Corona treatment machine on single sheets

Abstract

The present invention is aimed at the sector of the construction of machines for carrying out surface treatments on various materials: in particular the invention relates to a corona treatment machine (1) on single sheets (F) comprising: a high frequency generator; a voltage step-up transformer; at least one electrode (2) coated with insulating material arranged in an exhaust hood (3); a counter electrode (4) made of conductive material and earthed; feed means (5, 6) of single sheets to be treated along a direction of feed (x) toward a space comprised between said at least one electrode (2) and said counter electrode (3); pick up means (7, 8) of single treated sheets. Said counter electrode (4) comprises a chamber (9), placed under vacuum pressure by air suction means. Said chamber (9) comprises: a wall (10) provided with a plurality of holes (11) adapted to act as surface for conveying said single sheets (F) underneath said at least one electrode (2); a suction mouth (12) operatively connected to said suction means. The vacuum pressure of said chamber (9) is obtained by means of the suction of air through said holes (11) so as to maintain the single sheets (F) being treated adhering to said wall.

Description

[0001] CORONA TREATMENT MACHINE ON SINGLE SHEETS

[0002] Technical field of application

[0003] The present invention is aimed at the sector of the construction of machines for carrying out surface treatments on various materials: in particular the invention relates to a machine for corona treatment to be carried out on single sheets, which can also be very thin.

[0004] Background art

[0005] As is known, corona treatment consists in general of applying an electric discharge of considerably intensity to the surface of a given substrate, with the aim of increasing its active tension and consequently improving the bonding capacity of printing inks, stickers or coatings.

[0006] Corona treatment it is often applied to polyethylene, polypropylene, PVC or polyester films, but more generally it can treat almost all plastic materials and also some films made of non-plastic materials, such as paper and aluminium.

[0007] A corona treatment machine, according to the prior art, essentially consists of a high frequency generator, a voltage step-up transformer connected to a plurality of electrodes, and a counter electrode coated with insulating material and electrically earthed. The system can also be built using electrodes coated with an insulating material and a counter electrode that is not coated, made of a conductive material and earthed.

[0008] The substrate to be treated is fed through the space, defined air gap, between the electrodes and the counter electrode: in this way the surface of the substrate is activated by the electrical discharge that is triggered between the live electrodes and the earthed counter electrode.

[0009] Typically, applications are carried out in-line, with continuous feed of the reel of material, with treatment of roll-to-roll type.

[0010] There are also in-line applications for treating single sheets of conductive materials, such as sheets of aluminium or other metals which, after being inserted between the live electrodes and the earthed counter electrode, act as counter electrode and trigger the discharge. However, with these devices it is only possible to treat relatively thick sheets, of at least 1 mm.

[0011] Instead, to treat single sheets made of non-conductive material, currently only benchtop workshop applications, with manual insertion of the sheet and limited treatment speeds, exist.

[0012] These applications have various limits when requiring to treat much thinner and / or non-conductive materials, such as sheets of laminated paper, or sheets of polyethylene, polypropylene, PVC or polyester, which must be fed through the air gap in which corona discharge takes place, which requires an earthed counter electrode.

[0013] Even more disadvantageously, with the workshop applications currently in use it is difficult to hold the single sheets in place during the treatment steps, above all in the case of particularly thin sheets (range 50-300 micron) and sheets of small size. In fact, it must be considered that corona discharge produces ozone, which, for environmental and safety reasons, is collected via an overhead exhaust hood in which the electrodes are positioned. This suction tends to lift the thin sheets, with the risk of jamming thereof between the electrodes. The same problem of lifting of the sheets can also occur due to incoming air flows if high operating speeds are used. Current applications do not provide for the possibility of guaranteeing the correct position of the sheets to be treated, maintaining them adhering to the counter electrode, above all at high speeds (greater than 60 m / min). For this reason, no in-line applications exist.

[0014] Furthermore, corona discharge causes heating of the counter electrode which can cause an expansion thereof and consequently misalignment of the air gap (distance between electrode and counter electrode), resulting in uneven surface treatment and the transmission of heat to the treated sheet, with possible negative consequences on the sheet, if it is heat sensitive. Current applications are unable to maintain the parts in contact with the sheets to be treated at a low temperature, which can result in possible damage thereto.

[0015] Presentation of the invention

[0016] The object of the invention is to overcome these problems.

[0017] The main object of the invention is to produce a corona treatment machine on single sheets with solutions that guarantee the correct position of the single sheets during corona treatment, required for correct triggering of the electric discharge and for the success of the treatment, without the sheets undergoing thermal shock.

[0018] Another object of the invention is to produce a corona treatment machine on sheets that can also be particularly thin, and reaching a wide range of operating speeds, resulting in a reduction in costs and the possibility of operating in-line with other machines in a process in which corona treatment is required.

