水性油墨 化学品

Acrylic emulsion binders (Tg-adjusted from -10°C to +50°C) are the main film formers in waterborne flexo inks for corrugated and paper. Alkali-soluble resins (ASR, styrene-acrylic copolymers) provide quick drying and good printability for waterborne gravure on films. High-MW acrylic solution resins give excellent gloss and block resistance in premium applications.

Waterborne ink drying relies on evaporation of water assisted by IR and hot air dryers. Drying speed is adjusted by anilox roll volume (lower volume = thinner film = faster dry), air impingement system, and alcohol co-solvent level (ethanol/IPA accelerates drying). At very high speeds (>200 m/min), IR dryers and multiple drying zones are necessary.

Waterborne inks based on alkali-soluble resins must maintain pH 8.0–9.5 to keep the binder in solution. Below pH 8, the resin may precipitate and viscosity rises dramatically. Amines (AMP, TEA, ammonia) are used as neutralizers. During printing, ammonia evaporates and pH drops — this is controlled by pH monitoring and periodic addition of pH adjuster.

Food-safe waterborne flexo and gravure inks use binders compliant with FDA 21 CFR 175.300, the EuPIA inventory, and the Swiss Ordinance positive list. Ammonia and amine neutralizers must be selected to avoid migration. Pigments must be food-safe grades free of regulated heavy metals. Set-off and migration testing in food simulants are mandatory before commercial use on direct-contact food packaging.

Waterborne inks foam readily due to surfactants and high-shear circulation. Mineral-oil, silicone, and silicone-free polymer defoamers are used at 0.1–0.5% by weight. Defoamer compatibility with the binder is critical — a mismatched defoamer causes craters and loss of adhesion. Modern low-foam surfactant chemistry is reducing the need for defoamer in sensitive food-packaging formulations.

Waterborne flexo inks use HASE associative thickeners or alkali-soluble acrylic resins for shear-thinning rheology. Cellulosic thickeners (HEC) are sometimes used for cost. Inorganic thickeners (clay, fumed silica) are added for sag resistance. The rheology profile must allow clean ink release from the anilox at high shear while maintaining film integrity at low shear on the substrate to prevent dot gain and bleeding.