Objective In order to solve the problem of low water resistance of traditional water-based inks for decoration paper and low impregnation resin amount of printed decoration paper, an amide compound modified casein water-based ink was prepared by chemical modification.

Method Caprolactam (CPL), hydroxymethacrylamide (NMA) and diacetone acrylamide (DAAM) were used to co-modify casein to prepare modified casein emulsions, and the corresponding water-based inks and printed decoration papers were also prepared. By testing the properties of modified casein and the corresponding water-based inks and printed decoration papers, the changes in water resistance of water-based inks and impregnation resin amount of printed decoration papers, as well as the mechanism of the combined modification of casein by CPL, NMA and DAAM were analyzed.

Result After adding the modifier to casein, a large number of amino groups were introduced into casein system, and a dense film could be formed after drying. The Zeta potential of modified casein emulsion was −45.0 mV, with the viscosity of 1 482.0 mPa·s, water contact angle of 14.2°, and soaking residual rate for 40 min of 80.5%. The water vapor transmission rate of modified casein film was 586.0 g/(m²·24 h), and its water permeability was significantly lower than that of casein film. Therefore, the water resistance of modified casein water-based ink printing decoration paper was significantly improved. There was no loss after soaking for 40 min, and the impregnation amount of printed decoration paper was higher than that of commercially purchased casein water-based ink. At 210 ℃, the color difference ΔE < 1, the color of printed decoration paper showed little change.

Conclusion Compared with unmodified casein, the water and heat resistance of CPL, NMA and DAAM co-modified casein can be greatly improved, and the impregnation amount of printed decoration paper can meet the production requirements.