Plasma treating apparatus

Abstract: A plasma treating apparatus for a sheet-like structure which comprises a generally drum-shaped first discharge el­ ectrode assembly (2) rigidly mounted on a rotary shaft (17) for rotation together therewith so as to extend through a vacuum vessel, which sheet-like structure is adapted to follow the outer periphery of the first discharge electrode assembly, and a second discharge electrode assembly (3) dis­ posed within the vacuum chamber so as to confront the first discharge electrode assembly (2). The vacuum vessel (1) is electrically insulated from an electric circuit (6) which is con­ nected with both of the first (2) and second (3) discharge elec­ trode assemblies, through the intervention of insulating members (14, 15) for electrically insulating the both from each other. These insulating members (14, 15) are interposed between a cylindrical body of the drum of the first discharge electrode assembly (2) and the rotary shaft (17).

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention generally relates to an apparatus for treating a sheet-like structure such as, for example, a plastics film, or fabrics or the like with plasma to improve chemical, physical, mechanical, optical and/or electrical properties, and/or a surface structure of the sheet-like structure. More specifically, the present invention relates to the plasma treating apparatus of a type comprising a vacuum vessel filled with a plasma and having a rotatably supported, drum-shaped discharge electrode assembly along which the sheet-like structure is passed for the plasma treatment at low temperature. Description of the Prior Art: Recently, the plasma treatment has attracted the attention of those skilled in the art as an effective method of treating a sheet-like structure much as, for example, a plastics film, or fabrics with plasma to improve chemical, physical, mechanical, optical and/or electrical properties, and/or a surface structure of the sheet-like structure. More specifically, it is well known from, for example, JP-A-57-18737, published in 1982, and JP-A-60-149441, published in 1985, that, by the plasma treatment, the weldability, the frictional property, the feeling or handling property, the luster and/or the color fixing property of the sheet-like structure can be improved so as to avoid a build-up of an electrostatic charge, as to facilitate the surface hardening or roughening, as to avoid the occurrence of blocking or as to permit the dyed color to be thickened. The known plasma treatment apparatus for treating the sheet-like structure with plasma such as disclosed in any one of the above mentioned publications makes use of, as is the case with the predecessor of such apparatus, a generally cylindrical discharge electrode assembly fixedly mounted on a rotary shaft extending through a vacuum vessel, and a generally rod-shaped discharge electrode assembly disposed within the vacuum vessel in face-to-face relationship with the drum-shaped discharge electrode assembly. According to this prior art plasma treating apparatus, arrangement has been made to avoid any possible occurrence of a plasma discharge from both of the discharge electrode assemblies into the vacuum vessel by insulating the vacuum vessel from, for example, an electric circuit system with which both of the discharge electrode assemblies are connected, thereby to minimize the consumption of an electric power. It has, however, been found that, since the drum-shaped discharge electrode assembly is fixedly mounted direct on the rotary shaft for rotation together therewith, the rotary shaft is also electrically charged during the operation of the apparatus. Because of this, a plasma discharge tends to occur from the rod-shaped discharge electrode assembly to the rotary shaft, resulting in the consumption of a relatively increased amount of electric power. Also, the plasma treatment apparatus designed specifically for the plasma treatment of a sheet-like structure tends to be bulky in view of the fact that the sheet-like structure to be treated with plasma has a substantial width and, therefore, in order for the plasma treatment apparatus to be adopted in practice by industries, the plasma treatment apparatus must have a handling capacity sufficient to correspond with a relatively great quantity of plant investment. In other words, in order for the handling capacity of the plasma treatment apparatus to be increased, the input, originally large, to the plasma treatment apparatus for creating a plasma-filled atmosphere must be further increased to increase the plasma density within the vacuum vessel. However, within the vacuum vessel filled with a plasma having a very low electric resistance, the increase of the input would result in the local unevenness of electrical distribution between the discharge electric circuit, disposed within, but electrically insulated from the vacuum vessel, and the vacuum vessel, and, therefore, because of this, insufficient electric insulation may occur at a corner area, for example, at an area between the rotary shaft extending through the vacuum vessel and a portion of the vacuum vessel adjacent the rotary shaft, allowing an electric current to flow through the vacuum vessel wherefore an inner wall of the vacuum vessel is electrically overcharged (being luminous) so as to result in the instantaneous abnormal spark discharge. Accordingly, the plasma discharge occurring within the vacuum vessel becomes unstable to such an extent that the plasma treatment apparatus can no longer be operated continuously. SUMMARY OF THE INVENTION The present invention has, accordingly, been devised with a view to substantially eliminating the above discussed problems inherent in the prior art plasma treatment apparatus and has for its essential object to provide an improved plasma treatment apparatus for the treatment of the sheet-like structure with plasma which can be continuously operated with the supply of a relatively large amount of electric power while minimizing the consumption of the electric power and which can, therefore, be adopted in practice by industries. In order to accomplish the above described object of the present invention, there is