APPARATUS FOR PROVIDING AN ELECTROSTATIC AID TO A ROTOGRAVURE PRINTING

Abstract

 An electrostatic assistance apparatus for rotogravure printing comprising a pressing cylinder (1), antistatic systems for eliminating the static electricity, and an electrostatic transmitter (11, 111, 207) for the electrostatic charging of the pressing cylinder (1); the apparatus is characterized in that it comprises a generator (8, 108, 208) powered with low voltage, advantageously 24Vdc.

Description

[0001] The present invention relates to an electrostatic assistance apparatus for rotogravure printing.

[0002] Rotogravure printing or rotogravure is a direct and rotary printing.

[0003] The ink is transferred to the material to be printed through a modular system of cells of various depths of the printing cylinder.

[0004] The printing cylinder directly releases the ink to the material to be printed, pressed by an idle roll covered with a thick layer of rubber.

[0005] The printing cylinder consists of a metal roll sometimes covered by a thin layer of copper on which the subject to be printed is engraved. The engraved areas are inked by an inkwell, sometimes provided with an inking roll, and the excess ink is removed by a blade.

[0006] After this step, the engraved roll discharges the ink directly onto the medium to be printed.

[0007] Liquid rotogravure ink generally consists of solvents or water-based inks.

[0008] "Missing dots" are one of the most common quality problems during rotogravure printing processes.

[0009] A system commonly used in an attempt to eliminate such a problem is that of increasing the pressure of the pressing roll.

[0010] Electrostatic assistance apparatuses currently used operate with a 230V mains power supply and comprise an external high-voltage generator connected to the charge devices by means of high-voltage cables.

[0011] High-voltage cables close to the cylinders and the other printing members are subject to possible deterioration and damage which may be, and in fact have been, the cause of fire.

[0012] It is a task of the present invention to make an electrostatic assistance apparatus for rotogravure printing which ensures increased safety while avoiding the use of high-voltage cables close to the pressing cylinders.

[0013] Within the scope of this task, it is an object of the invention to provide an apparatus which allows a consumption reduction with respect to traditional apparatuses.

[0014] It is a further object of the present invention to provide an electrostatic assistance apparatus for rotogravure printing which ensures a complete and accurate transfer of the ink to the materials to be printed, also at higher production speeds, without resorting to excessive pressure of the pressing cylinder.

[0015] This and other objects, which shall become apparent below, are achieved by an electrostatic assistance apparatus for rotogravure printing comprising a pressing cylinder, antistatic systems for eliminating the static electricity, and an electrostatic transmitter to electrostatically charge the pressing cylinder; said apparatus comprising a generator body powered by low voltage.

[0016] Moreover, this and other objects are achieved by an electrostatic assistance apparatus for rotogravure printing comprising a pressing cylinder, antistatic systems for eliminating the static electricity, and an electrostatic transmitter to electrostatically charge the pressing cylinder; said apparatus comprising a generator body powered by low voltage, wherein the generator body is arranged inside the apparatus and is configured to generate, inside the apparatus, a high voltage required to electrostatically charge the pressing cylinder.

[0017] According to the present invention, the generator body is powered with 24Vdc.

[0018] Further features and advantages of the object of the present invention shall become more apparent from a discussion of the description of a preferred, but not exclusive, embodiment of the invention, disclosed by way of non-limiting example, with the assistance of the accompanying drawings, wherein:

figure 1 is a elevation view of a pressing cylinder provided with the direct charge apparatus, according to the present invention;

figure 2 is a partial sectional elevation view of the pressing cylinder provided with the direct charge apparatus of the present invention;

figure 3 is a partial cut-out perspective view of the cylinder in the preceding drawings;

figure 4 is an enlarged cut-out view of a detail of the preceding figure;

figure 5 is a partial cut-out perspective view of the cylinder in the preceding figures;

figure 6 is an enlarged cut-out view of a detail of the preceding figure;

figure 7 is a elevation view of a pressing cylinder provided with the direct charge apparatus, according to a further aspect of the invention;

