Surface modification of Quinacridone Red (QR) pigment was carried out using a low temperature NH
3-plasma. The dispersion behavior of such treated QR pigments was studied in three water soluble acrylic resins which had different hydrophilicities. The longer the NH
3-plasma treating time was, the more the hydrophilicity (the heat of immersion in water) was given to the QR surface.
As the heat of immersion (HI) increased, the gloss of QR-dispersed paste increased at first, reached a maximum when the HI was about 0.25J/m
2, and then decreased. On the other hand, as the HI increased, the yield value of the pigment-dispersed paste decreased at first, reached a minimum when the HI was about 0.25J/m
2, and then gradually increased. The same tendencies were observed within this experiment, though the resins were different in hydrophilicity. However, the higher gloss and the lower yield value of QR-dispersed paste were obtained by using the resin of the lower hydrophilicity.
From these results, the existence of the optimum hydrophilicity value of pigment surface, that had been expected in our previous study, was experimentally confirmed.
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