provided an improved plasma treatment apparatus which comprises a cylindrical first discharge electrode assembly, a second discharge electrode assembly disposed in face-to-face relationship with the first discharge electrode assembly, an electric circuit connecting between the first and second discharge electrode assemblies, and an electrically insulating material interposed between the rotary shaft, extending through the vacuum vessel, and a cylindrical body of the first discharge electrode assembly. According to the present invention, since the vacuum vessel is, as is the case with the prior art plasma treatment apparatus, electrically insulated from the electric circuit, a loss of plasma being discharged into the vacuum vessel can be minimized or substantially eliminated. Also, since the electrically insulating material is interposed between the rotary shaft and the cylindrical body, the rotary shaft itself can be electrically insulated from the first discharge electrode assembly and, therefore, there is no substantial possibility that a plasma discharge may occur from the second discharge electrode assembly to the rotary shaft. Moreover, since the rotary shaft is electrically insulated from the first discharge electrode assembly and the vacuum vessel is also electrically insulated from the electric circuit with which both of the first and second discharge electrode assemblies are connected, there is no substantial possibility that, for example, a narrow corner area between the vacuum vessel, through which the rotary shaft extends, and a portion of the rotary shaft extending through the vacuum vessel may be insufficiently insulated electrically, and, therefore, there is no substantial possibility of the occurrence of the abnormal spark discharge. BRIEF DESCRIPTION OF THE DRAWINGS In any event, the present invention will become more clearly understood from the following detailed description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as being limitative of the present invention in any what whatsoever, whose scope is to be determined solely by the appended claims. In the drawings, like reference numerals denote like parts in the several views, and: Fig. 1 is a schematic sectional view showing the construction of a plasma treatment apparatus according to a first preferred embodiment of the present invention; Fig. 2 is a longitudinal sectional view of the plasma treatment apparatus shown in Fig. 1; Fig. 3 is a longitudinal sectional view, on an enlarged scale, of an outer end portion of a rotary shaft; Fig. 4 is a view similar to Fig. 2, showing another preferred embodiment of the present invention; Fig. 5 is a sectional view showing the manner by which an electrically insulating material is fitted so as to cover one end portion of a drum-shaped discharge electrode assembly in the plasma treatment apparatus shown in Fig. 4; Fig. 6 is a perspective view, on an enlarged scale, of a second discharge electrode assembly used in the apparatus shown in Fig. 4; Fig. 7 is a schematic side view, with a portion cut away, of a piping system through which a cooling medium is alternately supplied to and drained from the discharge electrode assembly shown in Fig. 6; Figs. 8 and 9 are front elevational and side views, respectively, showing the piping system shown in Fig. 7; Fig. 10 is a longitudinal sectional view showing an essential portion according to a third preferred embodiment of the present invention; Figs. 11 and 12 are front elevational and side views, respectively, showing a fourth preferred embodiment of the present invention; Fig. 13 is a longitudinal sectional view showing the manner by which an electrically insulating material is fitted so as to cover one end portion of a drum-shaped discharge electrode assembly according to a fifth preferred embodiment of the present invention; and Fig. 14 is a schematic sectional view showing the construction of a different type of the plasma treatment apparatus applied for the treatment of a sheet-like structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Fig. 1, a vacuum vessel generally identified by 1 accommodates therein a cylindrical electrode assembly 2 (or a first discharge electrode assembly) and a second discharge electrode assembly 3 comprised of a plurality of generally rod-shaped electrodes disposed radially outwardly of the cylindrical electrode assembly 2 and extending in parallel relationship with each other and also with the cylindrical electrode assembly 2. These discharge electrode assemblies 2 and 3 are adapted to be applied with an electric voltage from a source of alternating current 4 through a transformer 5 and an electric circuit 6 connected with both of the discharge electrode assemblies 2 and 3. The vacuum vessel 1 is made of stainless steel and is maintained at a very low pressure by means of an evacuator 8, used to establish a substantial vacuum inside the vacuum vessel 1, while filled with a plasma treatment gas supplied from a pressurized gas vessel 7 containing a pressurized plasma treatment gas. This vacuum vessel 1 has auxiliary vacuum vessels 1A and 1B positioned on respective sides of the vacuum vessel 1 and flanged to the vacuum vessel 1 in fluid communication therewith, said auxiliary vacuum vessels 1A and 1B accommodating therein a sheet feeder unit 11 and a sheet take-up unit 13, respectively. Reference character A represents a sheet material which is supplied from the sheet feeder unit 11 towards the sheet take-up unit 13, then motor-driven, through a plurality of guide rolls 12, a substantially intermediate portion of said sheet material A being turned around the cylindrical discharge electrode assembly 2. In other words, while the sheet material A is drawn out from the sheet feeder unit 11 and reeled onto the sheet take-up unit 13 through the guide rolls 12 and around the cylindrical discharge electrode assembly 2, the web of sheet material can be continuously treated with low-temperature plasma as it passes over the cylindrical discharge electrode assembly 2 within the vacuum vessel 1 filled with the plasma atmosphere. Referring now to Fig. 2, the cylindrical discharge electrode assembly 2 is provided With a coolant jacket (a continuous, but