BPCOAT – SR Series

Powder coating is a surface coating method consisting of resin, pigment, additives and fillers. It is possible to apply the powdered paint directly to the surface to be coated. Powder coating is economical and environmentally friendly at the same time. Although the electrostatic powder coating sector has shown serious developments, it is still a developing technology. As BOYASAN, we are developing ourselves and our products in parallel with this.

The major advantages of powder coating used for protective and decorative coating are as follows;

• Environmentally friendly (no solvents or volatile organic compounds)
• Resistant to chemicals
• Saves energy
• Process stages are reliable
• Extremely economical
• Ease of application (ready to use)

Powder coating generally includes the following:

• Binders (resin, hardeners)
• Additives
• Pigments
• Filling

The Powder Coating production process consists of three steps;

Raw Material Mixing: All weighed chemicals are mixed with a mixer for a known period of time until a homogeneous mixture is obtained.

Extrusion Process: The mixture is melted and kneaded. After passing through cooling rollers and cooling belt, it is crushed into small particles.

Micronized Grinding: With specially developed grinding machines, it is milled at appropriate intervals for different applications (particle size distribution). When the appropriate particle size is obtained, it is packaged and ready for use.

• Qualicoat Quality Certificate
• RoHS (Restriction of substances hazardous to human health) Certificate
• ISO 9001:2015 Quality Certificate
• OHSAS ISO 18001:2007 Certificate
• ISO 14001:2004 (EMS)

Our PE product group used for architectural applications on aluminum surfaces is approved by Qualicoat Quality Certificate. We also have a RoHS certificate for restriction of substances harmful to human health for our products. Our quality control and quality assurance procedure is regulated by ISO 9001:2015 Management System Certificate.

We protect our workers and workforce by reducing the risk of unexpected injuries with OHSAS ISO 18001:2007 certificate issued for Occupational Health and Safety Management System (OHSMS).
Our company fulfills the requirements of ISO 14001:2004 to develop an Environmental Management System (EMS) to protect the environment with less waste.

All our products are controlled by technical engineers working in the quality control department by subjecting them to the tests described below.

Reactivity Test
Gel time test is applied to determine the relative reactivity of a powder coating with a specific formulation. This test is an important application in determining whether the powder coating is flowing or not, surface appearance after curing and storage stability.

Particle size distribution
Particle size distribution is one of the most important aspects for final product performance. It affects many properties such as fluidization during the application phase, spraying in the gun chamber, back ionization, poor charging, transfer efficiency, penetration into regions under the influence of Faraday cage and film surface appearance.

Different methods are applied for particle size distribution measurement. In our laboratory, the most reliable method for powder coatings, the wet-measured laser diffraction device, is used and the particle size distribution that is most suitable for the application area is adjusted and ground.

Glossiness
Gloss in powder coating is measured objectively with a gloss meter according to EN ISO 2813 standards, usually at an angle of 60 degrees.

Expected values

• Bright 71-100 GLOSS
• Semi-matte 31-70 GLOSS
• Matte 0-30 GLOSS

Coating Thickness

Coating thickness in powder coating is measured with a micrometer according to EN ISO 2808 standards. Paint thickness is measured from five areas of 1 cm2 each on the surface and approximately 3 readings are taken at each point. The average of the values read at each point is written in the test report as “measurement result”.

Adhesion Test
According to EN ISO 2409 standards, scratches are created on the painted metal surface, parallel and diagonal to each other with a distance of 1 mm. And a standard tape is applied over this area. Evaluation is made according to the amount of film broken on the tape which is quickly pulled off.
Evaluation: Gt(0) No error.

Kaping Test (Cracking)
According to EN ISO 1520 standards, a ball of a certain diameter is pushed in the opposite direction to the painted surface (slow deformation). The depth of the ball in the plate is measured until the cracking starts. This amount of depth defines the crack resistance.

Flexibility (Bending)
According to EN ISO 1519 standards, the cylindrical bending test is used to measure the flexibility resistance of paint. It is a measure of flexibility, stretching and adhesion when the painted metal is subjected to deformation. Cylinders of different diameters are used in the measurement. The test panel is rotated around a cylinder of known diameter. The diameter of the cylinder without deformation is given as a result.

Impact Test
According to EN ISO 6272 standards, the deformation of the painted panel is checked with a mechanical test device. It works by throwing a mass of 1 kg at the painted metal surface from different heights (applied bilaterally to the painted surface). The result in impact is evaluated in kg.cm at a height where no cracking occurs.

