Key words: semi continuous feeding; Microemulsion polymerization; Soap free emulsion polymerization; Styrene acrylic emulsion; Latex film properties

       Using synthetic resin instead of grease and water instead of organic solvent has become one of the main development directions of coating industry. Paper water-based varnish is a new type of varnish with the improvement of the glazing requirements of packaging materials and the enhancement of people’s awareness of environmental protection. Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       Its advantages of advanced technology, convenient use and economic rationality make it have great development prospects. It has gradually replaced solvent based varnish and oily varnish, and will occupy a dominant position in the printing and packaging industry.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       At present, the water based varnish is generally used as the water emulsion type. According to the polymerization method, it mainly includes ordinary emulsion polymerization, microemulsion polymerization, core-shell emulsion polymerization and soap free emulsion polymerization. The first 3 polymerization methods, especially microemulsion polymerization, used more emulsifiers in the preparation process. 

         The residual emulsifiers would affect the transparency, water resistance and glossiness of the latex film, and at the same time, cause environmental pollution and limit their application. Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       The emulsifier free emulsion polymerization without emulsifier has overcome the disadvantages caused by the addition of emulsifiers, but its reaction system is unstable. The size of the latex particles is large and the distribution is uneven.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

        The gloss of latex film is poor, which limits its application in paper glazing. In this work, non pre emulsified semi continuous feeding method was used, and some advantages of microemulsion polymerization and soap free emulsion polymerization were absorbed. Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

      Appropriate amount of emulsifier was added in the initial stage of polymerization, adding proper amount of hydrophilic monomer in the later stage of polymerization, which not only reduced the total amount of emulsifier, but also ensured the stability of the reaction system, and achieved good results.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

1 experimental part

1.1 raw materials

       Styrene (st): chemically pure, Dongda chemical plant, Dongli District, Tianjin; Methyl methacrylate (MMA): analytical pure, Shanghai Ying Chemical Co., Ltd; Butyl acrylate (BA): chemically pure, Tianjin Institute of chemical reagents; Bifunctional monomer (s monomer for short): Industrial polymerization grade,Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       commercially available; Acid-1: chemically pure, Shanghai reagent No. 1 Factory; Acid-2: chemically pure, Tianjin Institute of chemical reagents; Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       Sodium dodecylbenzene sulfonate (SDBS): chemically pure, central chemical plant of Shanghai reagent station; Polyethylene glycol octyl phenyl ether (OP): chemically pure, Shanghai reagent No. 1 Factory; ADevelopment Of Styrene Acrylic Waterborne Varnish For Printing Paper

       ammonium persulfate (APS): analytical pure, Beijing No. 3 chemical reagent factory; Ammonia: analytical pure, Zhengzhou No. 2 Chemical Reagent Factory; Triethylamine: analytical pure, Beijing chemical plant; Sodium bicarbonate: analytical pure, commercially available; Disodium hydrogen phosphate, analytically pure, commercially available.

Preparation of 1.2 styrene acrylic emulsion

       In a four port reactor equipped with stirrer, thermometer, reflux condenser and separating funnel, emulsifier and distilled water are added first, stirred, heated to a certain temperature, a small amount of monomers (st, MMA, Ba, etc.) are added, emulsified and then initiator is added.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       Then, the subsequent monomers and initiator are added by semi continuous method, and the reaction is held at a certain pH value and temperature for a certain time, Adjust the pH value to 7 – 8, cooling, discharging, that is, styrene acrylic emulsion.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

1.3 testing of emulsion properties

After the gel content was polymerized, gel in the inner wall of the reactor and the emulsion in the reaction system was collected and dried to constant weight (Wg). σ）：

(1) gel content ( σ） Calculation formula

Where: WM is the total mass of monomer put into the reaction system.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

         The monomer conversion was determined according to gb1725-79 (88). That is, add a certain amount of sample into the dry and clean Petri dish weighed W, weigh the mass W0 of the sample, bake it in a 105 ℃ blast oven to constant weight, weigh the mass W ‘of the Petri dish and latex film, and calculate the monomer conversion P according to the following formula:Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

(2) Calculation formula of monomer conversion p

Formula: WP is the total output of emulsion. M1 and M2 are the feed amounts of initiator and emulsifier in the reaction system.Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

       The solid content of the emulsion was determined by gB1725-79 (88). Add a certain amount of sample into a dry and clean Petri dish weighed W, weigh the mass W0 of the sample, and bake it in a 105 ℃ blast oven to a constant weight W ‘, then the solid content x is calculated according to the following formula:Development Of Styrene Acrylic Waterborne Varnish For Printing Paper

(3) Calculation formula of solid content x

       The viscosity is measured at room temperature with NDJ-79 rotary viscometer (manufactured by mechanical and electrical factory of Tongji University)Development Of Styrene Acrylic Waterborne Varnish For Printing Paper