Enhancement of water-resistant water-based decorative paper casein ink by combined amino compounds

Casein aqueous ink was widely used in the area of paper printing as finishing materials for wood-based furniture products. However, the water-based ink has poor water resistance limiting the application. In this study, the ink binder of casein was modified with compound of N-methylolacrylamide (NMA), diacetone acrylamide (DAAM), and caprolactam (CPL) to enhance the water resistance, while balancing the glue absorption capacity. The effect of NMA concentration on the performance of casein aqueous ink was also assessed. The modified aqueous inks were roll-coated on the decorative base paper. The results showed that the stability, hydrophilicity and water resistance of the modified casein were significantly enhanced. Therefore, remove redundancy casein inks showed significant improvements on water stability, water resistance and glue absorption. When the content of NMA was 1.5 g, the average hydrodynamic size and the absolute value of Zeta potential of casein were 350 nm and -45 mV, respectively, showing the improved stability in water system. Thus, the surface contact angle of casein was minimal of 34.1°, and the water retention rate was maximal at 72.5%. The maximum water retention rate of the modified casein ink was obtained at NMA content of 1.5 g with hydrodynamic size of 120 nm and zeta potential of – 31 mV, At this time, remove repetition of casein ink reached 136%, which was a significant increase of 29.5% uptake compared with the unmodified casein ink. These findings indicate that there is a strong correlation between the stability, water resistance, and hydrophilicity of casein and the stability and water resistance of casein inks, and that modified casein has a great potential for application as a water-based ink joining material for decorative papers.