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Printing Properties of Water-based Pigmented Inkjet Inks on the Oxygen-plasma Modified Polylactide Sheets 234 The Journal of the Royal Institute of Thailand Vol. 37 No. 1 Jan.-Mar. 2012 Figure3 Printingqualityof thecontinuous tonereproductionofPLAsheets (a) theuntreatedand treated sheets at (b) 70 W, 30 s; (c) 100 W, 30 s; (d) 30 W, 20 min and (e) 30 W, 25 min The exposure time has a marked effect on the exposed surface roughness (Ra distance) and RMS as shown in Figure 6. As presented in Figure 2(c) and Figure 2(d), one can see that the number of pikes was reduced but their heights were sharply increased. The number of pikes and grooves are then proposed to give good ink adhesion to the PLA surface. The effect of exposure time on surface roughness indicated that longer exposure times produced the higher RMS values (more roughness). It is inevitable to note that the higher exposure times at 30 and 40 min cannot print the inks to the full tonal density with good quality.