Dielectric plasma chamber apparatus and method with exterior electrodes

Abstract

A dielectric barrier discharge plasma generator includes a dielectric chamber. The chamber contains or incorporates a solid surface that is to be treated with non-thermal plasma. The dielectric chamber can be substantially sealed and confine an atmosphere therein. An atmosphere control system is provided for controlling the atmosphere within the chamber. At least one or two electrodes are located outside of the dielectric chamber. When actuated by an appropriate source of plasma generating electrical power the electrodes cause the generation of a solid surface modifying non-thermal plasma in a plasma zone within the dielectric chamber. A transport system is provided for moving the electrode and the dielectric chamber relative to one another. A plasma zone is confined within the dielectric chamber adjacent to the electrodes, and remains substantially stationary relative to the electrodes. The dielectric chamber carries the solid surface through the plasma zone. The solid surface remains substantially stationary relative to the dielectric chamber.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates in general to methods and devices for applying a non-thermal plasma treatment to objects to change the object's surface characteristics, and, more particularly, embodiments of the present invention relate to treating solid surfaces in a substantially sealed dielectric barrier discharge plasma chamber system with exterior electrodes.[0003]2. Description of the Prior Art[0004]The use of non-thermal plasma to modify the surface properties of many solids for many different purposes is well known. Thermal plasma generators typically operate at temperatures where most metals melt or vaporize, so they are unsuitable for use with organic polymers, and the like. Non-thermal plasma treatment of the surfaces of objects changes the electrical charge, physical and / or chemical properties of the surface. Such properties include, for example, surface tension, biocompatibility, functionality, and the like. See, for...

AI Technical Summary

Benefits of technology

[0019]The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available non-thermal plasma generator systems and methods. The present invention effectively resolves at least the problems and shortcomings identified herein. In particular, embodiments of the present invention provide a dielectric barrier discharge plasma generator for the treatment of solid surfaces wherein at least a plasma generating electrode is positioned outside of and separately moveably from a substantially sealed dielectric chamber. The walls of the chamber comprise dielectric material to provide a dielectric barrier positioned between the electrodes and the workpiece. A workpiece is placed or occurs within the dielectric chamber. In various embodiments, the dielectric chamber and the workpiece may be one and the same, or the workpiece may be fully or partially enclosed within the dielectric chamber. A plurality of separate dielectric chambers may be provided. A gap is provided within the dielectric chamber in which non-thermal plasma may form. An atmosphere control system is provided to control the atmosphere within the chamber. A transport system is provided for moving the electrodes and the dielectric chamber relative to one another. Plasma generating electrical power is supplied to the electrode(s). When the breakdown voltage is achieved in the plasma zone, non-thermal plasma forms. The non-thermal plasma stays in a plasma zone between the electrodes during this relative movement. The solid surfaces that are treated with non-thermal plasma are moved with the dielectric chamber. Solid surfaces include those that are not fluid. Fluids assume the shape of the container that confines them. Solids are capable of sustaining their own shape. Solids include gels and sols that are capable of sustaining their shapes without support. Solid surfaces are not limited to surfaces of any particular texture. Woven materials and mats (particularly filters) have solid surfaces, as do particulate and granular materials. Many smooth surfaces are solid, as are many permeable and impermeable surfaces. The system is particularly adapted to continuous operations, which permits automation of the process, and the use of non-thermal plasma treatment in the mass production of plasma treated solid surfaces, which results in substantial economies of operation. Production rates go up by several orders of magnitude when operations are improved from batch to continuous.

[0024]The use of an elongated workpiece permits long lengths to be treated very quickly. Lengths with aspect ratios (length to internal diameter) of greater than 100 to 1 may be quickly and conveniently treated with plasma. Lengths of longer workpieces may be selectively treated. For example, if a 100 foot length of treated tubing is desired, and a 1,000 foot long reel of the tubing is available, the entire reel can be quickly evacuated to a pressure of from approximately 1 to 100 Torr, and only the first 100 foot length is treated. Millimeter sized tubing may be easily treated. Relatively flexible tubes may be treated, because the pressure is not reduced to a level where the tube collapses. Pressures in the millitorr range would collapse many of the tubes that are particularly benefited by this plasma treatment.

[0036]Making the electrodes separable from the dielectric chambers permits the use of multiple dielectric chambers with one set of electrodes. It also substantially reduces the costs of producing both the chambers and the electrodes. Particularly for purposes of mass production, a large number of interchangeable dielectric chambers can be loaded with workpieces. The atmospheres within each chamber can be adjusted to desired values of pressure and composition before the chamber is mated to a set of electrodes. The pre-prepared dielectric chambers may be placed one by one in plasma treatment association with the electrodes. Conveying such chambers past one or more sets of electrodes at a continuous rate or in a regular stop and go motion permits the automation of the operation for purposes of mass production.

[0037]In those embodiments where separate individual chambers are individually loaded with workpieces, the dielectric chambers may be advantageously shaped to accommodate the specific workpieces, and as much as 80 to 90 percent of the volume inside of a particular dielectric chamber is occupied by the workpiece. Such a void volume of 10 to 20 percent reduces, for example, the load on the vacuum pump and cycle times, and minimizes the consumption of reagents, if any are employed. The generally separate external electrodes may also be shaped to accommodate the specific chamber-workpiece assemblies. The dielectric chamber walls and the electrodes may be shaped to provide approximately a constant gap between the surface of the workpiece and the electrode. The use of external separate electrodes allows the electrodes to be manufactured inexpensively, as needed, to accommodate different shaped chamber-workpiece assemblies. Cooling may be provided for the electrodes where they are subjected to continuous use. Typically, cooling fluid (liquid or gas) is used to cool the electrodes.

Problems solved by technology

Thermal plasma generators typically operate at temperatures where most metals melt or vaporize, so they are unsuitable for use with organic polymers, and the like.

At high power settings, the surface of the workpiece may be etched or damaged.

Such systems are expensive to make.

Operating expenses are high because of the pumps, the maintenance, and the long cycle times, which tend to be in the order of several minutes.

Such systems are typically too expensive to build to fit one particular part.

A particular workpiece may not fit well in the chamber, so it does not receive a uniform surface treatment, or it may leave a lot of empty space in the chamber.

This empty space must be evacuated at considerable operating expense.

It is very hard to maintain a stable glow discharge between the electrodes in air, because of significant plasma instabilities.

It is practically impossible to form a uniform plasma in air at atmospheric pressure for gaps of more than approximately 5 cm.

Vacuum chambers with electrodes within the chamber in dielectric barrier discharge systems are well known, but they are expensive to buy and operate, because they typically must operate in the millitorr pressure range and at high voltages.

Also, the construction of in-chamber electrode systems is expensive.

The chambers with internal electrodes are generally too expensive to custom build to fit a single part, so they are made big enough to accommodate a variety of different parts or a plurality of parts of the same configuration.

They require expensive two stage pumps to bring the pressure down into the millitorr range.

Images