Coatings 2025 , 15 , 214
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2.3.7. Heat Sealability Test Heat sealability of the coating was tested using a separate hot tack device (KOPP LABORMASTER HCT 3000), and the sealing strength was measured applying standard ASTM F88M-15 with Lloyd LS5 universal testing machine. The sealing temperatures were 170 ◦ C for both A-POP and S-POP. A-POP was sealed for 1 s under the pressure of 650 N. S-POP needed 2 s of sealing under 800 N pressure.
3. Results and Discussion 3.1. Coating Process
PLAX and bioORMOCER ® layers were coated on the substrates A and S using a roll-to-roll coating line at semi-pilot and industrial scale. The first PLAX layer was coated at an industrial scale coating line (Walki Ylöjärvi, Finland) to demonstrate the coatability of PLAX at higher speeds and volumes. The coating finish was even, matte and visually intact. bioORMOCER ® and the top layer of PLAX were applied at a semi-pilot scale using a gravure coater method (SutCo: VTT, Finland) (Figure 1a,b). bioORMOCER ® and PLAX were suitable for the coating method as they were picked up efficiently and transferred evenly onto the substrate. Some foaming issues were faced while coating PLAX, leaving a risk of pinholes. The coatings seemed visually even in the case of both dispersions; bioORMOCER ® left a clear glossy finish (Figure 1c), and PLAX appeared as matte with a tint of beige colour (Figure 1d). No visual differences between the base papers were observed.
Figure 1. Images from the coating process. ( a ) bioORMOCER ® is poured into the coating station. ( b ) PLA-X dispersion at the coating station. ( c ) Visual appearance of A-PO. ( d ) SutCo-line during the coating run of S-POP.
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