What is the roll coating technique?

Recent studies indicate that roll coating, a technique commonly used in manufacturing, involves the application of coatings onto a substrate as it moves through a series of rollers. This process is efficient and allows for uniform coating of various materials.

This post aims to provide a basic overview of the roll coating process, often referred to as roll-to-roll coating. We invite your feedback and hope this information proves beneficial for you and your associates.

Roll-to-roll processing is a fabrication method that coats, prints, or laminates fluid materials onto a flexible rolled substrate material, continuously feeding it through a series of rollers from unwind to rewind. This technique comprises several rollers, forming a web path that winds the substrate to perform various operations while applying materials to create or produce a product.

Diving deeper, roll coating encompasses a pre-metered coating, utilizing a series of rollers to meter and apply coating liquid onto a substrate. Initially, a metered film of coating liquid forms on the roller surface before being applied to the substrate, allowing the amount of coating delivered to be almost independent of the fabric’s properties. Controlled mainly by the fluid type, applicator roller, and relative speed of the rotation surfaces, this process ensures precise application despite variations in substrate thickness.

Single Rotating Roller

The most straightforward roll coating configuration utilizes a single rotating roller. The lower half of the roller is submerged in a coating liquid bath, while the upper half contacts the substrate. As the roller rotates, a film of coating liquid layers on its surface, some of which transfers to the substrate. The hydrodynamics govern the amount of coating, influenced by factors such as the rotation speed of the roller, substrate speed, and the rheological properties of the coating fluid (including surface tension, viscosity, and density). Here, one roller serves both as a metering and an application device. However, adding more rollers enhances control.

Three-roll Coating

Three-roll coating incorporates a metering roller, an applicator roller, and a backup roller. Among common configurations are nip feed coating and L-head coating. In nip feed coating, the metering roller and applicator roller create a nip filled with coating liquid acting as a reservoir. The applicator roller picks up this liquid, with the metering roller rotating in the opposite direction to control the amount delivered to the substrate. Any remaining liquid on the metering roller is removed by a doctor blade to avoid defects like streaks or roughness on the film applied to the substrate supported by the backup roller. This setup minimizes coating fluid usage, although it may risk leakage when dealing with low-viscosity liquids.

In L-head coating, a liquid film develops on the applicator roller while it comes into contact with the coating liquid metered by the metering roller, before depositing onto the back-up roller. To enhance coating speed, an additional roller called a pick-up roller, which runs at a reduced speed, can be included, forming a four-roll pan-fed coating system.

In reverse metering, applicator and metering rollers rotate in opposing directions, whereas when they rotate in the same direction, it is termed forward metering. Typically, reverse metering yields a smoother and more stable film compared to forward metering, making it the preferred choice.

Roll coating employs various materials for application, including water-based solutions, solvent-based coatings, and hot melts, where solid pellets are melted between heated rollers, forming a film that is then applied to the substrate, which is usually preheated beforehand.

Web Tension Control in Roll-to-Roll Systems

The success of roll-to-roll processing highly depends on precise control of web tension. Maintaining uniform tension across the substrate as it travels from roll to roll is vital for production quality. Any slight variations in tension can compromise the applied material on the substrate, potentially making the final product unusable.

Roll-to-Roll Applications & Industries

R2R processing finds application across various sectors, including IT, electronics, energy, textiles, medical, and metal fabrication, among others. Flexible materials are often vital for the end products, which range from electronic devices and solar panels to thin-film batteries and fuel cell membranes. For instance, large-area electronic devices like flexible displays or circuit boards are produced through R2R processing utilizing rolls of plastic film or metal foil.

National Polymer is at the forefront of R&D and manufacturing, specializing in formulation chemistry, pilot coating, coating technologies, deformulation, reformulation, batch optimization, and production. For further insights into our capabilities, reach out to us today.

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If you wish to know more, kindly visit aluminum roller surface coating process.