Doctor Blade Coating: How It Works, And Why We Use It

Curious about doctor blade coating? No worries. Conversion Technologies International has the details.

What is doctor blade coating?

Doctor blade coating is a specific type of coating that’s reliant on a knife (or “doctor blade”). We use the blade to spread viscous coatings across a substrate, ensuring the layer is as smooth and even as possible. The process begins as we deposit the coating—usually in a liquid of paste-like form—on the substrate. From there, the blade scrapes over it, flattening the solution into its coating form. The benefit of using a doctor blade is the level of precision provided. The gap between the blade and the substrate controls the thickness of the coating. This also determines the viscosity and shearing of the coating, offering an additional level of control.

We can apply the doctor blade coating method with not only liquid solutions and pastes, but adhesives and slurries. The process corresponds with several different applications, including:

• Manufacturing materials. In this case, we can use a doctor blade coater when working with ceramics, pharmaceutical products, and adhesive tapes.
• Textiles and paper. For certain projects, we apply solutions to fabrics or papers. This may be a part of the printing process. Otherwise, we may want to apply protective coatings, making water- or fire-resistant products. Doctor blade coating is one of the best possible adhesive coating methods for this purpose.
• Energy and electronics. At times, we need to coat products like fuel cells, thin-film solar cells, and battery electrodes. Look no further: A doctor blade coating machine can help ensure the results you need. Through this process, we can apply coatings to everything from films to fabrics, plus metals and paper. It allows you a lot of flexibility, while at the same time creating consistent results. It also cuts down on waste, saving you both time and money.

What are the 4 types of coatings?

Doctor blade coating is a coating method—but we can apply it to a variety of different coatings themselves. Although you’ll find many types across the market, four stand out the most. This is due to factors like durability, expense, and efficiency. Generally speaking, the manufacturing industry favors:

• Acrylic coatings. These coatings have an immediate, major benefit: They dry quickly. This adds an extra element of efficiency, though it decreases the malleability of the coating. In other words—if you make a mistake with an acrylic coating, you can’t fix it as easily as you would with others. However, it’s resistant to corrosion and aesthetically holds up against wear and tear. Additionally, acrylic coatings preserve colors longer than alternatives. With this in mind, we use it for a number of different industrial applications. We also prefer it for roofing and concrete coating projects.
• Polyurethane coatings. What sets polyurethane apart is its resistance to UV rays. This makes it ideal for outdoor projects in hotter environments. It’s also quite resistant to abrasion, both structurally and aesthetically. We often apply it to bridges, cars, and industrial flooring for this reason.
• Epoxy coatings. You’ll find a lot of benefits to epoxy coatings—there’s a reason why it’s so popular amongst manufacturers. It’s quite durable and resistant to corrosion, lasting longer than many competitors. Furthermore, it’s notable for its adhesive qualities. Epoxy is one of the strongest adhesive coating methods on the market. We frequently use it in marine applications, as well as many industrial settings.
• Alkyd coatings. This coating is more specialized than some others. However, it helps protect steel against rusting. And as steel is one of the foundational industrial materials, alkyds are rather important. If you’re working with steel, you’ll probably need this coating.

How does doctor blade affect print quality?

A doctor blade has a major impact on the quality of a printing project. When we’re working with industrial roll coating methods, the doctor blade acts as a final stopping point. It scrapes away the excess solution, ensures it’s flat, consistent, and exactly the level of thickness you need.

When it comes to printing in particular, it impacts the sharpness of the final image. It also controls the ink metering and color consistency, while cutting down on friction—and therefore errors. Used correctly, a doctor blade prevents ink shadowing, over-inking, and spitting. Ultimately, the doctor blade process improves printing quality significantly.

Frequently Asked Questions

It’s normal to have further questions. That’s why we’re covering a few more!

What’s a gravure doctor blade?

“Gravure doctor blade” or “gravure blade” is another term you might see used to define doctor blades. In this case, we use the blades to process gravure printing cylinders. Gravure relates directly to printing, as opposed to other processes related to coating.

What’s a coating head?

A coating head (sometimes referred to as a slot die head) acts as part of a coating machine. It applies a liquid coating solution to a moving substrate. Typically, these substrates include metal, paper, and plastic film. The solution lies within an internal well, which the machine pushes through a slot distributed by the coating head. It’s not only precise, but highly efficient.

What are other coating processes?

We can’t list all coating processes—there are too many! But some popular processes include dip coating, spray coating, roll to roll coating, and powder coating.

What should we do next?

If you’re still curious about doctor blade coating (and other processes), good news: CTI can help! Call us at 419-924-5566 or contact us here for further information.