Rosin-based tackifiers find continued use in hot melt adhesives because of their unique property of providing compatibility to a wide variety of adhesive components. Unmodified rosins, however, are easily oxidized on account of their main constituent, abietic acid, containing a conjugated double bond, tertiary carbon atoms, and allylic hydrogen atoms.

Because of their tendency to degrade, natural rosins must be modified to meet the stability requirements of the hot adhesives. Improved stability can be developed by several processes such as hydrogenation, disproportionation, and dimerization, followed by esterification of the rosin with glycerol or pentaerythritol.

Esterification Catalyst and Bleaching Agent

Various catalyst systems such as TNPP, calcium acetate, zinc acetate, and zinc oxide are used to accelerate the esterification reaction times.

A particularly exceptional catalyst for esterification is Ciba® IRGAMOD® 195. It offers the shortest reaction time and produces a resin with reduced color and lower acid number. In addition, Ciba® IRGAMOD® 195 imparts a “carry through” antioxidant effect by offering improved heat stability of the final resin.

Ciba® IRGANOX® B 551 combines the esterification catalyst with a bleaching agent, which is useful in further improving the initial color of rosin esters. Esters produced with this system also have superior high temperature and storage stability, compared to other esterification additives.

Stabilization

For more detailed recommendations regarding your particular application, please contact us.