Method of folding a portion of dielectric sheet material

Abstract: A method of folding a portion (2, 3) of dielectric sheet material, the method including the steps of mating with a support (4) a sheet (5) including the portion (2, 3) for folding; folding the portion (2, 3) onto an outer surface (6) of the support (4); and generating an electrostatic force of attraction between the portion (2, 3) and the outer surface (6) of the support (4).

Description: The present invention relates to a method of folding a portion of dielectric sheet material. The present invention is particularly advantageous for use on overwrapping machines, particularly cellophaning machines for substantially parallelepiped packets, to which the following description refers purely by way of example. On cellophaning machines of the above type, a sheet of transparent synthetic heat-seal material, normally polypropylene, is folded into a U about a respective product comprising a substantially parallelepiped packet, so that two opposite portions of the sheet project beyond the product; the two portions are then folded one on top of the other and onto an outer surface of the product to form a tubular wrapping; and the wrapping is stabilized by heat-sealing the two portions together. On known cellophaning machines, at least a first of said portions is normally folded onto an outer surface of the product by means of a folding element, which moves back and forth with respect to the product to fold the first portion squarely, and is then withdrawn, by moving either the folding element itself or the product, to free the folded first portion and enable the second portion to be folded onto the first, normally by means of a fixed folding element. On known cellophaning machines of the above type, folding the first portion poses serious difficulties, due to the tendency of the folding element, as it withdraws, to partly draw back the folded first portion. Moreover, the first portion must normally be retained by external elements during the time interval between being folded and heat-sealed. US-A-3274302 discloses a method for maintaining a thermoplastic film of dielectric material in contact with a product and in a predetermined position in relation to the product by employing electrostatic forces. In particular, the product is placed between electrodes chargeable to opposite polarities, and the film is placed over the product with its peripheral portions extending beyond the periphery of the product. The application of a potential across the electrodes results in the electrostatic charging of the film to a polarity opposite that of one of the electrodes, to which the peripheral portions of the film are thereby attracted. The product is placed on a support which is also an electrode, then the film is attracted to the support and positions the film on the product. According to the above known method, the film is maintained in a predetermined position in relation to the product by an electrostatic force acting between the peripheral portion of the film and a metal element contacting the product; however, having a metal element contacting the product poses a lot of problems in the modern cellophaning machines of the above type, in which the products, in particular the packets, travels with a substantially continuous and relatively high speed along a folding path. Furthermore, the two aforementioned opposite portions of the sheet, projecting beyond the product after the sheet is folded into a U about the respective product, have substantially no peripheral zones, which can be attracted by a metal element contacting the product for securing the sheet to the product. It is an object of the present invention to provide a method designed to eliminate the aforementioned drawbacks. According to the present invention, there is provided a method of folding portion of dielectric sheet material, the method comprising the steps of mating a sheet including said portion with a product, and folding the portion onto an outer surface of said product; and being characterized in that said product is made, at least externally, of dielectric material; the method further comprising the step of generating an electrostatic force of attraction between said portion and said outer surface of said product. A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic side view, with parts in section and parts removed for clarity, of a folding unit implementing the method according to the present invention; Figure 2 shows a schematic side view, with parts in section and parts removed for clarity, of a first variation of the Figure 1 folding unit; Figure 3 shows a schematic side view, with parts in section and parts removed for clarity, of a second variation of the Figure 1 folding unit; Figure 4 shows a schematic front view, with parts removed for clarity, of a detail of the Figure 3 folding unit. Number 1 in Figure 1 indicates a folding unit for squarely folding at least one of two portions 2 and 3 of dielectric sheet material. In the example shown, unit 1 forms part of an overwrapping machine, in particular a cellophaning machine, for overwrapping products 4 preferably comprising substantially parallelepiped packets made, at least externally, of dielectric material; and portions 2 and 3 constitute the end portions of a sheet 5 of dielectric overwrapping material, preferably