Study On Preparation And Characteristics Of Powder Coating For Dry Coat Of Paper

In conventional coating technique for paper, water-dispersed coating with30%-70%solid content is directly coated onto the surface of raw paper, and then water was dried bydifferent ways. However, there are some disadvantages in this technique, such as lots ofconsumption of water and energy, lowering the quality of raw paper and coated paper.Therefore, dry coating technique of paper was put forward. Dry coating technique of paperprovides an effective way to reduce the dosage of water and save energy compared toconventional coating technique for paper. Supercritical carbon dioxide which isenvironmental friendly has aroused much interest in the polymerisation of resin as a potentialsolvent for polymerization reactions. Particles of powder coating mingled poly(methylmethacrylate) resin and kaolin as pigment were obtained in the media of supercritical carbondioxide. The kaolin particles were modified by silane coupling agent KH-570and couplingagent of organic titanate NDZ-311respectively to improve the compatibility between thepigment and polymer. Ethyl acrylate was useed as co-monomer to regulate and control theglass-transition temperature of the synthetic resin to meet the demand of thermo-mechanicalfusing treatment process.In this paper, molecular weight and its distribution of polymer were determined by gelpermeation chromatography (GPC) method. The structure of the powder coating wasinvestigated by Fourier transform infrared spectroscopy (FT-IR). The thermo-stability of thesynthesized polymer was measured by thermo-gravimetry (TG). The glass-transitiontemperature of copolymer was determined by differential scanning calorimetry (DSC).Themixed particles were characterized by scanning electron microscopy (SEM).The experimental results showed that the molecular weight and its distribution of PMMAcan be effectively controlled when the reaction pressure was10MPa, reaction temperature650C, reaction time10hours, and the monomer concentration was10%, initiatorconcentration1%, stabilizer concentration10%. From SEM observation, it was found that thepigment granules were able to evenly disperse and embedded in the PMMA and didn’t showconglomeration. The modified kaolin can increase the thermal properties of powder coatingand control the molecular weight and its distribution of PMMA polymer. Addition of inorganic kaolin can improve powder coating’s thermo-stability. The glass-transitiontemperature of the powder coating can be effectively controlled by adjusting the co-monomerMMA/EA ratio, and the suitable value is0.6/0.4to0.7/0.3.