M. Mennig et al., Multilayer NIR reflective coatings on transparent plastic substrates from photopolymerizable nanoparticulate sols, THIN SOL FI, 351(1-2), 1999, pp. 225-229
A new synthesis and processing route for preparing multilayer interference
coatings on plastic substrates has been developed. For this purpose, alcoho
lic sols of surface modified (3-glycidoxypropyltrimethoxysilane, GPTS) SiO2
and TiO2 particles with sizes of 10 and 4 nm, respectively, were synthesiz
ed. Layers were prepared by dip coating, subsequent UV curing (2.1 J/cm(2))
acid thermal post treatment at 80 degrees C for 15 min. Refractive indices
of n(D) = 1.47 for SiO2 layers and n(D) = 1.93 for TiO2 were measured. As
an example, plastic sheets were coated by angle dependent dip coating with
withdrawal speeds from 3 up to 6 mm/s and sin inclination angle of 4 degree
s. By this way, one side of the substrate was coated with six quarterwave t
hick layers (peak wavelength at 750 nm), producing a reflective interferenc
e filter with a reflectivity of 72% between 650 and 900 nm. On the other si
de of the substrate, an interference filter with a reflectivity of 66% betw
een 800 and 1100 nm was produced simultaneously. The interference coatings
do nor show delamination or defects after boiling water test (H2O + 5 wt.%
NaCl, 8 h) and excellent adhesion (GT 0, TT 1) was obtained in the cross cu
t tape test. Yellowing did not occur (Delta(g) < 3) and the mechanical prop
erties of the interference filters were not altered after dry sun test at 7
60 W/m(2) for 270 h. For mechanical protection a nanocomposite hardcoat can
be applied on top of the NIR reflectance filters without changing the opti
cal properties remarkably. 0 1999 Elsevier Science S.A. All rights reserved
.