tortuous passage for the flow of a coolant) 2a for the passage of a cooling medium having a low electroconductivity such as, for example, distilled water or silicone oil, which jacket 2a is defined in a cylindrical wall portion of the drum forming the cylindrical discharge electrode assembly 2. Opposite end walls 2b of the cylindrical discharge electrode assembly 2 are generally spherically curved inwardly of the cylindrical discharge electrode assembly 2 in a direction close towards each other. The cylindrical discharge electrode assembly 2 is rigidly mounted on a rotary shaft 17 for rotation together therewith by means of annular electrically insulating members 14 and 15 and annular couplings 16 positioned at respective central portions of the opposite end walls 2b of the cylindrical discharge electrode assembly 2 while the rotary shaft 17 extends axially through the opposite end walls 2b. Each of the annular electrically insulating members 14 is of a generally U-shaped cross-section and comprises, for example, a glass lining 14 having an excellent weatherability, which glass lining 14 is lined to an annular collar 16a of the respective coupling 16. The glass lining 14 can be formed, for example, by applying a slurry of glass particles so as to form a slurry layer on a surface of the respective coupling 16 and then baking the slurry layer. On the other hand, each of the annular electrically insulating members 16 is made of, for example, polycarbonate resin. Reference numeral 30 represents a rubber ring seated in an annular groove defined in each of the opposite end walls 2b of the cylindrical discharge electrode assembly 2 for sealing an annular gap between the cylindrical discharge electrode assembly 2 and the respective electrically insulating member 14. Reference numeral 31 represents a rubber ring seated in an annular groove defined in the respective coupling 16 for sealing an annular gap between the respective coupling 16 and the rotary shaft 17. It is to be noted that, since the electrically insulating members 14 are lined to the respective couplings 16, annular gaps each between the respective coupling 16 and the associated electrically insulating member 14 is sealed as a matter of fact. Accordingly, the interior 2d of the cylindrical discharge electrode assembly 2 is completely sealed from the interior 1a of the vacuum vessel 1. The rotary shaft 17 is adapted to be driven by an electrically powered drive motor (not shown) positioned exteriorly of the vacuum vessel 1 and is rotatably supported by the vacuum vessel 1 at a substantially intermediate portion 17a and an inner end 17b thereof by respective bearing assemblies 18 and 19 each having a ball bearing 18a or 19a. In other words, the rotary shaft 17 extends coaxially through the cylindrical discharge electrode assembly 2 with its opposite end portions which protrude axially outwardly from the opposite end walls 2b of the cylindrical discharge electrode assembly 2 in a direction away from each other and which are in turn supported rotatably. Reference numeral 18b represents a mechanical seal provided in the bearing assembly 18 for sealing the interior 1a of the vacuum vessel 1 from the atmosphere. The rotary shaft 17 has two axial bores 17c for communicating the interior 2d of the cylindrical discharge electrode assembly 2 to the outside of the vacuum vessel 1, which axial bores 17c are defined in the rotary shaft 17 so as to extend axially inwardly from the outer end 17d of the rotary shaft 17. A copper tube 20 having its outer peripheral surface coated with an insulating layer 26 of electrically insulating material such as, for example, fluorine contained resin is, as best shown in Fig. 3, inserted into each of the axial bores 17c with a small annular gap 17e formed between the insulating layer 26 and the inner peripheral surface of the respective axial bore 17c. Each of the copper tubes 20 has a coolant passage 20a defined therein over the entire length thereof for the flow of a cooling medium and is fluid-connected with the coolant jacket 2a through a respective flexible tubing 21 so that the copper tubes 20, the flexible tubings 21 and the coolant jacket 2a can altogether define a continuous flow passage for the flow of the coolant medium extending from one of the coolant passages 20a in the respective copper tubes 20 to the other of the coolant passages 20a via the coolant jacket 2a. Accordingly, so far shown, the cooling medium can be supplied from the coolant passage 20a in one of the copper tubes 20, which is positioned above the other of the cooper tubes 20 as viewed in Fig. 2, into the coolant jacket 2a through the upper flexible tubing 21 and, after having flowed through the coolant jacket 2a, can be discharged from the coolant jacket 2a to the outside through the lower flexible tubing 21 and then through the coolant passage 20a in the other of the copper tubes 20, which is positioned below such one of the cooper tubes 20. Reference numeral 32 shown in Fig. 3 represents a gas coupling for supplying therethrough a plasma treatment gas, originating from the pressurized gas vessel 7 shown in Fig. 1, into the interior 2d of the cylindrical discharge electrode assembly 2 through a port 17f defined in the rotary shaft 17 and then through the annular gaps 17e within the axial bores 17c. It is to be noted that the axial bores 17c are sealed from the atmosphere by means of a plurality of rubber seal rings 33 for each axial bore 17c which are located in tight contact with the respective copper tube 20 at the outer end portion of the rotary shaft 17 and inner surface of the respective axial bore 17c as best shown in Fig. 3. Thus, the interior 2d of the drum-shaped discharge electrode assembly 2 is filled with the plasma treatment gas and is maintained at a pressure higher than the pressure inside the interior 1a of the vacuum vessel 1. The rod-shaped discharge electrodes 3 are fixed at their opposite ends to spaced apart retaining members 22A and 22B which are in turn, supported within the vacuum vessel 1 by means of insulators 23. One side of the electric circuit 6 is inserted into the vacuum vessel 1 through an input terminal 6a insulating the vacuum vessel 1 from the electric