CORONA DISCHARGE TREATMENT APPARATUS

Abstract: A corona discharge treatment apparatus comprises a base electrode 1 and a discharge electrode 2. One of the electrodes 2 is connected to a high frequency and high voltage source, and the other electrode 1 is earthed. The electrodes connected to the source are immovable, while the other electrode 1 is earthed and is allowed to make the movement for presenting the surface to be treated of the object and the discharge electrode to each other. Thus with the corona discharge treatment apparatus of this invention, accidents such as an electric shock or a short-circuit, are less likely, and troubles are reduced.

Description: This invention relates to a corona discharge treatment apparatus used for activating a surface of an object to be treated to improve its surface property. For example, automobile bumpers made of polyolefine material, or the like, may be subjected to corona discharge treatment for improving their surface properties. An apparatus for performing this corona discharge treatment has been developed that is equipped with a base electrode for making contact with an object and a discharge electrode which is adapted to activate a surface to be treated of the object by the corona discharge phenomenon that occurs when a high voltage is applied between the base and discharge electrodes, with the surface to be treated of the object and the aforementioned discharge electrode presented to each other. To perform such a corona discharge treatment, a high voltage needs to be applied between the base electrode and the discharge electrode. In order to achieve this, one of the electrodes must be connected to a high frequency and high voltage source, and the other electrode must be earthed. If the object has many surfaces to be treated, it is necessary, at the treatment stage for each surface to be treated, to vary a direction or orientation of the object or the electrode to be connected to the high frequency and high voltage source, thereby presenting the surface to be treated of the object and the electrode to be connected to the high frequency and high voltage source to each other. In the aforementioned corona discharge treatment apparatus, this movement for presentation has been provided by moving the electrode to be connected to the high frequency and high voltage source. An example of such a corona discharge treatment apparatus appears in Japanese Pantent Publication (examined) No. 60-46133. In the corona discharge treatment apparatus shown in the Patent Publication No. 60-46133, a base electrode is installed on a support and on this base electrode, an object is mounted. Above the object, there is arranged an opposite electrode (discharge electrode) which has a flexible discharge device and is connected to the high frequency and high voltage source. A surface to be treated of the object and the discharge device are presented to each other by moving on a straight line or rotating the support together with the base electrode, or by moving up - down, swiveling or rotating the opposite electrode together with the discharge device, so that each surface to be treated of the object having many faces may be collectively and concentrically subjected to the discharge treatment. Further, in another corona discharge treatment apparatus which was developed separately from the corona discharge treatment apparatus shown in the Patent Publication No. 60-46133, an electrode to be connected to the high frequency and high voltage source is also designed to be vibrated for enhancing the effect of the corona discharge treatment. However, since such conventional corona discharge treatment apparatuses are designed to allow the electrode that is connected to the high frequency and high voltage source to be moved, accidents such as an electric shock or a short-circuit often result from an unexpected contact of the electrode with an operator or installation, or troubles often result from spark or coming-apart of contacts. EP-A-0055686 describes a corona discharge treatment apparatus comprising a base electrode for making contact with an object to be treated and a discharge electrode for applying a high voltage between it and the base electrode. The apparatus is adapted to activate a surface to be treated of the object when the base and discharge electrodes are presented to each other. The discharge electrode is connected to a high frequency and high voltage source, while the base electrode is earthed. The base and the discharge electrode are allowed to make movements for presenting the surface to be treated of the object and the discharge electrode to each other. According to the present invention there is provided a corona discharge treatment apparatus for activating a surface to be treated of the object by corona discharge, comprising a base electrode for making contact with the object to be treated and a discharge electrode, the surface to be treated of the object and the aforementioned discharge electrode being presented to each other, one of the said electrodes being connected to a high frequency and high voltage source while the other electrode is earthed, characterised in that only the earthed electrode is allowed to make the movement for presenting the surface to be treated of the object and the discharge electrode to each other, and in that the earthed electrode is designed to be moved by operating means, which are adapted to make vibrating movements. An apparatus can be constructed in accordance with the invention which is less prone to accidents such as electric shocks and less prone to trouble. By causing the earthed electrode to make vibrating movements an enhanced corona discharge treatment is effected. