Patent Application
20090045168
Not applicable.
The invention generally relates to systems for charging, and thereby altering certain characteristics of, the surfaces of articles, for example wettability, or the ability of the surface to take on liquids, such as inks, dyes and adhesives that may be applied to the articles for marking or other purposes. In particular, the invention relates to treater stations providing improved surface treatment of elongated articles, such as wires, cables and the like.
It is common for articles to have printing, coating or bonding directly on the surfaces of the articles to serve any number of purposes, including for example, decoration and textual or graphical indicia of a characteristic of the article or its use. For example, it is common for wire and cable to have its outer sheath flagged, coated or printed with striping to indicate wire gauge or intended polarity.
The dielectric material, such as fluoropolymers, polyalkylenes, and the like, used for wire and cable insulation or sheathing typically provides low surface energy, chemically inert surfaces. Furthermore, the extrusion processes in which the insulation or sheathing is formed onto the wire or cable can create localized variations in surface roughness, porosity and crystallinity caused by factors such as variations in baking temperatures, line speed and humidity. Consequently, the surfaces of these articles often have roughness, porosity, and wettability characteristics that are often unsuitable for printing, coating and bonding applications.
The properties of these surfaces can be improved, for example to better apply adhesives and inks, by treating the surface of the material to raise its surface tension. Surface tension can be raised using any of a number of known techniques including IR, UV, x-ray and gamma ray irradiation, electron and ion beam bombardment, ozone exposure and flame, chemical, corona and plasma treatments.
Corona treaters have been used for many years, however, plasma treaters are widely recognized as providing a more uniform and controllable surface treatment than corona treaters. In plasma treaters, the treatment zone is infused with an inert gas that is partially ionized by the energized electrodes. Early plasma treaters required that the pressure of the ionized gas was reduced well below atmospheric pressure. This required expensive and cumbersome vacuum chambers and pumps to maintain the low pressure at the treatment zone. However, more recently treaters forming plasma at atmospheric pressure have been developed, see U.S. Pat. No. 5,456,972. In this process, often termed “glow discharge plasma” treatment, the plasma would form at atmospheric pressure provided an inert gas, typically helium, was used, a dielectric was applied between the electrodes and the operating frequency and voltage of power source was properly selected. The operating frequencies ranged up to as much as 100 kHz, however it was typically operated at much less so as not to avoid the ambient air from being too readily ionized by the high frequency electric field, and thus forming corona treatment rather than the more effective plasma treatment.
Furthermore, these techniques are often used to effect surface treatment in large scale operations as part of an assembly or other process line. The material is ordinarily fed through a treatment zone in which the surface energy of one surface of the material is raised.
Many chemical, corona and plasma treater stations exist for treating the surfaces of papers, laminates and other thin web stock in which the material is supported in the treatment zone by a roller typically serving as a ground electrode. An active electrode is located on the opposite side of the material from the roller to produce an electric field through which the web passes.
However, treater stations of this type are not typically suitable for articles that have a greater three-dimensional profile, such as wire and cables, because the increased spacing between the electrodes required to accommodate the thickness of such articles can diminish or destroy the formation of the corona or plasma, for example, and thus the effectiveness of the treatment.
As a result, such articles have been conventionally treated with systems having discrete discharge heads or cylindrical electrodes. In the former case, one or more discharge heads are arranged to direct a beam or other spray of ionized particles at a discrete location of the wire or cable. In the latter case, the wire or cable is threaded into cylindrical electrode and passed through a curtain of ionized particles. Because the wires and cables are elongated articles which are often treated in long lengths, the use of discrete discharge heads can be disadvantages because of the narrow beams can readily burn or damage the surface or create inconsistencies in treatment should the line speed be varied. The use of cylindrical electrodes requires the articles to be threaded through the treater, thus complicating integration with other components of the line.
The present invention provides a treater system that addresses the above-mentioned concerns and facilitates the surface treatment of three-dimensional objects, particularly elongated articles such as wires, cables and the like.
Specifically, in one aspect the invention provides a surface treater system for treating the surface of an elongated article. The treater has a guide for supporting the elongated article along a treatment axis. First and second elongated electrodes, each extending primarily essentially parallel to the treatment axis, are spaced apart to define an elongated treatment zone extending along the treatment axis between the electrodes. An elongated nozzle extends primarily essentially parallel to the treatment axis proximate the first and second electrodes for introducing a working media into the treatment zone and dispersing it along the treatment axis. A power supply operatively connected to the first and second electrodes ionizes the working media in the treatment zone along the treatment axis and thereby increases the tension at the surface of the elongated article.
