The requirement of color coated board for back paint is not high, but compared with primer, it still has certain weather resistance and flexibility requirements. The back paint is applied on the back of the coil, mainly for protection, while providing
appearance and certain durability. The film is required to have good corrosion resistance, scratch resistance, adhesion resistance and processability, but there are no requirements for decoration and outdoor durability. The commonly used back coatings
are epoxy type, alkyd type and polyester type. Because of the poor durability of the first two kinds, most of the surfaces are not primed, and then coated with 5 μ m primer. From the construction and use of the division, can be divided into three
types of back paint, can also be used
(1) The coating structure on the back of the substrate is Primer Plus back paint for the substrate with high corrosion resistance. At this time, the back paint mainly plays the role of shielding protection, and can be used with the same variety as the top paint, but the performance requirements are lower than the top paint, only the scratch resistance, adhesion resistance and processability are required to meet the requirements. Generally, amino alkyd resin can be used as film-forming resin for back paint, such as soybean oil modified short oil alkyd resin and melamine resin back paint. Qi and blood
(2) There is no primer on the back of the substrate, only one coat of back paint. At this time, it plays a double role of primer and back paint. In addition to scratch resistance, adhesion resistance and processability of back paint, it must also have good corrosion resistance. Generally, the film-forming materials can be ring amino, epoxy polyester and polyester polyurethane. In order to improve the corrosion resistance of the back paint, in addition to coloring pigments, anti-corrosion pigments should be added in the coating.
(3) when the pre coated metal coils are mainly used to prepare foam sandwich panels, the backing paint must also be adapted to the manufacturing process of the sandwich panels in addition to requiring good adhesion and mechanical properties to primers or substrates. For example, direct injection foaming process requires good adhesion of lacquer to foamed materials, and the bonding process of foam core should be matched with the binder used. The film can be made of epoxy polyester or polyester polyurethane.