White opaque film with low transparency with high dielectric strength

摘要

The foil has 50 wt% of crystallizable thermoplastic polyester, 1-20 wt% of barium sulfate and titanium dioxide and 1-25000 ppm of optical brighteners related to the weight of the thermoplastics of a pigmented layer. The polyester units are ethyleneglycol and terephthal acid and/or isophthal acid, naphthalin-1,5-dicarbonicacid or naphthalin-2,6-dicarbonicacid. The polyester (greater than 50 wt%) is polyethylene terephthalate, polyethylene naphthalate or their mixtures. The foil further comprises a base layer, sealable surface layers. The surface layer contains polyethylene terephthalate, polyethylene naphthalate or a copolymer of polyethylene terephthalate-polyethylene naphthalate. The foil exhibits 1-20% of transparency and yellow value with a thickness of 50 mu m, white degree of greater than 85%, dielectric strength of larger than 150 kv/mm, void-index of larger than 87% and density of larger than 1.39 kg/dm3>. The foil: is corona treated for the additional functionality; exhibits an additional functionality and shrinks of smaller than 2.5% in longitudinal and transverse direction when it is heated at 150[deg]C for 15 minutes; has adhesive coating with aminosilane or silicone; and is equipped with hydrolysis stabilizers, ultraviolet stabilizers and flame retardant for obtaining the additional functionality. An independent claim is included for production a white opaque foil.