The Importance of Pre-Treatment for Coil Coating Applications

Pre-Treatment for Coil Coating ApplicationsThe Efficiency of a Continual Coil Coating Process

The journey of coil coating begins with the entry stage, where bare metal coils are meticulously placed on a decoiler or unwinder. The coil’s front end is fed up to a joiner, linking it seamlessly to the back end of the previous coil through mechanical means. This straightforward yet crucial process, known as coil splicing, offers a cost-effective and low-maintenance approach, creating a robust bond for a continuous process. This contributes to the efficiency of the coil coating process.

While mechanical stitching is the norm for joining coils, alternatives such as adhesive tape or welding are another one of the diverse methods used on coil coating lines. Once the joint is formed, the coil accelerates into the accumulator at a quicker speed than the process can remove it to create a buffer of material.

CLEANING: The Prerequisite for Pristine Coil Coated Surfaces

Before any coating is applied, the surface of the coil must undergo a thorough cleaning. Impurities, including oil, carbon, grease, or abraded metal particles, must be eradicated. The cleaning process may consist of multiple stages, including a rotary abrasive brush section to remove localized corrosion products. Different substrates demand specific cleaning methods, such as alkaline cleaners for steel and zinc-coated substrates, alkali or acidic cleaning for aluminum surfaces, and occasional electrolytic cleaning for aluminum processing lines.

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PRETREATMENT: Elevating Compatibility and Performance

Pretreatment takes center stage, aiming to establish compatibility between the metallic substrate and the applied organic coating. This step ensures optimal adhesion and corrosion resistance characteristics, a crucial foundation for the success of any coil coating process. Chemical conversion or pre-treatment is a necessity to ensure the proper adherence of organic coatings to metallic surfaces.

Pretreatment solutions are applied through spray, a simple roller-coater known as a chemcoater, or immersion, with subsequent rinsing. The chemcoater, equipped with rollers for both coil surfaces, controls the coating application by adjusting speed and pressure. Drying, achieved through a low-temperature oven or the heat within the metal substrate, completes the pretreatment process.

Conventional conversion coatings like alkaline oxide, zinc phosphate, iron phosphate, and, for special applications, chromates, play a crucial role. No-rinse processes, based on chromates or modern chrome-free chemistry, bring environmental benefits by reducing effluent and minimizing plant requirements, leading to energy and capital savings.


Post-pretreatment, the painting process unfolds in two stages: application of primer and application of the finish coat. Coatings are applied using a roller coater directly onto the substrate. The variety of coil coating lines, ranging from single coater and oven lines to tandem lines with two or more coaters and highly specialized lines with three coaters and three ovens, cater to diverse markets and applications.

UNICHEM Coatings: A Legacy of Excellence

UNICHEM stands as a leader among custom coating and industrial adhesive suppliers with over 50 years of experience. Offering a diverse range of coatings, including Acrylic, Polyesters (Flexlain), PVC/Plastisol (Vinyloid), and PVC/VA (Vinyloid), UNICHEM specializes in custom-developed coatings applied via coil coating.

With a team of resin and coating experts, UNICHEM ensures cutting-edge solutions for various industries, including:

UNICHEM offers coating and adhesive solutions for these markets, and others with custom coil-applied solutions. UNICHEM understands that the intricate process of entry, cleaning, and pretreatment in coil coating is the key to achieving impeccable finishes.

We help our customers with troubleshooting problems arising in their coating processes and provide solutions that improve product quality and process efficiency.

Consider UNICHEM as your partner in your coil coating application, providing unmatched expertise and solutions for your prepainted metal applications. Contact us to explore how UNICHEM coatings can elevate your coil coating experience.