figure 8 is a partial sectional elevation view of the pressing cylinder in the preceding figure;

figure 9 is a partial cut-out perspective view of the cylinder in figures 7 and 8;

figure 10 is an enlarged cut-out view of a detail of the preceding figure;

figure 11 is a perspective view of the data transmission circuit, in annular shape;

figure 12 diagrammatically shows the ink in a rotogravure cell under the effect of the electric field created by the apparatus of the present invention;

figure 13 is a perspective view of a pressing cylinder provided with the charge apparatus with bar (top loading), according to a further aspect of the invention;

figure 14 is a side elevation view of the cylinder in the preceding drawing;

figure 15 is a front elevation view of the bar of the apparatus in figure 13;

figure 16 is a perspective view of the bar of the apparatus in figure 13;

figure 17 is a perspective view of the data transmission circuit, in linear shape.

[0019] With particular reference to the numeric references of the aforesaid drawings, the electrostatic assistance apparatus for rotogravure printing according to the invention, for example of the direct charge type or top loading type, is an electrostatic assistance system for rotogravure printing of materials such as paper, cardboard and plastic film, which ensures the complete and accurate transfer of the ink to the material to be printed by means of polarization of the ink.

[0020] The electrostatic assistance apparatus for rotogravure printing comprises a pressing cylinder 1, antistatic systems for eliminating the static electricity, an electrostatic transmitter 11, 111, 207 for the electrostatic charging of the pressing cylinder 1; a generator body 8, 108, 208 powered with low voltage, in which the generator body 8, 108, 208 is arranged inside the apparatus and is configured to generate, inside the apparatus, a high voltage required in particular by the electrostatic transmitter to electrostatically charge the pressing cylinder 1.

[0021] The apparatus is installed in the printing unit of rotogravure machines.

[0022] Each printing unit comprises an electrostatic assistance apparatus for printing as herein described, a printing cylinder, a dye holder pan and a blade.

[0023] The printing cylinder is a metal roll sometimes covered by a thin layer of copper on which the subject to be printed is engraved.

[0024] The pressing cylinder 1, or sleeve, is an idle roll covered with a thick layer of rubber.

[0025] The dye holder pan is an ink container where the printing cylinder draws the color.

[0026] The blade is a blade which scrapes the excess ink on the printing cylinder.

[0027] As mentioned above, the apparatus of the present invention comprises antistatic systems for eliminating the static electricity, and an electrostatic transmitter 11, 111, 207 for the electrostatic charging of the pressing cylinder.

[0028] The electrostatic transmitter 11, 111, 207 may be of two types, i.e. of a first type which performs the "contact" or "direct charge" electrostatic charging of the pressing cylinder, as with the electrostatic transmitters 11 and 111 in figures 1 to 11, or of a second type which performs the "non-contact" or "top loading" charging of the pressing cylinder, as with transmitter 207 in figures 12 to 17.

[0029] The electrostatic transmitter 11, 111, 207 is configured to transmit and distribute a high-voltage electrostatic charge generated by the generator body 8, 108, onto the surface of the pressing roll 1.

[0030] According to a first aspect of the invention, the antistatic systems comprise 24V antistatic bars having a high deionizing power (manufactured by ACE) for eliminating the static electricity. The electrostatic transmitter performs the "contact" or "non-contact" electrostatic charging of the pressing cylinder always at 24V.

[0031] Paper, cardboard or film material is neutralized by a first of said antistatic bars having a high deionizing effect at the inlet of the printing unit in order to eliminate any electrostatic charge present therein.

[0032] Then, the electrostatic transmitter 11 for the electrostatic charging of the pressing cylinder 1 creates a homogeneous and intense electric field in the conductive and semiconductive layer of the latter through direct contact with the core of the pressing roll 1.

[0033] The electric field is then transferred from the pressing cylinder 1 to the printing cylinder so as to ensure a particular polarization of the ink in the cells and accordingly, a perfect transfer thereof to the paper or film to be printed.

