Fourier Transform Infrared Analysis of Varnish Curing Kinetics
ATR-FTIR cure kinetics tracking links acrylate double bond conversion percentages directly to monomer migration safety and substrate blocking performance.
Vitrification
Surface Coating
Thermal sealing creates a dense nonporous glassy film across the paperboard substrate during high temperature conversion. Vitrification forms this continuous mineral barrier by melting inorganic additives into a stable silicate matrix that resists moisture migration. Converting plants apply this glassy layer to packaging grades requiring grease resistance without plastic extrusion.
The process locks down porous cellulose fibers beneath a rigid inorganic shield. Liquid penetration halts entirely at the coated boundary.
Barrier Integrity
Molecular packing determines how well the converted sheet survives creasing and folding under high production speeds. Vitrification prevents liquid ingress by eliminating the microscopic voids that normally permit capillary action through paper. Converters test this performance by measuring water drop absorption times across random samples from the finished reel.
Low porosity scores indicate complete conversion of the mineral coating into an impermeable barrier state. Structural failure occurs only when mechanical bending exceeds the elastic limit of the glassy matrix and microfractures the protective face.
Process Control
Kiln temperature regulates the phase change required for proper glass formation on the moving web. Vitrification demands exact thermal management because insufficient heat leaves the coating chalky and porous. Production lines monitor pyrometer feedback to maintain the narrow window between complete melting and substrate charring.
Cooling rates dictate whether the glassy layer retains residual stress that compromises score line flexibility downstream. Operators adjust conveyor speed continuously to match dryer output against incoming base stock weight variations.