Another aspect of the invention provides a plasma treater for treating an elongated article. The treater has a cabinet creating a treatment chamber open at opposite ends of the cabinet. A guide is mounted at each open end of the cabinet for guiding the elongated article and establishing a treatment axis therebetween passing through the treatment chamber along which the elongated article is disposed. An electrode assembly is mounted within the treatment chamber. The electrode assembly has an active electrode coupled to high voltage and a ground electrode coupled to ground, each disposed essentially parallel to the treatment axis. The electrodes are spaced apart to define a treatment zone along the treatment axis between the electrodes. An elongated gas nozzle, which extends essentially parallel to the treatment axis adjacent to the active and ground electrodes, is coupled to a gas line for introducing a gas into the treatment zone and dispersing it along the treatment axis. Energization of the power supply causes the gas to ionize and form plasma in the treatment zone along the treatment axis.
Yet another aspect of the present invention provides a process for charging the surface of elongated articles. The process includes supporting an elongated article along a treatment axis so that it extends primarily in the direction of extension of the treatment axis. An electrode assembly is provided which has at least a first electrode coupled to high voltage and a second electrode coupled to ground. The electrode assembly is disposed so that the first and second electrodes extend primarily essentially parallel to the treatment axis and are spaced apart to define an elongated treatment zone along the treatment axis. A working media is provided within the treatment zone, and upon energizing the electrode assembly, the working media within the treatment zone is ionized along the treatment axis, which thereby increasing the surface tension of the elongated article. The elongated article can be supported on movable guides and conveying along the treatment axis through the treatment zone.
The advantages of the invention will be apparent from the detailed description and drawings. What follows are one or more preferred embodiments of the present invention. To assess the full scope of the invention, the claims should be looked to as no one embodiment is intended to fully set forth the scope of the invention.
Referring now to the drawings, in particular
More specifically now, the cabinet 12 defines a work space for treating the elongated articles that is accessible through an opening 22 extending along the front and sides of the cabinet 12, as shown in
The exact configuration and electrode count of the electrode assembly 12 can be varied, provided that two different components constitute the positive (or charged) electrode and the ground electrode, or that the electrodes are appropriately phase-shifted so as to effect discharge between them. In some cases in which the article to be treated has a suitable conductive element, that conductive element by constitute an electrode, in particular the ground electrode. However, in typical applications, there will be at least one dedicated active (or positive) electrode and at least one dedicated ground (or negative) electrode. The quantity of electrodes can be selected based on the application, considering factors such as cost, level of refinement needed, size of the articles and line feed rate. Moreover, the placement of the electrodes with respect to the treatment axis 30 can also be varied. For example, with the proper selection and wiring of the electrodes, two or more electrodes could be placed to one side of the treatment axis 30, with none or one or more electrodes opposite polarity on the opposite side of the treatment axis 30. More specifically, successive alternating polarity electrodes could be provided on each side of the treatment axis 30. Or, one or more pairs of opposed polarity electrodes could be positioned on the same side of the treatment axis 30 such that the plasma formed therebetween would interact with the article form one side of the treatment axis 30. Similar polarity electrodes could also be situated on the same side of the treatment axis 30 provided the article itself or a separate electrode at the other side of the treatment axis 30 provided the ground. Or one or more pairs of opposed polarity electrodes could be situated on opposite sides of the treatment axis 30. For example, in the treater 10 shown in the figures, the electrode assembly 16 includes one active electrode 32 and one ground electrode 34 that are spaced apart on opposite sides of, and parallel to, the treatment axis 30 to define a treatment zone 36 therebetween.
As mentioned above, it is possible for two or more electrodes to be charged, that is connected to high voltage, without one or more corresponding ground electrodes, provided the electrodes are phase-shifted. For example, one electrode could be coupled the high voltage transformer at 0 degrees and another at 180 degrees so that the two are 180 degrees out of phase. The two electrodes will have opposite polarity and will effect discharge between them, as would an active and ground electrode pair. Using active (charged) electrodes without corresponding ground electrode(s) is beneficial when treating articles having a grounded conductor. This is because the potential of both (or all) of the electrodes varies from the potential of the treated article, which is at ground potential, and thereby better facilitates discharge between each electrode and the treated article compared to when using ground electrodes that are at the same potential as the treated article. This results in better treatment from each side of the treatment axis having an electrode, and thus can more readily treat the fully periphery of the article.
As shown in
The electrodes 32 and 34 a primary dimension of extension that is parallel to the treatment axis 30, and thus, the treatment zone 36 is lengthy and able to treat a sizable length of the articles at once. This speeds the treatment process and also improves the consistency and homogeneity of the treatment since less variations in operational parameters, such as feed rate, charge dispersion, charge intensity, will occur per unit length of the treated article. For this reason, the treatment provided by the present invention is an improvement over that provided by the shorter cylindrical electron treaters and the discrete discharge head treaters. In the treater 10 described herein, each of the electrodes 32 and 34, and thus the treatment zone 36, is 250 mm in length. However, it is contemplated that the electrodes 32 and 34 could range between about 25 and 2,500 mm depending on the application.