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which: FIG. 1a shows a front fiew of a corona discharge treatment apparatus according to this invention; FIG. 1b shows a side view of the apparatus of FIG. 1a; FIG. 2a shows a plan view of the discharge electrode 2 and a part of the electrode fitting members of the apparatus of FIG. 1; FIG. 2b shows a sectional view taken along the line X - X' of FIG. 2a; FIG. 3 is a plan view showing the electrode fitting members of the apparatus for FIG. 1; FIG. 4 is a perspective view for explanation of the movement of the operation stand 3 of the apparatus for FIG. 1; FIG. 5a shows a front view of another corona discharge apparatus in accordance with the invention; FIG. 5b shows a side view of the apparatus of FIG. 5a; and FIG. 6 is a perspective view showing in a simplified form an example in which a group of such apparatuses are arranged along a continuous line. FIGS. 1 (a) and (b) represent an embodiment of the corona discharge treatment apparatus of this invention. As shown in these Figures, this corona discharge treatment apparatus is equipped with a base electrode 1 for making contact with the object A, a discharge electrode 2 for applying a high voltage between it and this base electrode, and an operation stand (operating means) 3 for mounting the base electrode 1 and the object A. In this embodiment, the object A is an automobile bumper made of polyolefine resin material, which has a large number of surfaces to be treated which face in different directions. The base electrode 1 has a surface configuration matched to the configuration of the inside surface of the object A, to be in contact with the inside surface of the object A, and is earthed through the operation stand 3. This base electrode 1 is formed of a plastic mould and a conductive metal layer formed by applying a conductive coating on its surface that is adjacent the object. The conductive coating is applied by electroless plating in this embodiment. Other methods may be used. For example, a method based on a coating with conductive paint, vapor deposition or sticking of aluminum foil or conductive tape, may also be employed. The base electrode may alternatively be composed of a conductive moulding of, for example, aluminum material, and the like. As shown in FIGS. 2 (a) and (b), the discharge electrode 2 is composed of an electrode wire fitting member 20 and a large number of electrode wires 21 fitted thereto and hanging therefrom. The electrode wire fitting member 20 is composed of an electrode wire supporting plate 200 and an electrode wire setting plate 201. These two plates 200 and 201 hold therebetween the bent portion of the electrode wire 21 bent in U-shape. The length of the hanging part of the electrode wire 21 is, for example, 50 to 600mm. The discharge electrode 2 is mounted on an electrode mounting frame 23, as shown in FIG. 3. In this electrode mounting frame 23, a large number of windows 231 are formed. Three discharge electrodes 2 are fitted in each window 231. This fitting is done, as shown in FIGS. 2 (a) and (b), by inserting a spacer 232 made of rubber between the electrode mounting frame 23 and the electrode wire fitting member 20 and fastening the electrode mounting frame 23 and the electrode wire fitting member 20 by means of bolts 233, nuts 234 and washers 235. Since the discharge electrode 2 is mounted in this way, it is possible to provide the discharge electrode 2 at the required position and over the required area. The discharge electrode 2 is connected to the high frequency and high voltage source, not shown in these figures, so that the application of the high voltage may be done from the electrode wires 21. The electrode mounting frame 23 is hung from a supporting frame 26 held by a treatment housing 25 through insulating glass pieces 24. The discharge electrode 2 and the electrode mounting frame 23, exclusive the tip portions of the electrode wires 21, are surrounded with an acryl plate 27. As hereabove-described, the discharge electrode 2 is connected to the high frequency and high voltage source and immovably arranged at a high level. The operation stand 3 is equipped with a head part 30 on which the base electrode 1 and the object A are mounted. The head part 30 is provided with an earthing portion 301 and is designed to be rotatable through 90° around a shaft 303 by a torque actuator 302 with cushions. The speed of this rotation is set at 3 to 5 mm/sec, for example. The head part 30 is mounted on the rotor 311 of the torque actuator 310 with 3 point stop cushions, to be tiltable through 180° (90° fore and 90° aft) around the rotor 311. The tilting speed is, for example, 6 to 12 mm/sec. On the opposite side of the rotor 311 from the head part 30 a balance weight 312 is fitted to the rotor 311 in such a way as to counter-balance the head part, thereby making the tilting of the head part 30 smooth. The torque actuator 310 is mounted on an up - down vibrating stand 32. A rod of a hydraulic cylinder 331 fixed on a fore - aft movable stand 33 and a guide bar 330 are fitted on the bottom surface of the up - down vibrating stand 32. The guide bar 330 is passed through a guide cylinder 332 of the fore - aft movable stand 33, to be slidable up and down. By the operation of the hydraulic cylinder 331, this up -down vibrating stand 32 is designed to make