circuit 6 and is in turn connected with the rod-shaped discharge electrode assembly 3, whereas the other side of the electric circuit 6 is connected with the cylindrical discharge electrode assembly 2 through a slip ring 25, the copper tubes 20 and a conductor 27. The vacuum vessel 1 is electrically insulated from the electric circuit 6 and is maintained in a condition grounded to the earth. It is, however, to be noted that both of the discharge electrode assemblies 2 and 3 of the electric circuit 6 are maintained in a condition not grounded and are strictly insulated from the vacuum vessel 1. In the construction as hereinabove described, since according to the present invention the vacuum vessel 1 is, as is the case with the prior art apparatus, electrically insulated from the electric circuit 6, there is no substantial possibility that any discharge of plasma may occur from the rod-shaped discharge electrode assembly 3 towards the vacuum vessel 1 and, therefore, any possible waste of an electric power can be substantially eliminated. Also, the cylindrical discharge electrode assembly 2 and the rotary shaft 17 are electrically insulated from each other with the intervention of the insulating members 14 and 15 between a cylindrical body 2c of the cylindrical discharge electrode assembly 2 and the rotary shaft 17. In this way, the rotary shaft 17 is electrically insulated from the cylindrical discharge electrode assembly 2 and, therefore, there is no possibility that any discharge of plasma occurs from the rod-shaped discharge electrode assembly 3 towards the rotary shaft 17, wherefore any possible waste of the electric power can be substantially eliminated. Moreover, since the rotary shaft 17 is electrically insulated from the cylindrical discharge electrode assembly 2 and the vacuum vessel 1 is also electrically insulated from the electric circuit 6 with which both of the discharge electrode assemblies 2 and 3 are connected as hereinbefore fully described, there will be no possibility that insufficient electric insulation may occur at a relatively narrow corner area, that is, at a location between that intermediate portion 17a of the rotary shaft 17 which extends through the wall of the vacuum vessel 1 and the neighboring bearing assembly 18 fast with the wall of the vacuum vessel 1. Accordingly, there is no substantial possibility of the occurrence of abnormal arc discharge at the inner surface of the wall of the vacuum vessel 1 and, therefore, the plasma treatment apparatus can be operated continuously. In addition, since the portions of the rotary shaft 17 which protrude outwardly from the cylindrical discharge electrode assembly 2 are electrically insulated from the cylindrical discharge electrode assembly 2, the rotary shaft 17 can be maintained in a condition not electrically charged and, therefore, there is no substantial possibility that the operator may receive an electric shock. Furthermore, since the rotary shaft 17 is not electrically charged by the reason hereinbefore described, there is no possibility that any arc discharge may occur at the mechanical seal 18b which is exposed to the plasma atmosphere and which is generally complicated in structure. Accordingly, the plasma treatment apparatus can be operated continuously for a prolonged length of time. Similarly, since any possible arc discharge may not occur at the bearing 19a, a design can be employed to install the bearing 19a within the vacuum vessel 1 whose atmosphere is filled with plasma. Since the relatively heavy cylindrical discharge electrode assembly 2 can therefore be supported on the rotary shaft 17 within the vacuum vessel 1 by means of the bearings 18a and 19b positioned on respective sides of the drum-shaped discharge electrode assembly 2, the spacing between these two bearings 18a and 19a can be minimized as compared with the case in which they are positioned outside the vacuum vessel 1 and, therefore, not only can the rotary shaft have a reduced diameter, but the bearings 18a and 19a can also be minimized in size. Where a design is employed wherein the rotary shaft 17 and the cylindrical discharge electrode assembly 2 are electrically insulated from each other and, however, no copper tubes which serve as an electric conductor are inserted through the rotary shaft 17 such as shown in and described later with reference to Fig. 4, no electric power supply can be effected from the electric power source, positioned externally of the vacuum vessel 1, to the cylindrical discharge electrode assembly 2 through the rotary shaft 17. In this design, in order for the electric power to be supplied to the cylindrical discharge electrode assembly 2, the slip ring 25 is required to be positioned inside the vacuum vessel 1. However, in the embodiment shown in and described with reference to Figs. 1 to 3, the rotary shaft 17 rotatable together with the cylindrical discharge electrode assembly 2 carries the copper tubes 20 inserted therethrough and one of the copper tubes 20 is electrically connected with the electric circuit 6, such one of the copper tubes 20 serving as an electric conductor through which the electric power can be effectively supplied from the power source to the cylindrical discharge electrode assembly 2. Therefore, even though the rotary shaft 17 and the cylindrical discharge electrode assembly 2 are electrically insulated from each other, the slip ring 25 for supplying the electric power therethrough to the cylindrical discharge electrode assembly 2 then rotating together with the rotary shaft 17 can be advantageously positioned outside the vacuum vessel 1 as hereinbefore described. The positioning of the slip ring 25 outside the vacuum vessel 1 is advantageous in that any possible contamination of the plasma atmosphere within the vacuum vessel 1 and/or any possible occurrence of arc discharge which would result from the presence of metallic particles worn off from the slip ring can be effectively eliminated and, therefore, the plasma treating apparatus according to the present invention can be advantageously operated continuously for a prolonged length of time. Also, in order to accomplish a favorable plasma treatment, countermeasures have to be taken