What is Rod Coating? Techniques and Applications Unveiled



Rod coating is a simple wet processing technique used to deposit a thin layer of solution onto a substrate. It involves a rod being placed above a substrate and dragged over a pool of fluid, resulting in the fluid being spread into a thin film or coating. Rod coating is commonly used in the development of applications such as automotive paints, photovoltaic cells and lithium ion batteries. This coating method is also referred to as drawdown coating and rod coating, or wire rod coating and Mayer rod coating, depending on the type of rod used.

Types of coating rod

There are two main coating rods which are extruded wire rods and spiral film applicator and they are the same in application and can be used interchangeably.
Extruded wire rod
Extruded wire rod is the simplest type, which is a straight rod suspended at a known distance above a substrate and passed through ink to leave a wet film. Using cold extrusion technology, continuous spiral grooves of different sizes are extruded on a smooth steel rod, and the thickness of the wet film coating is controlled by the different sizes of the spiral grooves. The rod does not come into contact with the substrate in the width of the coating area.
Wound wire rods
A wound wire rod is a type of applicator used to apply coatings onto substrates with controlled coating thickness. They are composed of metal, with metal or plastic rods wrapped around them in a spiral or helical pattern, leaving gaps or controlled gaps between the metal rings. Then use a wound wire rod to apply the coating material onto the substrate, leaving a thin and uniform coating. There are various sizes and configurations of wound wire rods with different wire diameters and ring spacing, which can achieve different coating thicknesses. The wire diameter and loop spacing determine the gap or clearance between the wire loops, which in turn determines the thickness of the coating applied. Usually, larger wire diameters and wider ring spacing result in thicker coatings, while smaller wire diameters and narrower ring spacing result in thinner coatings.

In a close wound wire rod, the wire is wound as densely as possible, completely covering the rod. This configuration typically produces a thinner wet film and is suitable for less viscous fluids that can easily be self-level. Open wound wire rods have wires spaced further apart, exposing some of the rods. The pitch of the winding becomes a critical variable, altering the wet film thickness. Open wound rods are generally better suited for more viscous fluids because the fluid needs to self level less once the rod has been drawn through it.
The advantage of extruded wire rod is that there is no possibility of wire breakage and they are easier to clean, while the advantage of wire rod is that they follow the Mayer rod testing principle more strictly. Due to the different principles of forming grooves between wire rod and smooth rod, the actual coating amount used may vary during the experimental process.

Related machine–coating machine

An Automatic coating machine is a device used for coating thin films in laboratories, replacing manual coating and automating coating to improve the accuracy and efficiency of coating. The working principle of the laboratory automatic coating machine is to evenly coat the sample on the substrate by controlling the coating head and coating parameters, forming the desired thin film.
Our coating machine — TM1000 motorized coating machine is a basic spiral film applicator (wire rod) coating machine that adopts a new spiral film applicator installation method and has speed control and coating length adjustment functions. It is suitable for coating samples of coatings, inks, paints, slurries, lithium batteries, pressure-sensitive adhesives, polymer materials, etc. It can be scraped and applied on glass, cardboard, and fabrics.
Maybe you want to know more about coating machine

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