Buchholz Hardness
According to EN ISO 2815 standards, powder coating hardness is most reliably measured by Buchholz. It consists of a sliding metal wheel-shaped weight with sharp corners and is left on the test panel for a certain period of time. The length of the mark is an indicator of surface hardness.

Salt Spray Test
According to EN ISO 7253, a 1 mm wide cross-shaped cut is made on three witness plates and placed in a hot, humid and salt spray environment. The test period is 1000 hours and is checked every 200 hours. This test shows the corrosion resistance of the painted panels in a salty environment. For best results, a maximum leakage of 16 mm2 is allowed around a 10 cm scratch and no more than 2 large blisters should appear on the surface of the plate.

BPC electrostatic powder coatings are packed in 25 kg PP bags and cardboard boxes as standard.
Powder coating should be stored at maximum 25 º C and 50-60% relative humidity. When stored under these conditions, powder coatings can be used until at least 12 months after the production date. In case of longer storage at higher temperatures, there is a high risk of moisture and various technical problems.

Electrostatic Powder coating:

• Must be protected against high temperature (>25 º C)
• Must be protected from moisture and water
• Protected from other dust and dirt
• Storage conditions may be different for each product, so be sure to check the product analysis certificate.

Electrostatic powder coating application project usually consists of three steps:

1- Pretreatment of Metal Surface Cleaning
Powder coating is primarily applied on steel, galvanized steel, aluminum, copper and zinc alloy metal surfaces. Metal surfaces are prone to rapid oxidation. Therefore, the surface is lubricated to prevent oxidation, which causes various problems during painting. In other words, in order to obtain the highest performance, the metal surface must be cleaned with various chemical methods. Oil, soil, metal oxides, rubber and plastics must be thoroughly removed from the surface.

For the selection of the appropriate process and chemicals, the following details should be determined

• Type of metal and level of protection required
• Degree of contamination
• Field of application

2- Electrostatic Powder Coating Gun Systems
The most common method of applying powder coating to a metal surface is spraying using an electrostatic gun. In general, two charging methods are known: corona charging and tribo charging:

Corona Charging
In corona charging, dust particles are charged with the help of voltage. An electric field is created between the electrode and the grounded metal surface. The powder particles passing through this field are charged and adhere to the grounded surface. Corona charging is suitable for all types of powder coatings.

Advantages

• Fast charging due to high voltage
• The electrical field generated by the voltage supports the adhesion of dust particles to the surface
• Suitable for different types of powder coatings
• Size differences in particle distribution are acceptable
• Paint film thicknesses can be adjusted by changing the voltage
• Fast color change and cleaning is possible
• Reduced wear and parts replacement

Disadvantages

• Reduced ionization due to strong electric field
• Faraday effect with strong voltage (uneven coating on corners and edges)
• Voltage changes cause orangeing

Tribo Loading
In tribocharging, powder particles are charged by rubbing against the inner surface of the gun. The particles rubbing against the inner surface, which is usually Teflon coated, are stripped of electrons. The positively charged powder particle exits the gun and is carried by the air current to the grounded product and adheres.

Advantages:

• No Faraday effect, better penetration into corners and edges
• Ensures even and homogeneous coating
• No orangeing due to good flowability
• Provides very good automation possibilities
• No high voltage generator required

Disadvantages

• Specially produced paint is required; not all paint types provide high performance
• Paint performance is affected by uncontrolled airflow
• Small particles of 10 microns are difficult to charge
• Color changes and cleaning is not easy and takes a long time
• Conditioning of the particles takes a long time and efficiency decreases during long runs
• Increased wear and therefore shorter replacement intervals
  Since it takes longer to charge the particles, the amount of powder applied is lower, so more guns are needed

How to choose the method of application (Corona, tribo):

3- Curing
Thermosetting powder coating starts to melt during baking, gains fluidity to form the required surface and then creates a chemical chain reaction. Normally powders are cured between 160 -200°C for 5-25 minutes. Curing time and temperature may vary according to the type and characteristics of the product.

Some of the powder paint sprayed with an electrostatic gun adheres to the surface to be coated. Painting efficiency is defined as the ratio of the amount of powder deposited on the part to be coated to the total paint sprayed. The evaluation is done as a percentage, such as efficiency/100.

Increasing transfer efficiency will reduce the amount of powder overspray and reduce the amount of recycling. High transfer efficiency offers the user low cost, high efficiency and high quality.

Important issues affecting painting efficiency:

Gun voltage/current: The optimal voltage range is between 30 and 100 kV. Higher voltages generally increase the amount of recycling. The ideal current draw is 10 to 20 microamps, uA, to ensure good transfer efficiency and the best spread to areas under the influence of the Faraday cage.

