凹版油墨 化学品

Gravure inks operate at much lower viscosities (15–30 seconds Din 4 cup) than flexo inks because engraved cells must release ink cleanly at printing speeds up to 400 m/min. NC-based gravure inks are diluted to working viscosity with toluene or ethyl acetate. This low viscosity makes gravure inks more sensitive to evaporation control during a print run.

Polyurethane (PU) binders are preferred for lamination-grade gravure inks — they provide superior bond strength in adhesive lamination and are compatible with most flexible packaging lamination adhesives. NC/PU blends offer a compromise. Pure NC inks are used for surface printing on cellophane or paper where lamination is not required.

Gravure inks require pigments with very fine particle size (D97 < 2 µm ideally) to prevent cell blocking and doctor blade streaking. High color-strength pigments reduce ink film weight. Light-fast and heat-stable pigments are essential for retort packaging. Process color gravure uses standard CMYK phthalocyanine blues, yellows, and reds engineered for the gravure process.

Solvent blends are designed for controlled evaporation rate (matched to press speed and inter-station distance) and viscosity stability through the run. Toluene was the historical primary solvent but has been replaced by ethyl-acetate / IPA / ethanol blends in food-packaging applications. Solvent-retention testing confirms residual solvent < 10 mg/m² for compliance with EuPIA and FDA food-packaging requirements.

Wet-on-wet ink trap requires careful balance of surface tension, ink tack/viscosity, and substrate energy. Each downstream color should have slightly higher surface tension than the previous one for good trap. Tackifier resins and surfactant levels are adjusted accordingly. Online densitometry monitors trap performance, with deviations flagged for ink adjustment within minutes during production.

Gravure cylinders are engraved electromechanically (most common) or by laser. Cell geometry (depth, opening, screen ruling) is matched to ink rheology and target ink film weight. Solventborne inks use deeper cells (35–45 µm) with 70–100 lpcm screen rulings. Waterborne inks may use shallower, wider cells. Doctor blade angle and pressure are critical for clean cell emptying without scumming on non-image areas.