[0034] A second bar of said antistatic bars having a high deionizing effect is arranged at the outlet of the printing unit so as to completely eliminate the static electricity present on the printed material.

[0035] Figure 12 diagrammatically shows the ink in a rotogravure cell under the effect of the electric field created by the apparatus of the present invention.

[0036] The variation in shape of the surface of the ink causes part of the ink to move onto the surface of the cylinder so as to ensure a perfect contact with the substrate.

[0037] With particular reference to figures 1 to 11, the apparatus according to the present invention comprises a rotary joint 15, 115 directly coupled to a ferrous part of the pressing cylinder 1.

[0038] The aim of this embodiment is to transmit a high-voltage charge to the rubber part of the pressing cylinder, called "sleeve", by means of the rotary joint 15, 115.

[0039] This rotary joint 15, 115 may be made in at least two embodiments.

[0040] According to a fist embodiment shown in figures 1 to 6, the rotary joint 15 comprises a fixed outer part 5 and a rotating inner part 8' rotationally engaged in the fixed outer part 5.

[0041] According to this embodiment, the rotary joint 15, preferably the rotating inner part 8', is directly coupled to the inner part, or work table, of the pressing cylinder arranged inside the pressing cylinder 1, preferably behind the printing unit.

[0042] In a second embodiment shown in figures 7 to 10, the rotary joint 115 comprises a fixed outer part 105 and a rotating inner part 108' rotationally engaged in the fixed outer part 105.

[0043] According to this second embodiment, the rotary joint 115, preferably the rotating inner part 108', is directly coupled to an end of the axis of the pressing cylinder arranged externally to the pressing cylinder 1, preferably behind the printing unit.

[0044] In the first embodiment, shown in figures 1 to 6, joint 15, preferably the rotating inner part 8', is integral with the pressing cylinder 1 inside the printing unit; the insulation of the supports 12 of the pressing cylinder 1 is not required for this type of application.

[0045] In the second embodiment, shown in figures 7 to 10, joint 115, preferably the rotating inner part 108', is integral with the pressing cylinder 1 and is installed outside the printing unit; the insulation of the supports 112 of the pressing cylinder 1 is required for this type of application.

[0046] With particular reference to figures 1 to 6, joint 15, preferably the rotating inner part 8' of the joint, is integrally installed with the central body 18, or table, of the pressing cylinder 1 where a rubber tube, called sleeve, is fitted, which comprises an insulating part 2, or insulating layer, in contact with the ferrous part 10 of the pressing cylinder 1, a second conductive part 3, or conductive layer, made of conductive material positioned between the insulating part 2 and an outer part 4, or outer layer, made of semiconductive material. According to one embodiment, the outer layer comprises conductive material.

[0047] The conductive part 3 of the sleeve has a contact point 33 forming a conductive ring 19 inside the insulating tube 2 to allow an electric contact with electrical transmission points of the joint.

[0048] In other words, the pressing cylinder 1 comprises an insulating layer 2 fitted on the central body 18, a conductive layer 3 fitted on the insulating layer 2, an outer semiconductive layer 4 fitted on the conductive layer 3.

[0049] As shown in figure 5, the conductive layer 3 comprises at least one contact point 33 adapted to form an electric contact between transmitter 11 and the conductive layer 3 through the insulating layer 2.

[0050] For example, the conductive layer 3 comprises a conductive ring comprising said at least one contact point 33, and transmitter 11 comprises a pin or contact cable 19 in electric contact with the conductive ring.

[0051] The direct charge rotary joint 15 is integrally installed with the inner part of the pressing cylinder and consists of a fixed part 5 formed by a non-rotary outer ring made of plastic material blocked behind the printing unit.

[0052] Advantageously, the direct charge rotary joint 15 has a rotating inner part 8' integrally installed with the inner part of the pressing cylinder 1 and a fixed outer part 5 formed like a non-rotating outer ring, for example made of plastic material.

[0053] A supply connector 6 for the electrical connection of the direct charge joint is positioned on the fixed part 5.

