Development of styrene-acrylic waterborne varnish for printing paper

Using styrene, methyl methacrylate, butyl acrylate, etc. as monomers, some features of microemulsion polymerization and soap-free emulsion polymerization were absorbed, and non-pre-emulsified semi-continuous feeding was used to synthesize styrene-acrylic copolymer emulsion. The effects of pH modifiers, subsequent monomer addition time, and holding reaction time on the properties of emulsions and latex films were studied. The results showed that the monomer conversion, emulsion solids content and gel fraction of the obtained emulsion were 95.31%, 42.66% and 0.41%, respectively; the gloss of the latex film was 94.8%, the water absorption was 19.2%, and the latex film was Hardness, flexibility and adhesion are excellent.

Keywords: semi-continuous addition; microemulsion polymerization; soap-free emulsion polymerization; styrene-acrylic emulsion; latex film properties

The use of synthetic resins instead of oils and oils instead of organic solvents has become one of the major developments in the coatings industry. Paper-based water-based glazing oil is a new type of glazing coating that appears with the improvement of the glazing requirements of packaging materials and the enhancement of people's environmental awareness. Its advanced technology, convenient use, and economical and reasonable advantages make it a great deal. The development of the future, has gradually replaced the solvent-based coating and oil-based coating, will dominate the printing and packaging industry.

At present, water-based varnishes are generally based on aqueous emulsions. According to polymerization methods, they mainly include common emulsion polymerization, microemulsion polymerization, core-shell emulsion polymerization, and soap-free emulsion polymerization. The first three polymerization methods, especially the microemulsion polymerization, use more emulsifiers in the preparation process. Residual emulsifiers will affect the transparency, water resistance and gloss properties of the latex film, and also cause environmental pollution. Limit its use. The non-emulsifier-free soap-free emulsion polymerization overcomes the disadvantages caused by the addition of the emulsifier, but the reaction system is unstable, the formed latex particles are large in size, have uneven distribution, and cause poor glossiness of the latex film. Limits its application in paper coating. In this work, non-pre-emulsified semi-continuous feeding method was adopted, and some advantages of microemulsion polymerization and soap-free emulsion polymerization were drawn. The appropriate amount of emulsifier was added at the initial stage of polymerization, and the appropriate amount of hydrophilic monomer was added at the later stage of polymerization. The total amount of emulsifier also ensures the stability of the reaction system and achieves better results.

1 Experimental section

1.1 Raw materials

Styrene (St): chemically pure, Dongli Chemical Plant, Dongli District, Tianjin; methyl methacrylate (MMA): analytically pure, Shanghai Yingyuan Chemical Co., Ltd.; butyl acrylate (BA): chemically pure, Tianjin Institute of Chemical Reagents; Difunctional monomer (S monomer for short): Industrial polymerization grade, commercially available; Acid-1: Chemical purity, Shanghai Reagent No.1; Acid-2: Chemical purity, Tianjin Institute of Chemical Reagents; Sodium dialkyl benzene sulphonate (SDBS): chemically pure, Shanghai Reagent Station Central Chemical Plant; polyethylene glycol octyl phenyl ether (OP): chemically pure, Shanghai Reagent No. 1; ammonium persulfate (APS): analysis Pure, Beijing Chemical Reagent No.3 Plant; Ammonia: Analytical Pure, Zhengzhou Chemical Reagent Plant No.2; Triethylamine: Analytical Pure, Beijing Chemical Plant; Sodium Bicarbonate: Analytical Pure, Commercial; Disodium Hydrogen Phosphate, Analytically Pure, Commercially Available .

1.2 Preparation of styrene-acrylic emulsion

In a four-port reactor equipped with a stirrer thermometer reflux condenser and separatory funnel, first add the emulsifier and distilled water, stir, heat up to a certain temperature, add a small amount of monomer (St, MMA, BA, etc.), emulsify and then add Initiator, then, adopt the semi-continuous method to add subsequent monomers and initiators, hold the reaction for a certain period of time at a certain pH and a certain temperature, adjust the pH to 7~8, reduce the temperature, discharge, and obtain the styrene-acrylic emulsion.

1.3 Test of emulsion properties

Gel Content After the polymerization reaction, collect the gel in the inner wall of the agitator shaft blade reactor and the emulsion in the reaction system, dry it to constant weight (Wg), and calculate the gel content (σ) according to the following formula:

(1) Calculation formula for gel content (σ)

Where: Wm is the total mass of monomer introduced into the reaction system.

Monomer conversion was determined as gB1725-79 (88). A certain amount of samples were added to a dry and weighed Petri dish. The mass W0 of the sample was weighed and dried in a forced air oven at 105°C to a constant weight. The mass of the Petri dish and the latex film was weighed. The monomer conversion P is calculated as follows:

(2) Conversion rate of monomer P

In the formula: WP is the total output of the emulsion; m1, m2 are the amount of initiator and emulsifier in the reaction system.

The solids content of the emulsion was determined in gB1725-79 (88). A certain amount of sample was added to a dry and weighed Petri dish. The mass W0 of the sample was weighed and dried in a forced air oven at 105° C. to constant weight W′. The solid content X was calculated as follows:

(3) Solid content X calculation formula

Viscosity was measured at room temperature using an NDJ-79 rotary viscometer (manufactured by Tongji University).






Source: Dongguan Printing Network