PROCESS AND APPARATUS FOR THE ELECTRICAL TREATMENT OF AIR-CUSHION FILMS

Abstract: The invention relates to a process and a device for treating conducting and non-conducting materials, especial­ ly air-cushion films (1). The treating consists of a spark discharge between electrodes, which acts on the material. When doing this, in the case of an air-cushion film first of all the zone (12) where the recess bottoms (11) and the recess sides (13) meet is treated, followed by another working cycle to treat the recess bottoms (11).

Description: PROCESS AND APPARATUS FOR THE ELECTRICAL TREATMENT OF CONDUCTING AND NON-CONDUCTING MATERIALS The invention relates to a process and an apparatus for treating conducting and non-conducting materials, for example plastic, paper, metal and/or fabric webs or moulded bodies of these materials, especially air-cushion films, consisting of a first, smooth plastic film and second plastic film provided with recesses, in which the two films are bonded together in such a way that the first film seals the recesses of the second film, for increasing the surface energy with at least one electrode designed as a profile or knife electrode tangentially to a counter-electrode designed as a roller electrode, which is arranged on the same side of the material to be#treated. Apparatus of the type referred to above is known. In one known device, the counter-electrode is designed as a roller electrode and the live electrode is designed as a profile or knife electrode (German Laid Open Specification 24 61 865). These known devices serve to improve the adhesivity between one material which may be conducting or non-conducting and a second material, for example a plastic film, which is in a more or less molten state. With the known devices, the conducting or non-conducting initial material is supposed to be prepared in such a way that the second material can be applied to the initial material in an optimum manner. Air-cushion films (initial material), especially for packaging purposes, are frequently provided on their sides designed with recesses with a sticky second material. The object of this is to ensure that the object to be packed simply has to be wrapped and the adhesive power of the second material guarantees that the air-cushion film on the packaged object cannot slip off. When the packaged material is unpacked, no residue of the adhesive second material must remain on the object originally packed. For this purpose it is necessary that the adhesive second material should possess maximum bonding to the air-cushion film. From German Registered Design 79 14 659 a corresponding air-cushion film is known in which a layer consisting only of adhesive is applied to nub bottoms and the bordering curved transition zones which have been pre-treated exclusively by abrasion or oxidation. This German Registered Design, however, contains no references to the execution of this pre-treatment. In the production of air-cushion films, during vacuum shaping of the recesses irregular bottom surfaces are imparted. These irregularities lead during pre-treatment, for example as a result of a corona discharge, to irregular results. In consequence of the variable pre-treatment the adhesive second material is not evenly distributed or not bonded uniformly to the recesses. As a result of this residual deposits may remain on the packaged objects. From German Laid Open Specification 28 47 495 a device is known in which air-cushion films are pressed by a spring or by electrostatic charge on to the roller electrodes. In a parallel arrangement of the recesses of the air-cushion film, but also in the case of a staggered arrangement of the recesses of the air-cushion film, the torque of the air cushions concluded in the recesses is variable. These variable torques lead to a constantly pulsating movement of the springs. Bound up vith a "lagging behind of the air-cushions in respect of the roller electrode in the direction of movement of the air-cushion film, there also occurs an irregular treatment of the recess bottoms and the adjacent curved transition zones. The cylic irregularities thus occurring are just as disadvantageous as the above-mentioned irregularities resulting from the mode of production of the air-cushion films. Pressing the air-cushion film on to the roller electrodes by an electrostatic charge on the air-cushion film leads to an adverse effect on the corona field if one operates with two profile or knife electrodes tangetially to the roller electrode. From German Laid Open Specification 24 61 865 a device is known in which the roller electrode lies at the top end of a pressure chamber which is impinged on by gas and the profile or knife electrodes form the top closure of this pressuure chamber. As a result of a discharge gap between the profile or knife electrodes and the roller electrode the material for treatment is acted on by pressure in this zone. Particularly in the case of structured surfaces such as the recess side of air-cushion films, the result of this is that the material to be treated is set into oscillations which have an adverse effect on the treatment. In addition, the discharge gap must be comparatively narrow, which does not facilitate optimum cooling of the roller electrode by the gas current. The object of present invention is to provide a process and an apparatus in which a uniform treatment of the surface of the conducting or