to avoid any possible generation of heat from one or both of the rotary shaft 17 and the copper tubes 20 which would occur as a result of the consumption of a substantial amount of electric power. However, in the foregoing embodiment, since the coolant jacket 2a defining the passage for the flow of the cooling medium and the copper tubes 20 are fluid-connected in series with each other and, therefore, no extra coolant passage defining piping is needed for cooling the copper tubes 20, that is, that portion of the electric circuit 6 which is inserted through the rotary shaft 17. Moreover, in view of the fact that the copper tubes 20 are used as an electric conductor, the copper tubes 20 which would generate heat can be effectively cooled. In addition, since the rotary shaft 17 is made of stainless steel having a relatively low magnetic permeability and also a relatively small volume resistivity, there is no possibility that heat may be generated by the magnetic induction induced by the flow of the electric current through the copper tubes 20. It is to be noted that, although in the foregoing description reference has been made to the use of the two copper tubes 20 one used for the supply of the cooling medium into the coolant jacket and the other for the return flow or discharge of the used cooling medium from the same coolant jacket, alternatives would be to use one or three or more copper tubes instead of the two copper tubes such as shown and described. Where one cooper tube is employed, the rotary shaft 17 may have correspondingly one bore of a diameter greater than the outer diameter of the copper tube such that the hollow of the copper tube and an annular space between the wall defining such one bore in the rotary shaft and the outer peripheral surface of such one copper tube can be used for the in-flow and out-flow of the cooling medium relative to the coolant jacket. Yet, in the foregoing embodiment, the interior 2d of the cylindrical discharge electrode assembly 2 has been shown and described as sealed from the interior 1a of the vacuum vessel 1 by the action of the rubber seal rings 30 and 31. On the other hand, the supply of the gaseous medium into the interior 2d of the cylindrical discharge electrode assembly 2 through the gas coupling 32 as hereinbefore described forces the pressure inside the interior 2d of the cylindrical discharge electrode assembly 2 to be higher than that inside the interior 1a of the vacuum vessel 1. Accordingly, there is no substantial possibility that the plasma gas inside the interior 1a of the vacuum vessel 1 may enter the interior 2d of the cylindrical discharge electrode assembly 2 and, hence, no possible plasma discharge will be induced within the interior 2d of the cylindrical discharge electrode assembly 2, permitting the plasma discharge to be stabilized. Where the plasma treatment gas is introduced from the pressurized gas vessel 7, shown in Fig. 1, into the interior 2d of the cylindrical discharge electrode assembly 2 such as effected in the foregoing embodiment, any possible reduction of the purity of the plasma treating gas within the vacuum vessel 1 can be avoided by a portion of the gaseous medium leaking from the interior 2d into the interior 1a of the vacuum vessel 1. It is to be noted that, if desired, the interior 2d of the cylindrical discharge electrode assembly 2 may be communicated to the atmosphere through the port 17f (shown in Fig. 3) defined in the rotary shaft 17. In such case, since the interior 2d will not be filled with any plasma atmosphere and the pressure inside the interior 2d may be of a value equal to the atmosphere, any possible occurrence of a local spark discharge within the interior 2d can be advantageously minimized and the plasma discharge can be stabilized. Yet, since the insulating members 14 exposed to the plasma atmosphere as shown in Fig. 2 are in the form of the glass lining having an excellent weatherability, it will not be deteriorated substantially consequent upon the insulating members 14 being treated with the low-temperature plasma and/or in the presence of the arc discharge. Accordingly, there is no possibility that the insulating members 14 themselves may be damaged and/or an impurity gaseous medium may be generated within the vacuum vessel 1. It is, however, to be noted that, instead of the use of the glass lining, one or a mixture of ceramic material, fine ceramic material and plastics having a resistance to heat, a resistance to ultraviolet rays and/or a resistance to electron rays can be used as a material for each of the insulating members 14. Figs. 4 and 5 illustrate the plasma treatment apparatus according to another preferred embodiment of the present invention. In the embodiment shown in Fig. 4, the cylindrical body 2c of the cylindrical discharge electrode assembly 2 is fixedly mounted on the rotary shaft 17 through generally plate-like, opposite insulating members 40 each having a central hole through which the rotary shaft 17 extends. The cylindrical discharge electrode assembly 2 has its opposite annular ends 2e to which respective annular insulating members 41 are firmly secured by the use of fitting bolts 42 with bolt receiving bores 41a in the annular insulating members 41 being in turn closed by respective electrically insulating plugs 43 as shown in Fig. 5, whereby the opposite annular ends 2e are substantially completely covered by the annular insulating members 41. Each of the insulating members 40 and 41 is made of, for example, polycarbonate resin or ceramics. The interior 2d of the cylindrical discharge electrode assembly 2 is hermetically sealed from both of the atmosphere and the interior 1a of the vacuum vessel 1 by the insulating members 40, the rubber rings 30 and 31, etc. In Fig. 4, the rotary shaft 17 is formed with an axial bore 17g through which a piping 17a is inserted so that the in-flow passage 44 for the cooling medium and the out-flow passage 45 for the same cooling medium can be defined inside and outside the piping 17a, respectively. Reference numeral 46 represents connecting sleeves (tubings) made of insulating material such as, for example, rubber, and operable to fluid-connect the in-flow and out-flow