| 摘要 |
Disclosed are low-formaldehyde aqueous dispersions of vinyl ester/ethylene, e.g., vinyl acetate/ethylene (VAE), copolymers suitable for use in adhesives for applications such as tobacco or food products wherein only very low levels of formaldehyde are permitted. Such dispersions are prepared by emulsion copolymerization of a monomer mixture comprising a vinyl ester, ethylene, a stabilizing system comprising polyvinyl alcohol preferably having a degree of hydrolysis of at least 97 mole %, and a selected type of free radical redox polymerization initiator system. This selected redox initiator system comprises both a water-insoluble oxidizing agent and a sulfuric acid-based reducing agent. The monomer mixture which is polymerized is substantially free of co-monomers which yield free formaldehyde upon drying or curing of the dispersion and is also substantially free of ethylene oxide-containing emulsifiers. The aqueous dispersions resulting from polymerization of this monomer mixture has a solids content in weight percent and a Brookfield viscosity in millipascal-seconds such that the ratio of solids content to the natural logarithm of viscosity ranges from about 6.34 to about 8.25 wt %/ln(mPa·s). The dispersions herein also have a formaldehyde content of less than about 5.0 ppmw as determined by ISO-15173. |
