Plasma Treatment of Polymers

Abstract

Plasma treatment of polymers encompasses a variety of plasma technologies and polymeric materials for a wide range of applications and dates back to at least the 1960s. In this article we provide a brief review of the United States patent literature on plasma surface modification technologies and a brief review of the scientific literature on investigations of the effects of plasma treatment, the nature of the plasma environment, and the mechanisms that drive the plasma–surface interaction. We then discuss low‐radio‐frequency capacitively coupled nitrogen plasmas and their characteristics, suggesting that they provide significant plasma densities and populations of reactive species for effective plasma treatments on a variety of materials, particularly when placing the sample surface in the cathode sheath region. We further discuss surface chemical characterization of treated polymers, including some results on polyesters treated in capacitively coupled nitrogen plasmas driven at 40 kHz. Finally, we connect plasma characterization with surface chemical analysis by applying a surface sites model to nitrogen uptake of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) treated in a 40 kHz nitrogen plasma. This example serves to suggest an interesting practical approach to comparisons of plasma treatments. In addition, it suggests an approach to defining the investigations required to conclusively identify the underlying treatment mechanisms.

Keywords:

• Polymer surface modification
• Plasma treatment
• Plasma processing
• Surface treatment
• Polymer surfaces
• Surface analysis
• X‐ray photoelectron spectroscopy (XPS)
• Surface sites
• Treatment kinetics
• Surface kinetics
• Metallized plastics
• Metal–polymer adhesion
• Nitrogen plasma
• Nitrogen
• Oxygen plasma
• Oxygen
• Polymer
• Polyester
• Polystyrene (PS)
• Polyethylene (PE)
• Polycarbonate (PC)
• Polyethylene naphthalate (PEN)
• Polyethylene terephthalate (PET)

Acknowledgments

The authors gratefully acknowledge Professor Alex Fridman, Dr. David Glocker, Professor David Graves, Professor Herbert Sawin, and Dr. Kurt Sieber for many valuable discussions.

Notes

^aIn general, the term “corona discharge treatment” is actually a dielectric barrier discharge treatment, as the electrode and sample configuration include a dielectric material placed between two electrodes having an applied time varying high voltage. For web treatments, the treatment electrode or the grounded roller is covered with an insulating material, or the material being treated is insulating and completely covers the ground electrodes in the system. The discharge produced in such a system is also called a “silent discharge.” A discussion of this kind of discharge, its other uses, and helpful references can be found in Ref.[34]

^bWork at the Eastman Kodak Company on nitrogen plasma treated poly(ethylene-2, 6-naphthalate) has shown that rolls treated, wound in vacuum, and stored in roll format in room air maintain their wetting characteristics for several months. Some observations on small hand rolls of treated material showed little if any loss of wettability after as much as a year of ageing in room air.