passages 44 and 45 with the coolant jacket 2a. The rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n confronting the cylindrical discharge electrode assembly 2 (the first discharge electrode assembly) are, as best shown in Fig. 6, rigidly secured, or otherwise welded, at their opposite ends 3a to the respective retaining members 22A and 22B, which members 22A and 22B are in turn supported by the vacuum vessel 1 by means of the insulators 23 in Fig. 4. A generally cage-shaped discharge electrode assembly 3 (the second discharge electrode assembly) is constituted by these rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n and the retaining members 22A and 22B. This cage-shaped discharge electrode assembly 3 is of a design wherein the rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n are supported by the retaining members 22A and 22B while having spaced an equal pitch from each other, and is in turn supported within the vacuum vessel 1 while the retaining members 22A and 22B are connected to respective support brackets 56A and 56B which are secured to the respective insulators 23. While each neighboring rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n are preferred to be spaced an equal pitch from each other, such a deviation may be in practice tolerable due to considerations of the cost required to assembly or manufacture that half or less of the total number of the rod-shaped discharge electrodes may be spaced from each other a pitch with deviation equal to or smaller than 3 times, preferably 1.3 times, the average outer diameter of all of the rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n . Each of the retaining members 22A and 22B for supporting the rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n so as to permit the latter to occupy a portion of the imaginary circle may be of a split construction comprising two or more members if desired due to considerations of the manufacturing and/or fitting procedures and/or for the purpose of convenience in maintenance and servicing. Reference numerals 57A and 57B represent supply and discharge ports, respectively, for the flow of the cooling medium. In the illustrated embodiment, the cage-shaped discharge electrode assembly 3 is so designed as to be positively cooled by the cooling medium and, for this purpose, each of the rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n is of a type having a coolant passage defined therein and, on the other hand, each of the retaining members 22A and 22B is of a construction having a coolant passage defined therein for the supply and discharge of the cooling medium into and from the rod-shaped discharge electrodes 3₁, 3₂, ... and 3 n . Each of the supply and discharge ports 57A and 57B is, as illustrated in Fig. 7 in terms of the discharge port 57B as a representative example, of such a design as to be fluid-connected with a supply or discharge piping 59, fixedly extending through the vacuum vessel 1, through a respective connecting tubing 58 of 30mm or more in length made of insulating material such as, for example, ceramics, and, by the intervention of the insulating connecting tubing 58, any possible occurrence of a local spark and an instantaneous abnormal ark discharge around the supply or discharge piping 59 can be minimized considerably as compared with the case wherein no insulating connecting tubing is employed. Figs. 8 and 9 illustrate the details of the cage-shaped discharge electrode assembly 3 provided with the cooling system, wherein Fig. 8 is a front elevational view thereof and Fig. 9 is a side view thereof. In this illustrated instance, a coolant passage 22PA defined in one of the retaining members 22A serves as a supply passage communicated in common with the coolant passages 3P₁ to 3P n in the respective rod-shaped discharge electrodes 3₁ to 3 n , whereas a coolant passage 22PB defined in the other of the retaining members 22B serves as a discharge passage communicated in common with the coolant passage 3P₁ to 3P n in the respective rod-shaped discharge electrodes 3₁ to 3 n . It is to be noted that, in the plasma treatment apparatus according to the second preferred embodiment, the slip ring 25 shown in Fig. 4 is arranged within the vacuum vessel 1 and is connected with a portion of one annular end 2d of the cylindrical discharge electrode assembly 2 through a conductor 47. The remaining structural details thereof are substantially identical with that in the first preferred embodiment shown in Fig. 2 and, therefore, will not be reiterated while like parts are designated by like reference numerals. According to the second preferred embodiment shown in and described with reference to Figs. 4 to 9, since the annular opposite ends 2e of the cylindrical discharge electrode assembly 2 are covered by the insulating members 41, any unnecessary plasma discharge from the rod-shaped discharge electrode assembly 3 towards the annular ends 2d of the cylindrical discharge electrode assembly 2 can be avoided. Also, this feature brings about an additional advantage in that any possible elevation of temperature in the vicinity of the opposite ends 2e of the cylindrical discharge electrode assembly 2 can be avoided, the plasma treatment can be effected uniformly over the entire surface of the sheet-like structure. Moreover, since the coolant jacket 2a is communicated with the coolant passages 44 and 45 through the connecting sleeves 46 made of insulating material, the electric current is permitted to flow from the cylindrical discharge electrode assembly 2 to the rotary shaft 17 only through the cooling medium and, therefore, the rotary shaft 17 can be very strictly insulated electrically from the cylindrical discharge electrode assembly 2. In addition, since the hermetically sealed interior 2d of the cylindrical discharge electrode assembly 2 is filled with the atmosphere, not the plasma atmosphere, because it is assembled in the atmosphere and not supplied with the plasma treatment gas, any possible occurrence of the local spark within the interior 2d can be minimized and tee plasma discharge can be stabilized. Furthermore, since the plural rod-shaped discharge electrodes 3₁ to 3 n are arranged to be retained by