uses a single polymer matrix with conductive filler, then the device achieves a clear trip transition at the polymer's melting temperature, but the device exhibits significant thermal derating with increased resistance in the low temperature state as temperature rises
Solution Approach 1:
The patent uses a composite polymer system consisting of a primary polymer matrix (e.g., polyethylene) and a secondary polymer with higher melting temperature (e.g., polypropylene or PVDF). This composite structure allows the primary polymer to provide the sharp trip transition while the secondary polymer maintains structural integrity and reduces thermal expansion in the low temperature state, thereby stabilizing resistance against thermal derating
Solution Approach 2:
The patent modifies the thermal and mechanical parameters of the polymer matrix by blending polymers with different melting temperatures and thermal expansion coefficients. The secondary polymer's higher melting point and lower thermal expansion compensate for the primary polymer's thermal expansion below its melting point, reducing the separation of conductive filler particles and maintaining stable resistance in the low temperature state
2Stability of the object's composition
If the polymer matrix expands with increasing temperature below the trip temperature, then the material maintains structural integrity, but the expansion causes separation of conductive filler particles leading to increased electrical resistance
Solution Approach 1:
The secondary polymer acts as a counterweight to the thermal expansion of the primary polymer matrix. Due to its higher melting temperature and lower thermal expansion coefficient, the secondary polymer constrains the overall thermal expansion of the composite, preventing excessive separation of conductive filler particles and maintaining stable electrical resistance in the low temperature state
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The addition of high temperature and low thermal expansion polymer fillers reduces the thermal derating of PPTC devices, maintaining low electrical resistance up to higher temperatures and improving processing stability, as demonstrated by reduced resistance ratios and process jumps in the PPTC materials.
Implementation Method 1
the polymer matrix may also expand as a function of increasing temperature. This expansion is a characteristic of the thermal properties of the polymer matrix, and may cause an increase in electrical resistance as conductive filler particles become separated
Implementation Method 2
the at least one polymer filler may comprise a second polymer, different from the first polymer, wherein the at least one polymer comprises a first melting temperature
Implementation Method 3
the polymer material, such as a melting transition or a glass transition. At such a transition temperature, sometimes called a trip temperature
Implementation Method 4
the conductive filler that provides a mixture that transitions from a low resistance state to a high resistance state, due to changes in the polymer material
Implementation Method 5
The resistance of the PPTC device may be altered by direct heating due to temperature increase in the environment of the circuit protection element, or via resistive heating generated by electrical current passing through the circuit protection element
Data Source
AI summary
A novel polymer positive temperature coefficient (PPTC) material, device, and method of fabrication. One example of polymer positive temperature coefficient (PPTC) includes a polymer matrix, the polymer matrix comprising a first polymer. The PPTC material may further include a conductive filler, disposed in the polymer matrix; and at least one polymer filler, dispersed within the polymer matrix. The at least one polymer filler may comprise a second polymer, different from the first polymer, wherein the at least one polymer comprises a first melting temperature, and wherein the second polymer comprises a second melting temperature, the second melting temperature exceeding the first melting temperature by at least 20 C.