| With printing technology's developing continuously, in printing industry, the requirement of printability is improving continuously. For instance, paper sheet's pick resistance is need to be higher because of the improvement of printing machine's speed, and paper sheet also is needed to have good printing opacity when lower-basic weight paper is developing. Thus, all these requirements promoted the studies and development of poly-emulsion surface sizing agent tremendously. Poly-emulsion surfacesizing agents take more and more importance in papermaking industry. They are related to the tendency of papermakers material's composition adjusting, printing process diversity and being higher speeded, and the tendency of producing higher qualitative paper products. Surface coating act on the surface of paper sheet straightly, thus it also recovers a series of operating problems, such as the pollution of machine system and frothing and lower sizing degree under high temperature. So, a new polymer-emulsion surface sizing agent (belongs to styrene acrylic emulsions, SAE) was synthesized in lab, and on the foundation of the traditional styrene-acrylic resin emulsion, adopting emulsion polymerization and adding functional monomer to modify the traditional emulsion. Then putting it into surface sizing operating to test its performance.Main results have been obtained as following:1 , The emulsion polymerization will be remarkably influenced by the selectivity of monomer, the proportion of soft monomer and hard monomer, the accession of functional monomer. The performance and the application capability of the polymer emulsion are influenced by the above factors. With the increase of proportion of hard and soft monomer, the smoothness of paper sheet increased first and then decreased. The water absorption value of paper sheet decreased first and then increased. If the proportion of hard and soft monomer changed from 1:1 to 2:3, the smoothness of paper sheet will be better, and the water absorption value of paper sheet will be lower. Adding functional monomer to the traditional emulsion will occur crosslinking to form three —dimensional reticulation so as to improve water resistance of the membrane. But the dosage of functional monomer should not be too high. It would be best to control it no more than 4 percent of the total dosage of monomer.2 , The emulsion polymerization also was influenced by the dosage of emulsifier and initiator, reaction temperature and reaction time and agitating speed. With the increase of the dosage of emulsifier, the polymerization velocity increased, and the stability to electrolyte became higher. But if the dosage of emulsifier was too high, the water resistance of sized paper sheet will be affected. Thus if the dosage of emulsifier was from 1.5 to 3 percent of total dosage of monomer and the dosage of initiator is from 0.6 to 0.7 percent of total dosage of monomer, and the reaction last for about 2 to 3 hours under 82±1℃, the emulsion polymerization will be completed well.3 , During the process of surface sizing, oxidized starch and polymer emulsion surface sizing agent were combined to use them together. Using oxidized starch in surface sizing will improve the intensity and smoothness of paper sheet so as to make paper sheet more exquisite. Addingpolymer emulsion surface sizing agent will improve water resistance and pick resistance of paper sheet. As a result, linting and pull-up phenomenon were decreased well and printability was improved well. The better combining ratio is: oxidized starch takes from 90 to 95 percent of the sizing liquid, polymer emulsion takes from 5 to 10 percent of the sizing liquid.
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