PVDF PTC Over-Current Protection for High-Voltage Thermal Stability
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Solution Overview
Problem
Existing over-current protection devices face challenges in achieving high voltage endurance capability and thermal stability, particularly at high temperatures, due to the complexity of formulation design and the inadequate utilization of PVDF crystalline phases.
Innovation Solution
The device employs PVDF with adjusted proportions of α-PVDF, β-PVDF, and γ-PVDF crystalline phases, along with carbon black as a conductive filler, to enhance voltage endurance and thermal stability without additional additives, and includes a heat-sensitive layer with a polymer matrix and flame retardants for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional additives are added to improve voltage endurance capability at high temperature, then voltage endurance capability is improved, but formulation design becomes complicated
Solution Approach 1:
The invention changes the parameter of crystalline phase proportion in PVDF from conventional single-phase focus to multi-phase control (α-PVDF 5-20%, β-PVDF 5-20%, γ-PVDF 70-85%). This parameter change enables the base polymer to provide sufficient voltage endurance capability at high temperature without requiring additional additives, thus resolving the contradiction between reliability improvement and formulation complexity
Solution Approach 2:
The invention creates a composite crystalline phase structure within PVDF by controlling the proportions of α-PVDF, β-PVDF, and γ-PVDF. This internal composite structure provides enhanced voltage endurance capability through the synergistic effects of different crystalline phases, eliminating the need for external additive compounds and simplifying the overall formulation
2Temperature
If PVDF is used as matrix for high temperature application, then thermal stability is improved, but voltage endurance capability is insufficient without additional additives
Solution Approach 1:
The invention modifies the crystalline phase composition parameters of PVDF to achieve both high temperature stability and excellent voltage endurance capability. By controlling γ-PVDF at 70-85% for thermal stability and incorporating α-PVDF (5-20%) and β-PVDF (5-20%) for electrical performance, the material simultaneously achieves high temperature operation capability and superior voltage endurance without requiring additional additives
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 thin-type over-current protection device that maintains excellent voltage endurance and thermal stability, capable of withstanding higher voltages and temperatures without burnout, with a thickness as low as 0.2 mm and a power endurance of 4.6 W/mm², while recovering from tripped states effectively.
Implementation Method 1
the electrical resistance of the PTC conductive composite material remains extremely low at normal temperatures, so that the circuit or 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 2
the main crystalline phases of PVDF are a phase, p phase, and γ phase, and PVDF in these three phases may be referred to as α-PVDF, β-PVDF, and γ-PVDF, respectively
Data Source
AI summary
An over-current protection device includes a first metal layer, a second metal layer and a heat-sensitive layer laminated therebetween. The heat-sensitive layer exhibits a positive temperature coefficient (PTC) characteristic and includes a first polymer and a conductive filler. The first polymer consists of polyvinylidene difluoride (PVDF), and PVDF exists in different phases such as α-PVDF, β-PVDF and γ-PVDF. The total amount of α-PVDF, β-PVDF and γ-PVDF is calculated as 100%, and the amount of γ-PVDF accounts for 33% to 42%.