HYDROPHOBICALLY-MODIFIED POLYACRYLIC ACIDS FOR WB TACKIFYING RESIN DISPERSIONS

Tackifier resins (TRs) are of considerable significance in numerous ad hesive applications, where they are compounded with elastomers as part of the adhesive formulation. TRs serve as a solid solvent for the ela stomers. The low molecular weight fractions of the elastomer are disso lved by the tackifier, while the high molecular weight fractions exist as partially solvated aggregates. This system behaves as reinforcing agent embedded in a tacky semi-solid matrix (1) and has a lower modulu s and higher glass transition temperature than the unmodified elastome r. The lower modulus promotes bond formation and, coupled with the hig her T-g, allows the system to resist bond rupture. Polymers typically tackified include ethylene vinyl acetate, styrene-butadiene rubber, na tural rubber, polyisobutylene, styrene block copolymers and acrylics. [GRAPHICS] There are two main classes of TRs: synthetic materials and natural derivatives. The class of synthetic materials can further be d ivided into the sub-classes of petroleum resins, pure monomer resins a nd phenolics. Natural derivatives are based on either polyterpenes or rosins. The manner in which TRs are incorporated into the formulations is dependent on the form of resin used, the nature of the adhesive pr oduct and the properties desired. Solvent-based, hot melt and waterbor ne adhesives may utilize resins of all types and forms. Resins may var y from oils to solids melting at temperatures > 100 degrees C. For wat erborne adhesives, TRs may be added directly if they are oils or as em ulsions for higher melt point tackifiers. Methods of emulsification wi ll be reviewed in this paper, with major emphasis on hydrophobically m odified polyacrylic acid (HMPAA or Pemulen resin) stabilized emulsion s. Advantages of using HMPAA over other emulsifiers are examined. A ca se study of the emulsification of a petroleum hydrocarbon resin is pre sented.