The preparation methods of water-borne dispersible resins can be divided into several kinds.
Water-borne dispersible resin is a kind of water-borne resin which has no hydrophilic group or a certain (relatively few) hydrophilic group on the resin molecule. It is insoluble or can not be completely dissolved in water, but it can be dispersed in water through certain preparation or processing methods to form water dispersion with water as medium. The preparation methods of water-borne dispersible resin can be divided into self-emulsifying method and external emulsifying method.
1. Self-emulsifying method
Internal emulsification, also known as internal emulsification, refers to the resin molecular chain contains a certain amount of hydrophilic components that can neutralize and salt, but can not be completely dissolved in water. When preparing the aqueous dispersion of the resin, no additional emulsifier is needed. It is a method of stabilizing the water dispersible emulsion by using a small amount of hydrophilic components contained in the molecular chain itself and mixing with water and stirring. This method does not need to add cosolvents, so in the preparation of water-borne coatings, adhesives and other products, self-emulsifying water-borne dispersible resins account for the vast majority. In the past decade, the self-emulsifying water-borne technology of various resins, especially the research and development of multi-hybrid water-borne resins, has been exceptionally rapid.
2. External emulsification
External emulsification, also known as forced emulsification, means that resin molecules do not contain hydrophilic components at all, or contain only a small number of hydrophilic segments or groups in the molecular chain, but not enough for self emulsifying to obtain stable emulsion. Therefore, when preparing the water dispersive system, additional emulsifiers must be added, and forced emulsification (high speed agitation, colloid mill or homogenizer) must be added. In order to get better stability of water dispersible emulsion, this method is called external emulsification.
3. Comparison of Self-emulsification and External Emulsification
Comparatively speaking, because of the residual of hydrophilic small molecular emulsifier, the performance of the resin film after curing is influenced by the residual of hydrophilic small molecular emulsifier. The self emulsifying method can eliminate such defects. The waterborne dispersion resin is mainly prepared by self emulsifying method. But in some kinds of waterborne resins, such as waterborne epoxy resin, with the development of new emulsifiers, such as waterborne epoxy emulsifier and waterborne epoxy curing agent, as well as the emergence of efficient emulsification technology and equipment, the preparation of waterborne dispersion resin emulsion by external emulsification has aroused great interest and attention.