Dust Flow Rate (air setting): Too high air velocity reduces transfer efficiency and makes application difficult, especially in recessed areas such as corners. Small dust particles are carried to the surface to be painted with the help of air and adhere to the surface by electrostatic attraction. If the air speed of the system is too high, the dust particles will hit the surface and fall off before they can adhere. This is because compressed air speed is a greater force than electrostatic attraction.

This means high transfer efficiency with low airflow-speed, more consistent and uniform film thickness, less orange peel appearance and less wear on the gun assembly, resulting in longer part replacement times.

Gun Position-Distance: The distance between the gun and the part to be painted is an important consideration for transfer efficiency. If the gun is too far away from the part to be painted, the particles will move away from the target by the force of gravity or air flow. If the gun is too close, the voltage will drop and the current will increase. If the current continues to increase and exceeds the optimum values (10 to 20 microamps), the amount of free ions formed between the gun tip and the part to be painted also increases. The free ions adhere to the surface faster than the powder particles, leading to back ionization (powder particles returning or falling off without adhering).
The recommended distance is 15-20 cm for manual application and 20-30 cm for automatic application.

Conveyor Density: The position of the hangers on the conveyor will affect the Transfer Efficiency. Increasing the number of hangers as close to each other as possible will increase the transfer efficiency. Because the space between the parts to be painted will decrease, there will be a significant decrease in the amount of paint sprayed into the air.

Gun Spray Heads: Different gun tips affect the Transfer Efficiency. Two types of tips are commonly used; fan spray nozzle and conical spray nozzle. The fan spray nozzle provides a large dust cloud and faster spraying. The conical nozzle, on the other hand, has tips of different diameters, allowing for smoother spraying and the possibility of working with dust clouds of different sizes and widths. Different nozzles should be tried to ensure the most suitable spraying for the part to be painted.

Humidity and Temperature: The humidity and temperature of the environment are among the most important factors affecting the performance of the powder coating system. Changes in temperature and humidity affect powder fluidization, filter efficiency, filter life and powder charging (consistent and efficient spraying). Too much heat causes the powder to undergo physical and chemical changes. Too much humidity causes the powder to block. Too dry air adversely affects the charging of the paint.

For high transfer efficiency, the relative humidity should be 50-60% and the ambient temperature should be no more than 25 ºC.

Grounding: Proper grounding is one of the most critical aspects for Transfer Efficiency. If the grounding is not sufficient, the powder particles move in different directions and form an uneven coating on the surface. This increases paint consumption. The grounding system should be checked regularly and all components should be grounded to the ground with a resistance not exceeding 1 megaohm.

Powder Particle Size: Proper particle size distribution is important for Transfer Efficiency. It is very difficult to fluidize and inject very small particles. At the same time, the amount of charge per unit weight is higher in small particles. Therefore, although the charging properties of small particles are high, they are easily affected by air flow. This reduces the transfer efficiency.

Large particles, on the other hand, move in a more linear motion towards the surface to be painted after leaving the gun and are more affected by strong electrostatic force or gravity. Very large particles fall to the ground before they can adhere to the surface due to gravity.
Fine particles stick more easily to flat surfaces, but it is very difficult for them to penetrate and stick to corners and edges under the Faraday effect. Thick particles with more linear motion spread more easily to corners and edges.

If the film thickness does not increase during painting and spreading becomes difficult, it means that there is an increase in the number of fine particles in the paint used.

The most advantageous feature of powder coating is the ability to reuse recycling (paint spilled during painting). Considering negligible loss in the collection filtration systems and on the suspension hooks, powder coating can be reused with an efficiency of about 95%.

In general, the amount of spilled paint can be in the range of 25% – 15% (25% recycling + 75% virgin paint). The ideal amount is about 15%, which has little effect on the particle size distribution of the mixture. To determine the ideal recycling amount, it is necessary to know the initial transfer efficiency. The initial transfer efficiency depends mostly on the application process and system maintenance (gun, hoses, grounding, etc.). Poor maintenance leads to an increase in the amount of recycling poured into the collector, which in turn increases the amount of recycling.

Poor grounding system affects transfer efficiency and leads to increases in recycling.
Painting should not be done for a long time with fixed gun setting values, because the particle size distribution of the mixed powder (zero paint + recycle) in the feed tank will change over time. For this reason, in order to maintain the surface appearance during long painting processes, the gun settings must be readjusted according to the paint in the gun tank.

NOTE: The points mentioned above are valid for flat paints. For textured, lumpy and other special effect paints, the recycling amount should be used in smaller quantities so as not to change the surface appearance.