up and down vibration, for example, with a stroke of 200mm and at a speed of 2 to 5 mm/sec. The fore - aft movable stand 33 is mounted on a right - left transfer stand 34 through a slide bearings 333 and slide rails 334 and designed to be moved fore or aft, for example, with a stroke of 200mm and at a speed of 2 to 10 mm/sec, by the working of a hydraulic cylinder 335 fixed on the right - left transfer stand 34. The right - left transfer stand 34 is mounted on a horizontal vibrating stand 35 through slide bearings 343 and slide rails 344 and is designed to move right or left, for example, with a stroke of 400mm and at a speed of 4 to 20 mm/sec, by the working of a hydraulic cylinder 355 fixed on the horizontal vibrating stand 35. The horizontal vibrating stand 35 is mounted on an up - down movable stand 36 through link balls 350. The drive of a three-phase geared motor 360 fixed on the up - down movable stand 36 is transmitted though sprockets 361 and 362, to be horizontally vibrated at a rate of 20 to 80 rpm, for example. The up - down movable stand 36 is mounted on a conveyor stand 37 through a hydraulic lifter 363, to be moved up and down, for example, with a stroke of 800mm and at a speed of 10 to 15 mm/sec, by the working of the hydraulic lifter 363. The conveyor stand 37 is mounted on a base 38 through slide bearings 370 and slide rails 371. On the base 38, a ball screw 381 is arranged in the direction along the slide rails 371. This ball screw 381 is designed to be rotated by a three-phase geared motor with a brake 382. A ball screw nut 383 is meshed to this ball screw 381. The ball screw nut 383 is fitted to the conveyor stand 37, so that as the ball screw 381 is turned normal - reverse, the conveyor stand 37 is moved fore - aft, for example, with a stroke of 2,320mm and at a speed of 13 mm/sec (180 mm/sec max.). This transfer movement is employed when the object A is conveyed into or out of the apparatus. The operation stand 2, being composed as hereabove described, is adapted to make rotational movement B, tiling movement C up -down vibrating movement D, fore - aft transfer movement E, right -left transfer movement F, horizontal vibrating movement G, up - down shifting movement H and conveying in - out movement I (see FIG. 4). The base electrode 1 and the object A installed on the operation stand 3 are moved by the operation stand 3 making these movements. In order to activate the surface to be treated of the object A, the discharge electrode 2 and the surface to be treated of the object A need to be presented to each other. The movement of the base electrode 1 effected by the rotational movement B, the tilting movement C, the fore - aft transfer movement E, the right - left transfer movement F, the up - down shifting movement H and the conveying in - out movement I, of the aforementioned movements, serves as the movement for presenting the discharge electrode 2 and the surface to be treated of the object A to each other (hereinafter referred to as "presentation movement"). That is, this corona discharge treatment apparatus presents the discharge electrode 2 and the surface to be treated of the object A to each other for whatever position and orientation of the surface to be treated, either upward or side-facing, by effecting the presentation movement of the base electrode 1, making use of the aforementioned various movements of the operation stand 3. The up - down vibrating movement D and the horizontal vibrating movement G are movements for vibrating the object A, with which to enhance the effect of the corona discharge treatment. As hereabove described, this corona discharge treatment apparatus is of a design such that the discharge electgrode 2 is connected to the high frequency and high voltage source and immovably arranged, while its base electrode 1 is earthed and only this base electrode 1 is allowed to make the movement for accommodating the surface to be treated of the object A and the discharge electrode 2 to each other. Since, as above-described, the electrode to be connected to the high frequency and high voltage source is immovably installed and only the electrode to be earthed is moved, the possibility of the electrode connected to the high frequency and high voltage source touching an operator or installation is almost eliminated, affording freedom from electric shock or short-circuiting. Moreover, the possibility of spark or coming-apart of contacts is avoided. Further, if the electrode to be connected to the high frequency and high voltage source is placed at a high level as in this embodiment, the possibility of its touching the operator, etc., will be further reduced, thus improving safety. In order to keep the discharge electrode 2 immovable, it is of course preferable to have the operation stand 3 make the vibrating movements for enhancing the effect of the corona discharge treatment as in this embodiment. FIGS. 5 (a) and (b) shown another embodiment. As shown in these Figures, the mechanism for executing the conveying in - out movement I also serves as the mechanism for executing the force - aft transfer movement E in this embodiment. That is, moving the object A fore - aft for accommodating the surface to be treated of the object A and the discharge electrode 2 to each other is done by making use of the conveying in - out movement I. In this embodiment, an up - down shifting movement mechanism in the form of a hydraulic lifter 363 is provided between the up - down vibrating movement mechanism and the horizontal vibrating