Phase Structure of Pressure Sensitive Adhesives Prepared from Solution and Emulsion

摘要

Pressure sensitive adhesive (PSA) is generally designed to have its glass transition temperature (Tg) below the room temperature (RT), because the performance of the PSA is much influenced by the viscoelastic nature of the bulk PSA. To obtain PSA with appropriate performances, tackifier resins are mixed with base polymers such as rubbers and acrylics. Typical tackifier resin has a Tg above RT and that of base polymer is much lower than RT. If the tackifier is miscible with base polymer, Tg of PSA becomes midway between them, and if immiscible, the bulk PSA has two Tg and the viscoelasticity of PSA much differ from the miscible case. Thus the miscibility of the components affects the bulk properties of PSA. Drawing phase diagrams is simple and plain estimating method of miscibility. I and my co-workers have investigated a series of phase diagrams for the components of the acrylic PSA, natural rubber based PSA and ethylene vinyl acetate copolymeric hot melt adhesive. But all that investigated was prepared by solution polymerization and cast from the solution. Nowadays much attention is paid to the emulsion of PSA and the hot melt PSA keep emulsified PSA, addition of emulsifier is necessary. From the viewpoint of the thermodynamics, the system of the emultion type PSA is more complicated than that of solution type. For the first step of the investigation of this complicated phenomenon, the simplified system is designed and compared.