VR203 - IGP Metallic Effects
IGP Metallic Effects Contain High-Coverage Aluminum Pigments and are Usually Silver-Gray to Silver Gloss.
Introduction
This Processing Instruction, VR 203, was prepared in order to provide users with assistance in processing IGP powder coatings with a metallic effect (D -> 5th position of the IGP article description). The metallic impression of these metallic coatings is produced by high-coverage aluminum particles near to the surface. In order to sustainably protect these pigments from oxidation, metallic coatings of this type must be overcoated with a transparent protective coating.
IGP metallic effect powder coatings which are overcoated with clear varnish must be identified with an “H” at the 11th position of the article description.
IGP effect powder coatings come in five main processing categories, from 1-STAR * to 5-STAR*****. The metallic effect products are all labeled as category 1* because they are much more challenging to process than single-color powder coatings without metallic effect particles.
Project Organization
One Batch, one Application Facility, Identical Parameters
If parts with metallic effect powder coatings are installed directly adjacent to each other, determine the required powder amount for the entire order, plus a certain reserve, and coat the entire order with a single production batch number. This minimizes color and effect differences when coating the entire order. Experience shows that the results in terms of shade and effect characteristics vary due to the differing coating equipment characteristics from the various manufacturers.
Electrostatic parameters such as the level of the applied high voltage, the current limiter setting (μA) as well as the utilization of ion-leakage rings can significantly impact the charging behavior as well as the shade and effect formation. It is strongly advised to prepare limiting samples prior to the start of production and to use them throughout the entire production and output inspection in order to check the shade and effect.
Processing
When processing IGP metallic effects, we recommend using corona guns with a negative polarity electrostatic charge. Corona guns and their nozzles must be suitable for the processing of metal effect powder coatings. It is not necessary to limit the spray current to < 80 μAmpere.
Due to the proportion of metallic effect pigments, a limitation of the spray current can lead to short circuit effects and, consequently, a charging loss of the metallic effect powder coating to be processed. Increasing the nozzle spray air to max. 0.5 m3/h counteracts a charge loss via the short circuit effect.
Depending on the formula and proportion of effect agent, an ion-leakage ring can improve the flow characteristics. Any manual application that is necessary in semi-automatic operation should always be performed as a preliminary coat. When dealing with objects to be coated on both sides (e. g. profiles), the side that will be primarily visible should be coated last. It is recommended to set the high voltage to between 50 and 60 kV when finishing the metal effect powder coating with clear varnish.
Recovery Operation
Due to the proportion of overspray that is recovered via the separation system, a concentration of effect pigments may occur when recovery by means of filter when processing metallic effects. Alternatively, a reduction of effect pigments may occur when recovery via cyclone.
Powder facilities equipped with a cyclone recovery system do not separate the finest powder particles and effect particles in the cyclone. Instead, these particles are continuously removed from the powder. This removal offsets the effect to shade ratio. This usually results in the shade becoming darker.
In order to avoid shade changes caused by effect losses during coating, the processing of IGP metallic effects that were manufactured in the IGP Mica Bond process (H10 suffix) can only be performed in pure loss mode without recovery powder. When automatically processing IGP metallic effects that were manufactured in the IGP Premium Bond process (H30 suffix), approx. 10 % of recovered powder can be added to appropriate batch sizes provided that an ideal mixture of fresh powder is ensured. However, the coater remains responsible for creating a tolerable and reproducible shade. In all cases, it is advisable to prepare limiting samples prior to the start of production and to use them throughout the entire production and output inspection in order to check the shade and effect.
Suspension of the Parts
The suspension of the parts must be determined prior to coating (horizontal or vertical). The intermediate spacing between the coating objects within the hangers as well as the spaces between the hangers must be kept as small and regular as possible. If there are large distances between the hangers, it is advisable to automatically switch the guns on and off via a parts detection system.
Furthermore, it must be ensured that similar components are always coated together. Mixing thick and thin-walled parts in the coating process must be avoided at all costs.
Earthing
Special attention must be given to sufficient earthing when processing coating powders with a metallic effect. This measure significantly contributes to a uniform shade and effect formation consistency.
Curing
Depending on the melt viscosity, the temperature management in the stoving oven and the mass of the coated components may cause a change in the effect (visually apparent as a difference in shade). This means that varying curing temperatures and heating speeds must be avoided. Furthermore, thick and thin-walled parts must be coated separately.
Resistances and Technical Data
This information can be found in the the respective data sheets.
Other Applicable Documents
Safety data sheet SD 110
TI 000 classification of effect powder coatings
In-house trials and tests must be performed in all cases. The information stated here must be treated as directives. Coating facility-specific deviations may occur.
In-house trials and tests must be performed in all cases. The information stated here must be treated as directives. Coating facility-specific deviations may occur.