[0054] According to an embodiment, such a connector 6 is configured to be powered by low voltage, preferably 24Vdc.

[0055] Two bearings 7 are installed in the fixed part 5 for the mechanical rotation of the inner part 8' with respect to the fixed part 5 and for the transmission of the 24Vdc power supply from the fixed part 5 to the inner part 8', i.e. to the generator body 8 of the direct charge joint 15.

[0056] The inner part 8' indeed accommodates, or is, a generator body 8 powered by low voltage, e.g. 24Vdc, adapted to generate a high-voltage charge adapted to be transferred to transmitter 11, which is adapted to distribute such a high-voltage charge to the surface of the pressing cylinder 1.

[0057] The inner part 8', i.e. the generator body 8, is made of plastic material and is integral with and insulated with respect to the ferrous part 10 of the pressing cylinder. According to an embodiment, the inner part 8', i.e. the generator body 8, comprises plastic material and is integral with and insulated with respect to the ferrous part 10 of the pressing cylinder.

[0058] More specifically, the inner part 8' comprises a plastic material casing which accommodates the generator body 8 and is integral with and insulated with respect to the ferrous part 10 of the pressing cylinder.

[0059] There are a data transmission circuit 9 and an electronic generator 14 inside the generator body 8.

[0060] In other words, the generator body 8 is arranged in the inner part 8' of the direct charge joint 15, which is integrally installed with the central body, or table, of the pressing cylinder 1.

[0061] Therefore, the generator body 8 is arranged inside the electrostatic assistance apparatus. Thereby, it is avoided to arrange the generator body 8 external to and at a distance from the apparatus. The generator body 8 is powered by low voltage, as mentioned above, therefore the electric cables leading to the apparatus are powered by low voltage, thus avoiding the aforesaid risks of fire.

[0062] As is clearly shown in the embodiments in figures 1 to 6, the generator body 8 is directly associated with the electrostatic transmitter 11, preferably is integrated in the electrostatic transmitter 11.

[0063] The apparatus comprises a rotary joint 15, said rotary joint 15 comprising a fixed outer part 5 and a rotating inner part 8' pivotally engaged in said fixed part 5, said rotating inner part 8' being integral with said pressing cylinder 1 and comprising said generator body 8, said generator body 8 being in electric contact with said electrostatic transmitter 11 arranged in said pressing cylinder 1.

[0064] The annular-shaped data transmission circuit 9 is diagrammatically shown in figure 11.

[0065] The data transmission circuit 9 receives the 24Vdc power supply by means of the two bearings 7 and manages, transmits and adjusts current and voltage parameters for the correct operation of the electronic generator, moreover it transmits all the control and operating parameters to an external unit.

[0066] The electronic generator 14 receives the data from the transmission circuit 9 and transfers, through the current and voltage transmission point 33, a high-voltage charge into the conductive layer 3 and into the semiconductive layer 4 of the pressing cylinder 1.

[0067] In other words, transmitter 11 is electrically connected both to the generator body 8 and to the outer surface of the pressing cylinder 1, preferably to the conductive layer 3 and to the semiconductive layer 4, by means of the current and voltage transmission point 33.

[0068] In other words, transmitter 11 receives the high-voltage charge from the generator body 8 and transfers it to the outer surface of the pressing cylinder 1, preferably to the conductive layer 3 and to the semiconductive layer 4, by means of the current and voltage transmission point 33.

[0069] In this embodiment, the joint does not transfer any high-voltage charge to the ferrous part 10 of the pressing cylinder 1, the same indeed is completely insulated, as described above.

[0070] Here, the insulation of the rotating supports 12 of the pressing cylinder is not required.

[0071] With particular reference to figures 7 to 10, referring to the second embodiment, the joint 115, preferably the rotating inner part 108' of the joint 115, is integrally installed with the rotating axis 100 of the pressing cylinder 1 and consists of an insulating part in contact with the ferrous part 10 of the pressing cylinder 1, which in turn is arranged externally behind the printing unit.

