Effect of Modification Methods of Polyurethane Latexes on Its Properties and Adhesion to BOPP Film of the Inks

Polyurethane (PU) latexes are difficult to be applied in PE or PP thin film inks because of their weak adhesion, and low polarity and low surface tension of PE and PP thin films. In this paper, two kind of different polyurethane latexes were prepared by modifying their hard and soft segments, respectively. The effects of modification methods on the properties of the polyurethane latexes and the adhesion fastness of the corresponding inks on BOPP were studied. The as prepared PU latexes by using both modification methods have good stability and improved adhesion on the BOPP films. However, using glycerol monooleate (GMO) to modify hard segments of PU increases the proportion of the hard segment with higher polarity in the whole molecule, and in turn increases the glass transition temperature (Tg) of PU, so a slight excess use of GMO demonstrates significant effect on the adhesion and low temperature performance of the ink. The maximum adhesion on BOPP of the corresponding ink is only 35%. The modification on the soft segments using polyester polyol (BY3003) nearly do not affect the Tg and the low temperature performance of PU, therefore the maximum adhesion of the ink reaches 97%.