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What is the effect of the paint on the back of the painted board

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What is the effect of the paint on the back of the painted board

Color coating on the back of the paint requirements are not high, but relative to the primer, it still has certain weather resistance and flexibility requirements.
The back paint is applied to the back of the coil, mainly for protection, but also for appearance and durability.
Paint film is required to have good corrosion resistance, scratch resistance, adhesion resistance and processing, but no decorative and outdoor durability requirements.
 
Commonly used back paint epoxy type, alkyd type, polyester type three.
Because of the poor durability of the first two, has not been used;
At present, the amino polyester type for the majority.
The composition of the polyester back coat is essentially the same as the top coat.
 
At present, most of the paint on the backside of the painted board is directly applied to the pre-treated substrate, generally without priming, and can also be applied to the backside paint after painting 5 m primer.
From the construction and use on the division, the back paint can be divided into three categories.
 
(1) for those with higher anti-corrosion performance, the coating structure on the back of the substrate is primer and backing paint.
At this time, the back paint mainly plays a protective role in shielding, can be used with the same variety of finish paint, but the performance requirements than the finish paint is lower, only the scratch resistance, adhesion resistance and processing meet the requirements.
From the economic point of view, amino alkyd resin can be used as film forming resin, such as soybean oil modified short oil alkyd resin and melamine resin back paint.
 
(2) no priming on the back of the substrate, only one back paint.
At this time it plays the dual role of primer and back paint, in addition to the back paint scratch resistance, adhesion resistance and processing, but also must have good anti-corrosion performance.
Film-forming substances are generally available as epoxy-amino, epoxy-polyester and polyester-polyurethane.
In order to improve the corrosion resistance of the back paint, in addition to coloring pigment, in the paint also need to add anti-corrosion pigment.
 
(3) when the pre-coated metal coil is mainly used to prepare foam sandwich board, the back paint requires good adhesion and mechanical properties of the primer or substrate, but also must adapt to the sandwich board manufacturing process.
For example, for direct injection foaming process, the requirements of the back paint to foaming materials have a good adhesion;
For the foam core board sticking process, the required backing paint matches the adhesive used.
Film - forming materials are generally epoxy - polyester or polyester - polyurethane.
In order to ensure that the sandwich material has enough adhesion and anti-viscosity after winding in production, the back paint can not be used to reduce the surface tension of the paint film additives and surface sliding agent, should rely on the hardness of the film itself to prevent winding adhesion.