The invention relates to the technical field of optical thin films, and particularly discloses a high-
birefringence laminated reflecting film and a preparation method thereof. According to the laminated reflecting film, 4, 4 '-
biphenyl dicarboxylate modified PET is used as a
raw material of an A layer, PMMA or PETG is used as a
raw material of a B layer, the difference value of the
glass transition temperatures Tg of the
raw material of the A layer and the raw material of the B layer is controlled to be smaller than or equal to 5 DEG C, and the laminated reflecting film formed by alternately laminating the raw material of the A layer and the raw material of the B layer is subjected to synchronous two-way stretching and
heat setting treatment; according to the application, PET is modified by the BB
monomer, and a biaxial stretching process and the content of the BB
monomer are regulated and controlled for the first time, so that Tg difference values of the raw materials of the layer A and the raw materials of the layer B are close, meanwhile, a
refractive index difference value is increased, the reflecting film with excellent optical performance and mechanical performance can be obtained with a small number of lamination
layers, and the reflecting film has high in-plane
birefringence, high in-plane
birefringence, high in-plane birefringence, high in-plane birefringence, high in-plane birefringence and high in-plane birefringence. And the
reflectivity reaches 74% or above.