Paper & Board Coatings Chemicals

Styrene-butadiene (SB) latex is the most widely used binder for coated woodfree and mechanical paper — providing high gloss, good binding strength, and excellent runnability on high-speed blade coaters. Styrene-acrylate latex offers better water resistance and reduced ink setoff for cast-coated and specialty papers. Acrylic latex is used for barrier-coated and food-safe packaging grades.

Coating kaolin (china clay) — fine-particle, delaminated, or calcined grades — is the primary pigment in most paper coatings, providing good coverage, smooth surface, and printability. Ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) are used at high loading for brightness. Titanium dioxide (TiO2) is added at low levels for maximum opacity.

Barrier coatings for food packaging (grease, water, mineral oil barriers) use specialty latex (styrene-acrylate, PVDC, or fluoropolymer-free alternatives), PVOH, or starch-based systems applied by blade, curtain, or film-press coating. Multiple thin layers are often more effective than one thick layer. Recyclable and repulpable barrier coatings are now mandated in many markets.

Premium gloss-coated woodfree papers receive 8–12 g/m² coating per side. Mid-coated grades are 5–8 g/m² per side. Lightweight coated (LWC) magazine paper is 6–9 g/m² per side on mechanical-pulp base. Triple-coated cast-coated paper for premium packaging exceeds 30 g/m² total. Coat weight is measured continuously by beta-gauge or NIR for closed-loop control during high-speed production.

Food-safe paper barrier coatings must comply with FDA 21 CFR 176.170 (aqueous food) and 176.180 (fatty food), or with EU Regulation 10/2011. PFAS-free grease-barrier coatings use specialty styrene-acrylate latex with high MW or PVOH-starch blends. Water-vapor-barrier coatings combine multiple thin layers of different polymers. Repulpable and recyclable certifications are increasingly mandated by retail brands.

High-speed coating (1500+ m/min on woodfree paper machines) faces challenges of dewatering, dryer blistering, edge stability, and break frequency. Latex Tg, particle size, and coat color rheology must be optimized for the coating method — blade requires Newtonian or slightly pseudoplastic rheology, while curtain coater needs high elasticity. Online sensors monitor coat weight and moisture for closed-loop control during long production campaigns.