Patent Application
20070235427
Certain terminology is used in this specification and appended claims. In order to provide a clear and consistent understanding of the specification and appended claims, including the scope to be given such terms, the following definitions are provided:
About Atmospheric Pressure. An embodiment of the invention involves the generation of an ionizing gas plasma. While gas plasmas can be produced under various levels of vacuum, the invention uses a plasma generated at essentially atmospheric pressure. While no conditions of vacuum or above-atmospheric pressure are deliberately produced by carrying out the method of the invention, the characteristics of the gas flow may create a deviation from atmospheric pressure. For example, when using a method of the invention to treat the inside of a cylindrical object, the gas flowing into the cylinder may result in a higher pressure within the cylinder than outside the cylinder. The term also means that atmospheric gases (i.e., air) are present when generating the ionizing gas plasma. Vacuum plasma systems, on the other hand, use vacuum pumps and vacuum chambers to remove nearly all atmospheric gases prior to generating an ionizing gas plasma.
Break-Out. An embodiment of the invention involves surfaces in sliding contact with one another. When the surfaces are in contact but at rest, a force must be applied to one of the surfaces to initiate movement. This applied force must be increased until the frictional forces opposing movement are overcome. The point at which the applied force just surpasses the frictional force and movement is initiated is known as break-out.
Chatter. Repetitive stick-slip movement associated with the movement of surfaces in contact with one another is known as chatter. When a lubricant is present between the surfaces, chatter can occur when the lubricant is squeezed out from between the surfaces, resulting in an increase in the coefficient of friction. A larger force must then be applied to the surfaces in order to initiate movement, which can cause a sudden, exaggerated movement. Chatter occurs when this cycle is repetitive.
Coefficient of Friction. The coefficient of friction relates to the amount of force necessary to initiate movement between two surfaces in contact with one another, or to maintain this sliding movement once initiated. Numerically, the term is defined as the ratio of the resistive force of friction divided by the normal or perpendicular force pushing the objects together.
Electron Beam Radiation. Electron beam radiation is a form of ionizing radiation produced by first generating electrons by means of an electron gun assembly, accelerating the electrons, and focusing the electrons into a beam. The beam may be either pulsed or continuous.
Friction. Friction is a resistive force that prevents two objects from sliding freely against each other.
Gamma Radiation. Gamma radiation is a type of electromagnetic waveform, often emitted at the same time the unstable nucleus of certain atoms emits either an alpha or beta particle when the nucleus decays. Gamma radiation, being an electromagnetic waveform, is similar to visible light and x-rays but of a higher energy level which allows it to penetrate deep into materials.
Gas Plasma. When sufficient energy is imparted to a gas, electrons can be stripped from the atoms of the gas, creating ions. Plasma contains free-moving electrons and ions, as well as a spectrum of electrons and photons.
Ionizing. Ionizing means that enough energy is present to break chemical bonds.
Parking. Syringes used in medical applications are often pre-filled prior to use and then stored. The amount of time between filling the syringe and discharging the syringe is known as parking time. In general, parking increases the break-out force.
Stick-Slip. The difference between static and kinetic coefficients of friction is known as stick-slip. In systems where a lubricant is present, high mating forces can squeeze the lubricant out from between the surfaces in contact with one another. An increased force is then required to initiate sliding movement of the surfaces. This movement may occur suddenly, caused by the surfaces coming into contact with a lubricant-rich area. If the lubricant is again forced out from between the surfaces, they can begin to bind. The sliding motion can stop until the force is increased enough to once again initiate movement. This alternating sticking and slipping is called stick-slip.
Stiction. The overall phenomenon of stick-slip is known as stiction.
Referring in detail to the drawings, wherein like numerals represent like elements in multiple drawings, in
The opening 9 in the outer electrode 3 may generally conform to the shape of the workpiece 2. The opening 9 may be sized slightly larger than the workpiece 2 to facilitate insertion and removal of the workpiece 2. The workpiece 2 has an inner diameter, and the inner electrode 4 has an outer diameter that is smaller than the inner diameter of the workpiece 2, thereby creating an annular space between the inner electrode 4 and the inner surface of the workpiece 2. This space is known as the plasma discharge zone (
Removeably attached to the bottom of the outer electrode 3 is a gas distribution manifold 6 with gas inlet fitting 10. The gas distribution manifold 6 serves to introduce a gas (or mixture of gases) in which the ionizing gas plasma will be generated into the workpiece 2 so that the gas flows in the space between the inner electrode 4 and the inner surface of the workpiece 2. In an embodiment having multiple openings 9 in the outer electrode 3, each inner electrode 4 may be electrically connected to the other inner electrodes 4, as shown by the connecting wire 8. Also shown in
To illustrate the impracticality of vacuum plasma systems (as opposed to plasma systems that operate at about atmospheric pressure) for production operations, a brief discussion of the vacuum plasma device and process is provided along with a comparison to atmospheric pressure plasma systems. The vacuum plasma process is conducted under conditions of extreme vacuum (typically less than 50 torr and in some instances less than 1 torr, compared to standard atmospheric pressure of 760 torr) in order to evacuate as much of the atmospheric gases from the vacuum chamber as possible. In the vacuum plasma process, the presence of atmospheric gases interferes with generating the ionizing gas plasma. Atmospheric pressure plasma systems are not significantly affected by the presence of atmospheric gases along with the gas in which the plasma is generated. The vacuum plasma process requires a chamber capable of withstanding the forces of extreme vacuum and having the ability to be sealed adequately to avoid leaking while under vacuum.