[0072] The rotary joint 115 comprises a fixed outer part 105 and a rotating inner part 108' pivotally connected to the fixed outer part 105. The rotating inner part 108' may comprise, for example as shown in figures 9 and 10, the generator body 108 and transmitter 111, said transmitter 111 being electrically connected to the generator body 108.

[0073] A low-voltage supply connector 106 for the low-voltage power supply of the generator body 108 is positioned on the fixed outer part 105.

[0074] The rotating inner part 108' is fixed to the rotation axis 100 of the pressing cylinder 1.

[0075] Transmitter 111 is electrically connected to an ferrous part 10 of the pressing cylinder so as to transfer the high-voltage electric charge generated by the generator body 108 to the surface of the pressing cylinder 1.

[0076] The direct charge rotary joint 115 is integrally installed with axis 100 of the pressing cylinder 1 and consists of a fixed part 105, formed by a non-rotary outer ring made of plastic material blocked behind the printing unit, and positioned on it is a supply connector 106 for the electrical connection of the direct charge joint.

[0077] In other words, a low-voltage supply connector 106 adapted to supply the generator body 108' with low voltage is fixed on the fixed outer part 105.

[0078] Two bearings 107 for the mechanical rotation and for the transmission of the 24Vdc power supply to the inner part 108, i.e. the generator body, of the direct charge joint are installed on the fixed part 105.

[0079] In other words, the rotary joint 115 comprises bearings 107, preferably two, interposed between the fixed outer part 105 and the rotating inner part 108', and they are arranged and configured to form an electric contact between the low-voltage supply connector 106 and the generator body 108.

[0080] The inner part 108', i.e. the generator body 108, is made of plastic material and is integral with the ferrous part 10 of the pressing cylinder 1. According to one embodiment, the inner part 108', i.e. the generator body 108, comprises plastic material and is integral with the ferrous part 10 of the pressing cylinder 1.

[0081] Preferably, the inner part 108' has a casing made of plastic material which houses the generator body 108, said casing being integral with the ferrous part 10 of the pressing cylinder 1.

[0082] The generator body 108 comprises a data transmission circuit 109 and an electronic generator 114 therein.

[0083] The data transmission circuit 109 receives the 24Vdc power supply by means of the two bearings 107 and manages, transmits and adjusts the current and voltage parameters for the correct operation of the electronic generator 114, moreover it transmits all the control parameters to an external unit.

[0084] The electronic generator 114 is applied mechanically and is directly connected to a joint connecting pin 100'.

[0085] The joint connecting pin 100' is keyed to the axis of the pressing roller 100 by means of threading or by means of joint in the joint connecting point 113, so as to transmit a high-voltage charge to the whole pressing cylinder 1.

[0086] In other words, transmitter 111 is fixed to, and is in electric contact with, the joint connecting pin 100', which is fixed to, and is in electric contact with, the rotating axis 100 of the pressing cylinder 1, and the rotating axis 100 is fixed to, and is in electric contact with, the ferrous part 10 of the pressing cylinder 1.

[0087] Thereby, transmitter 111 transmits the high-voltage electric charge generated by the generator body 108 to the outer surface of the pressing cylinder 1 by means of the joint connecting pin 100', the rotating axis 100 of the pressing cylinder 1, and the ferrous part 10 of the pressing cylinder 1.

[0088] In this case, the pressing cylinder 1 is supported by rotating supports 112 provided with electric insulation.

[0089] The pressing cylinder 1 in turn transfers a high-voltage charge into the conductive layer 3 and into the semiconductive layer 4 of the pressing cylinder 1.

[0090] Here, since the whole body of the pressing cylinder receives a high-voltage charge, there is a need to insulate the rotating supports 112 of the pressing cylinder 1.

[0091] In other words, also in the second embodiment shown in figures 7 to 10, the generator body 108 is in the inner part 108' of the direct charge joint, which is integrally installed with the rotating axis 100 of the pressing cylinder 1.

