Anodize

WHAT IS ANODIZING?
Anodizing is a simple electrochemical process developed more than 50 years ago that forms a protective coating of aluminum oxide on the surface of the aluminum. The lifetime of the finish is proportional to the thickness of the anodic coating applied.

Aluminum oxide is a hard, durable, weather resistant substance that protects the base metal. The coating may be colored by dyeing or may exhibit bronze tones through diffraction phenomena produced by the coating. The coating grows from the base aluminum metal by this electrochemical process. The coating is integral to the metal and can not peel or flake. The structure of the coating is many small hexagonal pores, which are filled with a "seal" that hydrolyzes these pores to fill them with inert aluminum oxide.

ADVANTAGES OF ANODIZING

1. In general anodizing is less expensive than painting with the exception of coil painted products.
2. Anodizing is harder than PVDF. Anodizing is better for aluminum in high traffic areas where the coating is subject to physical abuse and abrasive cleaners.
3. Anodizing cannot peel off. The coating is actually part of the metal.
4. Anodizing gives aluminum a deeper, richer metallic appearance than is possible with organic coatings. This is because an anodized coating is translucent, and one can see the base metal underneath the coating. This translucence contributes to color variation problems, but anodizers are doing a much better job of controlling the amount of color variation than in the past. Computerized color matching with quantitative, objective color data is now possible.
5. Anodizing is unaffected by sunlight. All organic coatings will eventually fail due to exposure to ultra-violet light.

In 1988 the Aluminum Anodizer's Council was formed by a group of anodizers who were concerned that the market was unaware of the benefits of anodizing. The paint manufacturers were comparing excellent paint to poor anodizing. It was no longer common knowledge in the commercial construction industry that there is a difference between good and bad anodizing. Anodizing which is improperly sealed has poor chemical resistance. Brand new anodizing with a thin coating thickness is nearly identical in appearance to an Aluminum Association Class I (very thick!!) anodized finish. Very thin (sub-Class II) anodized coatings are unsuitable for use on exterior curtainwall or metal roofing.

The advantage of a thicker anodic coating is its durability and longer life. The Achilles heel of anodizing is it's chemical resistance. Eventually the surface of an anodic coating may succumb to acidic pollutants in urban environments. Anodized surfaces, like other building components, must be protected from acidic attack during construction.

After many years anodized surfaces may accumulate dirt and stains that look similar to chalking paint. This "chalk" can be removed with a mild detergent combined with an abrasive cleaning technique. A small amount of the anodic coating can actually be removed, leaving behind a renewed anodized finish which can last for another twenty years. This is why anodizers say their product is "renewable". Once an organic coating has failed, the only options are to re-coat the surface with another paint or replace the metal. When an anodized coating appears to have failed, cleaning often results in a renewed appearance.


POWDER COATINGS
Liquid paint is composed of pigment, resin, and solvent. Powder paint is simply pigment encapsulated in a powdered resin and is thus simply thought of as "Paint without the solvent." Powder coatings and liquid coatings made from the same resin and pigment will have practically the same performance characteristics. For a given resin, the decision to use a powder or liquid coating is simply a question of application technique.

The real advantage of powder is the reduction in air pollution compared to liquid coatings. When powders are cured in an oven they emit no VOCs. A disadvantage of powder is the large batch sizes that are typically required by powder coatings. The powder manufacturers are aware of this problem and a few of them keep colors in stock that they distribute in small batches. Several companies manufacture exterior grade powders using a Polyester TGIC resin. Polyester TGIC powders are currently available in more stock colors than any other powder. Several companies stock hundreds of colors of Polyester TGIC powders.

Some resins are more easily manufactured in liquid coatings and some are more easily manufactured in powder coatings. A particular resin is usually manufactured in either powder or solvent based coatings, but not both. Examples of this are epoxy which is predominantly a powder coating, and PVDF which historically has been manufactured as a liquid coating. Many of the perceived advantages of powders over liquid coatings such as hardness and gloss are actually characteristics of the resin.

Powder coatings from most manufacturers are only available in large batches and custom colors can be very expensive. This is because each batch of powder must be ground to order using expensive grinding equipment. Solvent born colors will continue to maintain their niche in the market because of the ease with which small batches can be mixed. The ability to "mix and match" gives painters and their customers unequaled flexibility and ease of use.
Southern Aluminum Finishing also applies epoxy based powders for interior applications such as furniture.