Corona Discharge

Corona Discharge

Corona Discharge - Enhancing adhesion capabilities

In the manufacturing world, specific materials are preferred for producing specific products. While those materials may have positive characteristics such as malleability, strength, and heat resistance, for example, they may not have the surface energy to accept adhesives, coatings, paints, or printing well. If those treatments don’t adhere properly, they peel, flake, and fail. The result is a low-quality product.   

corona-discharge-2The low surface energy of certain materials often leads to poor adhesion of inks, glues, and coatings because they possess significantly high surface energies. To achieve optimum adhesion, it’s vital that the base material’s surface energy is equal to or higher than the surface energy of the substance which is applied to it, such as an adhesive or paint. Fortunately, a corona discharge can be used to effectively activate a surface in order to make it more receptive to a coating. 

What is a corona discharge?

A corona discharge is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. Corona plasma is generated by applying high voltage to an electrode with a sharp tip, where the plasma forms. A linear array of electrodes is often used to create a glowing bluish-purple curtain of corona plasma through which material to be treated is passed. This causes surface activation of the material, increasing its surface energy by bombarding it with plasma ions.

Plasma treatments come in two basic processes: vacuum and atmospheric plasma. Vacuum plasma utilizes a vacuum pump to remove most of the air from a chamber, creating a low-pressure environment conducive to ionizing the remaining air or gases with a strong electrical field that produces the plasma.

Corona discharge is an atmospheric plasma, which requires no vacuum. Produced by electrically energizing air or gases as they pass through a nozzle at surrounding atmosphere or normal pressure using a pulsed electric arc generated by high voltage discharge, it enables plasma treatments to be applied directly in-line with a manufacturing assembly process. Without the need for a vacuum chamber, extremely long products can be easily treated with short processing times, immediately prior to gluing, bonding, or coating.

Corona discharges come in two forms, positive and negative, which is determined by the polarity of the electrode used to produce the corona. Positive and negative coronas are similar but there are some key differences. Positive corona discharges have a much lower free electron density than negative coronas. However, the electrons in a positive corona discharge are concentrated and contain more energy. Negative corona discharges appear larger than positive ones. This is due to the free electrons being more spread out and more abundant.

What materials and products can benefit from corona discharge?

Corona discharge treatments are highly effective on virtually any surface format including dimensional objects, sheets, and roll goods that are handled in a web format. Corona discharges are widely used to treat a variety of materials and products in the plastic film, extrusion, and converting industries, including:

  • Polypropylene
  • Polyvinylchloride (PVC)
  • Polyethylene terephthalate (PET)
  • Polyethylene
  • Vinyl
  • Paper
  • Paperboard stock
There are several basic corona treatment system configurations used for treating materials in web form. They are defined essentially by the location of the dielectric material in the station: conventional, bare roll, double dielectric, and convertible. The configuration that is best for a given application depends mainly on the material being processed.

Corona discharge surface treatment is an effective and efficient process for increasing the surface tension of a wide variety of materials, parts, and packaging in order to provide a surface that is more receptive to inks, coatings, or adhesives. Highly consistent and controllable, the process continues to be adapted for new applications using both standard and innovative materials.

To learn more about the use of plasma in manufacturing, please read our eBook titled "Manufacturer’s Surface Activation Guide for Improved Adhesion."



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