Atmospheric pressure plasma systems perform at atmospheric pressure, so no vacuum chamber is necessary. Sealing against leaks is no concern for atmospheric pressure plasma systems because the presence of atmospheric gases is not significant to the process, allowing the apparatus 1 to be of a relatively simple design. In order to remove the atmospheric gases from the vacuum chamber, a vacuum pump is required. The vacuum pump adds considerable cost and complexity to the apparatus. No vacuum pump is required for atmospheric pressure plasma systems. The vacuum plasma process must be a batch process because of the need to evacuate atmospheric gases from the vacuum chamber and create vacuum conditions. In contrast, atmospheric pressure plasma systems can be readily adapted to a continuous production line, resulting in a considerable improvement over a vacuum plasma system.
The gas in which the ionizing gas plasma is generated may be a noble gas including, for example, helium, neon, xenon, argon, and krypton. Alternatively, the gas may be an oxidative gas including, for example, air, oxygen, carbon dioxide, carbon monoxide, and water vapor. In yet another alternative, the gas may be a non-oxidative gas including, for example, nitrogen and hydrogen. Mixtures of any of these gases may also be used, and atmospheric gases may be also be present.
In one embodiment, the power supply 13 may be a radio frequency power supply. In another embodiment, the power supply 13 may be ionizing radiation. The ionizing radiation source can be gamma radiation or electron-beam radiation. Typically, commercial gamma irradiation processing systems use cobalt-60 as the gamma radiation source, although cesium-137 or other gamma radiation source may also be used. Commercial electron-beam radiation systems generate electrons from an electricity source using an electron gun assembly, accelerate the electrons, then focus the electrons into a beam. This beam of electrons is then directed at the material to be treated. The surface may be exposed to an ionizing radiation dosage ranging from about 0.1 megarad to about 15 megarads.
The workpiece 2 may be made of any dielectric material. Typically, the dielectric material is a plastic, a polymer, a ceramic, or glass. The workpiece 2 may also be made of a metal with any of these dielectric materials encapsulating the electrodes.
One embodiment is a method to treat the surface of a workpiece 2, or to treat a coating on the surface of a workpiece 2. According to one embodiment, a workpiece 2 is placed in an opening 9 present in an outer electrode 3. The opening 9 may be generally the same shape as the workpiece 2 and also serves as a holder for the workpiece 2. An inner electrode 4 may then be inserted at least partially within the workpiece 2. The inner electrode 4 is smaller in diameter than the inner diameter of the workpiece 2, creating a space between the inner electrode 4 and the inner surface of the workpiece 2. This space is the plasma discharge zone. The spacing between the inner electrode 4 and the inner surface of the workpiece 2 may range from about 1/64 inch to about 6 inches. A gas is then introduced into the plasma discharge zone, and the pressure within the plasma discharge zone is maintained at about atmospheric pressure. A power supply 13 connected between the inner electrode 4 and outer electrode 3 energizes the gas, producing an ionized gas plasma. The ionizing gas plasma is produced for a predetermined period of time which may range from about 0.001 second to about 5 minutes. In another embodiment, the predetermined period of time may range from about 0.01 second to about 1 minute. When a coating is present on a surface of the workpiece 2, the method may initiate a chemical reaction between the chemical species present in the coating. The lubricity of the surface of the workpiece 2 may be greater after treatment by the method than before treatment. In another embodiment, the method may be used to treat a surface of an uncoated workpiece 2.
The embodiments described above may be useful for treating a coating applied to the surface of a workpiece. An example coating is described in U.S. patent Ser. No. 10/791,542 filed on Mar. 2, 2004, which is herein incorporated by reference in its entirety. The coating, after being treated using the apparatus 1, shows improved fixation on an inner surface of the workpiece. That is, the coating has less of a tendency to be dislodged when another surface is in sliding frictional contact with the coated surface of the workpiece. Additionally, the lubricity of the coated surface of the workpiece is improved after being treated with the present invention.
It is understood that the embodiments described herein are intended to serve as illustrative examples of certain embodiments of the apparatus and methods. Other arrangements, variations, and modifications of the described embodiments may be made by those skilled in the art. No unnecessary limitations are to be understood from this disclosure, and any such arrangements, variations, and modifications may be made without departing from the spirit of the invention and scope of the appended claims. Stated ranges include the end points of the range and all intermediate points within the end points.
The present application claims the benefit of Provisional Application No. 60/788,933 filed Apr. 4, 2006, entitled “Apparatus for Plasma Treating a Workpiece and Method Therefor.”
| Number | Date | Country | |
|---|---|---|---|
| 60788933 | Apr 2006 | US |