[0092] In other words, the generator body 108 is arranged inside the electrostatic assistance apparatus. This avoids arranging the generator body external to and at a distance from the apparatus.

[0093] The generator body 108 is powered by low voltage, as mentioned above, therefore the electric cables leading to the apparatus are powered by low voltage, thus avoiding the aforesaid risks of fire.

[0094] Accordingly, as is clearly shown in figures 7 to 10, also in this second embodiment, the generator body 108 is directly associated with the electrostatic transmitter 111, preferably is integrated in the electrostatic transmitter 111.

[0095] According to the second embodiment therefore, the apparatus comprises a rotary joint 115, said rotary joint 115 comprising a fixed outer part 105 and a rotating inner part 108' pivotally engaged in said fixed part 105, said rotating inner part 108' being integral with said pressing cylinder 1 and comprising said generator body 108 and said transmitter 111, said generator body 108 being in electric contact with said electrostatic transmitter 111 arranged in said rotating inner part 108'.

[0096] According to a further aspect of the invention, the electrostatic transmitter performs a "non-contact" electrostatic charging with the pressing cylinder.

[0097] Similarly to the "contact" system, the paper, cardboard or film material is neutralized by the first antistatic bar having a high deionizing effect at the inlet of the printing element in order to eliminate any electrostatic charge present therein.

[0098] Then, the electrostatic transmitter 207 creates a homogeneous and intense electric field in the semiconductive layer of the latter through non-direct contact on the outer surface of the pressing cylinder 1.

[0099] The electric field is then transferred from the pressing cylinder 1 to the printing cylinder so as to ensure a particular polarization of the ink in the cells of the printing cylinder and accordingly, a perfect transfer thereof to the paper or film to be printed.

[0100] A second antistatic bar having a high deionizing effect is arranged at the outlet of the printing element so as to completely eliminate the static electricity present on the printed substrate.

[0101] According to this further embodiment, shown in figures 13 to 17, the apparatus comprises a bar 200 for transmitting electrostatic energy to the outer and semiconductive surface of the pressing cylinder 1.

[0102] Such a bar 200 is arranged at a minimum distance from the surface of the pressing cylinder 1, and not in contact therewith, preferably is arranged parallel to the axis of the pressing cylinder 1. Bar 200 is fixed while the pressing cylinder 1 is rotatable about the axis thereof.

[0103] Bar 200 comprises the generator body 208 therein, powered by low voltage for generating a high voltage required for the operation of the apparatus.

[0104] Bar 200 further comprises an electrostatic transmitter 207 therein, for the electrostatic charging of the pressing cylinder 1.

[0105] The bar, in particular the electrostatic transmitter 207, has electrodes for transmitting current and voltage to the pressing cylinder 1 not directly in contact with the outer surface of the pressing cylinder itself.

[0106] The aim of this application is to transmit a high-voltage charge to the rubber part (sleeve) of the pressing cylinder 1.

[0107] Bar 200 consists, for example, of a "U"-shaped profile constructed with special resins and specific physical features.

[0108] Bar 200 comprises current emitting electrodes 207 of the transmitter and an electronic voltage/current generator 209 therein. That is, bar 200 comprises both the generator body 208 and the transmitter 207 therein.

[0109] Both the electrodes and the generator body are incorporated in resin.

[0110] A connector 206 for the low-voltage power supply, preferably 24Vdc, is positioned outside the profile.

[0111] The position of the 24Vdc supply connector 206 may vary according to the specific needs.

[0112] Bar 200 belongs to the apparatus and the generator body 207 is inside the bar, therefore the generator body is arranged inside the electrostatic assistance apparatus for rotogravure printing also in this third embodiment.

[0113] Both the generator body 208 and the electrostatic transmitter 207 are associated directly or integrally with each other also in this third embodiment since they are assembled together in the same bar 200 which is inside the apparatus. It has been practically ascertained how the invention achieves the preset task and objects.