polypropylene, which is folded about a respective product 4 to form a tubular wrapping (not shown). For which purpose, sheet 5 is first folded into a U in known manner (not shown) about respective product 4, so that end portions 2 and 3 project beyond an outer lateral surface 6 of product 4. Product 4 and respective U-folded sheet 5 are then fed, by conveying means (not shown) and in a direction 7, through unit 1, which comprises a polarizing assembly 8 and a folding assembly 9 in series with each other in direction 7. Polarizing assembly 8 comprises an electric source 10, and two parallel plates 11 and 12 made of electrically conductive material. Plates 11 and 12 define a passage 13 for receiving a product 4 and respective U-folded sheet 5 with portions 2 and 3 facing and parallel to each other, and parallel and adjacent to respective plates 11 and 12, and are connected electrically to respective poles of source 10 to define the plates of a capacitor 14 for generating an electric field through passage 13. Folding assembly 9 comprises at least one folding element 15 in turn comprising a flat plate 16 preferably, but not necessarily, made of dielectric material. Plate 16 is perpendicular to direction 7, and is connected to the output of a linear actuator 17 to move, in a direction 18 perpendicular to direction 7, to and from a folding position in which plate 16 engages and squarely folds one of portions 2 and 3 - in the example shown, portion 3 - onto surface 6 of product 4. In the example shown, a further folding element (not shown) similar to folding element 15 obviously provides for folding portion 2 onto surface 6 and part of portion 3. In actual use, as they travel in direction 7, product 4 and respective U-folded sheet 5 gradually enter the electric field generated by capacitor 14; on an outer surface 19 of each portion 2, 3 facing respective plate 11, 12, the electric field induces surface electric charges 20 opposite in sign to the electric charges distributed on plate 11, 12; at the same time, the electric field induces, on an inner surface 21 of each portion 2, 3, surface electric charges 22 opposite in sign to respective electric charges 20; and this charge distribution remains on sheet 5 for a given time after the sheet leaves passage 13 and proceeds with respective product 4 in direction 7 to folding assembly 9. Upon folding assembly 9 engaging portion 2, 3, inner surface 21 is brought into contact with surface 6 of product 4, and induces, on surface 6, charges 23 opposite in sign to charges 22, and which cooperate with charges 22 to retain portion 2, 3 firmly contacting surface 6 by electrostatic attraction, even when portion 2, 3 is released by plate 16 of folding element 15. In the Figure 2 variation, plate 12 is dispensed with, and the Figure 1 result is achieved by assembling folding element 15 at polarizing assembly 8, and connecting plate 16 - in this case, made of electrically conducting material - to the pole of source 10 formerly connected to plate 12. In the Figure 3 variation, polarizing assembly 8 has no plates 11, 12, and linear actuator 17 of folding element 15 is replaced by an actuating device 24 for swinging plate 16 about an axis 25 extending along one end of plate 16, perpendicular to the traveling direction 7 of products 4, and parallel to portions 2 and 3. Plate 16 rotates about axis 25 between a first position in which plate 16 is parallel to direction 7, with a respective surface 26 facing and parallel to outer surface 19 of portion 2, 3 of sheet 5, and a second position in which plate 16 is perpendicular to direction 7, with respective surface 26 facing surface 6 of product 4. As it swings from the first to the second position, plate 16 folds portion 2, 3 squarely onto surface 6 of product 4. In the Figure 3 and 4 variation, plate 16 is made of electrically conducting material, and comprises, on surface 26, a number of seats 27 having an inner covering 28 of electrically insulating material, and each housing a respective pad 29 made of electrically conducting material, and the outer surface of which is coplanar with surface 26. Portion 2, 3 is polarized by connecting plate 16 to the pole of source 10 formerly connected to plate 12, and pads 29 to the pole of source 10 formerly connected to plate 11, so as to define a capacitor 30. The electric field generated by capacitor 30 induces, on the outer surface 19 of portion 2, 3 facing plate 16, surface electric charges 20 locally opposite in sign to the electric charges distributed on plate 16 and plates 29. At the same time, the electric field induces, on the inner surface 21 of portion 2, 3, surface electric charges 22 locally opposite in sign to respective electric charges 20. And, when plate 16 is positioned facing surface 6, the electric field induces, on surface 6, charges 23 locally opposite in sign to charges 22, and which cooperate with charges 22 to retain portion 2, 3 firmly contacting surface 6 by electrostatic attraction, even when portion 2, 3 is released by plate 16 of folding element 15. In other words, in Figure 1, portion 2, 3 is folded onto surface 6 after being polarized, whereas, in Figures 2 and 3, polarization and folding are performed simultaneously. In both cases, however, portion 2, 3 is retained firmly folded onto surface 6 for a given length of time, with no need for any sort of external retaining member.