[0019] These objects are achieved with a corona treatment machine on single sheets comprising:

[0020] - a high frequency generator;

[0021] - a voltage step-up transformer;

[0022] - at least one electrode coated with insulating material arranged in an exhaust hood;

[0023] - a counter electrode made of conductive material and earthed;

[0024] - feed means of single sheets to be treated along a direction of feed toward a space comprised between said at least one electrode and said counter electrode;

[0025] - pick up means of single treated sheets, characterized in that said counter electrode comprises a chamber, placed under vacuum pressure by air suction means, where said chamber comprises:

[0026] - a wall provided with a plurality of holes adapted to act as surface for conveying said single sheets underneath said at least one electrode;

[0027] - a suction mouth operatively connected to said suction means, where the vacuum pressure of said chamber is obtained by means of the suction of air through said holes so as to maintain the single sheets being treated adhering to said wall.

[0028] In a possible variant of the invention, said vacuum pressure chamber comprises a baffle interposed between said wall and said suction mouth so as to divide said chamber in two, where said baffle comprises a plurality of gaps with air passage area decreasing toward said suction mouth.

[0029] Alternatively, said suction mouth is arranged centrally or laterally with respect to said chamber.

[0030] Advantageously, said suction mouth comprises valve means adapted to throttle the flow rate of the air flow drawn through said holes.

[0031] In a preferred variant of the invention, said vacuum pressure chamber comprises a first and a second opening, arranged on opposite walls, symmetrically with respect to said direction of feed of said single sheets being treated.

[0032] Even more advantageously, said wall comprises a plurality of heat dissipating fins which extend, inside said chamber, from a face thereof opposite the face on which said single sheets being treated are conveyed.

[0033] According to a possible embodiment, said wall comprises a quadrangular shaped plate arranged crosswise to said direction of feed of said single sheets.

[0034] According to further aspects of the invention, said feed means and said pick up means comprise pairs of driving rollers and counter rollers arranged crosswise to said direction of feed of single sheets to be treated, upstream and downstream of said chamber, respectively.

[0035] In particular, said drive rollers have a variable section and comprise ridges and troughs alternated with each other, and said machine comprises covering surfaces provided with openings from which said ridges protrude so that they can cooperate with said counter rollers.

[0036] In a preferred variant of the invention, said at least one electrode is coated with a ceramic material and said counter electrode is made of aluminium alloy.

[0037] The invention has important advantages: management of the air flows, drawn through the vacuum pressure chamber that produces said counter electrode, allows optimization of the corona treatment process on thin single sheets.

[0038] The air flows, drawn both through the holes of the wall of the chamber and through the two opposite lateral openings, allow the single sheets being treated to be held in place, as well as cooling of the wall of the chamber that acts as counter electrode and suction of at least part of the ozone generated by the electric discharge.

[0039] The vacuum pressure that is created in the chamber, through suction of air through the holes of the wall of the chamber, maintains the single sheets adhering to the counter electrode, even when high operating speeds (greater than 60 m / min) are reached.

[0040] The air flows generated and the heat dissipating fins which extend from the wall are able to maintain the counter electrode in contact with the single sheets at a low temperature, preventing damage to said sheets, and preventing expansion of the counter electrode which would cause misalignment of the air gap.

[0041] The two different air inlet channels, both the holes on the wall and the opposite lateral openings of the chamber, allow cooling of the counter electrode regardless of the size of the sheet being treated: for small sheets, the air passes both through the holes on the wall and through the lateral openings; for sheets the size of the whole of the counter electrode, the air passes above all through the opposite lateral openings preventing the suction effect from retaining the sheets and jamming the machine.

[0042] The perforated baffle interposed between said wall and said suction mouth allows uniform suction through the holes of the wall. Advantageously, the gaps of the baffle with air passage area decreasing toward the suction mouth to which the suction means are connected ensure a uniform suction force on the single sheets and constant cooling of the wall that forms the counter electrode.

[0043] Thanks to the invention it is possible to treat sheets made of different materials (conductive and non-conductive), with thicknesses within a wide range of thicknesses (50 micron - 1 mm), with variable speeds ranging from 1 m / min to 150 m / min.

