Powder coating 

Powder coatings for aluminum

Aluminium powder coating

For powder coating to the metal surface, including aluminum, apply an electrostatic method. This method is to form an electrostatic field between the piece to be coated and the powder particles, which come from the spray gun. Powder moves under the action of compressed air and receives the output of the electric charge gun. Since coloring metallic article is grounded, the electrically charged powder particles are attracted to the surface. Due to the electric charge of the powder particles are firmly connected with the surface of aluminum parts or products, for example, aluminum profile. They are used as horizontal (figure 1), and vertical (figure 2) powder spraying systems.

See. more Aluminium powder coating

1-gorizontalnoe-nanesenie-poroshkaFigure 1 - Line powder coating
with horizontal hanging aluminum profiles [1]

2-vertikalnoe-nanesenie-poroshkaFigure 2 – Line powder coating
with vertical hanging aluminum profiles [1]

In the next step of the process powder coating product coated with a powder layer supplied in a special oven, where the powder is melted and spread evenly over its surface. The temperature in the furnace is from 160 ° to 200 ° C, and the processing continues in it about 15-20 minutes, depending on the type of powder coating and the type of product to be painted. This furnace is called a polymerization oven, because it is not only the melting of the powder, but the chemical reaction between its organic components. After exiting the furnace, a uniform and durable coating on the article, which is firmly bonded to its surface.

The minimum thickness of a standard finished powder coating is from 60 micrometers. Coating thickness control is carried out with special devices (figure 3).

3-kontrol-tolshshiny-pokrytiyaFigure 3 - Control of the thickness of the finished powder coating [1]

Factors appearance of a powder coating

The appearance of a powder coating depends on:

  • the color tone of the powder paint;
  • the degree of gloss of the powder coating;
  • structure and surface texture, which is coated;
  • quantity, the size and shape of the pigments in the powder;
  • processing conditions in the curing oven.

Components of powder paint and their functions

Powder paints are a mixture of solid materials. Each of these materials perform their function in forming the powder coating and subsequent work.

The components of powder coatings are:

  • Polymer binders (level and stability of properties)
  • Pigments (color, appearance, resistance to climatic influences)
  • Additives (increasing fluidity and other functional properties)
  • Fillers (stabilization of the properties of a mixture of components)

The chemical composition and structure of the binders and pigments are the most important for the stability of the surface of the powder coating to the effects of weather and climatic factors.

4-poroshkovye-kraski-pokrytiyaFigure 4 - Powder paints and powder coatings [1]

Binders powder paints

The main types of organic binders in powder paints, which are used for coloring building aluminum, are:

– Polyester:

  • standard binders, which are used for painting building elements and products;
  • provide good resistance to climatic influences;
  • have various modifications;

– Polyurethane and acrylic:

  • They are the basis for coatings, which are resistant to graffiti;
  • more fragile, than polyester;
  • apply in cases, when the coating should be regularly cleaned and washed.

– Fluoropolymer:

  • the most resistant to climatic influences;
  • most expensive.

Standard powder coatings generally have a polyester base and always in stock manufacturers or suppliers. Cover other types of, usually, made to order.

Selection of powder coatings for aluminum

When choosing powder paints for applying them to aluminum products, the following factors are considered:

  • Coating appearance (color, shine)
  • Required protective properties of the coating for aluminum (atmospheric pollution)
  • Additional characteristics (for example, “anti-graffiti”, pollution resistance)
  • Lifetime maintenance cost (cleaning, prevention)
  • cost of

quality categories of powder coatings for aluminum

One of the largest manufacturers of painted aluminum for the construction industry, the German corporation Schüco, depending on the purpose of the painted aluminum products and the climatic region, in which they will work, classifies powder coatings into three main categories [1]:

  • Standard (facade) - polyester coatings for curtain walls, windows and doors
  • Special - modified polyester coating, and polyurethane and acrylic coatings
  • fluoropolymer

Standard powder coating is performed according to the specifications such certification organizations, as the Qualicoat and GSB in Europe or in the US AAMA. Special coatings, for example, resistant "graffiti" or fluoropolymer coatings require individual certification tests.

Standard polyester powder coating

Polyester powder coatings most often used for elements of building facades, ie curtain walls, marts, window, doors in a very wide range of colors. Conventional polyester coatings are characterized by high resistance to aging and climatic influences. these properties, as well as high production of these coatings enable their use in building envelope with warranty, for example, for the climatic conditions in Europe during the 10 years [1].

In addition to colors from the RAL, this group includes coatings coatings with special colors, for example, on scales NCS and RDS. Generally, This group covers recommended for use in European countries with moderate ultraviolet stresses and climatic influences.

Polyester coatings with improved resistance to contamination

This type of coating polyester comprises an additive, coating which provides resistance to contamination. This modification impurities complicates the ability to adhere to the surface of polyester powder coating, and also makes it less time-consuming washing and cleaning. Such powder coatings are produced in a wide range of colors, for standard coatings, and for coatings with improved resistance to climatic influences.

These powder coatings require cleaning and washing at most, than every 18 months. It provides them permanently attractive appearance and reducing their maintenance costs.

Polyester coatings with increased resistance to climate

Powder coatings increased climate resistance - a cover element for facades, which provide them with improved stability under severe climatic conditions. These climatic conditions apply, for example, combination of intense solar radiation, high temperature and high humidity. In such circumstances, the conventional polyester powder coating the surface will lose most of its color for several years. This is a result of breakage of chemical bonds in the polymer and chemical changes of pigments. Powder coatings with improved resistance to climatic influences prevent these changes in the coating composition by the use of more stable polymers and pigments. However, this is achieved by limiting the choice of colors.

Polyurethane and acrylic powder coatings

Polyurethane and / or acrylic powder coatings have special functional properties - increased resistance to "graffiti".

This property is due to the fact, These polymers - polyurethane and acrylic - provide a very dense cross-linking its molecules, and in addition, attractive appearance. The high degree of crosslinking makes the coating less convenient for the application of paints drawings spreyernymi, and also provides for easier removal of drawings.

Fluoropolymer powder coating

Currently fluoropolymer powder coatings are the most resistant to external use on building structures. The use of fluoropolymers as binder gives the best possible protection from destruction of chemical bonds under the influence of ultraviolet radiation and harsh weather conditions. Only the most stable of these pigments are used in paints, which are able to withstand both harsh conditions during their trials, and a real tough climatic influences. They can be used in virtually all climatic zones of the Earth.

Advantages of fluoropolymer powder coatings compared to known liquid PVDF paints:

  • no emissions of volatile organic substances harmful to the environment;
  • coating in a single layer, rather than two or four layers.

Source:
1. Powder Coating of Aluminium Surfaces - Technical Information Corporation Schüco, 2012.

See. also The quality control of coating powders: indicators, methods, standards - Guide