In recent years, the application of epoxy resins has gradually increased, and the fields involved have also become wider and wider. It is closer to people's lives, and people pay more and more attention to epoxy resins. The epoxy resin manufacturer asks everyone here, how does the epoxy resin achieve water-based? I believe many people do not know, the following Kang Yu reveals the secret for everyone.
Epoxy resin manufacturers
1. Chemical modification method
The chemical modification method is also called self-emulsification method, that is, some hydrophilic groups are introduced into the epoxy resin molecular chain, or block or graft, so that the epoxy resin obtains self-emulsifying properties. When this modification polymerizes When the substance is emulsified with water, the hydrophobic polymer molecular chain will aggregate into particles, and the ionic groups or polar groups are distributed on the surface of these particles. Because of the same charge, they repel each other as long as certain dynamic conditions are met , Can form a stable water-based epoxy resin emulsion, which is the basic principle of chemical modification method to prepare water-based epoxy resin. According to the different properties of the hydrophilic group with surface active effect, the waterborne epoxy resin emulsion prepared by chemical modification can be divided into three types: anionic, cationic and nonionic.
2. Mechanical method
The mechanical method is the direct emulsification method. The ball mill, colloid mill, homogenizer, etc. can be used to grind the solid epoxy resin into micron-level epoxy resin powder, and then add an emulsifier aqueous solution, and then disperse the particles in water by mechanical stirring; or The epoxy resin and emulsifier are mixed, heated to an appropriate temperature, and water is gradually added under vigorous stirring to form an emulsion. The advantage of using a mechanical method to prepare an aqueous epoxy resin emulsion is that the process is simple and the amount of emulsifier required is small, but the size of the dispersed phase particles of the epoxy resin in the emulsion is large, the particle shape is irregular and the size distribution is wide. The stability of the emulsion is poor, the particles easily collide with each other and coagulation occurs, and the film-forming performance of the emulsion is also poor. Of course, increasing the temperature during stirring and dispersion can promote the more effective adsorption of emulsifier molecules on the surface of the epoxy resin particles, so that the epoxy resin particles can be dispersed more stably in the aqueous phase.
3. Curing agent emulsification method
Aqueous epoxy resin system usually adopts curing agent emulsification method to prepare aqueous epoxy resin emulsion. Epoxy resins in such systems are generally not emulsified in advance, but are mixed and emulsified by an aqueous epoxy curing agent before use. Therefore, such curing agents are both crosslinking agents and emulsifiers. The water-based epoxy curing agent is based on polyamines. The polyamine curing agent is added, grafted, chain extended and blocked, and the surface active non-ionic surface active segments are introduced into its molecules. Liquid epoxy resin with molecular weight has good emulsification. The advantage of using a curing agent emulsification method to prepare an aqueous epoxy resin system is that the epoxy resin is directly emulsified by the curing agent before use, without considering the storage stability and freeze-thaw stability of the epoxy resin emulsion; the disadvantage is that the prepared emulsion is suitable Short period.
4. Contrast transfer method
Conversion is a more effective method for preparing high molecular weight epoxy resin emulsion. The emulsion used in type II waterborne epoxy resin coating system is usually prepared by inversion method. Converse reversal refers to the process of mutual conversion of the continuous phase in a multi-component system (such as oil/water/emulsifier) under certain conditions. For example, in the oil/water/emulsifier system, the continuous phase changes from the water phase to the oil phase ( Or from the oil phase to the water phase), in the continuous phase transition zone, the interfacial tension of the system is relatively low, so the size of the dispersed phase is relatively small. The usual preparation method is to mix the emulsifier and the epoxy resin uniformly under high shear conditions, and then slowly add water to the system under certain shear conditions. As the amount of water added increases, the entire system gradually changes from The water-in-oil type changes to the oil-in-water type, forming a uniform and stable water-dilutable system. The emulsification process is usually carried out at room temperature. For solid epoxy resins, it is often necessary to use a small amount of solvent and heating to reduce the viscosity of the epoxy resin before emulsification