non-conducting material is improved, by avoiding the defects of the prior art. This problem is solved according to the invention in a process according to the Preamble of Claim 1 by the characterising part of Claim 1 and an apparatus according to the Preamble of Claim 2 by the characterising part of Claim 2. The process according to the invention achieves an intensive and uniform treatment of -the recess bottons and the adjacent curved transition zones. The apparatus according to the invention is especially suited to carrying out this process. Without the recesses being greatly deformed, it makes possible at the first roller electrode an equalisation of all the recesses in the zone in question. At the second roller electrode a direct physical contact between the roller electrode and the recesses of the air-cushion film is avoided and at the same time the corona field has a long-lasting effect on the recess bottoms. The present invention is illustrated by the following Drawings. In these: Fig. 1 shows a partially cut away diagrammatical front view of the apparatus according to the invention, Fig. 2 shows a diagrammatical cross-section through a roller electrode with two profile or knife electrodes, Fig. 3 shown a diagrammatical cross-section through a roller electrode with a pin electrode. Referring to Fig. 1 an air-cushion film 1 comes in the direction of the arrow from a run-in roller 14. It is passed over three roller electrodes 3 of a first type. Over two roller electrodes 4 of a second type the air-cushion film 1 passes to a run-out roller 15. Between the last of the roller electrodes 3 of the first type and the first of the two roller electrodes 4 of the second type between the two roller electrodes 4 the air-cushion film 1 is guided by two support rollers 16. The air-cushion film 1 progresses - in a manner which cannot be seen from this illustration - so that its recesses point in the direction of the roller electrodes 3 or 4. On both sides of each of the roller electrodes of the first type there are located a pair of knife electrodes 5. Behind each of the roller electrodes 3 and 4 of both types there are air chambers 6. The pressure in these air chambers 6 preferably amounts to 300 to 600 mm water col. The top ends of the air chambers 6 surround the roller electrodes 3 and 4 of both types up to a maximum of half their circumference. The air current flowing out of the air chambers 6 serves to cool the roller electrodes 3 and 4 of both types and to cool the air-cushion film 1. By having the roller electrodes 3 and 4 of both types only partly surrounded by the air chambers 6, a build-up of air causing the air-cushion film 1 to oscillate and hence removing it from the field of action to the corona field is avoided. The frequency of the spark discharge of all the electrodes preferably amounts to 20 to 30 khz for an output voltage of a mxaimum of 15KV. Fig. 2 represents a roller electrode 3 of the first type in greater detail. It can clearly be seen how the air-cushion film 1 with the recesses 11 pointing in the direction of the roller electrode 3 of the first type runs over this roller electrode 3 of the first type in a slightly curved path. The sector where the air-cushion film 1 rests on the roller electrode 3 of the first type is chosen in such a way that at least one recess bottom 11 is always in contact with the roller electrode 3 of the first type. On both sides of this contact zone is located a pair of knife electrodes 5. These knife electrodes 5 are shielded by means of inslulating plates 7 in the direction of the roller electrode 3 of the first type. These insulating plates 7 consist preferably of polytetrafluorethylene. They have the effect of preventing the sparks from discharging too soon on the roller electrode 3 of the first type. With the roller electrodes 3 of the first type it is important that the recesses of the air-cushion film 1 should be put under pressure as far as possible, which means that first of all they arch up towards the knife electrode 5 lying in the direction of movement, thereafter to be inflated opposite the knife electrode 5 located in the opposite direction of movement. As a result of this an optimum treatment of a zone 12 where the recess bottoms 11 meet recess sides 13 is achieved. Fig. 3 represents a roller electrode 4 of the second type in greater detail. The air-cushion film 1 has no direct contact with roller electrode 4 of the second type. It. is positioned by the support rollers 16 (not shown in this illustration) at a suitable distance. The pin electrode 9 is surrounded by a ceramic sleeve 8. The effect of this is to divert the corona field from the roller electrode 4 of the second type a little and hence to act for longer on the recess bottoms 11. The roller electrodes 3 of the first type serve in conjunction with their knife electrodes 5 first and foremost for the treatment of the transition zone 12 of the recess bottoms 11 to form a nub shell 13. The roller electrodes 4 of the second type serve first and foremost for the treatment of the recess bottoms 11 themselves. It has been shown to be advantageous for all the roller electrodes 3 and 4 and also the run-in roller 14 and run-out roller 15 to be driven. In this connection it is especially advantageous for the run-in roller 14 and the electrode rollers 3 and 4 to be driven in parallel, whilst the run-out roller 15 can be controlled separately.

