PROCESS AND INSTALLATION OF MANUFACTURING A PERFORATED TUBULAR PLASTIC FOIL BY ACTION OF A LASER BEAM, PERFORATED TUBULAR PLASTIC FOIL AND PLASTIC BAG FORMED FROM SUCH A TUBULAR PLASTIC FOIL

Abstract: A continuously conveyed tubular plastic foil (1) is perforated by a laser beam which is focused by means of a mirror or lens (12) on the perforation forming plane (13, 13'), lying at the focal point of the mirror or lens (12), of a tautly conveyed tubular plastic foil. For taut conveyance of the tubular foil (1) it is guided over a support (14) placed in the tubular foil, or over supporting plates (15, 15a) lying outside the tubular foil and provided with foil suction means (17) and with laser beam transmission apertures (16). The slightly tapering perforations (2) with a minimum aperture at the inside of the tubular foil (1) form, on the one hand, a pattern of parallel lines (A) running in the lengthwise direction and, on the other hand, a patterm of parallel lines (B) which run at an angle relative to the longitudinal axis of the flattened tubular foil. A bag can be formed from the tubular foil. An installation for perforation comprises, in addition to a laser beam source (11), lens beam-directing means (18) and a lens or mirror (12), a support (14) to be placed in a tubular foil, or supporting plates (15, 15a) provided with apertures (16) and with foil suction apertures (17), for taut conveyance of the tubular foil in a perforation forming plane (13, 13').

Description: Title: Process and installation of manufacturing a perforated tubular plastic foil by action of a laser beam, perforated tubular plastic foil and plastic bag formed from such a tubular plastic foil. The invention relates to a process and an installation of manufacturing a perforated tubular plastic foil through the action of a laser beam. Such a process for perforating a plastic foil using a laser beam is known. Plastic foils perforated with a laser beam in fact constitute a very suitable material for the production of bags for packing loose material in suitable quantities of, for example, 25 kg. Since in the filling of the bags with loose powder-type material this loose material is conveyed with air, after the bag has been filled a quantity of air is left behind between the particles of the powder material, and this air must be able to excape while leaving the powder material behind in the bag. Moreover, after filling, these perforations permitting a rapid deaeration must also be sealed quickly and as well as possible, in order to prevent loss of material and the penetration of moisture into the bag. However, when a plastic tubular foil lying in a flat position is being perforated, it is difficult to obtain perforations of the desired size. If the plastic foil material to be perforated is too thick, a conical perforation being large at the entry side of the laser beam and small at the opposite side is produced. This means that in a tubular foil which is lying flat a relatively large or even too large a perforation is produced in the top layer of the foil, and a relatively small or too small a perforation in the layer of the foil underneath it, which is integral with the top layer of the foil on which the laser beam acts directly and first. Another disadvantage is that when the tubular foil is lying flat the two layers of plastic lying closely on top of each other are together of such great thickness that the laser beam is difficult to focus over the entire thickness of the two layers of foil, which means that during the perforation with the laser beam melting of the perforation edges occurs. In the case of perforating the plastic tubular foil with a layer of air between the two layers of plastic of the tubular foil the problem is that the laser beam is then not focused sharply enough, while the amount of energy for formation of the perforations becomes unacceptably high, and consequently too large perforations are formed and are, moreover, formed in imprecisely defined places. The object of the invention is now to provide a process of manufacturing a perforated tubular plastic foil through the action of a laser beam on the tubular wall of a tubular foil thereby forming perforations ranging from 50 to 250 /urn in size, and in which perforations of the desired size are obtained in the correct place and with the correct dimensions, without melting of the perforation edges and without inad issibly high energy consumption. This object is achieved according to the invention in that during the perforating action the wall part to be perforated and lying free from the remaining wall of the tubular foil is guided tautly in a perforation forming plane on which the laser beam is focused. By guiding the wall part of the tubular foil to be perforated tautly in a perforation forming plane, the laser beam can now be focused accurately, and an accurately defined perforation can therefore be obtained. It is particularly advantageous for the laser beam to be focused using at least one lens and/or mirror on the perforation forming plane which lies at the focus of the lens and/or mirror. In this way perforation apertures which meet the required standards in the optimum way are obtained with the optimum use of energy. It is expedient if during the perforation action two opposite wall parts of the tubular foil are each perforated in a perforation working plane, so that the perforations can be distributed uniformly over the tubular foil surface. In the process according to the invention the tubular foil is advantageously conveyed continuously, which means that a large number of perforations can be formed quickly . An intermittent laser beam expediently moves at right angles to the direction of conveyance along the continuously moving tubular foil, thereby forming a pattern of perforations placed in parallel lines. In order to guide the wall part to be perforated tautly in a perforation forming plane, it is advisable to guide this wall part over a support placed in the tubular foil. In this way it is possible in a simple manner to achieve taut guidance of the wall of the tubular foil in a perforation forming plane. It is also advisable according to another embodiment to guide the wall parts to be perforated tautly over a supporting surface lying outside the tubular foil, and having slits for transmitting laser beams, said supporting surface being provided with tubular foil wall suction means. In this way no support need be fitted in the interior of the tubular foil, which means that in the event of breakdowns in the continuous process complicated actions do not need to be carried out. The invention also relates to a plastic bag formed from a perforated tubular plastic foil by using the process according to the invention. In particular, the invention also comprises a perforated tubular plastic foil with perforation apertures ranging from 50 to 250 _ιm formed by laser beam, and provided with a pattern of