Claims: A method of folding at least one portion (2, 3) of dielectric sheet material, the method comprising the steps of mating a sheet (5) including said portion (2, 3) with a product (4), and folding the portion (2, 3) onto an outer surface (6) of said product (4); and being characterized in that said product (4) is made, at least externally, of dielectric material; the method further comprising the step of generating an electrostatic force of attraction between said portion (2, 3) and said outer surface (6) of said product (4). A method as claimed in Claim 1, characterized in that said sheet (5) is mated with said product (4) for folding the sheet (5) about the product (4) in a substantially U-shape configuration, wherein two portions (2,3) form two outer longitudinal faced flaps; a first (2; 3) of said portions (2, 3) being folded onto said outer surface (6) of the product (4) by folding means (15) engaging the first portion (2, 3); said electrostatic force of attraction being generated between said first portion (2; 3) and said outer surface (6); said first portion (2; 3) being abandoned by said folding means (15); and a second (3; 2) of said portions (2, 3) being folded onto said outer surface (6) of the product (4) and onto said folded first portion (2; 3). A method as claimed in Claim 1 or 2, characterized in that said electrostatic force of attraction between said first portion (2; 3) and said outer surface (6) is generated by forming a first given distribution (22) of electric charges on an inner surface (21) of said first portion (2; 3), and a second distribution (23) of charges of opposite sign on said outer surface (6). A method as claimed in Claim 3, characterized in that said first distribution (22) of charges is formed by polarizing said portion (2, 3) by means of an electric field prior to said step of folding the portion (2, 3); said second distribution (23) of charges being formed by induction by said first distribution (22) of charges as said portion (2, 3) is folded. A method as claimed in Claim 4, characterized in that said electric field is formed by means of a number of plates (11, 12) made of electrically conducting material and located on either side of a path (7) of the products (4); said plates (11, 12) forming the plates of a capacitor (14); and said folding step being performed by means of a folding element (15) downstream from said capacitor (14). A method as claimed in Claim 3, characterized in that both said distributions (22, 23) of charges are formed simultaneously by polarization by means of an electric field. A method as claimed in Claim 6, characterized in that said electric field is formed by means of a number of plates (11, 16) of electrically conducting material; said plates (11, 16) forming the plates of a capacitor (14); and said folding step being performed within said electric field by means of a folding element (15) forming one of the plates of the capacitor (14) generating said electric field. A method as claimed in Claim 6, characterized in that said electric field is formed by a folding element (15); said folding element (15) performing said folding step. A method as claimed in Claim 8, characterized in that said folding element (15) comprises a number of substantially coplanar plates (16, 29) electrically insulated with respect to one another, and forming the plates of a capacitor (30) generating said electric field.

Inventors: RONCONI GIUSEPPE, RONCONI, GIUSEPPE
Applicants: CO ME SCA COSTRUZIONI MECCANIC, CO.ME.SCA. COSTRUZIONI MECCANICHE SCARPERIA S.R.L.
Application year: 1997
Main classification: B65B61
IPC codes: B65B61, B65B11