[0044] Brief description of the drawings

[0045] The advantages of the invention will be more apparent hereunder, in the description of preferred embodiments provided by way of nonlimiting example and with the aid of the figures, wherein:

[0046] - Fig. 1 illustrates, schematically and in longitudinal section, a corona treatment machine on single sheets according to a first possible variant of the invention;

[0047] - Figs. 2 and 3 illustrate, schematically and in longitudinal section and in cross section, respectively, a corona treatment machine on single sheets according to a possible variant of the invention;

[0048] - Fig. 4 illustrates, in a top plan view, a detail of Fig. 3;

[0049] - Figs. 5 and 6 illustrate, schematically and in longitudinal section and in cross section, respectively, a corona treatment machine on single sheets according to a further possible variant of the invention;

[0050] - Fig. 7 illustrates, in a top plan view, a detail of Fig. 6;

[0051] - Fig. 8 illustrates, in an axonometric view from above, the lower portion of a corona treatment machine according to the invention;

[0052] - Fig. 9 illustrates a detail of the view of Fig. 8.

[0053] Detailed description of preferred embodiments of the invention

[0054] With reference to Fig. 1 , there is illustrated, schematically, a machine 1 for carrying out corona treatment on thin single sheets F, fed in sequence along a processing line, comprising:

[0055] - a plurality of electrodes 2 coated with insulating material, connected to an electric generator and to a voltage step-up transformer according to the prior art;

[0056] - an electrode carrying upper exhaust hood 3, adapted to remove the ozone produced by the electric discharge generated by the corona treatment;

[0057] - a counter electrode 4 made of conductive material and earthed, arranged facing said electrodes 2, so as to delimit therewith a treatment space (air gap) into which said single sheets F are fed;

[0058] - feed means 5, 6 of single sheets F to be treated along a direction of feed x toward said treatment space comprised between said electrodes 2 and said counter electrode 4;

[0059] - pick up means 7, 8 of treated single sheets F from said treatment space.

[0060] Said upper exhaust hood 3 comprises a suction mouth 20 connected to a high pressure centrifugal fan, and valve means (not illustrated) adapted to throttle the flow rate of the air flow drawn in.

[0061] Said counter electrode 4 comprises a chamber 9, in which a vacuum is generated by air suction means (not illustrated), for example comprising a high pressure centrifugal fan.

[0062] Said chamber 9 comprises an upper wall 10, adapted to act as surface for conveying said single sheets F along said direction of feed, underneath said electrodes 2.

[0063] In the variant illustrated, said wall 10 comprises a quadrangular shaped plate arranged crosswise to said direction of feed x of said single sheets F.

[0064] Said wall 10 comprises a plurality of holes 11 through which external air is drawn in, by means of said suction means, to generate the vacuum pressure in said chamber 9.

[0065] The suction of air through said holes 11 retains the single sheet F, during its passage through the air gap, advantageously perfectly adhering to said wall 10, i.e., to said counter electrode 4, while it is hit by the treatment discharges and subjected to the suction generated by the exhaust hood 3.

[0066] Said vacuum pressure chamber 9 comprises a lower suction mouth 12, operatively connected to said suction means. Said suction mouth 12 is arranged centrally with respect to said chamber 9.

[0067] Said suction mouth 12 comprises valve means (not illustrated) adapted to throttle the flow rate of the air flow drawn through said holes 11 .

[0068] Said suction means comprise a high pressure centrifugal fan with a flow rate greater than the suction flow rate of the upper exhaust hood 3.

[0069] With particular reference to Figs. 2, 3 and 4, there is illustrated a corona treatment machine 1 as described above, where said vacuum pressure chamber 9 further comprises a perforated baffle 13, interposed between said wall 10 and said suction mouth 12, so as to divide said chamber 9 in two.

[0070] Said baffle 13 comprises a plurality of gaps 14 for the passage of air drawn through the holes 11 of the wall toward said suction mouth 12.

[0071] Said gaps 14 have an air passage area decreasing toward said centrally arranged suction mouth 12 (Fig. 4).

[0072] With particular reference to Figs. 5, 6 and 7, there is illustrated a corona treatment machine 1 where the suction mouth 12 is arranged laterally with respect to said chamber 9. Also in this variant, said chamber 9 comprises a baffle 13 provided with gaps 14 with air passage area decreasing gradually toward the lateral suction mouth 12 (Fig. 7).

[0073] As is apparent from the schematic views of Figs. 3 and 6, from the axonometric view of Fig. 8 and from the detail of Fig. 9, said vacuum pressure chamber 9 comprises a first 15 and a second 16 opening; said openings 15, 16 are arranged on opposite lateral walls of said chamber 9, symmetrically with respect to said direction of feed x of said single sheets F being treated.

[0074] Said opposite openings 15, 16 help to cool the counter electrode 4 when the single sheets F being treated have a width such that they block all the holes 11 of the wall 10, and also prevent the suction effect that could block the single sheet F under the electrodes 2.

[0075] Moreover, to hep to cool the counter electrode 4, said wall 10 comprises a plurality of heat dissipating fins 17 which extend, inside said chamber 9, from a face thereof opposite the face on which said single sheets F being treated are conveyed (Fig. 9).

