Technical information

SELECTING A COATING

In selecting different components, requirements to the end product must be ascertained first. Knowing the applicable detailed requirements, the customer and paint manufacturer can choose a product that meets relevant needs. In addition to popular basic types of powder coating, powder paints can be manufactured to meet specific requirements.

In selecting a coating and coordinating relevant aspects with the supplier, it is important to keep in mind the following key factors:

  • quality and durability of powder coating;
  • noted operational characteristics (UV resistance, gloss level, chemical resistance, etc.);
  • cost-quality relationship;
  • baking temperature of powder coating.

For an easier selection, refer to the below table for an overview of the basic properties of different powder coating types:

Epoxide Epoxypolyester Polyester Polyurethane Reinforced polyurethane
(SELAC XPRAY)
General information Product recommended for environments requiring excellent chemical resistance, excellent corrosion resistance, and low resistance to outdoor conditions Product recommended when paint coat is required to have good elasticity and corrosion resistance Very well suited for outdoor conditions. Excellent resistance to UV rays. Excellent mechanical properties Well-suited for use where good UV-resistance and chemical resistance are required Well-suited for use where excellent UV-resistance and chemical resistance are required (Anti-Graffiti products)
Specific weight Depends on color tone and formula 1.3 – 1.8 g/cm³ Depends on color tone and formula 1.3 – 1.8 g/cm³ Depends on color tone and formula 1.3 – 1.8 g/cm³ Depends on color tone and formula 1.3 – 1.8 g/cm³ Depends on color tone and formula 1.3 – 1.8 g/cm³
UV resistance very low low very good good – very good good – very good
Chemical resistance to acids and alkalis good – very good

(depending on formula)

sufficient – good

(depending on formula)

sufficient good good – very good

(depending on formula)

Principal area of application Specialty products are used where high corrosion resistance and chemical resistance are required (anti-corrosion primers, pipes, container tanks) Indoor premises, industry, home appliances, office furniture Outdoor premises, architectural objects, garden furniture, industry, etc. Outdoor conditions where average chemical resistance is required For indoor and outdoor use. Well-suited for environments where excellent chemical resistance is required. Graffiti resistant products (bus stop, trains, garbage cans, mailboxes)
Salt spay test (ISO 3786 – ASTM B117) (Dependent on pre-treatment of surface) Pre-treatment Zn phosphate:

min. duration 1,000 h

Pre-treatment Zn phosphate:

min. duration 500 h

Pre-treatment Zn phosphate:

min. duration 500 h

Pre-treatment Zn phosphate:

min. duration 1,000 h

Pre-treatment Zn phosphate:

min. duration 1,000 h

Calculation of paint quantities

The theoretical paint quantity required for painting – Mt (kg) – is calculated based on the below formula:

Mt = K* A  (kg)

10 * V

in which Mt = theoretical amount of paint used (kg)

Kk = thickness of dry paint coat (μm)

A = painted surface (m²)

V = dry weight content of paint (volumetric %).

Actual amounts of paint used are always higher than theoretical amounts. Profile filling requires more paint than calculated and more paint will also be used for unevenly painted surfaces and as caused by paint loss (mis-spraying). Also, a certain amount of paint will be left on containers and tools.

The presumed actual amount of paint used – Mk – is calculated based on the below formula:

Mk = 10 * K* A  (kg)

V (10 – H)

H = paint loss percentage (%)

 

PAINTING QUALITY

Following the below instructions ensures a quality paint coat and significantly saves time spent on painting:

  • Painters must review relevant paint product descriptions and safety data sheets.
  • Paintable surfaces must be treated at the required pre-treatment level and must not be soiled or oxidized before painting.
  • Powder paints used must have been correctly stored; the powder should not be contaminated and should not have been kept in an open package.
  • Before applying the powder, it must be fluidized for a few minutes. If the powder paint is overly moist, the paint will clot in the application box rather than have an airy texture in the application process. Excessive moisture may also cause issues in relation to the equipment used, causing the gun to “spit” paint.
  • In applying the paint, make sure there are no unpainted spots or transparencies. It is important to apply the paint in as even a coat as possible.
  • Surfaces which are hard to access after assembly of a structure should be painted before assembly.
  • In the case of a baking process, the temperature-time relationship prescribed for a specific paint must be kept in mind. If the mass of a part is so large that the required temperature is not achieved during the prescribed baking process, the part must be heated beforehand. Otherwise, the paint will stick poorly to the base surface. Temperatures above those prescribed may cause lighter paints to change their tone. Keeping painted parts in the oven for shorter periods of time or heating said parts at lower temperatures causes the paint to be underbaked. Underbaked paint will stick poorly to the base surface. The paint coat will be brittle, causing easy damage in the case of impact. Make sure temperatures are even in all parts of the oven. It is recommended to check this once a year, using a relevant device which measures the oven’s temperature at different heights.
  • After a painted item is removed from the oven and cooled, check the surface for unpainted spots or other mistakes undermining the painted result, such as traces of running paint, transparencies, the surface tension effect (the so called orange peel effect on a smooth paint), craters, or pores. It is also important to check if the paint is sticking well to the surface, this especially when painting aluminum surfaces. To avoid above issues, it is extremely important to make sure the oven is set to the correct temperature regime and the painting device is set up correctly.
  • Measure paint coat thickness to make sure a sufficiently thick paint coat has been applied. A paint coat thickness gauge is used to measure above thickness. Relevant contracts often require paint coat thickness to be measured. Requirements to paint coat thickness are prescribed in terms of nominal thickness of the coat. Definitions of nominal thickness of the coat differ across standards.

GENERAL ADDITIONAL SAFETY INFORMATION

Instructions provided in MSDS (material safety data sheet) must be followed. Use of a respirator is recommended during painting.

Powder paints constitute a powdery material – avoid heavy concentration of powder in the air as this may cause a risk of explosion.

As transported products, most of the powder coatings are not classified under ADR.