Plasma and Surface Treatment

by Pillar Technologies

The terms "plasma treater" and "surface treatment" have connected more in the last few years than ever before. "Plasma" seems to be the new buzz word in surface treatment, even though claims were made as early as the late nineteen-sixties about the advantages of exposing polymer surfaces to a plasma of partially ionized gas.

Plasma is a substance where many of the atoms or molecules are effectively ionized, allowing charges to flow freely. This collection of charged particles containing about equal numbers of positive ions and electrons exhibits some properties of a gas but differ from a gas in being a good conductor of electricity and in being affected by a magnetic field. With the addition of heat or other energy, a significant number of atoms release some or all of their electrons. This leaves the remaining parts of those atoms with a positive charge, and the detached negative electrons are free to move about. These atoms and the resulting electrically charged gas are said to be "ionized". When enough atoms are ionized to a point that significantly affects the electrical characteristics of the gas, it is a plasma. Plasmas can carry electrical currents and generate magnetic fields and the most common method for producing a plasma is by applying an electric field to a gas in order to accelerate the free electrons.

Processes like Corona Treatment, Gas Atmosphere Plasma, Flame Plasma, Atmospheric Plasma, Low Pressure Plasma, Vacuum Plasma, Glow-discharge Plasma, and Plasma Etching all rely on the properties of plasma. Each of the methods listed have respective differences between them, and are chosen based on the desired surface effects and material qualities. These differences include cost, size, safety, and results. All are very important, however the most significant factor in making your decision is using the correct method to get the results you need. Too often, purchase decisions are made to save cost, or to fit into existing space, only to find out that the equipment does not achieve the results for which it was originally intended.

The corona treatment process is at the simple end of the plasma scale, and is a lower cost alternative for treatment of many plastic films, foils, papers, etc. to enhance the adhesion to other materials by increasing the surface energy. If the desired surface qualities go beyond what a normal corona discharge system can provide, another plasma technology should be considered.

Material selections are usually based on the primary engineering properties required for the end product while secondary characteristics of the surface are sometimes sacrificed. Designers must carefully balance their selection of specially formulated and expensive materials or material combinations to achieve the desired balance of properties that they require. In many cases, the materials, which provide the desired surface properties, lack some of the primary properties that they desire. This often requires the use of expensive multilayer construction, or in some cases, abandoning potential products due to the high cost associated with these engineering requirements. One alternative solution is plasma technology. This type of system can provide certain material surface characteristics without sacrificing the primary engineering qualities of the material. The technology is capable of altering the surface of a material only a few molecules deep, thus making a profound difference in the material for an unlimited number of applications. Desired effects such as bond strength, superior adhesion characteristics, and chemical reactivity along with micro thin coating deposition by plasma polymerization can be achieved.

The buzz on plasma will continue to grow as the material requirements and process needs change. Since there are so many different plasma technologies available today, it is important to investigate and understand what each of these technologies can do, and where they may fit in your plasma and surface treatment needs.

Looking Ahead ...Mark Stoll, General Manager

As Dick Washebeck pointed out in his article, "Plasma" is an often misunderstood, sometimes misused term. And, although corona has been a workhorse, the mainstay of surface treating for the past forty years, technologies ... plasma and others ... are here and on the horizon. As the materials being treated become more complex, as the material thickness decreases and the processing speeds increase, controlled atmospheres, specialty dialectrics and other such improvements in equipment design must follow.