The electrodes 32 and 34 are mounted within the working space of the treater 10 by an electrode mount 40. The electrode mount 40 has a large bracket or plate 42 to which bolt adjustable mounting clamps 44, four in all for the treater 10 described herein. Specifically, each of the clamps 44 has a base 46 that bolts onto the bracket 42 via a bolt 48. Adjustment of the bolt 48 and a locking collar 50 allows for adjustment of the vertical position of the clamp 44. The base 46 has a notch 52 at one end where a clamp piece 54 is bolted to the base 46. The notch 42 receives an end of an electrode mount 56, which is in turn mounted to one of the electrodes 32 and 34. In this way, the electrodes 32 and 34 can be held in a fixed position relative to the treatment axis 30, and also may be readily mounted and dismounted by adjusting the bolts holds the clamp pieces 54 as well as adjusted vertically (as noted by the arrows in
The principles of the present invention can be used to provide corona, chemical corona and/or plasma discharge treatment, using a single gas or a mixture of gases, including air, one or more inert gases (such as nitrogen and helium), or other suitable gas chemistry mixtures, including mixtures of inert and reactive gases (such as oxygen, hydrogen, acetylene, etc.) as the working media. Further, with the present invention the treatment can be achieved at atmospheric pressure, thereby avoiding the need to pressurize or evacuate the treatment zone 36.
The treater 10 described herein effects plasma treatment by ionization of the appropriate working media injected into the treatment zone 36 from the working media system 18. Plasma treatment provides high surface energies at the surface being treated, thus raising its mean surface energy and effecting a more homogeneous surface finish as compared to corona treatment. Moreover, a high frequency power supply, such as a high voltage AC power supply operable up to 300 kHz, may be used to effect an even more homogenous surface than lower frequency plasma treatment. The treater 10 can be operated at lower frequencies as well and will provide at least corona level treatment with the enhanced uniformity of plasma treatment.
Helium has been determined to be a suitable gas for effect plasma discharge, and a helium content as low as 80 percent helium can be sufficient for plasma to form. However, the specific gas or gas mixture used as the working media can be selected by on the application, such as the material composition of the article being treated. U.S. Pat. No. 6,429,595, at col. 5, line 13 to col. 6, line 23, the disclosure of which is hereby incorporated by reference, provides a discussion of suitable gas chemistry and operational parameters of the type suitable for use with the present invention.
The working media system 18 includes one or more supply tanks (not shown), for example each containing an inert or reactive gas, and one or more supply lines 60 for injecting the working media into the treatment zone 36. With reference to
To contain the working media within the treatment zone an axial barrier member 66 (see
By preventing the working media from escaping at the front side, the barrier member 66 aids in maintaining the integrity of the working media and the characteristics of the discharge. It also permits high operating frequencies to be used at atmospheric pressure without the risk of ionizing the ambient air rather than the intended working media, which could effect corona treatment, rather than the higher quality plasma treatment. Furthermore, the barrier member 66 helps ensure that the surface of the article is treated homogeneously about its entire cross-sectional periphery.
An alternative to the barrier member 66 is shown in
The electrodes 32 and 34 have a hollow interior such that the cooling system 20 can deliver air directly into the electrodes 32 and 34. This has several advantages. First, the cooling air passes by the entire surface area of the interior walls of the electrodes 32 and 34, thereby maximizing heat transfer. Moreover, the compressed air does not draw in contaminants from the work area, which could otherwise be carbonized on the electrodes 32 and 34 and cause arcing during operation. Furthermore, the cooling air does not evacuate or otherwise disrupt the working media in the treatment zone 36, which would adversely affect the quality of the treatment.
Generally, the cooling air system 20 includes a source of compressed air (not shown) and lines 68 for delivering the cooling air to the electrodes 32 and 34. The cooling air lines 68 can be any suitable solid or flexible conduit for carrying air, such as polyethylene tubing. Referring to
Although not shown, the interior of the electrodes 32 and 34 could be partitioned to define two or more air flow passages, in which case the cooling air system 20 could be configured to flow cooling air in opposite directions through the electrodes 32 and 34. This can serve to provide more uniform cooling along the length of the electrodes 32 and 24 by introduced cooling air from opposite ends. Moreover, various flow path configurations through the electrodes 32 and 34 could be provided.
Moreover, as a further alternative construction of the treater 10, one or both of the electrodes 32 and 34 could be porous, such as a porous metal, having porosity similar to the diffuser nozzle(s) mentioned above. In this case, the working media could be directed from the working media system 18 directing into and through the porous electrode(s) without the need for a separate nozzle and diffuser.
It can be appreciated that many variations are possible from the preferred embodiment described above without departing from the spirit of the invention. Reference should therefore be made to the claims for interpreting the entire scope of the invention.
This application claims benefit to U.S. provisional application Ser. No. 60/956,606, filed Aug. 17, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60956606 | Aug 2007 | US |
