Reactive Diluent
Difunctional monomer used to adjust the viscosity and flexibility of ultraviolet curable inks and varnishes on paper and board. Tripropylene glycol diacrylate provides a balance between rapid curing and the ability of the cured film to bend without cracking. This property is necessary for packaging applications where the board is subjected to sharp folds and scores during the converting process.
Surface Adhesion
Chemical structure of the molecule promotes good wetting and bonding to the fibrous substrate, which prevents the ink from peeling or flaking. When tripropylene glycol diacrylate is used in the formulation, the resulting coating maintains its integrity even when the package is handled roughly or stored in cold environments. This monomer is often preferred for its low volatility and its ability to act as a solvent for solid photoinitiators and other additives.
Migration and Odour
Residual amounts of the monomer must be kept to a minimum in food contact materials to avoid potential contamination and off flavours. Because tripropylene glycol diacrylate is relatively large compared to other diluents, its migration rate through the cellulose matrix is often slower, but it still requires careful monitoring. Modern ink systems are designed to achieve nearly complete conversion to ensure the finished product meets all safety and sensory requirements.
Final coatings are tested for residual odours.