Claims: Claims: 1. Process for the treatment of conducting and non-conducting materials, for example plastic, paper, metal and/or fabric webs or moulded bodies of these materials, especially air-cushion films, consisting of a first smooth plastic film and a second plastic film provided with recesses, in which both films are bonded to each other in such a way that the first film seals the recesses of the second film, for increasing the surface energy with at least one profile or knife electrode tangentially to a counter-electrode designed as a roller electrode, which is arranged on the same side of the material to be treated, characterised by the fact that an air-cushion film (1) is treated at a zone (12) where the recess bottoms (11) and recess sides (13) meet and the recess bottoms (11) are also treated, and that the treatments comprise of spark discharges between electrodes. 2. Apparatus for treating conducting and non-conducting materials, for example plastic, paper, metal and/or fabric webs or moulded bodies of these materials, especially air-cushion films consisting of a first smooth plastic film and a second plastic film provided with recesses in which the two films are bonded to each other in such a way that the first film seals the recesses of the second film, for increasing the surface energy with at least one profile or knife electrode tangentially to a counter-electrode designed as a roller electrode, which is arranged on the same side of the material to be treated, especially for carrying out the process according to Claim 1, characterised by the fact that viewed in the running direction of an air-cushion film (1) at least one roller electrode (3) of the first type with knife electrodes (5) arranged on both sides is arranged in front of at least one roller electrode (4) of a second type with a pin electrode (9) arranged tangentially to the roller electrode (4) of the second type. 3. Apparatus according to Claim 1, characterised by the fact that an insulating plate (7) is fitted to the surface of at least one knife electrode (5) turned to the roller electrode (3) of the first type. 4. Apparatus according to Claim 3, characterised by the fact that the insulating plate (7) consists of polytetrafluorethylene. 5. Apparatus according to one or more of Claims 2 to 4, characterised by the fact that the pin electrode (9) is surrounded by a ceramic casing (8). 6. Apparatus according to one or more of Claims 2 to 5, characterised by the fact that the pin electrode (9) is arranged in the direction of running of the air-cushion film (1) in front of the roller electrode (4) of the second type. 7. Apparatus according to one or more of Claims 2 to 6, characterised by the fact that viewed in the direction of running of the air-cushion film (1)D in front of the roller electrodes (3, 4) a run-in roller (14) and/or after the roller electrodes(3, 4) a run-out roller (15) is arranged. 8. Apparatus according to one or more of Claims 2 to 7, characterised by the fact that at least one roller electrode (3 or 4) and/or at least the run-in roller (14) and/or the run-out roller (15) are driven 9. Apparatus according to Claim 8 Dcharacterised by the fact that all roller electrodes (3D 4) and the run-in roller (14) are driven synchronously and the run-out roller (15) is separately adjustable. 10. Apparatus according to one or more of Claims 2 to 9, characterised by the fact that below the roller electrodes (3 and 4) air chambers (6) are arranged which attain at most half the height of the roller electrodes (39 4) and are impinged on by gas. 11 Apparatus according to Claim iO# characterised by the fact that the air chambers (6) are inpinged on by air at a pressure of 300 to 600 mm water col 12. Apparatus according to one or more of Claims 2 to 11, characterised by the fact that an output voltage of a maximum of 15 KV A/C with a frequency of 20 to 30 khz is applied to all electrodes (3D4s 5 and 6) 13. Apparatus according to one or more of Claims 2 to 12, characterised by the fact that, viewed in the direction of running of the air-cushion film (1), a supporting roller (16) is arranged between the last roller electrode (3) of the first type and the first roller electrode (4) of the second type and/or between the roller electrodes (4) of the second type.

Inventors: GRUBER, RUDOLF, STURM, VALENTIN
Applicants: THE BRITISH PETROLEUM COMPANY P.L.C.
Application year: 1983
Main classification: B29C59
IPC codes: H01T19, B29C59