Polyurethane materials are widely used in polymer protective film coatings on metal surfaces. In order to ensure its durability, the thickness of the coating needs to be controlled in most cases.
We used the MProbe VisHR Film Thickness Gauge to measure the thickness of polyurethane coatings on four metal surfaces. The substrates of these four samples are aluminum, steel and two nickel, which we respectively marked as: Al, SS, Ni-1, Ni- 2. The optical dispersion model of polyurethane uses the Cauchy approximation model, and its refractive index is about 1.5. When analyzing spectral data, we use 1.47. (The refractive index has relatively little influence on the measurement results, and a change in the refractive index of 0.01 will cause a thickness error of about 0.01um). Data were analyzed using a thick film algorithm (Fast Fourier Transform algorithm).
Measurement result:
| sample | Coating Thickness (microns) |
| Aluminum (Al) | 52.2 |
| Steel (SS) | 40.3 |
| Nickel (Ni-1) | 21.3 |
| Nickel (Ni-2) | 41.1 |
The following is the spectral data analysis:
Figure 1. The reflectance spectrum curve of the sample, the green is the reflectance spectrum of the steel sample (SS), the red is the reflectance spectrum of the aluminum sample (Al), and the bottom two curves are the spectral curves of the nickel sample (Ni-1, Ni-2)
Figure 2. Data analysis of a steel sample, using the Fast Fourier Transform algorithm, with a coating thickness of 40.3um
Figure 3. Data analysis of an aluminum sample, using the Fast Fourier Transform algorithm, with a coating thickness of 52.2um
Figure 4. Data analysis of a nickel sample (Ni-1), using the Fast Fourier Transform algorithm, with a coating thickness of 21.3um
Figure 5. Data analysis of a nickel sample (Ni-2), using the Fast Fourier Transform algorithm, with a coating thickness of 41.1um