parallel lines (A) of successive perforations formed by laser beam, while in the transverse direction the perforations form a pattern of parallel lines (B) running at an angle relative to the longitudinal axis of the tubular foil across the width of the flattened tubular foil, and a bag formed therefrom. Finally, the invention relates to an installation for carrying out the process according to the invention, at least comprising a device for forming a laser beam, tubular plastic foil suppporting means, tubular plastic foil conveying means for conveying the tubular foil, tubular plastic foil discharge means, a lens and/or mirror for focusing a laser beam on a tubular plastic foil wall part, and laser beam action interruption means, which is characterized in that the installation comprises tubular plastic foil supporting means guiding a wall part of a tubular plastic foil to be perforated tautly in a perforation forming plane, while the other part of the tubular plastic foil lies free from this perforation forming plane, and beam directing means and lenses for focusing the laser beam on the above-mentioned perforation forming plane. The supporting means are expediently a support to be placed inside a tubular foil, and over which the tubular foil can be guided tautly. It is particularly advantageous for the supporting means to comprise a frame with at least one plate having one or more slits for transmitting laser beams, and tubular foil wall suction means. The installation according to the invention at least has lenses set up in such a way that the focal point of said lens lies in a perforation forming plane. The invention will now be explained with reference to an example of an embodiment as shown in the drawing, in which : - Fig. 1 shows a top view of a tubular plastic foil with perforations formed by using the process of the invention; - Fig. 2 shows an installation for carrying out the process according to the invention with a support to be placed inside a tubular foil; - Fig. 3 is a cross section of an installation for carrying out the process according to the invention, in which the tubular foil supporting means form a frame with a plate having slits for transmitting a laser beam; and - Fig. 4 shows a plastic bag formed from a perforated tubular plastic foil obtained by the process according to the invention. As can be seen in fig. 1, a tubular foil 1 is provided with perforations 2 ranging from 50 to 250/tιm in size . The perforations form a pattern of parallel lines (A) in the lengthwise direction of the tubular plastic foil 1, and in the transverse direction of the tubular plastic foil the perforations 2 form lines (B) which run at an angle relative to the longitudinal axis of the foil. These lines A and B are shown as dashed lines. Fig. 4 shows a plastic bag 3 made from a tubular plastic foil perforated by the process according to the invention, with a transverse seal forming a bottom 3, and a filling aperture 5 bounded by a peripheral edge 6. Fig. 2 shows an installation for carrying out the process according to the invention. This installation comprises a stock reel 7 for tubular plastic foil 1, tubular foil conveying means in the form of feed rollers 8 for conveying a tubular foil, tubular plastic foil discharge means in the form of discharge rollers 9, and a storage reel 10 for storing perforated tubular plastic foil 1. The tubular foil can be conveyed continuously by means of the feed rollers 8 and discharge rollers 9. The installation is also provided with a laser beam source 11 and a number of lenses 12 placed next to each other, and each set to make the laser beam act on a perforation forming plane 13, 13' where a tubular foil wall la, lb is being conveyed tautly. The perforation forming plane 13 and 13' is formed by a support 14 placed in the tubular foil 1, with tubular foil wall la, lb being conveyed tautly over this support 14. The support 14 is held fixed by supporting rollers 19. The above-mentioned perforations 2 are obtained by fitting a number of lenses 12 arranged across the width of the tubular foil, and making the laser beam act upon the adjacent lenses 12. Through working with several lenses 12 and a moving lens beam-directing means, it is possible to make do with one laser beam source 11. Since the intermittent laser beam, which alter¬ nately directs a beam on one lens 12 at a time by means of lens beam-directing means 18, is always focused here by the lens 12 in question on the perforation forming plane 13, 13', perforations of the desired size of 50 to 250 jm are obtained in the correct place. Fig. 3 shows a different embodiment of an instal¬ lation for carrying out the process according to the invention. Here the perforation forming plane is formed by supporting plates 15, 15a, provided with apertures 16 for transmitting a laser beam. Foil suction apertures 17 in the plates 15, 15a suck the foil walls la and lb against these plates, thereby guiding the walls la, lb of the tubular foil 1 tautly in a perforation forming plane 13, 13' on which the laser beam can be sharply focused. The perforation forming planes 13, 13' lie at the focal point of the lenses 12. It is expedient to work with mirrors 18, in particular with beam-directing means designed with one or more rotatable mirrors 18 in order to be able to direct the laser beam towards one lens 12 of a number of adjacent lenses 12, and subsequently on the perforation forming planes 13, 13' which always lie at the focal point of the lenses 12. The rotation facilities of the mirrors 18 are shown schematically by the curve 20. A laser beam emitted by the laser beam source 11 is directed by rotating mirror 18 onto one of the lenses 12 and then by this lens 12 onto the perforation forming plane 13 or 13' , where the tubular foil is conveyed tautly. The path of a laser beam is indicated by dashed line 21. Although two laser beam sources 11 are shown in the figure, it is also possible to work with one source 11. The pattern of the perforations shown in fig. 1 is obtained by focusing one laser beam onto a continuously conveyed tubular foil above which a set of lenses 12 is set up at regular intervals from each other over the width of the foil web. The laser source works intermittently in such a way that the laser beam acts successively on the next lens 12 in the transverse direction. In view of the conveyance of the tubular foil in the period of time in which the laser beam acts on the first lens and subsequently on the lens following in the transverse direction of the foil, the perforation 2" formed by the following lens 12 will lie lower, as seen in the lengthwise direction, than the perforation 2'. In the finished foil the perforations 2' to 2'"" consequently lie on an imaginary line B which runs at an angle relative to the longitudinal axis of the tubular foil. The perforations are preferably made slightly tapered, with a minimum aperture at the inside of the tubular foil.