movement mechanism. A right - left transfer movement mechanism is installed between the conveying in - out movement mechanism and the horizontal vibrating movement mechanism. Other arrangements are similar to those of the aforementioned embodiment, although the configurations are somewhat different. In the figures, 33' denotes a supporting stand for up -down vibration. In this embodiment, for example, respective movements are conducted as follows. The rotational movement is made with the rotational angle 90° and the rotational speed 3 to 5 mm/sec. The tilting movement is performed with the tilting angle 180° and the tilting speed 6 to 12 mm/sec. The up - down vibrating movement is conducted with the stroke 220 mm and the speed of vibration 2 to 5 mm/sec. The up - down shifting movement is made with the stroke 800 mm and the shifting speed 12 to 20 mm/sec. The right - left transfer movement is performed with the stroke 400 mm and the transfer speed 2 to 5 mm/sec. The horizontal vibrating movement is made with the eccentricity width 10 to 15 mm and the speed of vibration 20 to 80 rpm. The conveying in - out movement is executed with stroke 2,000 mm and the transfer speed 10 to 20 mm/sec. The apparatuses of the aforementioned two embodiments are designed to carry out the treatment of all surfaces to be treated of the object A on the operation stand 3 of a single unit. But, as shown in FIG. 6, the treatment may be carried out continuously on a plurality of operation stands 3. In this embodiment, as shown in FIG. 6, a plurality of the discharge electrode 2 are arranged along the transfer directions of the transfer means (a conveyor) 5. Each of these discharge electrodes 2 is connected to the high frequency and high voltage source and immovably arranged at a high level, to activate only a part of the surface to be treated of the object A. That is, the discharge electrodes arranged along the transfer direction are intended to take on activation of, successively, a first side face a, an upper face b, a second side face c, a first rising face d and a second rising face e of the object A. The stations at which these discharge electrodes 2 are arranged are called, sequentially in the transfer direction S, a first side face treating zone, an upper face treating zone, a second face treating zone, a first rising face treating zone and a second rising face treating zone. A plurality of the operation stands 3 are carried on a conveyor type transfer means 5. These operation stands 3 are cyclically transferred around a circuit composed, as indicated by the arrow mark R, of two load conveyors 6 and 7 so installed as to be coupled to the terminal and starting parts of the transfer means 5 and another conveyor 8 which joints these conveyors 6 and 7. These transfer means 5, discharge electrodes 2, etc., are put in a housing (not shown in this figure). The base electrode 1 is fixed integrally with the object A and earthed through the operation stand 3. The object A, as shown in FIG. 6, is introduced from the direction of the arrow mark P to the aforementioned transfer means 5, then, successively carried in the direction of the arrow mark S, during which time period, the object A is tilted to have its first side face a turned upward in the first side face treating zone, the upper face b in the upper face treating zone, the second side face c in the second side face treating zone, the first outer side face d in the first rising face treating zone, and the second outer side face e in the second rising face treating zone, respectively. In each treating zone, the base electrode 1 is caused to make the presentation movement by the desired movement of the operation stand 3, thereby presenting the discharge electrode 2 and the surface to be treated of the object A to each other. When a high voltage is applied between the two electrodes 1 and 2, the surface of the object A in contact with the electrode wires 21 of the discharge electrode 2 is subjected to the discharge treatment. The object A which has been subjected to surface treatment in all the treating zones is taken out in the direction of the arrow mark Q as shown in FIG. 6. When the corona discharge treatment is performed along a continuous line, as shown in FIG. 6, it can be carried out efficiently on an industrial scale. For enhancing the effect of the corona discharge treatment, gas may be blown toward the surface of the object A. When the gas is blown onto the surface to be treated of the object A, the activation of the surface to be treated is promoted and the surface property is improved, this improvement being achieved with small power consumption. Particularly, when a gas such as air or oxygen is used, such gas is not necessarily blown against the surface of the object A as it is, but it may be first passed around the electrode and turned into ozone, which is then blown against the surface of the object A, for more adequately achieving the aforementioned activation. Warming the gas before blowing increases the effect of treatment, leading to shortening of treating time. The preferred temperature range is 30° to 100°C. The gas to be blown against the discharging part, may for example be nitrogen, oxygen, carbon dioxide, carbon monoxide, ammonia, oxides or nitrogen, halogenated carbons, halogenated hydrocarbons, vinyl compounds, argon or helium, air, either used singly or in combinations of two or more gases. In this invention, the movement for presenting the discharge electrode 2 and the surface to be treated of the object A to