PTC Conductive Composite Material for Overcurrent Protection
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Solution Overview
Problem
Existing PTC conductive composite materials face challenges in achieving low resistance and miniaturization due to limited conductive capacity of carbon black, high resistance with metal powders requiring encapsulation, and poor reproducibility with metal carbide ceramic powders.
Innovation Solution
A PTC conductive composite material with a crystalline polymer matrix and a solid solution conductive filler, such as metal carbide, dispersed uniformly, achieving a volume resistivity of less than 300 μΩ·cm, and an overcurrent protection device with two metal foils sandwiching the composite material, ensuring low resistance and good reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon black is used as conductive filler, then good resistance stability is achieved, but limited conductive capacity prevents achieving low resistance
Solution Approach 1:
The patent uses a composite conductive filler system combining metal carbide ceramic powder (providing stability) with metal powder (providing high conductivity). This composite approach allows the material to achieve both low resistance and good stability without requiring encapsulation, resolving the contradiction between resistance stability and conductive capacity
Solution Approach 2:
The patent optimizes the particle size distribution and volume ratio of different fillers (metal carbide ceramic powder at 10-50 μm and metal powder at 1-10 μm) to achieve the desired electrical properties. By carefully controlling these parameters, the material achieves low resistance while maintaining stability without encapsulation
2Quantity of substance
If metal powder is used as conductive filler, then extremely low resistance is achieved, but encapsulation is required to prevent oxidation which increases resistance
Solution Approach 1:
The patent combines metal powder with metal carbide ceramic powder in a specific ratio. The metal carbide ceramic powder acts as a protective phase that prevents oxidation of the metal powder particles, eliminating the need for external encapsulation while maintaining the low resistance properties of the metal powder
Solution Approach 2:
The metal carbide ceramic powder serves as an intermediary protective layer around the metal powder particles, preventing direct contact with oxygen in the air. This intermediary approach allows the metal powder to maintain its conductive properties without requiring additional encapsulation structures
3Device complexity
If metal carbide ceramic powder is used as conductive filler, then no encapsulation is needed, but poor combination with polymer makes resistance reproducibility difficult to control
Solution Approach 1:
The patent creates a composite filler system where metal carbide ceramic powder and metal powder work synergistically. The metal powder improves the polymer-filler interface compatibility and provides a more uniform distribution, while the metal carbide ceramic powder maintains structural stability. This composite approach enhances resistance reproducibility compared to using metal carbide ceramic powder alone
Solution Approach 2:
The patent creates local regions with different filler compositions and particle sizes within the polymer matrix. The combination of finer metal powder particles (1-10 μm) and coarser metal carbide ceramic powder particles (10-50 μm) creates a hierarchical structure that improves both processing uniformity and electrical property reproducibility
4Quantity of substance
If conductive filler content is increased to achieve low resistance, then room temperature resistance decreases, but PTC effect intensity may be reduced
Solution Approach 1:
The patent optimizes the volume ratio of conductive fillers to polymer matrix and the particle size distribution to achieve a balance where sufficient conductive pathways exist at room temperature, but the crystalline polymer structure can still undergo phase transitions at elevated temperatures to produce the PTC effect. The specific filler content range (40-70 wt%) is critical for maintaining both low resistance and strong PTC characteristics
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 an overcurrent protection device with very low resistance at room temperature and excellent PTC intensity, enabling miniaturization of electronic components without the need for encapsulation, and maintaining stability through crosslinking or heat treatment.
Implementation Method 1
The resistance of positive temperature coefficient (PTC) conductive composite materials maintains extremely low under normal temperature, and can react to temperature changes very quickly. When an overcurrent or an over-temperature occurs, these materials exhibit a sharp increase in resistivity
Implementation Method 2
The solid solution conductive filler is uniformly dispersed in the polymer material, whose average particle size ranges from 0.1μm to 10 μm, and the volume resistivity is no more than 300 μΩ·cm
Data Source
AI summary
A PTC conductive composite material and the overcurrent protection device made of the material are disclosed. The PTC conductive composite material includes: (a) A matrix of crystalline polymer material at least, occupies 20%-70% of the volume fraction of the PTC conductive composite material, (b) One kind of conductive filler occupies 30%-80% of the volume fraction of the material. The solid solution conductive filler is uniformly dispersed in the polymer material, whose average particle size ranges from 0.1 μm to 10 μm, and the volume resistivity is no more than 300 μΩ·cm. The overcurrent protection device prepared by using the PTC conductive composite material as described above includes two metal foils, which are made into a sandwich, separated by a layer of the PTC conductive composite material.And the advantages of the overcurrent protection device of the invention are low resistance, good reproducibility of resistance and well PTC intensity.