The present invention elates to a vinyl acetate based polymer latex
composition obtained by emulsion polymerization of:
(a) polyvinyl alcohol,
(c) a monomer mixture comprising vinyl acetate, and (d) optionally one or
more additional co-monomer(s),
in presence of (c) 0.0001-0.05 wt. % of a chain transfer agent, based on
total monomer weight, said vinyl acetate based polymer latex composition
having a weight average particle size .gtoreq.400 nm and a higher shear
thinning factor than the vinyl acetate based polymer latex composition
(a), (b) and (d) obtained in the absence of the chain transfer agent (c).
According to one embodiment, emulsion polymerization is carried out in
presence of 0.001 to 0.05 wt. % of a chain transfer agent selected from
the group consisting of aldehydes and chain transfer agents having a
similar chain transfer constant with regard to vinyl acetate as the
monomer. According to another embodiment, emulsion polymerization is
carried out in presence of 0.0001 to 0.01 wt. % of a chain transfer agent
selected from the group consisting of thiols, mercapto acids, and chain
transfer agents having a similar chain transfer constant with regard to
vinyl acetate as the monomer. The invention also relates to an adhesive
comprising said vinyl acetate based polymer latex composition. Such
adhesive is preferably used in paper and packaging applications or as a
wood working adhesive or wood glue.
The invention further relates to a process of manufacture of a vinyl
acetate based polymer latex composition having a weight average particle
size >400 nm, including emulsion polymerization of vinyl acetate in the
presence of polyvinyl alcohol, optionally together with one or more
additional co-monomer(s), wherein the emulsion polymerization is carried
out in the presence of 0.0001 wt. % to 0.05 wt. % chain transfer agent,
based on total monomer weight.
