Powder coating is a popular process for applying polymer coating with protective, anticorrosive and decorative qualities.
This method was developed in the 1950s in Germany and during the 1960s the technology of electrostatic powder coating appeared. This technology was created due to the appearance of more strict requirements concerning the application of eco-friendly coatings and the need for coatings of a higher quality.
Principles of powder coating
The process of powder coating is based on the principle of positive and negative electric impulses that attract each other. The material that needs to be coated is blasted with a negative electrical charge and afterwards it’s powder coated in a certain color inside an aseptic chamber. The coating powder has a positive electrical charge. In this way the coating powder gets attracted by the negative electric charge and sticks to the material that should be coated. After that the product is placed inside a furnace that works with a high temperature. Therefore, the product’s powder coating is melted, polymerized and turned into a highly durable anticorrosive coating.
Characteristics of powder coating
One of the main characteristics of powder coatingis the lack of solvent in its content. This type of dye is made of tiny dust particles of organic compounds that contain resins, pigments and additional compounds.
Powder coating is a dry process in which the powder adheres to the surface of an object through an electrostatic effect.
Stages of the technology process
Powder coating includes three main stages:
- preparation of the material’s surface that needs coating;
- application of polymeric dyes;
- polymerization.
Stage 1
The first stage of dying with dust particles includes cleaning the material’s surface from dirt buildup, different chemical compounds such as oxides and grease. If the dirty zones don’t cover a large surface, the cleaning process can be done manually with the use of a towel soaked with a special detergent.
But if thorough cleaning is needed, the material is placed inside a special chamber where its surface is cleaned with fine steel particles or dust.
Those products that are going to be exposed outdoors after the dying process is completed undergo a phosphating process This contributes to the better adherence of the powder coating on the surface and it also improves the protective qualities of the metal.
Stage 2
During the second stage of the process the material is spray-painted. The spreading of the powder coating can be done with a paint spraying gun or inside a special camera.
During the use of a paint sprayer the dust particles get the electric charge they need and after that they spread onto the product’s surface in the form of aerosols.
During the dyeing process inside a chamber the powder coating is applied through an electrostatic pulverizer on the target material. And this material needs to be charged with a negative electric charge, so that the positively charged dye will stick firmly onto its surface.
The dye that doesn't stick on the material is captured by a filter system installed in the powder coating chamber, so that it can be used again.
Stage 3
The third stage is called polymerization (surface coating). In order for the dye particles to be melted and get stuck onto the surface of a material, this material needs to be exposed to a high temperature (from 150 to 250 degrees Celsius) in a special furnace. The temperature and exposure time depend on the powder dye type. But most often the entire polymerization process doesn’t take longer than 10 - 30 min.
After the dyed and polymerized products are baked, they are taken out of the furnaces and let to cool down. After that they are ready for delivery. In some cases if there is such a client request, the dyed products can be treated with a lacquer.
Necessary equipment for powder coating
Special equipment is needed so that all the stages of the technological process are completed. This equipment most often consists of:
Powder coating chamber
The powder coating chamber limits the spreading of undissolved particles and prevents dust from entering the production facilities. The powder coating chambers are usually equipped with air purifying filters that can catch the unused powder coating particles. Besides filters they also have compressors working with pressurized air (the so called “powder coating guns”)that spray the powdered dye. Theycan be installed inside or outside the powder coating chamber.Powder coating guns can be used in both production and in everyday life for powder coating at home.
Thermal furnace for polymerization
It’s used for thermic dye fixation on the surface of the coated product. Most often thermal furnaces for polymerization are electrical or gas-powered.They are equipped with a control panel for setting the exact time and temperature needed for polymerization to take place.
Transport system
Special transport system is used in the case of a large-scale mass production or powder coating of large elements and parts. With the help of this transport system we can move products from one stage to the next. The transport system consists of a conveyor belt on which the products are placed before the beginning of the powder dyeing process. This makes it possible for the powder coating to be done without pauses. As a result this saves time in the coating process and increases productivity.
Powder coating dye types
The main types of dry powder dyes are two depending on the circumstances in which a given powder coated product will be used:
- thermoplastic;
- thermo active.
The powder dyes from the first group are produced on the basis of thermoplastic fine film coating dyes, and the coating is formed by mixing powder dye particles without chemical transformation. Тhis type of powder coating is used most commonly for products that are going to be used in indoor spaces.
Thermoplastic powder dyes have decorative, protective qualities and they are also abrasion-resistant.
The film that is formed during the coating with a thermo active dye is a result of melting and a subsequent chemical reaction. This type of dye offers good protection against corrosion and chemicals. Its use is recommended for metal products that are designed for outdoor use.
Application of polymer powder dyeing
The spheres where polymer powder dyeing is most widely used are machine industry, motor vehicle production, furniture production (production of office furniture, chairs, metal products from steel and aluminum).
During the last few years the technology of powder coating method has been applied in the production of MDF products, coating construction elements, fencing supplies and other.
Powder coating of MDF products is a considerably new process that includesmore specific coating techniques which offer excellent results. These coating techniques guarantee cost-effective dye use and decreased time for coating MDF products.
Advantages of dry powder dyeing
Powder dyeing has many advantages compared to the other powder dyeing techniques and this isn’t surprising.
- The process is eco-friendly because it doesn’t contain materials that will have a negative impact on the environment.
- It’s a quick process. The whole powder coatingcycle is very short (around 1,5 - 2 hours).
- It guarantees very good protection against corrosion for the dyed products, as well as strength, shock-resistance, scratch-resistance, excellent coverage and cost-effectiveness.
When talking about cost-effectiveness we will make the following comparison. If the liquid dyes offer 30 to 60% dye utilization for coating a given product, the powder coating process offers 100% dye utilization.
Powder coated products don’t need special protective packaging because the dye used for them forms a strong protective film on each product.
Thanks to all these advantages powder coating takes up 70% of the dyes market that includes dyes designed for coating metal and non-metal products.
Powder coating is a method with a proven high quality and protection level. Its popularity and wide application continue to grow globally. Thanks to powder coating you can introduce into your production or property products with beautiful bright colors.
