Troubleshooting Subli-chromy: In order to achieve a high-quality decorative finish using sublichromy, the following processing considerations must be taken into account:
- Base powder coatings suitable for sublichromy have a typically a low hiding power. To avoid any inconsistency in the finished surface, a chromium phosphate treated aluminum should not demonstrate any “conversion marks.”
- The coating film thickness should be even (optimum between 80 and 100 µm). A variable thickness could give rise to inconsistent finishes because of the different hiding effect of the basecoat; even the decorative effect could change due to the uneven distribution of the transferred ink through the film.
- The curing parameters of the basecoat (times and temperatures) indicated by the powder manufacturer should be strictly adhered to, so you avoid any changes in the gloss level during a production run. Stops for a shift change or break should be avoided or carefully monitored.
- The transfer process must be performed according to the parameters (temperatures, times, pressures) indicated by the transferable support manufacturer. Too long transfer times could prevent the detaching of the transferable support after the process. Uneven temperatures and transfer pressures could cause halos of the decorative effect.
- Basecoat supports waiting for the transfer process should be kept in clean and dry conditions or the risk of dust or moisture deposition on the surface increases.
- Re-coating of aluminum profiles that have already been through the transfer process should be carefully evaluated since the transferred ink could “sublimate” through the new film.
- Some powder basecoats and decorative effects may give rise to different finishes if processed on different application and transfer plants.
- Basecoats that are the same color, but formulated with powder of different chemical composition, will have a similar weathering performance, but may have a different solvent resistance.
Naturall process
The Naturall process is also known as the “powder- on-powder coating system” as it is a five-stage process using two applications of powder coatings. This patented process to obtain a wood effect finishing on aluminum profiles can be achieved by using Qualicoat-approved, TGIC-free polyester powders:
- Substrate pretreatment;
- first layer powder base coat application (60 to 80 µm);
- melting process at 100º to 120ºC;
- second layer powder application—a flash coating of less than 10 µm through a patterned silk-
screen;
- and curing process (180º to 200°C for 20 minutes).
 |
| Figure 7: Patterned section layer of powder paint. |
After the final curing process, the patterned second layer of powder paint has penetrated into the first one, creating a compact and uniform layer of at least 60 µm thick. The final result is a powder-on-powder process and the surface appears similar to wood in look and feel with high performance outdoor weatherability characteristics. (See Figure 7.)
The most important advantage of the Naturall system over the sublichromy system is the absence of ink. Powder-on-powder processes offer a consistent coating of like chemistries whereas during the Sublichromy process the ink layer is a different chemistry than the base coat, which has different performance characteristics.
Aluminum profiles coated using the Naturall process can only be approved with powders that have been Qualicoat approved and provide the associated performance characteristics for external weatherability.
Effecta Process
The Effecta process is a patented process to obtain a wood effect finishing on aluminum profiles using a specially designed roller application technique with Qualicoat approved powders:
- first powder coatings application (60 to 80 µm);
- melting process at 100º to 120ºC,
- second powder coatings application;
- decorative dffect application—using a special roller;
- melting process at 100º to 120ºC;
- third powder coatings application (if desired);
- decorative effect application using a special roller (if desired);
- and curing process (180º to 200°C for 35 minutes using vertica curing lines).
After the curing process, the second layer and/or third of powder coating penetrates into the first one, creating a compact and uniform layer at least 60 µm thick. And similar to the Naturall process, the final result is an aluminum profile surface that has a similar look and feel as wood but with outstanding weatherability and outdoor performance characteristics. As with the Naturall technology, the most important technical advantage (there are other process and cost advantages) of the Effecta system versus the sublichromy system is the absence of ink in the transfer process.
For more information, contact Eugenio Gomez at (e-mail) eugeniogomez@rohmhaas.com.
