Preparation And Application Of Cationic Waterborn Polyurethane Surface Sizing Agent

Compared to sizing in pulp, the surface sizing can give special performance to paper and paperboard, and be positive to the improvement of their correlative physical performance, also of the writing performance and printability. It seems very improtant to prepare surface sizing agent, especially the polymer.The waterborn polyurethane, which takes the water as the dispersion medium, is noncombustible, non-toxic, free of contamination and good for energy conservation, convenient for operation and process. It can give birth to high size degree with a little dosage as its good film forming ability. Further more, the paper performance can be improved, so the aqueous polyurethane has get more and more attention.In the study, a series of steady waterborn polyurethane dispersions were synthesized using polyester glycol, toluene diisocyanate (TDI), 1,4-butylene-glycol and hydrophilic chain-extending agent by internal emulsification method, then the surface sizing was done for paper. The study consists of two parts: One is the synthesiztion and characterization of cationic aqueous-based polyurethane, the other is the analysis of the performance of surface sizing by cationic aqueous polyurethane and the condition of the surface sizing.In the study of the synthesiztion of cationic aqueous-based polyurethane, the effects of the molar ratio of NCO/OH groups, the variety and dosage of hydrophilic chain-extending agent, the sequence of adding material, the method and the degree of neutralization, the temperature of chain-extending reaction and the amount of acetone were discussed.The result showed that it can be emulsified easily, and the film hardness of the emulsion is high when the N-methyl diethanolamine was chosen as hydrophilic chain-extending agent. It is beneficial for synthesis technological and for the decrease of solvent dosage when the charging sequence is that polyester polyol and TDI were made to react firstly, then MDEA was added. Good performance of latex would be got when the method, which was doing neutralization firstly then doing emulsification, was chosed.The particle size of cationic aqueous polyurethane dispersions decrease when the molar ratio of NCO/OH groups and the dosages of MDEA and acetone increase. The viscosity of the dispersions incceases when the molar ratio of NCO/OH groups, the dosages of MDEA and the temperature of chain-expending inccease and the amount of acetone decrease. The water resistance of the coating film enhances when the molar ratio of NCO/OH groups and the dosage of acetone decrease and the dosage of MDEA and the temperature of chain-expending inccease.The correlative physical performance and sizing degree of the paper improved significantly when sized by cationic aqueous polyurethane dispersions synthesized in lab. Specially, compared with the paper sized with starch, rosin, even AKD, the printability of the ink jet printing paper improved significantly.In order to reduce the cost of sizing with PU, AKD was used to size in pulp and then the PU was used in surface sizing. The optimal dosage of AKD and PU was dicussed and the low cost was got.The results of our study are helpful for the development of the new surface sizing agent which can improve the water resistance and printability. It is helpful for meetting the development of surface sizing which gets higher requirement.