| Water-based ink has been developed quickly in recent years because of its non-harmful to the environment. Water-based ink is composed of alkali-soluble resin, latex, water and other accessory solvent. Styrene-acrylic resin, a typical one among all alkali-soluble resins, has the criteria of low molecular weight, narrow molecular weight distribution, high acid value and low Tg.Several kinds of typical resins for water-based ink were characterized by IR, H'-NMR, GPC and DSC. The main monomer structure unit are styrene, methyl methacrylate (methyl acrylate), and acrylic acid; the ratio of St ,MMA(or MA) andAA is about 5:2:3. Relative molecular weight: ~M~n =3700~5800, A/^=7600~13000, molecular weight distributional.6~2.4; Tg:92.7~106.6'C; acid value: 190-215.Through semi-continuous solution polymerization, series of styrene-acrylic resinwith low molecular weight (MH =3000~6000), narrow molecular weight distribution (Mw/Mn <2) and high acid value 200 (mg KOH/g) were synthesized in the research.The resin was characterized by IR, H'-NMR, GPC and DSC.The kinetics of the semi-continuous polymerization was studied. The copolymer composition during the reaction was determined. Reasons for the deviation from the copolymer composition of the final product to the calculated value were discussed based on the factors affecting the reactivity of monomers. Changes of the monomer concentration, initiator concentration, cumulative conversion and instantaneous conversion for total monomers during the polymerization process were also investigated. It showed the reaction rate is slow at the early stage of the reaction which resulted in the cumulation of the monomer amount. The automatic acceleration phenomenon happened during the polymerization process. It was found that the monomer addition rate, acrylic acid ratio and the addition way of the monomer and initiator affect the cumulative and instantaneous conversion. It was shown thatindecreasing the addition rate properly, combined with adding a certain amount of initiator (or initiator and monomer)at the beginning of the reaction is benefit to increasing the final cumulative conversion and the uniformity of the copolymer composition.The changes in the molecular weight and molecular weight distribution index of the resin during the semi-continuous polymerization were also researched. Owing to the obvious automatic acceleration phenomenon in the polymerization process due to the gel effect, the MW of the resin increase and the MWD of the resin become broaden gradually during the reaction. When the initiator amount added increases, MW of the resin decreases while MWD changes a little. Increasing the solvent content can weaken the gel effect and decreases MW of the resin while MWD become narrowed. It was also found that in the experimental range, changes in the added rate of monomers and initiator have little affection on the MW and MWD of the resin.The aqueous liquid of the resin after animation behaved as a Newtonian fluid. It was found that the viscosity of the liquid is related not only to the MW and MWD of the resin, but also to the uniformity of copolymer composition which closely related to the synthesis condition including the addition rate. The aqueous animation liquid of styrene-acrylic resin with low viscosity and high clarity was obtained from the resin with high acid and low molecular weight which was synthesized under proper addition rate.
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