the retaining members 22A and 22B thereby to present the cage-shaped discharge electrode assembly 3 which is in turn supported within the vacuum vessel 1, as compared with a general structural arrangement wherein the rod-shaped discharge electrodes 3₁ to 3 n are made to extend through the vacuum vessel 1 and are the supported in a cantilever fashion by a base positioned outside the vacuum vessel 1, a structure wherein the rod-shaped discharge electrodes 3₁ to 3 n extend through the vacuum vessel 1 is eliminated and, therefore, there is no possibility that the discharge may become unstable as a result of the occurrence of a local spark and an instantaneous abnormal arc discharge at a site where the rod-shaped discharge electrode assembly extend through the vacuum vessel, permitting the plasma treatment apparatus to be continuously operated for a prolonged length of time with the supply of a relatively large amount of the electric power thereto. Further, since a structure is employed wherein the plural rod-shaped discharge electrodes 3₁ to 3 n are supported at their opposite ends, and since the stresses which would be built up in the rod-shaped discharge electrodes 3₁ to 3 n can therefore be reduced as compared with that in the above described cantilever support structure, the rod-shaped discharge electrodes 31 to 3n may be employed having a reduced diameter and, therefore, the cost required to manufacture the apparatus can be minimized. In addition, the use of the rod-shaped discharge electrodes 3₁ to 3 n of reduced diameter permits the pitch between each neighboring rod-shaped discharge electrodes to be reduced and, therefore, permits the use of a considerably increased numbers of the rod-shaped discharge electrodes, thereby permitting the input electric power from the rod-shaped discharge electrodes to be increased markedly. Furthermore, since the plural rod-shaped discharge electrodes 3₁ to 3 n are fixedly supported at their opposite ends by the retaining members 22A and 22B, the position thereof will not change with time and, therefore, any deviation in quality does not occur in the products. Yet further, since the discharge electrode assembly 3 of the cage-shaped structure is of a structure wherein the rod-shaped discharge electrodes 3₁ to 3 n forming the discharge electrode assembly 3 are cooled by the use of the cooling medium, the surface temperature of each of the rod-shaped discharge electrodes 31 to 3n can be maintained at a constant value and also maintained uniform and, therefore, the low-temperature plasma treatment can be effected steadily for a prolonged length of time with no possibility of local temperature rise, that is, with no possibility that the sheet-like structure A being treated is excessively heated to such an extent as to result in modification of the quality of the products. Fig. 10 illustrates a third preferred embodiment of the present invention showing a modified form of the cage-shaped discharge electrode assembly 3 provided with the cooling system, and is a partially enlarged sectional view of the connection between the support member 22A and the rod-shaped discharge electrodes 3₁ to 3 n which corresponds to Fig. 9. In this embodiment, each of the coolant passages 3P₁ to 3P n in the respective rod-shaped discharge electrodes 3₁ to 3 n is provided with an orifice 60 so that, by suitably selecting the inner diameter of the orifice 60, the cooling medium flowing from the retaining member 22A towards each of the rod-shaped discharge electrodes 3₁ to 3 n can be uniformly distributed, into the rod-shaped discharge electrodes 3₁ to 3 n . In this embodiment, each of the orifice 60 is constituted by a small perforation defined in the retaining member 22A. Figs. 11 and 12 illustrate a fourth preferred embodiment of the present invention showing a further modified form of the cage-shaped discharge electrode assembly 3 provided with the cooling system, wherein Fig. 11 is a front elevational view of the cage-shaped discharge electrode assembly 3 and Fig. 12 is a side view thereof. In this embodiment, the coolant passage 22PA or 22PB in each of the retaining members 22A and 22B is partitioned by partitioning walls 61 so that each of the coolant passages 3P₁, 3P₂, ... and 3P n in the respective rod-shaped discharge electrodes 3₁ to 3 n can be arranged sequentially and in series. It is to be noted that, in the first preferred embodiment shown in Fig. 1, the annular ends 2e of the cylindrical discharge electrode assembly 2 may be covered by the insulating members 41 as is the case with the fifth preferred embodiment shown in Fig. 13. Also, the rod-shaped discharge electrode assembly 3 shown in Fig. 2 may be provided with the cooling system shown in and described with reference to Figs. 6 to 12. Fig. 14 illustrates a different plasma treatment apparatus for the sheet-like structure to which the present invention is applicable. In this figure, reference numerals 9 and 10 represents respective auxiliary vacuum chambers, and, while a plurality of sealing rolls (not shown) and sealing chambers (not shown) are arranged inside the auxiliary vacuum chambers 9 and 10 and along the direction of travel of the sheet-like structure A, the maintenance of the pressure within the vacuum chamber 1 at a predetermined value can be assisted by evacuating the sealing chambers to a vacuum so that the pressure can be progressively decreased from the atmospheric pressure. Although not shown, the present invention can be equally applicable to the arrangement wherein the sheet feeder unit 11 and the sheet take-up unit 13 are disposed within the vacuum chamber 1 together with both of the discharge electrode assemblies 2 and 3. From the foregoing description, it has now become clear that, according to the present invention, the waste of the electric power consumed by the plasma treatment apparatus for the sheet-like structure which consumes a relatively great amount of the electric power can be advantageously minimized and, also, the occurrence of the abnormal arc discharge can be effectively avoided, allowing the plasma treatment apparatus to have a handling capacity enough to permit it to be employed by industries and to be operated continuously.