[0114] Indeed, an electrostatic assistance apparatus for rotogravure printing powered with 24Vdc low voltage has been made, thus avoiding the use of high-voltage cables which instead are present on traditional apparatuses for transferring the current from an outer generator to the printing members.

[0115] According to the present invention, the high voltage required by the electrostatic assistance system is generated inside the apparatus by the electronic generator.

[0116] In other words, the generator body 8, 108, 208 is arranged inside the aforesaid apparatus in each of the embodiments described above. This allows the apparatus to be powered by low voltage, while the high voltage is generated inside the apparatus. Accordingly, the electrical cables leading to the apparatus are powered by low voltage, thus avoiding the risks mentioned above.

[0117] Obviously, any materials and dimensions may be used, according to the needs.

Claims

1. An electrostatic assistance apparatus for rotogravure printing, comprising a pressing cylinder (1), antistatic systems for eliminating the static electricity, and an electrostatic transmitter (11, 111, 207) for electrostatically charging the pressing cylinder (1); said apparatus being characterized in that it comprises a generator body (8, 108, 208) powered by low voltage, wherein the generator body (8, 108, 208) is arranged inside the apparatus and is configured to generate, inside the apparatus, a high voltage required to electrostatically charge the pressing cylinder (1).

2. The apparatus according to claim 1, wherein said low voltage is 24Vdc.

3. The apparatus according to at least one preceding claim, characterized in that said antistatic systems comprise a first antistatic bar having a high deionizing effect arranged at the inlet of a printing unit and which neutralizes the material to be printed in order to eliminate any electrostatic charge therein; said electrostatic transmitter (11, 111, 207) generating a homogeneous and intense electric field in a conductive and semiconductive layer of said pressing cylinder (1); said electric field then being transferred from the pressing cylinder (1) to a printing cylinder so as to perform a polarization of the ink present in cells of the printing cylinder and then a transfer of the ink to the paper or film to be printed; said antistatic systems comprising a second antistatic bar having a high deionizing effect, arranged at the outlet of the printing unit so as to completely eliminate the static electricity on the printed material.

4. The apparatus according to claim 3, characterized in that said electrostatic transmitter (11, 111) performs the electrostatic charging in contact with the pressing cylinder (1); said apparatus comprising a rotary joint (15, 115) directly coupled to a ferrous part (10, 100) of the pressing cylinder (1) and adapted to transmit a high-voltage charge to the rubber part (4) of the pressing cylinder (1).

5. The apparatus according to claim 4, characterized in that said rotary joint (15) is directly coupled to the inner part (10) of the pressing cylinder (1), which is arranged internally behind the printing unit.

6. The apparatus according to claim 3, characterized in that said rotary joint (15) is integrally installed with the central body or table of the pressing cylinder (1) where a rubber tube is fitted which comprises an insulating part (2) in contact with a ferrous part (10) of the pressing cylinder (1), a second conductive part (3) made of conductive material positioned between the insulating part (2), and an outer part (4) made of semiconductive material; wherein said conductive part (3) has a contact point (33) forming a conductive ring inside the insulating tube to allow the electric contact with electrical transmission points of the rotary joint (15); wherein said direct charge rotary joint (15) comprises a fixed part (5) formed by a non-rotary outer ring made of plastic material blocked behind the printing unit; wherein a supply connector (6) for the electrical connection of the direct charge joint (15) is positioned on the fixed part (5); wherein two bearings (7) for the mechanical rotation and for the transmission of the power supply to the inner part (8') are installed on the fixed part (5); wherein the inner part (8') is integral with and insulated with respect to the ferrous part (10) of the pressing cylinder (1); wherein there is a data transmission circuit (9) and an electronic generator (14) inside the generator body (8); wherein the data transmission circuit (9) receives the power supply by means of said bearings (7) and manages, transmits and adjusts the current and voltage parameters for the operation of the electronic generator, moreover it transmits all the control and operating parameters to an external unit; wherein the electronic generator (14) receives the data from the transmission circuit and transfers a high-voltage charge into the conductive layer (3) and into the semiconductive layer (4) of the pressing cylinder (1) through the current and voltage transmission point.

