Metallized polyimide films with high reflectivity and electroconductivity - Polyimides and Other High Temperature Polymers - page 402

same resistivity. In the measured temperature range, the surface resistivity practi-
cally does not change for all four surfaces. Temperature dependence of surface re-
sistivity ρ s (t) = ρ 0s (1 + α s t) (where ρ 0s and α s are at 20°C; ρ s - surface resistivity,
α s - thermal coefficient of resistivity) follows the equations:
1: ρ s (t) = 0.85 (1 + 9.3 · 10 -4 t) - glass side of Ag-Ni/Kapton 100HN
1*: ρ s (t) = 0.48 (1 + 1.5 · 10 -4 t) - air side
2: ρ s (t) = 0.87 (1 + 8.1 · 10 -4 t) - glass side of Ag/Kapton 100HN
2*: ρ s (t) = 1.22 (1 - 0.8 · 10 -4 t) - air side
It is obvious that temperature coefficients are lower than for pure silver for
which α = 0.0036 [30, 31]. Possible explanation of such behavior may be the in-
corporation of silver layer into the polymer matrix. Surface resistivity of Ni/PI
and Co/PI films measured at room temperature lies in the range 10-100 Ω/sq.
Fig. 10 shows reflectivity spectra of glass sides of four metallized Kapton 100
HN polyimide films measured in relation to silver reference mirror. Visually the
air side for thick Kapton films (500, 300, 200 HN) has slightly lower reflectivity.
Reflectivity for both sides of Kapton 100, 75, 50 and 30 HN is practically the
same. Reflectivity of the films at λ = 531 nm (wavelength of the most intense so-
lar irradiation) is 91% for Ag/PI film, 81% for Ag-Ni/PI, 47% for Ni/PI film and
41% for Co/PI film.
Figure 10. Reflectivity spectra of Kapton 100HN films metallized by: 1 - Ag; 2 - Ag-Ni; 3 - Ni;
4 - Co.