Changes in the performance of polyester film (taking mainstream PET mylar as an example) at differen

Changes in the performance of polyester film (taking mainstream PET mylar as an example) at different temperatures

The properties of polyester films, especially PET materials, are highly dependent on temperature, and their variation needs to be combined with key parameters such as glass transition temperature (Tg≈70°C), continuous service temperature (120°C), thermal deflection temperature (150°C), etc., which can be divided into the following categories according to the temperature range:

1. Low temperature range (-50°C~0°C): stable performance and improved rigidity

Mechanical properties: tensile strength and elongation at break change very little, only the elastic modulus increases slightly (rigidity enhancement), no obvious risk of brittle fracture, can withstand a certain low temperature impact, suitable for cold chain logistics packaging, low-temperature environment wire insulation and other scenarios.

Insulation performance: the dielectric loss (tanδ) is significantly reduced (molecular motion is slowed down, polarization is weakened), the breakdown voltage remains stable (≥18kV/mm), the insulation reliability is better than that of normal temperature, and it can be used for insulation liners of low-temperature electronic components.

Thermal deformation: No thermal shrinkage or deformation, excellent dimensional stability.

2. Normal temperature range (20°C~40°C): the best performance, suitable for most scenarios

Mechanical properties: Tensile strength (≥150MPa), elastic modulus (≥2.5GPa), and elongation at break (≥100%) are all in the optimal range, with good tear resistance and fatigue resistance, which can meet the needs of conventional applications such as electronics, packaging, and printing.

Insulation performance: low dielectric loss (tanδ≤0.005@50Hz), high breakdown voltage, stable corona resistance, and the core temperature range for cable wrapping and transformer insulation.

Thermal deformation: Thermal shrinkage ≤ 1% (120°C×30min conditions), almost no deformation at room temperature, and high dimensional accuracy.

3. Medium temperature range (40°C~120°C): slow decay of performance, can still be used for a short period of time

Mechanical properties: With the increase of temperature, the molecular motion intensifies, the tensile strength slowly decreases (about 80% of normal temperature at 120°C), the elastic modulus decreases (flexibility increases), and the elongation at break increases slightly, but there is no obvious thermal degradation, which can be used for short-term insulation of motor windings at 60°C~100°C.

Insulation performance: The dielectric loss increases slightly with the increase of temperature (tanδ≈0.01 at 120°C), and the breakdown voltage drops by about 10%~15%, but it can still meet the needs of medium and low voltage electrical equipment.

Thermal deformation: slight thermal shrinkage begins to appear (120°C×30min shrinkage rate is about 1%~2%), and long-term use needs to be controlled for a long time (recommended not to exceed 1000h).

4. High temperature range (120°C~150°C): The performance is significantly reduced, so caution should be used

Mechanical properties: The tensile strength drops to 60%~70% of normal temperature, and the elastic modulus is greatly reduced (easy to deform), and long-term exposure to this temperature will lead to slow aging of molecular chains, and the elongation at break decreases (brittleness), which is only suitable for short-term (≤100h) and low-stress scenarios (such as temporary electrical insulation).

Insulation performance: The dielectric loss rises sharply (tanδ≈0.03 at 150°C), the breakdown voltage drops by more than 30%, the corona resistance deteriorates, and it is prone to partial discharge, which is not suitable for high-voltage equipment.

Thermal deformation: The thermal shrinkage rate is up to 3%~5%, and the dimensional stability is poor, which may lead to the failure of the insulation structure due to shrinkage.

5. Ultra-high temperature range (>150°C): Serious failure of performance and unusable

After the temperature exceeds 150°C, the PET molecular chain begins to degrade thermally, and its mechanical properties collapse sharply (the tensile strength is less than 40% of normal temperature), and it is prone to softening and melting deformation.
The insulation performance is completely lost (dielectric loss > 0.05, breakdown voltage < 10kV/mm), and even with the release of a small amount of pyrolysis gas, only modified polyester film (such as high-temperature resistant PET, PET/PI composite film) can be used within 180°C for a short period of time, and ordinary PET is strictly prohibited from being used in this temperature range.