Chemical Industry: Introduction to Common Types of Polyurethane Coatings

Polyurethane coatings are classified according to the chemical composition and curing mechanism of the film-forming substance polyurethane. And divided. ProductionOn Single packaging and multi-packing.

(1) Polyurethane modified paint

This paint is also called urethane oil. The drying oil is first transesterified with the polyol and then reacted with the diisocyanate. Its drying is carried out through double bond oxidation in the air, and this paint dries quickly. Due to the presence of amide groups, its wear resistance, alkali resistance and oil resistance are increased. It is suitable for surface coating indoors, wood and cement, but has poor leveling properties, is prone to yellowing, and paints are prone to powdering.

(2 )hydroxybaseCurable polyurethane coating

Generally a two-component coating, component A contains isocyanate group, Component B generally contains hydroxyl groups. During use, the two components A and B are mixed and applied to react the isocyanate group and the hydroxyl group. Form polyurethane polymer. Can be divided into varnish, enamel and primer. It is the most diverse type of polyurethane coating. Can be used to create coatings ranging from soft to hard with glossy coatings. Used in metal, cement, wood, rubber, leather, etc.

(3) Sealed polyurethane coating

The film-forming substance of the closed polyurethane coating is similar to the aforementioned two-component hydroxyl-curing polyurethane coating, and is composed of polyisocyanate and hydroxyl-containing resin. The difference is that the polyisocyanate is blocked by phenol or other substances containing monofunctional active hydrogen atoms, so the two parts can be combined without reacting to become a one-component paint. When heated (150°C), phenol volatilizes, The urethane bond is cleaved to generate isocyanate, which then reacts with hydroxyl-containing resin to form a film.

This coating is mainly used as electrical insulating paint due to its excellent insulation properties, water resistance, solvent resistance, and mechanical properties. Performance, and the ability of general electrical materials to withstand baking is determined. The most effective electrical insulating paint is electromagnetic wire paint. Recently, it is also used for painting automobiles, etc.

(4) Moisture-curing polyurethane coating

The terminal group of this paint contains a -NCO group molecular structure, which can react with water in air with high humidity to form urea bonds and solidify into a film. It is an easy-to-use self-drying coating. The coating film is tough, dense, wear-resistant, corrosion-resistant, and has good anti-pollution properties. It can be used as a protective layer for floors, walls and mechanical equipment in critical areas of atomic reactors. Made into varnishes and paints. However, the drying rate is affected by the humidity in the air and is not suitable for the cold winter climate. A drier must be added at that time.

(5) Catalytic curing polyurethane coating

The structure of this type of coating is basically similar to that of moisture-curing coatings. The difference is that the NCO group of the prepolymer interacts with water molecules in the air through the use of a drier. And solidifies into a film. The film dries quickly and has good adhesion, wear resistance, water resistance and gloss. Can be used on wood, concrete, etc. Most varieties are varnish.