Overcurrent protection element

Abstract

This invention relates to an overcurrent protection element including two foils and a pile of PTC material layers set between the two foils and the material layer contains a macromolecular polymer backing and a conductive filling, and the backing includes at least a first crystallized macromolecular polymer(such as LDPE) and a second crystallized macromolecular polymer (such as PVDE), in which, the melting point of the second is higher than the first one for 50deg.C at least, said conductive filling is made of metal particles or oxygen-free ceramic powder with the selected volume resistivity smaller than 500mOhm.cm scattered in the backing, and the volume resistivity of the PTC material layer is smaller than 0.1Ohm.cm, when the resistance is increased to 1000 times that of the initial value R1, the temperature detracting the melting point of the first polymer is 15deg,C.

Description

technical field [0001] The present invention relates to an overcurrent protection element, more specifically, to an overcurrent protection element applied in a low load environment. Background technique [0002] Since the resistance of conductive composite materials with positive temperature coefficient (Positive Temperature Coefficient; PTC) characteristics has the characteristics of sensitive response to temperature changes, it can be used as a material for current sensing elements, and has been widely used in overcurrent protection elements or circuits. component. Because the resistance of the PTC conductive composite material can maintain an extremely low value at normal temperature, the circuit or battery can operate normally. However, when an over-current or over-temperature phenomenon occurs in the circuit or battery, its resistance value will instantly increase to a high resistance state (at least 10 4 ohm or more), and reverse the excessive current to achieve the ...

AI Technical Summary

Problems solved by technology

[0005] However, after long-term use of the PTC conductive composite material composed of LDPE as a polymer substrate, the resistance will gradually increase.

For example, after 100 cycles of thermal shock in the temperature range of -40°C to +85°C, the resistance will increase sharply from the initial 10mΩ to more than 1Ω, that is, the resistance cannot return to the initial value, and it is uncomfortable Applied to electrical devices with low loads such as batteries

[0006] Although it is known that the addition of high-density polyethylene (HDPE) to LDPE can improve the above-mentioned problem of poor resistance reproducibility, but because the melting points of LDPE and HDPE are similar (about 105°C and 130°C respectively) and there is mutual solubility, the trigger temperature Compared with the PTC conductive composite material with LDPE as the polymer base material, it is obviously higher (as shown in Figure 1), that is, the trigger temperature of the PTC conductive composite material is increased, thus losing the low-temperature protection characteristics

Therefore, if it is applied to lithium-ion batteries, there may be dangers such as burning or explosion.

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