Alfa Reçine Launches New Alkyd Resin "Alfakyd X48 W45" for Galvanized Metal Paint

1 - Galvanizing Process Galvanizing is a zinc coating process applied to steel sheets that creates a protective layer on both sides of the sheet. Depending on the desired properties, various zinc coating methods are available. Some of the most commonly used galvanizing processes today are: a - Hot-Dip Galvanizing, b - Electroplating, c - Hot Zinc Spraying.

1.1 Hot-Dip Process

Hot-dip galvanizing is a process in which steel is coated by immersion in molten zinc bath. The hot-dip galvanizing process has three basic stages: surface preparation, galvanizing, and inspection. (Figure 1)

1.2 Electroplating Process

Electroplating is a process in which a zinc layer is bonded to steel to provide protection against corrosion. In this process, the electroplating is carried out with the aid of electric current passed through a salt zinc solution using a zinc anode and a steel conductor. (Figure 2). It is the most effective protective coating method for narrow sections of machine parts such as gear wheels and fasteners.

Figure 1. Hot-Dip Galvanizing Process

However, there are differences between the corrosion-prevention effects of electroplated coatings compared to hot-dip galvanized coatings. In general, since this process achieves lower coating thickness and quantity, it is not recommended for use in outdoor environments without additional surface coating.

1.3 Hot Zinc Spraying

Hot spraying is based on the principle of melting zinc or other alloys at a heat source (flame, plasma, electric arc, etc.) and then spraying them (Figure 3). An important advantage of this method is that hot zinc spray can coat the metal surface with a much thicker film layer (up to 250 microns or more in some cases). Furthermore, very large parts that are difficult to coat with the hot-dip galvanizing process can be coated more easily using the hot zinc spraying method. In fact, regardless of which method is used, the purpose of all these methods is to protect metals against corrosion (i.e., rust formation) without requiring additional coating. Thus, the zinc layer will serve as a protective barrier between the steel and corrosive material. However, it is often necessary to provide an aesthetic appearance or extend corrosion resistance over much longer periods or increase resistance to various chemicals. In such cases, the galvanized surface usually needs to be coated with appropriate paint.

2. Painting Galvanized Metal Surfaces

Painting galvanized metals is more difficult than painting other metal surfaces. This is because the galvanized surface is coated with an oily material layer to prevent corrosion. When another organic paint is applied over the oily layer, the binder in the paint reacts with the zinc, creating an independent layer at the interface, and this sometimes causes the paint to peel or flake off.

2.1 Paint Options for Galvanized Metals

There are many types of paint available on the market for galvanized steel. These are mostly epoxy, polyvinyl butyral, urethane, acrylic, and alkyd resin-based paints. With the exception of alkyd-based paints, these offer the best performance in terms of galvanized surface adhesion, but their costs are quite high. However, alkyd resin-based paints stand out with their most important advantages over other acrylic, polyester, etc. resin-based paint equivalents, namely ease of application, high gloss, and low cost, while also providing the best aesthetic appearance. Nevertheless, despite their low cost, alkyd-based paints are not widely preferred because of their generally poor adhesion strength on galvanized surfaces. In fact, conventional alkyd-based fast air-drying paints adhere well initially when applied to galvanized metal surfaces, but begin to peel shortly thereafter. This is because the zinc on the surface of the galvanizing coating reacts with the alkyd binder in the paint, weakening the paint's adhesion strength. (Figure 4) [caption id="attachment_103419" align="aligncenter"] Figure 4. Paint peeling from galvanized metal surface[/caption]  

2.2 Steps to be Taken Before Painting:

The reason that makes it difficult for paint to adhere to galvanized metal is mostly due to a dirty oily layer formed on the surface (zinc white rust, grease). Therefore, the surface must first be thoroughly cleaned. Subsequently, if an appropriate paint is selected, the metal surface should no longer peel or flake off.

2.3 Surface Cleaning

In addition to the importance of the quality of the paint to be selected, another important issue is surface preparation before painting. Cleaning oxidized white rust (zinc) or oily residue from the surface is critical. Otherwise, the paint will not adhere. For this purpose, the entire surface must first be cleaned using an appropriate water-based chemical degreaser. Optionally, to further increase adhesion, the surface is first wiped with white vinegar and lightly abraded. Subsequently, if the surface is rubbed with sandpaper to remove oxidized zinc (white rust) residue, this can ensure lasting paint adhesion. Finally, the surface is wiped with water and allowed to dry.

3 - A New Alkyd Resin for Galvanized Metal Coating:

Alfa Kimya has developed a new alkyd resin suitable for rust-resistant metal coating. Unlike conventional alkyds, this alkyd resin has been developed using special raw materials, modification, and a new technology system, and provides good adhesion performance on galvanized steel, aluminum, copper, and brass with increased chemical resistance.

3.1 Alkyd Resin Product Name: Alfakyd X48 W45

  3.2 Properties and Applications: It is a high-viscosity oxidizable medium-oil alkyd resin containing a mixture of drying vegetable fatty acids. It has been developed specifically for coating galvanized and non-ferrous metals and wood materials.   As shown in Figure 5, the adhesion performance of the paint prepared with the newly developed alkyd resin (Sample 1) is considerably more successful compared to a competing galvanized paint (Sample 2). Furthermore, it is clear that the paint prepared with a general-purpose fast-drying short-oil alkyd resin (Sample 3) failed in the adhesion test.

4. Conclusion:

Alfakyd X48 W45 has been developed specifically for the production of paints and varnishes used for galvanized metal coating. Adhesion performance has been enhanced through the use of special raw materials, while other performance properties (drying, hardness, yellowing, and gloss, etc.) have been optimized. According to the above results, it is clear that the resin type and its properties have a significant effect on adhesion performance over galvanized metal. Furthermore, it should not be forgotten that removing grease and zinc residues before applying paint to a galvanized metal surface is also very important.   Abdulvahap Selim Çifçi Research and Development Manager Alfa Kimya Adem Aşçı Research and Development Chief Alfa Kimya