Quantifying Micro Surface Burnishing in Overprint Varnishes under Sled Shear
Surface burnishing under sled shear converts diffuse reflectance to specular gloss through silica displacement, controlled by matrix crosslinking and particle size.
Waterborne Acrylic Varnish
Coating Chemistry
Aqueous dispersion resins provide a protective barrier for printed substrates through the coalescing of solid polymer particles as the carrier medium evaporates. Waterborne acrylic varnish achieves its resistance profile through the physical entanglement of long chain polymers that form during the drying process. Manufacturers apply these formulations to improve rub resistance or gloss levels on folding cartons.
Polymer solids settle into the porous structure of the paper surface to create a film that guards against ink scuffing. Crosslinking agents sometimes add to the formulation to heighten durability against chemical spills or high humidity.
Application Dynamics
Wet film thickness adjustments control the final gloss level across different paper stocks. Printers use a metered roller or an anilox sleeve to distribute waterborne acrylic varnish with high consistency over the sheet. Drying energy requires a specific balance of infrared radiation and high velocity air to drive the water carrier away from the surface before the sheets enter the delivery pile.
Moisture content within the paper substrate fluctuates when the aqueous carrier penetrates too deeply into the fibres. Proper control of the coating weight prevents the curling or blocking of stacks during the post-press converting phase.
Substrate Compatibility
Surface energy defines how the liquid coating wets the printed graphic area to avoid beading or crawling defects. Porous uncoated papers absorb the liquid carrier faster than clay coated stocks, which demands a higher application weight to achieve an even finish. Calendering the paper surface prior to the application phase reduces the porosity and keeps the coating on the top layer to heighten the sheen.
Barrier performance decreases on stocks that contain high levels of recycled waste because the short fibres create a path for moisture to enter the sheet. The final film structure depends on the ability of the polymer to bridge the topography of the substrate without cracking.