Applications guidelines

Powder spray coating using thermosetting or thermoplastic technology requires the same four stages:

1. Metalwork preparation
   
2. Metalwork pre-treatment
3. Application and fusion/curing of the coating material
4. Final inspection for acceptable quality standard

However, due to the differences between and particular characteristics of these two technologies, there are variations during the stage involving application and fusion/curing of the coating material, in particular, and in the final thickness of the coating you will obtain.

For instance, because of differences in powder particle size, a Thermoplastic coating as a one-layer system generally offers greater coating thickness: 

• Optimum thickness of Thermosplastic one-layer system is 200 – 300 μm.
• Optimum thickness of Thermosetting primer layer is 60 – 80 μm.
• Optimum thickness of Thermosetting topcoat layer is 60 – 80 μm.

Thermosetting powders are solid resins that, when heated, melt, flow, and can crosslink with other reactive substances. After curing, a thermoset coating remains thermally stable, meaning it cannot be melted back. Thermoplastic powders, however, are based on more flexible resins that, when heated, melt and flow but cannot react and crosslink. Thermoplastic can be melted back.

1. Spraying advice

First layer: primer

The operator adjusts the settings according to the speed of the line and the spraying equipment in place (manual, automatic, number of guns) in order to obtain an optimum thickness of 60 – 80 μm.

^{Note: if the first layer is too thick (> 100 μm), spraying issues may occur when applying the topcoat (electrostatic repulsion).}

Settings

With Corona equipment, we advise a voltage of 60 – 80 kV and no limitation on the intensity.

Process

1. Start by spraying the main difficult parts of the piece to be coated (such as welds, Faraday cages, angles, etc.) where corrosion often begins. In other words, start with all the areas where corrosion might initially appear due to localised lower paint thickness.
2. Then, spray the easiest areas.
3. Lastly, we advise respraying the whole piece at a distance of 15 – 20 cm from the gun to harmonise thickness and improve edge coverage.

Second layer: topcoat

The topcoat is sprayed on immediately after the first layer is melted (or cured) and then cooled, without any preliminary treatment or handling, to avoid contamination. Bear in mind that the topcoat should be applied as quickly as possible (under four hours).

Please note:

If the manufacturing process flow is not straightforward, we advise taking appropriate measures to avoid contamination of the first layer (dust, humidity, grease etc.). Before starting to spray the topcoat on, we advise applying the rules and/or checking the points below:

• Do not touch the parts to be sprayed with a topcoat
• Ground contact must be good
• Hooks must be tidy to ensure good conductivity
• Thickness of first layer should be less than 100 μm. Based on the equipment, the operator adjusts the settings in order to obtain the required thickness and coating aspect.

Settings

With Corona equipment, we advise a voltage of 35 – 50 kV* and limitation of the intensity at 10 μA*, as well as an increase in the powder output as a consequence of the related drop in the electrostatic yield.

Spraying on a metallic topcoat requires tests to judge the aspect.

^{* Provided that the equipment allows these settings.}

Process

1. Start by spraying the main difficult parts of the piece to be coated (such as welds, Faraday areas, angles, etc.) where corrosion often begins. In other words, start with all the areas where corrosion might initially appear due to localised lower paint thickness.
2. Then, spray the easiest areas.
3. Lastly, we advise respraying the whole piece at a distance of more than 20 cm from the gun to harmonise thickness.

2. Curing conditions
 

First layer: please refer to the TDS for each of the primers used.

Second layer: the final two-layer system is cured according to the topcoat-curing window mentioned in the related TDS. Insufficient topcoat curing will result in a lack of flexibility and some intercoat adhesion issues.

Thermosetting 2-layer spraying

Thermoplastic - Thermosetting 2-layer spraying

1. Spraying advice

The operator adjusts the settings according to the speed of the line and the spraying equipment in place (manual, automatic, number of guns) in order to obtain an optimum thickness of 200 – 300 μm.

Settings

With Corona equipment, if amperage and voltage settings are available, we advise setting voltage to 100 kV and amperage to 5-15 µAmps. For Corona guns with voltage settings only, set voltage to 30-50 kV.

Please note:

- If the voltage is too low or the amperage too high, the film thickness will be low, and the powder efficiency may be reduced. If the charge is too high, the coating may suffer from craters caused by ‘back-ionisation’ and the coating of internal corners and the interstices of wire parts will be poorer because of the Faraday cage effect.

- Thermoplastic powder has a larger particle size than other conventional powder coatings and, therefore, if the powder is fed from a fluidised bed hopper, the amount of fluidising air must be increased.

Process

1. Start by spraying the main difficult parts of the piece to be coated (such as welds, Faraday cages, angles, etc.) where corrosion often begins. In other words, start with all the areas where corrosion might initially appear due to localised lower paint thickness.
2. Then, spray the easiest areas.
3. Lastly, we advise respraying the whole piece at a distance of 15 – 20 cm from the gun to harmonise thickness and improve edge coverage.

2. Fusion conditions

Please refer to the TDS for each of the products used. Depending on the metal substrate and thickness, heating time and temperature may vary from 160 to 220°C and 8 to 30 min.

Thermoplastic 1-layer spraying

Thermoplastic 1-layer dipping

^{The information provided here is based on our knowledge of the subject at the date of publication and only concerns Axalta Coating Systems’ systems. The information does not constitute a commitment or any form of guarantee under any circumstances.}