Claims: C L A I M S 1. Process of manufacturing a perforated tubular plastic foil through the action of a laser beam on the tubular foil wall, forming perforations ranging from 50 to 250 / urn in size, characterized in that during the perforation action the wall part (la, lb) to be perforated and lying free from the remaining wall of the tubular foil is guided tautly in a perforation forming plane (13, 13') on which the laser beam is focused. 2. Process according to claim 1, characterized in that the laser beam is focused using at least one lens (12) or mirror on the perforation forming plane (13, 13') which lies at the focal point of the lens or mirror. 3. Process according to claim 1 or 2, characterized in that during the perforation action two opposite wall parts (la, lb) of the tubular foil are each perforated in a perforation working plane (13, 13'). 4. Process according to claims 1-3, characterized in that the tubular foil (1) is conveyed continuously. 5. Process according to claims 1-4, characterized in that an intermittent laser beam moves at right angles to the direction of conveyance along the continuously moving tubular foil, thereby forming a pattern of perforations placed in parallel lines (A) and (B). 6. Process according to claims 1-5, characterized in that the wall part to be perforated is conveyed tautly over a support (14) placed in the tubular foil. 7. Process according to claims 1-5, characterized in that the wall part to be perforated is conveyed tautly over a supporting surface (15, 15a) lying outside the tubular foil and having slits (16) for transmitting a laser beam, said supporting surface (15, 15a) being provided with tubular foil wall suction means (17). 8. Process according to claims 1-7, characterized in that the perforations (2) are made slightly tapering with a minimum aperture on the inside of the tubular foil. 9. Plastic bag formed from a perforated tubular plastic foil by using the process according to one or more of claims 1-8. 10. Perforated tubular plastic foil with perforation apertures ranging from 50 to 250/um formed by laser beam, and provided with a pattern of parallel lines (A) of successive perforations formed by laser beam, while in the transverse direction the perforations form a pattern of parallel lines (B) running at an angle relative to the longitudinal axis of the tubular foil over the width of the flattened tubular foil. 11. Plastic bag formed from a perforated tubular plastic foil according to claim 10. 12. Installation for carrying out the process according to one or more of claims 1-8, at least comprising a device forming a laser beam, tubular plastic foil supply means, tubular plastic foil conveying means for conveying the tubular foil, tubular plastic foil discharge means, and at least one lens or mirror for focusing a laser beam on a tubular plastic foil wall part, and laser beam action interruption means, characterized in that the installation comprises tubular plastic foil supporting means (14; 15, 15a) guiding a wall part of a plastic tubular foil to be perforated tautly in a perforation forming plane, while the other part of the tubular plastic foil lies free from this perforation forming plane, and beam-directing means (18) and lenses (12) for focusing the laser beam on the above- mentioned perforation forming plane (13, 13'). 13. Installation according to claim 12, characterized in that the supporting means form a support (14) to be placed inside a tubular foil, and over which the tubular foil can be guided tautly. 14. Installation according to claim 12, characterized in that the supporting means comprise a frame with at least one plate (15, 15a) having one or more slits (16) for transmitting laser beams, and tubular foil wall suction means (17). 15. Installation according to claims 12-14, characterized in that the installation at least has lenses (12) set up in such a way that the focus of said lenses lies in a perforation forming plane (13, 13'). 16. Installation according to claim 12, characterized in that the installation has one or more rotating mirrors (18) for directing a laser beam onto the lenses (12) . 17. Installation according to claims 12-16, characterized in that the installation has conveying means (8, 9) for the continuous conveyance of the tubular foil (1).

Inventors: KOOPMAN ROELOF, VAN DIJK BEREND JAN, KOOPMAN, ROELOF, VAN DIJK, BEREND, JAN
Applicants: WAVIN BV, WAVIN B.V.
Application year: 1989
Main classification: B29C37
IPC codes: B23K26, B26F1, B29C37, B31B1, B65D33, C08J7