Proses pengecatan merupakan proses pelapisan dengan tujuan melindungi dan esetika dari produk yang dilapisi. Agar didapatkan permukaan hasil pengecatan yang bagus diperlukan kondisi permukaan yang bagus pula. Kondisi permukaan yang ada sedikit cacat akan tertutupi bila ketebalan lapisan cat yang menempel pada produk cukup tebal. Ketebalan lapisan cat ditentukan oleh jarak penyemprotan, kecepatan langkah ayun, tekanan spray gun dan tekanan tabung residu. Campuran bahan cat dengan pengencer juga berpengaruh pada ketebalan lapisan namun setiap produsen bahan cat telah memberikan rekomendsi perbandingan campuran yang terbaik. Peneliti menentukan jarak penyemprotan 100;150;200 mm, kecepatan langkah ayun 0,381;0,448 m/s, tekanan spray gun 10;12 Psi dan tekanan tabung residu 25;20 Psi. Menggunakan thickness gauge didapatkan ketebalan cat sebesar 0,1 mm pada jarak penyemprotan 100 mm, kecepatan langkah ayun 0,381 m/s, tekanan spray gun 12 Psi dan tekanan tabung residu 20 Psi.

The objective of this research was to investigate the effect of gamma irradiation on mechanical and thermal properties of fish gelatin films prepared from scales of Lates calcarifer. The films were irradiated by gamma rays at varied doses (0-50 kGy). The mechanical and thermal properties of irradiated gelatin films were measured by using colorimeter, Universal Testing Machine, Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared (FTIR) spectrophotometer. The results showed that increasing of irradiation dose up to 50 kGy, the color of irradiated film did not change significantly (p < 0.05). The tensile strength of irradiated film was increased with no differences among dose variation but there was no change on elongation at break value (p < 0.05). The DSC spectra of irradiated gelatin films showed that irradiation did not affect melting temperature (Tm). In contrast, the glass transition temperature (Tg) of irradiated film has slight tendency to increase with increasing of radiation doses. In general, the FTIR spectra confirmed that gamma irradiation up to 50 kGy affected the mechanical properties of gelatin films.

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