Archive: May 2023

Powder Coating Bonderized Steel

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Bonderized steel consists of hot dipped galvanized steel (G90 grade) that is pretreated with a phosphate followed by a chromate sealer and dried off in an oven. The process produces a dull, gray-colored finish. Bonderized is commonly referred to as “Paint Grip.” This product is commonly used for roofing, wall panels, and coil.

As for “Paintlok” or more precisely Electro Paintlok, it refers to electro-galvanized steel that has been pretreated with phosphate. The zinc coating is rather thin and withstands most forming operations. It has a dull gray matte appearance and is intended to be painted. Electro Paintlok is described in ASTM A591/A591M Standard Specification for Steel Sheet, Electrolytic Zinc-Coated, for Light Coating Weight Applications, with supplemental phosphatizing specified which can be used to enhance paint adhesion. By the way, this stuff is old school as Electro Paintlok was developed and trademarked by Republic Steel in 1942. The International Steel Group is the most recent owner of the trademark.

Galvannealed steel, which is considered a type of Electro Paintlok (see ASTM A653), is very similar to galvanized steel except it is comprised of a zinc-iron alloy rather than just zinc. Both are described in ASTM A653, with galvannealed designated by A or ZF and galvanized by a G or Z designation.

Both galvannealed and electro-galvanized are readily formable and weldable with no need to remove the coating. Both accept paint well. That said, normal hot-dipped galvanized (ASTM A653 any coating G or Z) can be problematic for paint adhesion.

Speaking of adhesion, Bonderized steel and Electro Paintlok already have a phosphate pretreatment. Nevertheless, I recommend a thorough cleaning of surface “oils and soils” combined with an adequate oven dry-off followed by a preheat to drive off gassing before applying a powder coating.

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Powder Coating Non-Conductive Substrates

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Much work has been done on formulations for wood and MDF, but other substrates such as fiberglass, drywall and many others are also viable options.

A variety of applications
Manufacturers of kitchen cabinetry, commercial casework, hospitality furniture, pre-finished sheet goods and office furniture manufacturers are extremely excited about the potential these low cure powder coatings can deliver. Improved technical performance and environmental footprint tick the functionality and environmental boxes that designers and manufacturers are looking for.

Learning from the past
Powder coatings for wood have been tried in the past, with limited results. Fortunately, we have learned from past challenges. The first real attempts began in the 1990s with the launch of a UV-cured acrylated polyester system, but drawbacks such as the lack of coating flexibility to accommodate the swell/shrink tendency of wood/MDF meant limited uptake.

This was followed up in the mid-1990s with UV-cured unsaturated polyester-urethane powders. These products provided the flexibility needed to accommodate this shrink/swell tendency, however, there were drawbacks due to the curing system. For example, UV light won’t cure what it does not “see,” thus limiting the type of shapes that can be coated. UV curing also limits the colors available. In addition, UV cure results in very high crosslink densities, which can yield poor inter-coat adhesion.

In the late 1990s-early 2000s, thermoset powders made it onto the heat-sensitive substrates stage and progress was made, especially in the MDF office furniture segment. Thermoset powders, which do not require UV cure, could be applied in thick film layers, re-coated, and could produce relatively smooth finishes with good edge coverage. However, there were still challenges. For example, if moisture was present, defects due to outgassing would often occur. Consequently, the application and cure process involved 15-20 minutes of pre-heating in a conventional oven, to achieve a substrate temperature of about 300°F and a very dry board. This meant more expensive grades of MDF had to be used — the “standard” MDF was not suitable. In addition, this application system required high-energy consumption and a large space requirement.

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CARC Paint Storage is Different than Every Day Paint Protection

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Military vehicles, equipment, ships and aircraft are all exposed to extreme conditions. For the U.S. Armed Forces, only military grade paints that meet stringent military standards are suitable for these conditions. Chemical Agent Resistant Coatings (CARC) are well-known military grade paints. Products meeting this specification resist the penetration of chemical agents and require special storage. This is important for decontamination. Vehicles exposed to chemicals are quickly cleaned and returned to service. There is no danger of chemical agents leaching out from the exposed paint. CARC coatings also aid infrared signature management. The camouflage colors cause vehicles to blend in with surroundings. They remain invisible even to infrared technology. Extreme heat, salt water and chemical agents can accelerate corrosion. The military uses zinc chromate primers for corrosion protection. These specialized military coatings are sensitive and represent an investment in protecting vital military vehicles and equipment. They require strict adherence to military grade paint storage parameters to prevent the paint from degrading. The most important of these parameters is temperature control.

The Effects of Temperature on Military Grade Paint
When the temperature of paint drops too low, it separates into its constituent parts. This effect is reversible by reheating the paint. But the more often the paint cycles through this process, the greater the chance that it will not completely mix together again. High temperatures destroy paints. They cause solvent evaporation and chemical changes. It is also important to have a consistent paint application temperature. Temperature variances cause paint viscosity variances, which result in poor quality finishes. Store military grade paint in a controlled temperature range to maintain paint quality and application consistency.

U.S. Chemical Storage Temperature Controlled Storage Buildings
U.S. Chemical Storage manufactures prefabricated paint storage buildings that meet the requirements of military grade paint storage. These buildings conform to NFPA-compliant storage for all types of chemicals. Different models are available depending on fire ratings and storage requirements.

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