each other includes not only the movement for transferring the object A before and after its corona discharge treatment, but also the transfer movement of the discharge electrode 2 before and after the corona discharge, when the base electrode 1 and the object A are immovably arranged. And further, the above movement includes the movement of the object A along the discharge electrode 2 or the movement of the discharge electrode 2 along the object A during its corona discharge treatment, which may be required when the discharge electrode is smaller than the surface to be treated of the object A. The electrode wire 21 may for example, comprise a string into which a large number of conductive monofilaments of stainless steel are plied. An austenitic stainless steel fiber (JIS SUS 27 - 43), trade name "NASLON" manufactured by Nippon Seisen Co., Ltd., for example, is preferably used as such a monofilament. The number of filaments to be plied is 10 to 3,000. When the electrode wire 21 is composed of a large number of monofilaments having an ultra-fine diameter plied together, the resulting electrode is not fragile nor too stiff, but has some handle and makes a slight touch on the surface of the object A. Moreover, stable and secure contact with the object is attainable because the wire 21 is formed of a large number of monofilaments. Thus, the discharge effect is stabilized as well as ensured, and neither the electrode wire 21 nor the object A will sustain injury. A similar discharge effect may be obtained using an electrode wire comprising a large number of monofilaments merely bundled together without being plied. However, its liability to fluffing detracts from its use as electrode wire. The aforementioned electrode wire 21 may be a fine chain formed by connecting links of, for example, iron, brass, aluminum or preferably, stainless steel. A link of such a chain, may have a length of 0.2 to 10mm in the connecting direction and of 0.1 to 5mm in the transverse direction. It is preferable that the high voltage source used for the corona discharge treatment usually gives a voltage of 10kV to 50kV, preferably 10kV to 30kV, and a frequency of 1kHz to 10kHz. The power supply output may be appropriately selected to meet the purpose. As the power supply circuit, a conventoinal known one may be used. However, it is desirable that such a circuit allows the discharge current which brings about plasmageneration to be arbitrarily controlled to meet the load requirement and also permit the frequency and the output of the high voltage source to be adjusted to their optimal levels. Besides, it is desirable to control the treating time to a specified time period by adjustably setting the time period for delivery of high voltage by adjusting the setting of a timer. If a stabilizing power source is provided in an electric circuit for applying high voltage, even a surface formed in a complex shape may be uniformly subjected to the plasma treatment. The corona discharge treatment apparatus of this invention is not limited to the examples hereabove described. The discharge electrode 2 may be set with its electrode wire fitting member 20 inclined. On the surface of the base electrode 1, a layer of dielectric substances such as, for example, glass, ceramics, plastics, enamel, asbestos, marble, slate, mica may be formed, as required, for attainment of uniform plasma treatment by prevention of local field concentration. Besides, although the base electrode 1 of the above-mentioned examples is placed integrally with the object A, it may be unified with the operation stand 3 or merely carried on the operation stand 3. Although in the above-described examples, the discharge electrode 2 is connected to the high frequency and high voltage source and immovably set and the base electrode 1 is earthed and adapted for movement by means of the operation stand (operating means) 3, it is also possible that the base electrode 1 is connected to the high frequency and high voltage source and immovably held and the discharge electrode 2 is earthed and designed to be movable by the operating means 3. In this case, the discharge electrode 2 may be vibrated by some operating means 3 for enhancing the effect of the corona discharge treatment.

Claims: A corona discharge treatment apparatus for activating a surface to be treated of an object by corona discharge, comprising a base electrode (1) for making contact with the object (A) to be treated and a discharge electrode (2), the surface to be treated of the object and the aforementioned discharge electrode being presented to each other, one of the said electrodes (2) being connected to a high frequency and high voltage source while the other electrode (1) is earthed, characterised in that only the earthed electrode (1) is allowed to make the movement for presenting the surface to be treated of the object (A) and the discharge electrode (2) to each other, and in that the earthed electrode (1) is designed to be moved by operating means (3), which are adapted to make vibrating movements. A corona discharge treatment apparatus according to claim 1 in which the said one electrode (2) is positioned high out of reach of operators, and means (3) for presenting the surface to be treated and the discharge electrode to each other including means (36) for raising the object on the earthed electrode (1).

Inventors: IKEDA, SHOJI, TSUTSUI, KOICHI, UEKI, KOJI
Applicants: NIPPON PAINT CO., LTD.
Application year: 1987
Main classification: H01T19
IPC codes: H01T19, C08J7, B29C59