PTC Over-Current Protection Layer With IPN for Thin Voltage Endurance
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Solution Overview
Problem
Existing over-current protection devices face issues with thermal instability and increased electrical resistance due to gaps or cracks forming under temperature variations, compromising their structural integrity and voltage endurance, especially in smaller form factors.
Innovation Solution
Incorporating a polyolefin-based copolymer into a polymer matrix to form an interpenetrating polymer network (IPN) within a heat-sensitive layer, which includes a polyolefin-based homopolymer, reduces thermal expansion and maintains structural integrity, allowing for a thinner design with improved voltage endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of the PTC material layer is reduced to make the device smaller, then the device size is decreased, but the voltage endurance capability is reduced and the device is easily burnt out
Solution Approach 1:
The patent employs a composite polymer matrix consisting of polyolefin-based homopolymer and copolymer. This composite material structure provides both mechanical strength and thermal stability, enabling the PTC material layer to maintain integrity at reduced thickness while withstanding high voltage stress without burnout.
Solution Approach 2:
The patent modifies the polymer matrix composition by incorporating polyolefin-based copolymer with specific gel fraction (30-80%) and molecular weight parameters. These parameter changes enhance the material's electrical breakdown resistance, allowing thinner layers to withstand higher voltages.
2Temperature
If the PTC material layer is subjected to high temperature environment, then the device can operate at higher temperatures, but gaps or cracks are formed in the PTC material layer, damaging structural integrity
Solution Approach 1:
The patent controls the gel fraction of the polyolefin-based copolymer within 30-80% and adjusts the molecular weight parameters to optimize thermal expansion characteristics. This parameter control reduces differential thermal stress between matrix and conductive filler, preventing gap formation and crack development under thermal cycling.
Solution Approach 2:
The composite polymer matrix of homopolymer and copolymer creates a more uniform thermal expansion profile. The copolymer's gel structure acts as a buffer that accommodates thermal stress, maintaining the integrity of the PTC material layer during temperature variations.
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 solution results in a thermally stable, ultra-thin over-current protection device with lower resistance-jump ratios and standard deviations, enhancing electrical performance and preventing burnout under high current and power conditions.
Implementation Method 1
the heat-sensitive layer may further include a polyolefin-based homopolymer, which is blended with the polyolefin-based copolymer to form an interpenetrating polymer network (IPN). The structure of IPN decreases phase separation between the polyolefin-based copolymer and the polyolefin-based homopolymer, and lowers coefficient of thermal expansion (CTE) of the heat-sensitive layer
Implementation Method 2
The polyolefin-based homopolymer has a first coefficient of thermal expansion (CTE), and the polyolefin-based copolymer has a second CTE. The second CTE is lower than the first CTE
Implementation Method 3
the heat-sensitive layer exhibits a positive temperature coefficient (PTC) characteristic and includes a polymer matrix and a conductive filler. the electrical resistance of the PTC conductive composite material remains extremely low at normal temperatures, so that the circuit or battery cell can operate normally. However, when an over-current or an over-temperature situation occurs in the circuit or cell, the electrical resistance will instantaneously increase to a high electrical resistance state
Implementation Method 4
The conductive filler is dispersed in the polymer matrix, thereby forming an electrically conductive path in the heat-sensitive layer
Data Source
AI summary
An over-current protection device includes a heat-sensitive layer and an electrode layer. The electrode layer includes a top metal layer and a bottom metal layer, and the heat-sensitive layer attached therebetween. The heat-sensitive layer exhibits a positive temperature coefficient (PTC) characteristic and includes a polymer matrix and a conductive filler. The polymer matrix includes a polyolefin-based homopolymer and a polyolefin-based copolymer. The polyolefin-based homopolymer has a first coefficient of thermal expansion (CTE), and the polyolefin-based copolymer has a second CTE lower than the first CTE. The polyolefin-based homopolymer and the polyolefin-based copolymer together form an interpenetrating polymer network (IPN).