Powder painting

23/02/2020

Powder paint is a coating which is applied in the form of dry powder by means of electrostatic spray guns that, by loading the paint particles, attracts them towards the product to be painted which is connected to an earthing system. Powder coating is a very widespread technique and it is used in various sectors such as aluminum extrusions, household appliances, bicycle and car parts, even large metal products.

The application of the powder coating is carried out, manually or mechanically, in special suction booths in order to collect the excess dust and avoid the attack of impurities and dirt present in the air. At the end of the painting, the products enter a polymerization oven, in this way the powder melts and creates a real coating. The temperature and cooking times vary according to the type of paint. As in the case of liquid painting, even for powder painting, the surfaces must be cleaned in advance as best as possible, otherwise serious aesthetic and physical defects would occur.

There are two basic types of powder coatings: thermosetting and thermoplastic. Thermosetting paints contain cross-linkers which, once cooked, react with the existing chemical groups present in the powder to undergo an irreversible polymerization, creating a permanent coating with different features and performances according to the chemical nature of the paint.
Instead, thermoplastic paints are capable of re-melting and re-solidifying, they are therefore used for those applications where more malleable and elastic coatings are needed over time, such as large pipes, joints, cement, wood, cylinders for fire extinguishers, oil and gas. The application of these paints is different from the thermosetting ones, flame sprays are in fact used, more complex than the normal electrostatic gun, but able to spray and adhere the coating directly on the field without the need to use additional ovens.

The most typical types of thermosetting powder coatings are the following ones:

  • Polyurethane
  • Polyester
  • Epoxy
  • Epoxy-polyester
  • Epoxy with fusion bond
  • Anticorrosive primer

Polyurethane powder painting
Polyurethane powder paint is a thermosetting product based on hydroxylated resins combined with poly isocyanates. It is often used as a top coat for both aesthetic and protective purposes. Although it does not guarantee the properties of polyester painting but it still has characteristics such as high durability, resistance to atmospheric and chemical agents, abrasions, impacts and scratches and it's easily washable. Polyurethane paints are therefore recommended for application on surfaces subject to high wear and where high chemical-physical resistance is required, for example it is used for lighting equipment, interior furnishings, auto accessories, fixtures, cylinders, mechanical components, parts of cars, machines and metal office furniture, coil coatings, heaters, stoves, boilers, small metal parts, electrical panels, shelving, air conditioners, windows, signs for road signs, alloy wheels, glass, ceramic and terracotta.

Polyester powder painting
The polyester powder paint guarantees excellent resistance to chemical, atmospheric agents, UV rays and chalking, it is therefore particularly suitable for the finishing of decorative or external products such as: window frames, agricultural machinery, mopeds, car accessories and road signs. The final cooking phase to facilitate hardening takes place at high temperatures, usually at 180 ° C for 20 minutes. It is also applied at low thicknesses, from 50 to 80 microns.

Epoxy-polyester powder painting
Epoxy-polyester powder coatings are composed of polyester and high-quality epoxy resins. They have features of adhesion, hardness, flexibility but also a moderate resistance to UV rays. Depending on the relationship between the two resins, powders with different characteristics are obtained. The epoxy-polyester powder coating is versatile, has multiple uses and satisfies the most different needs in internal applications. This type of painting is used for metal office furniture, shelves, appliances, cookers and kitchen hoods, camping items, hot plates, water heaters, household utensils, machines, computer cabinets and all metal objects for internal use.

Epoxy powder painting
The epoxy powder coating has peculiar qualities of adhesion and flexibility on the substrate, hardness and anticorrosive resistance. It is recommended for contact with chemicals and for interiors but, as it is not very resistant to UV rays, it is not recommended outdoors. Epoxy powder coatings are used to coat objects of domestic use or internal use in general, where resistance to oils, greases, hardness and elasticity are required. It can be applied with a high thickness for industrial products or with a lower thickness when a greater aesthetic result is desired. Relative times and temperatures are enough for hardening - about 10 minutes at 100°C.

Fusion bond epoxy painting
The difference with the normal epoxy paint is in the method of application: this paint is in fact applied electrostatically on already heated products, up to 250 ° C. In this way, the paint melts quickly on contact and the typical drying phase of the other paints is no longer necessary. It is used on products such as fittings, welds, pipes and internal surfaces. Relaxation and final aesthetic appearance are generally inferior to other types of paint.

Anticorrosive primer
The powdered anticorrosive primer offers exceptional protection against corrosion of ferrous metal surfaces, since it is able to create a strong protective barrier against the corrosive action of natural and chemical agents. Even in highly aggressive environments, the primer will guarantee a long life of the painted product. The anti-corrosive powder paint performs its maximum effectiveness if accompanied by an adequate pre-treatment cycle of the substrate (zinc salt phosphating or sandblasting). For a better aesthetic quality, the product can be painted over with other finishes.