As architects and designers look for more varied and exciting finishes, they are realizing the benefits that powder coatings can provide them with as a high-performance, environmentally responsible method of enhancing the beauty and durability of the buildings they design. In particular, the choice offered for coating aluminum profiles and cladding grows with new innovations in application and finishes, including decorative marbled and wood effects, providing architects and designers with quality powder coatings technology and unique finishes to differentiate and protect their designs.
Rohm and Haas Powder Coatings’ architectural products have been designed over many years to satisfy the unique requirements of the worldwide building products industry with all the environmental excellence of the powder coating process. Available to architects and applicators globally, the broad range of products in the architectural portfolio, designed to balance economics and performance, exhibit a range of outdoor weatherability and mechanical properties that can allow a user to meet the various demands of architectural governing bodies. These include the American Architectural Manufacturers Association (AAMA) specifications for organic coatings on aluminum extrusions and panels as well as the strict quality requirements of European architectural governing bodies – GSB, QUALICOAT (class 1 and 2) and British Standard (BS 6496 and EN12206-1).
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| Figure 1: Wrapping the profile with a film bag. |
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| Figure 2: Aluminum bars wrapped with film bags. |
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| Figure 3: Making contact with vacuum devices. |
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| Figure 4: Aluminum bars going into the oven at 200° C. (Click images to enlarge.) |
Wood Effect Finishing
Wood effect finishing has seen growth in popularity over the years, particularly in Europe, as a real alternative to typical architectural materials such as wood, marble and granite. The powder coated finish provides the high weathering performance of aluminum coupled with the decorative appearance of real wood. Decorative wood effects can be achieved in one of three ways: Sublichromy, Naturall1, and Effecta2.
Sublichromy Process
This process produces a wood effect pattern onto aluminum profiles using a transferable media coated with special inks in a three-step process. When placed under a significant combination of heat and low pressure, the pattern is transferred onto a surface that has been previously coated with a specifically formulated powder coating.
The procedure for Sublichromy is substrate pretreatment, basecoat powder application, and sublimation process.
Substrate pretreatment: The pretreatment process is key to ensure that the initial powder coatings layer achieves good adhesion to the surface and exhibits good corrosion resistance. Pretreatments can include current hexavalent chrome systems and more environmentally friendly trivalent and chrome-free methods.
Basecoat powder application: A Qualicoat- approved polyurethane or polyester TGIC or TGIC-free powder coating is applied to a coating thickness of up to 60 µm and then cured at 180° to 200°C for approximately 20 minutes. This provides the base cost for the transfer of the ink design onto the surface in the next stage.
Sublimation: The coated aluminum profile is wrapped in the bag that has the transfer ink coated on one side and sealed at one end and along the top. A vacuum is applied to the open end of the bag and the transfer ink comes into contact with the powder base coat. Sublimation—or ink transfer—occurs in the oven again at 150° to 160°C after which the bag is removed and the profile is allowed to cool. (See Figures 1 to 4.)
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| Figure 5: Visual inspection of a coated glass panel. |
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| Figure 6: Visual inspection of a coated glass panel. |
Qualicoat specifications for decorative finishes are equivalent to those for standard coatings finishes with the only difference being the color deviations. Since decorative effects don’t have a uniform appearance, and the colors of the base powder coat and ink transfer top coat can change each other in different ways, the Light Fastness test was introduced. This test evaluates the color deviation and gloss reduction at the same time to produce a Qualicoat measurement for the specification of the finish.
Another way to characterize the quality of the process is to verify the degree of ink penetration in the powder-coated base layer. This test can be performed using a metallographic microscope and inspecting the cross-section of a coated profile. This method makes it possible to monitor how much ink has penetrated into and through the base powder coating—better penetration improves the final performance of the coated product.
The ink penetration through the base coat can also be visually inspected by coating glass plates and inspecting the reverse side of the plates to determine the penetration of the transfer ink through the base coat. (See Figures 5 and 6.)
