In the papermaking industry, coating lubricants are essential additives that improve the runnability of coated board as it travels through paper machines and contacts various surfaces. By reducing friction and surface wear, lubricants help minimize defects, improve operational efficiency, and support higher-quality coated output . One question that frequently arises: Is coating lubricant water-resistant? The answer is more nuanced than a simple yes or no.
How Coating Lubricants Work in Paper Coating
Paper coating chemistry is typically comprised of three main components: pigments, binders, and additives. Additives make up the least amount of the dry weight of the coating yet contribute important properties-including lubricants, dispersants, and insolubilizers . When applied to the surface of printing paper or packaging board, coating lubricants create a smoother surface, enhance color performance, and add functional protection such as water and grease resistance when needed .
The Water Resistance Question
In paper coating applications, water resistance is not determined by lubricants alone. Crosslinkers, also referred to as insolubilizers, are specifically used to improve the water resistance and durability of coated surfaces. These additives react with water-soluble components-such as starch-containing coatings-reducing solubility and helping coatings maintain integrity during converting and printing processes .
Water resistance is typically measured using tests such as the Cobb value test (which measures water absorption) and the kit-oil test for grease resistance . Research has shown that coatings based on cationic starch may exhibit low water resistance (Cobb values up to 189 g/m²), but the addition of specific additives like bentonite can decrease wettability and improve resistance .
Factors Affecting Water Resistance
Formulation Matters
Some coating lubricants are formulated to provide both lubricity and water resistance. For example, certain calcium stearate lubricants improve flow and leveling characteristics while also contributing to surface performance . Other lubricants like sulfated oleic acid offer improved "healing" properties that permit coating at higher solids levels .
The Role of Crosslinkers
True water resistance in paper coatings typically comes from crosslinkers/insolubilizers rather than lubricants themselves. Products like blocked glyoxal crosslinkers reduce water solubility of starch-containing paper coatings without increasing reactivity, while potassium zirconium carbonate crosslinkers improve printability .
Industry Applications
For paper manufacturers, understanding water resistance is crucial. Coated paper products intended for food packaging, beverage cartons, or outdoor applications must maintain integrity when exposed to moisture. Lubricants with good compatibility with coating systems help solve issues like sticking to rollers while providing desirable surface properties and improved gloss .
Our Coating Lubricants
As a specialized paper chemicals supplier with over 20 years of industry experience, Luterra Advanced Materials offers coating chemicals designed to balance lubricity with other performance requirements. Our paper coating additives are formulated considering the entire coating system-pigments, binders, and crosslinkers-to achieve the water resistance and surface properties our customers need.
We look forward to the opportunity to work with you and help you optimize your industrial processes.