7. The apparatus according to claim 1 or 2, wherein said generator body (8, 108, 208) is directly, or integrally, associated with said electrostatic transmitter (11, 111, 207).

8. The apparatus according to claim 1 or 2 or 7, comprising a rotary joint (15), said rotary joint (15) comprising a fixed outer part (5) and a rotating inner part (8') pivotally engaged in said fixed part (5), said rotating inner part (8') being integral with said pressing cylinder (1) and comprising said generator body (8), said generator body (8) being in electric contact with said electrostatic transmitter (11) arranged in said pressing cylinder (1).

9. The apparatus according to claim 4, characterized in that said rotary joint (115) is directly coupled to an end (113') of the rotating axis (100) of the pressing cylinder (1), which is arranged externally behind the printing unit; said rotary joint (115) being integrally installed with the rotating axis (100) of the pressing cylinder (1) and consisting of an insulating part in contact with the ferrous part (10) of the pressing cylinder (1), which in turn is arranged externally behind the printing unit; said rotary joint (115) comprising a fixed part (105) formed by a non-rotating outer ring blocked behind the printing unit, said fixed part (105) comprising a supply connector (106) for an electrical connection; said fixed part (105) comprising two bearings (107) for the mechanical rotation and for the transmission of the power supply to an inner part (108') of said rotary joint (115), said inner part (108') being integral with the ferrous part (10) of the pressing cylinder (1); said inner part (108') comprising said generator body (108) therein, comprising a data transmission circuit (109) and an electronic generator (114); wherein said data transmission circuit (109) receives the power supply by means of said bearings (107) and manages, transmits and adjusts the current and voltage parameters for the operation of the electronic generator (114), said data transmission circuit (109) being adapted to transmit all the control parameters to an external unit; wherein said electronic generator (114) is applied mechanically and is directly connected to a joint connecting pin (100'); said joint connecting pin (100') being keyed to the pressing roller (10) by means of threading, or by means of a joint, to the joint connecting point (113), and transmitting a high-voltage charge to the whole pressing cylinder (1); wherein said pressing cylinder (1) transfers said high-voltage charge into the conductive layer (3) and into the semiconductive layer (4) of the pressing cylinder (1).

10. The apparatus according to claim 9, characterized in that said pressing cylinder (1) is supported by rotating supports (112) provided with electric insulation.

11. The apparatus according to at least claim 1 or 2 or 7, comprising a rotary joint (115), said rotary joint (115) comprising a fixed outer part (105) and a rotating inner part (108') pivotally engaged in said fixed part (105), said rotating inner part (108') being integral with said pressing cylinder (1) and comprising said generator body (108) and said transmitter (111), said generator body (108) being in electric contact with said electrostatic transmitter (111) arranged in said rotating inner part (108').

12. The apparatus according to claim 1 or 2, characterized in that the electrostatic transmitter performs a non-contact electrostatic charging with the pressing cylinder.

13. The apparatus according to claim 12, characterized in that it comprises a bar (200) for the transmission of electrostatic energy to the outer and semiconductive surface of the pressing cylinder (1), said bar (200) having electrodes for transmitting current and voltage to the pressing cylinder (1) not directly in contact with the outer surface of the pressing cylinder (1); said bar (200) consisting of a "U"-shaped profile and comprising electrodes (207) therein for emitting current and a voltage/current generator (209); said electrodes (207) and said generator (209) being incorporated in resin; a connector (206) for the electric supply being present outside the bar (200).

14. The apparatus according to claim 1 or 2 or 7, comprising a bar (200) arranged at minimum distance from the surface of the pressing cylinder (1) and not in contact therewith, wherein the bar 200 is fixed while the pressing cylinder (1) is rotatable, said bar (200) comprises the generator body (208) therein, powered by low voltage for generating a high voltage required for the operation of the apparatus, and further comprises an electrostatic transmitter (207) therein, for the electrostatically charging the pressing cylinder (1).

Drawing