Effects of application temperature in paper surface sizing with temperature-responsive starch on water repellency and flexographic printability

This study presents an evaluation of the application temperature on water repellence and printability in surface sizing with starch. Two different types of potato starch were used: one conventional oxidised starch and one with hydrophobic and amphoteric modification. The level of hydrophobic modification (HM) was low; the degree of substitution (DS) of the hydrophobically modified starch grade was equal to 0.03. Due to the temperature-responsive character of the modified starch, the sizing operations were performed at room temperature and at 70degreesC. The surfaces treated with the HM starch gained in hydrophobic nature with increasing sizing temperature. A comparison between the oxidised and the HM starch showed that the HM starch gave better print quality as reflected in measurement of white dots. The results obtained indicate clearly that there is a potential to develop a low-DS HM starch for coating/sizing of papers and board where barrier properties and printability are demanded.