The present technology relates to electrical insulation films, in particular capacitor films, and their use.
Capacitor films must withstand extreme conditions like high temperatures and high electrical breakdown strength. Additionally it is appreciated that capacitor films possess good mechanical properties like a high stiffness. Up to now there is the prevailing opinion in the technical field of capacitor technology that high electrical breakdown strength can be only achieved with a low level of electrical conduction caused by residual metals such as titanium, aluminium and boron. However traditional polypropylenes produced with a Ziegler-Natta catalyst are contaminated with high amounts of residual catalyst components. To achieve the desired very low levels of impurities to make the polypropylene suitable for capacitor films, the polypropylenes must be troublesome washed, a process which is time consuming and cost-intensive. To overcome the washing step polypropylenes produced in the presence of supported single-site catalysts have been developed, as for instance described in WO 02/16455 A1, with low levels of impurities including metallic and non-metallic impurities, like aluminium, titanium, silicon, and halogen (such as Cl and F). However to achieve this goal of low levels of impurities the process conditions must be controlled very carefully. Moreover such polypropylenes have the drawback that they cannot be processed in a stable way. In particular films based on polypropylenes produced in the presence of supported single-site catalysts suffer from sagging and break easily when manufactured.
Therefore the object of the present technology is to provide a capacitor film with a high temperature resistance and high electrical breakdown strength paired with good mechanical properties, in particular a high stiffness.