Anodization for Architectural Metal Constructions
Zinc phosphate coating elevates the natural crystalline aesthetics of hot dipped galvanized steel for decorative use. It is favoured for its natural, luxurious and stately ambiance and for the gray tones that settle over time.
|Main Features||-External use possible |
-Creates a natural tone that cannot be replicated with paint coat finishes
-Blends into surrounding atmosphere over time
|Hot Dip Galvanized Steel Material, Products|
|Category||Light Gray, Medium, Dark Gray|
|1100mm(W) x 4500mm(L) |
*Please consult us on any products over this size
|Remarks||The resulting colours or patterns of the zinc phosphate coating are highly dependent on conditions such as material composition or the thickness of the material, thus making the process an art as much it is science. Therefore, please contact us prior to making the final selection.|
■Purpose of Zinc Phosphate Coating
-Enhancing the Aesthetics
Steel is one of the cheapest materials used in architecture and is one that requires a treatment to resist corrosion. Amongst the typical coating, such as paint coats or galvanization, a hot-dipped galvanization is a popular option as it is maintenance-free, highly corrosion resistant and for its low cost. However, freshly treated hot dipped galvanized steel has a high sheen that is less desirable for a natural physique. The zinc phosphate coating dulls this sheen.
-Excellent Sub-coating Properties
Phosphate coating serves as surface preparation for further treatments, such as coating or painting, for its excellent adhesion and porosity that helps prevent under-film corrosion.
-Wear and Friction Resistant Joints
The crystal structure of zinc phosphate coating provides high wear and friction resistance. This property makes it an excellent choice for steel frame products joints.
■What is Zinc Phosphate Coating?
The application of zinc phosphate coating results in a layer of insoluble, crystalline phosphates (1～20μ). The resulting porous layer is composed of hopeite, phosphophyllite and other zinc phosphate compounds that combine with the hot-dip galvanization coat through the following process.
- 1. The galvanized metal reacts with the solution, causing zinc from the material to elute into the solution.
- 2. Zinc reacts with the solution to form zinc phosphate compound.
- 3. The zinc phosphate compounds precipitate on the surface.
■Characteristics of Zinc Phosphate Coating
Zinc phosphate coating is roughly twice as corrosion resistant to hot-dipped galvanization, although the performance depends on the coating thickness.
Galvanic corrosion is caused by differing electrochemical potentials in the material when a current flow. However, since zinc phosphate coating is a non-conductor, the coat prevents current flow, making it resistant to galvanic corrosion. The chemically produced coat is also resistant to flaking as it is modified on a molecular structural level.
As zinc phosphate coating is colourless, its gray tones are a result of reflections. This means that the coat is not affected by ultraviolet rays; absolving it from any concerns of weather resistance.
Additionally, the high porosity of zinc phosphate coating allows the induction of carbon dioxide and water particles within the atmosphere, allowing it to react to form a coat of basic zinc carbonate. This appears as the grey tones settling over time.
■Types of Zinc Phosphate Coating
Phozinc, KIKUKAWA’s proprietary zinc phosphate coating is available in three tones: dark, medium and light gray.
As a supplementary finish, a coat of clear coating can be added to prevent aging or a coat of coloured clear coating for a different aesthetic. Although limited to interiors, the clear coating can be polished for a luxurious shine.
■Zinc Phosphate Coating Process and Fabrication
The overall steps for zinc phosphate coating are as follows.
1 Hot dip galvanization
2 Setting up
3 Degreasing and cleaning the surface
Many of the treatments for zinc phosphate coating involve bathing the metal sheet in solutions. This implies that our product size will be limited by the size of the bathing containers. At KIKUKAWA, the size of the tub is 1600(H) mm x 1100(W) mm x 7000 (L) mm, however, our product is limited at 1100(W) mm x 4500(L)mm to ensure quality. Please consult us if you wish to fabricate a product over this size.
Various factors, such as the composition of the material, structure of the metal surface, thickness or its shape, influence the resulting tones and patterns of the zinc phosphate coating. This makes the finish closer to an art form. Additionally, the nature of the hot-dipped galvanization process tends to introduce imperfections for the resulting coat.
Therefore, please keep in mind that the appeal of zinc phosphate coating is in its natural physique, rather than an artificial uniformity, and that its tones change over time. Please note that this also makes spot repairs challenging.
■KIKUKAWA’s Zinc Phosphate Coating
Phozinc is Kikukawa’s proprietary zinc phosphate coating that has been elevated to be used for decorative panels. Through various past projects, we have gained the expertise for this finish. In the design stage, we take into consideration that the metal sheets are prone to deformation from hot dipped galvanization. During production, we conduct lot controls and treatment controls for quality assurance.
There are limitations for zinc phosphate coated products, such as material thickness or shape. However, Kikukawa has continuously provided solutions for our customer’s demands. Please consult us for project considerations or prior to the final selection.