PTC Multilayered Over-Current Protection Device with Segmented Resistance
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Solution Overview
Problem
Conventional over-current protection devices with PTC polymer layers suffer from poor electrical conductivity and adhesion issues between the polymer layers and electrodes, and their electrical properties such as volume resistance and withstand voltage do not meet industrial requirements.
Innovation Solution
An over-current protection device is designed with a PTC multilayered structure comprising a first polymer layer bonded to the electrode, an intermediate layered unit with a second polymer layer having a higher volume resistance than the first and third polymer layers, and the third polymer layer bonded to the second electrode, each with distinct polymer matrices and particulate conductive fillers, ensuring improved electrical conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single PTC polymer layer is used, then the device structure is simple, but the electrical properties (volume resistance, withstand voltage) do not meet industrial requirements
Solution Approach 1:
The single polymer layer is segmented into three distinct polymer layers with different volume resistances. The first and third layers have lower volume resistances for good electrical contact, while the intermediate second layer has higher volume resistance for electrical stability, creating a segmented structure that simultaneously achieves both structural simplicity and improved electrical properties.
Solution Approach 2:
Different regions of the multilayered structure are assigned different electrical properties. The first and third polymer layers have lower volume resistances optimized for electrode adhesion and current conduction, while the intermediate second layer has higher volume resistance optimized for electrical stability and breakdown resistance, achieving local quality optimization throughout the device.
2Ease of manufacture
If polyethylene-based composition is used for PTC polymer layer, then the material is easy to process, but the adhesion between polymer layer and electrodes is poor
Solution Approach 1:
The patent uses composite polymer materials where each polymer layer is formed from a mixture of polyethylene base resin and elastomer resin. This composite formulation maintains the processing ease of polyethylene while the elastomer component enhances adhesion to electrodes, resolving the contradiction between ease of manufacture and adhesion reliability.
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 device exhibits enhanced electrical properties, including a higher volume resistance for the second polymer layer compared to the first and third, leading to improved electrical stability and a higher passing ratio in breakdown tests, effectively preventing damage under high voltage and current conditions.
Implementation Method 1
The first, second and third polymer layers respectively have first, second and third volume resistances, and the second volume resistance is higher than the first and third volume resistances
Implementation Method 2
The PTC effect is a phenomenon that, when the temperature of the polymer matrix is raised to its melting point, crystals in the crystalline region start melting and result in generation of a new non-crystalline region. As the new non-crystalline region is increased to a certain extent and merges with the original non-crystalline region, the conductive path of the particulate conductive filler will become discontinuous and resistance of the PTC polymer material will increase rapidly
Data Source
AI summary
An over-current protection device includes first and second electrodes and a positive temperature coefficient (PTC) multilayered structure disposed between the first and second electrodes. The PTC multilayered structure includes a first polymer layer that is bonded to the first electrode, an intermediate layered unit that is bonded to said first polymer layer and that includes a second polymer layer, a third polymer layer that is bonded to and disposed between the intermediate layered unit and the second electrode. The first, second and third polymer layers respectively have first, second and third volume resistances, the second volume resistance being higher than the first and third volume resistances.