Claims: A plasma treating apparatus for treating a sheet-like structure which comprises a cylindrical first discharge electrode assembly (2) rigidly mounted on a rotary shaft (17) for rotation together therewith, said rotary shaft extending through a vacuum vessel (1), said sheet-like structure being adapted to follow the outer periphery of the first discharge electrode assembly (2); a second discharge electrode assembly (3) disposed within the vacuum vessel so as to confront the first discharge electrode assembly, said vacuum vessel being electrically insulated from an electric circuit (6) which is connected with both the first and second discharge electrode assemblies; and electrically insulating members (14,15) interposed between the cylindrical first discharge electrode assembly and the rotary shaft. The apparatus as claimed in Claim 1, wherein a conductor (27) connected with the first discharge electrode assembly (2) is inserted through the rotary shaft. The apparatus as claimed in Claim 2, wherein the first discharge electrode assembly (2) is provided with a first coolant passage means (2a) through which a cooling medium flows, said first coolant passage means (2a) being fluid-corrected in series with a second coolant passage means (20, 20a) for the flow of a cooling medium for cooling the conductor (27) inserted through the rotary shaft. The apparatus as claimed in Claim 1, wherein the first discharge electrode assembly (2) is provided with a first coolant passage means (2a), said first coolant passeage means being fluid-connected through a connecting tubing (21), made of insulating material, with a second coolant passage means (20a) defined inside the rotary shaft. The apparatus as claimed in Claim 1, wherein the first discharge electrode assembly (2) has a drum shaped interior which is communicated with a source (7) of gaseous medium containing a plasma treatment gas, and is maintained at a pressure higher than the pressure inside the vacuum vessel. The apparatus as claimed in Claim 1, wherein the first discharge electrode assembly has a drum shaped interior communicated to the atmosphere. The apparatus as claimed in Claim 1, wherein the first discharge electrode assembly has a drum shaped interior completely sealed. The apparatus as claimed in Claim 1, wherein the first discharge electrode assembly has opposite ends (2b) covered by respective insulating members (14, 15). The apparatus as claimed in Claim 1, wherein the second discharge electrode assembly (2) comprises a plurality of generally rod-shaped discharge electrodes (3₁ ... 3 n ) which are supported at opposite ends by respective retaining members (22A, 22B) while extending parallel to each other so as to occupy a portion of the imaginary circle following the outer periphery of the cylindrical first discharge electrode assembly (2) and also so as to represent a generally cage-shaped structure. The apparatus as claimed in Claim 9, wherein each of the rod-shaped discharge electrodes (3₁ ... 3 n ) has a first coolant passage (3P₁ ... 3P n ) defined therein for the flow of a cooling medium, and said retaining members (22A, 22B) form respective cooling passages for connecting inlet and outlet sides of the respective coolant passages of the rod-shaped discharge electrodes in parallel relation to each other. The apparatus as claimed in Claim 9, wherein each of the rod-shaped discharge electrodes (3₁ ... 3 n ) has a first coolant passage (3P₁ ... 3P n ) defined therein for the flow of a cooling medium, and said retaining members (22A, 22B) form respective cooling passages (22PA, 22PB) for connecting the respective coolant passages of the rod-shaped discharge electrodes in series with each other. The apparatus as claimed in Claim 10, wherein supply and discharge ports (57A, 57B) of each of the respective first coolant passages (22PA, 22PB) of the rod-shaped discharge electrodes are formed in the respective retaining members (22A, 22B). The apparatus as claimed in Claim 11, wherein supply and discharge ports of each of the respective first coolant passages of the rod-shaped discharge electrodes are formed in the respective retaining members. The apparatus as claimed in Claim 12, wherein said supply and discharge ports (57A, 57B) are fluid-connected through respective connecting tubings (58), each made of insulating material, with supply and discharge pipings (44, 45, 59) disposed so as to extend through the vacuum vessel. The apparatus as claimed in Claim 13, wherein said supply and discharge ports (57A, 57B) are fluid-connected through respective connecting tubings (58), each made of insulating material, with supply and discharge pipings (59) disposed so as to extend through the vacuum vessel.

Inventors: AKAGI TAKAO, KOYAMA MOTOYASU, NAMBA AKIRA, OKAGAKI ISAO, SAKAMOTO ITSUKI, TERAOKA HIDETOSHI, YAMAGUCHI SHINJI, AKAGI, TAKAO, KOYAMA, MOTOYASU, NAMBA, AKIRA, OKAGAKI, ISAO, SAKAMOTO, ITSUKI, TERAOKA, HIDETOSHI, YAMAGUCHI, SHINJI
Applicants: KURARAY CO, KURARAY CO., LTD.
Application year: 1987
Main classification: H05H1
IPC codes: H05H1, B29C59