[0076] With particular reference to the diagrams of Figs. 1 , 2 and 5 and to Fig. 8, said feed means and said pick up means for said single sheets F comprise pairs 5, 6 and 7, 8 of driving rollers and idle counter rollers adapted to grip said single sheets F entering and exiting from the air gap comprised between electrodes 2 and counter electrode 4.

[0077] Said pairs 5, 6 and 7, 8 of driving rollers and counter rollers are arranged crosswise to said direction of feed x di single sheets F to be treated, upstream and downstream of said wall 10, respectively.

[0078] Said driving rollers 5, 7 have a variable section and comprise ridges 5a, 7a and troughs alternated with each other, and said machine 1 comprises, before and after said wall 10, covering surfaces 18 provided with openings 19 from which said ridges 5a, 7a protrude so that they can cooperate with the corresponding upper counter rollers 6, 8.

[0079] Said electrodes 2 are coated with ceramic, but it is clear that the insulating material of the electrodes can be any and is not limited to the ceramic mentioned as preferred.

[0080] Said counter electrode 4 is made of aluminium alloy, but it too could be made of any conductive material.

[0081] The invention makes it possible to treat single sheets F made of different materials, such as paper, laminated paper or coated paper, sheets of plastic material, sheets of aluminium, all with thicknesses ranging from 50-1000 micron, also at high speeds, up to 150 m / min.

[0082] The invention can be modulated according to the operating speed and to the power density to treat a given material: several electrodes can be placed in series, with related electrode carrying exhaust hoods and several counter electrode plates, as well as several systems for conveying single sheets.

Claims

CLAIMS1 ) Corona treatment machine (1 ) on single sheets (F) comprising:- a high frequency generator;- a voltage step-up transformer;- at least one electrode (2) coated with insulating material arranged in an exhaust hood (3);- a counter electrode (4) made of conductive material and earthed;- feed means (5, 6) of single sheets to be treated along a direction of feed (x) toward a space comprised between said at least one electrode (2) and said counter electrode (3);- pick up means (7, 8) of single treated sheets, characterized in that said counter electrode (4) comprises a chamber (9), placed under vacuum pressure by air suction means, where said chamber (9) comprises:- a wall (10) provided with a plurality of holes (1 1 ) adapted to act as surface for conveying said single sheets (F) underneath said at least one electrode (2);- a suction mouth (12) operatively connected to said suction means, where the vacuum pressure of said chamber (9) is obtained by means of the suction of air through said holes (11 ) so as to maintain the single sheets (F) being treated adhering to said wall (10).2) Corona treatment machine (1 ) according to claim 1 , characterizedin that said vacuum pressure chamber (9) comprises a baffle (13) interposed between said wall (10) and said suction mouth (12) so as to divide said chamber (9) in two, where said baffle (13) comprises a plurality of gaps (14) with air passage area decreasing toward said suction mouth (12).3) Corona treatment machine (1 ) according to claim 1 , characterized in that said suction mouth (12) is arranged centrally or laterally with respect to said chamber (9).4) Corona treatment machine (1 ) according to claim 3, characterized in that said suction mouth (12) comprises valve means adapted to throttle the flow rate of the air flow drawn through said holes (11 ).5) Corona treatment machine (1 ) according to claim 1 , characterized in that said vacuum pressure chamber (9) comprises a first (15) and a second (16) opening, arranged on opposite walls, symmetrically with respect to said direction of feed (x) of said single sheets (F) being treated.6) Corona treatment machine (1 ) according to claim 1 , characterized in that said wall (10) comprises a plurality of heat dissipating fins (17) which extend, inside said chamber (9), from a face thereof opposite the face on which said single sheets (F) being treated are conveyed.7) Corona treatment machine (1 ) according to claim 1 , characterized in that said wall (10) comprises a quadrangular shaped plate arranged crosswise to said direction of feed (x) of said single sheets (F).8) Corona treatment machine (1 ) according to claim 1 , characterized in that said feed means and said pick up means comprise pairs ofdriving rollers (5, 7) and counter rollers (6, 8) arranged crosswise to said direction of feed (x) of single sheets (F) to be treated, upstream and downstream of said chamber (9), respectively.9) Corona treatment machine (1 ) according to claim 8, characterized in that said drive rollers (5, 7) have a variable section and comprise ridges (5a, 7a) and troughs alternated with each other, and said machine (1 ) comprises covering surfaces (18) provided with openings (19) from which said ridges (5a, 7a) protrude so that they can cooperate with said counter rollers (6, 8).10) Corona treatment machine (1 ) according to claim 1 , characterized in that said at least one electrode (2) is coated with a ceramic material and said counter electrode (4) is made of aluminium alloy.

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