Device and method for perforating web-shaped films, in particular plastic films

Abstract

The present invention relates to a device (10) for perforating web-shaped films (12), in particular plastic films, comprising a rotatably mounted needle roller (18) with a number of needles (20), a rotatably mounted first counter-roller (22), with which the film (12) can be brought into contact with the needle roller (18) in a first active region (42) such that the needles (20) are pressed into the film (12) with a first penetration depth (T1), and a rotatably mounted second counter-roller (24), with which the film (12) can be brought into contact with the needle roller (18) in a second active region (44) such that the needles (20) are pressed into the film (12) with a second penetration depth (T2), wherein the first penetration depth (T1) is less than the second penetration depth (T2). Furthermore, the present invention relates to a corresponding method for perforating web-shaped films.

Description

[0001] The present invention relates to a device and a method for perforating web-shaped films, in particular plastic films.

[0002] Plastic films used in the production of packaging, such as sacks or bags, should be air-permeable, at least in certain areas, when used to package bulk materials such as dust, flour, and granules. This allows trapped air to escape during filling, for example. Otherwise, trapped air pockets can lead to stacking difficulties during stacking and storage of the filled packaging, and even cause the sacks and bags to burst. However, permeability to water or sound may also be desirable, depending on the application. To achieve the desired permeability, the films are perforated, i.e., provided with holes.

[0003] Devices for perforating web-shaped films are known, to which the films can be continuously fed. The device has a needle roller, also referred to as a needle roll, with which holes can be pierced in the film. A counter-roller interacting with the needle roller is used to apply the required contact pressure to the film. Such devices are known, for example, from DE 34 37 414 C2, DE 44 36 679 A1, DE 102 05 599 A1, DE 195 44 330 C2, DE 197 14 429 A1, EP 0 802 026 A1, and EP 1 046 479 A1.

[0004] Further information on the technical field to which the present invention relates can be found in US 2012 / 0049404 A1, US 9 623 602 B2, DE 101 32 196 A1, WO 2018 / 042556 A1, JP H06 - 316 000 A and JP H04 - 210 399 A.

[0005] Counter rollers with a closed surface, in particular rollers with a rubber coating, and counter rollers with an open surface, which are typically formed by bristles, can be used.

[0006] It is desirable to have the holes of equal diameter, but this cannot always be guaranteed, especially with polyethylene (PE) films, for the following reasons. When perforating with a counter roller with a solid surface, very small holes are created which may close up more or less after perforation because the film material is only displaced but not pierced or not pierced sufficiently. To increase the penetration depth, the counter roller with a solid surface can be positioned closer to the needle roller. However, this carries the risk of the needles also penetrating the surface of the counter roller, which leads to increased surface abrasion and increased wear of the needles.As abrasion and wear increase, the uniformity of the diameters of the holes decreases and the probability that the needles do not pierce the film and no holes are created or that the holes are too small increases.

[0007] To produce larger holes, counter rollers with open surfaces, such as brush rollers, can be used. The needles can penetrate deeper into these compared to counter rollers with closed surfaces, without this type of counter roller being subject to increased abrasion. Wear on the needles is also low in this case. However, brush rollers have the property that the bristles form a gap between each other on the surface that interacts with the film, where a certain amount of empty space is created. This is because the surface area is larger at the outer diameter than at the base of the bristles. In the empty space, the brush rollers cannot exert any force on the film, which is why the contact pressure against the needle roller is reduced there.

[0008] When using brush rollers, the elastic film is pulled over the needle until the perforation force is so great that the needle penetrates the film. In this process, the film is stretched around the needle tip. At this point, the necessary perforation force may be greater than the force that the film can absorb in the stretched area. The result is that the film tears in the stretched area. An almost circular piece is torn out of the film and remains on the needle tip. This effect can occur very unevenly depending on the film material and the properties of the needles. For some applications, the holes created in this way are too large and / or the permeability provided is no longer within the tolerance range.In addition, the pieces torn out of the film lead to unwanted dust, which can interfere with further processing and in many cases must not adhere to the goods that are packaged in the film.

[0009] The object of one embodiment of the present invention is to propose a device and a method for perforating web-shaped films, in particular plastic films, with which it is possible to remedy the above-mentioned disadvantages using simple and cost-effective means and, in particular, to enable a defined, process-safe, reliable and largely dust-free perforation of web-shaped films.

[0010] This object is achieved by the features specified in claims 1 and 9. Advantageous embodiments are the subject of the subclaims.

[0011] One embodiment of the invention relates to a device for perforating web-shaped films, in particular plastic films, comprising - a rotatably mounted needle roller with a number of needles, - a rotatably mounted first counter roller, with which the film can be brought into contact with the needle roller in a first effective area such that the needles are pressed into the film with a first penetration depth, and - a rotatably mounted second counter roller, with which the films can be brought into contact with the needle roller in a second effective area in such a way that the needles are pressed into the film with a second penetration depth, wherein the first penetration depth is less than the second penetration depth.

[0012] One of the core ideas of the present disclosure is that the perforation is carried out at two spatially separate locations, namely in the first effective area and in the second effective area spaced therefrom. In the first effective area, the needles are inserted into the film with a first penetration depth, wherein the penetration depth is set such that the first counter roller is subject to no or only minimal abrasion. Consequently, the needles in the first effective area are also subject to reduced wear in this regard. In the second effective area, the needles are inserted into the film with a second penetration depth, wherein the second penetration depth is greater than the first penetration depth. The second penetration depth is selected such that the film is reliably pierced and the holes thus created have the desired diameter.The second counter roller can be designed in such a way that it is adapted to the action of the needles, for example it has a soft surface which leads to reduced wear of the needles when they penetrate the second counter roller.

[0013] The perforation is therefore performed in two stages. The holes are created by piercing the film, rather than by tearing it out due to stretching. This results in holes of equal or nearly equal diameters, while simultaneously minimizing needle wear and abrasion on the counter rollers.

[0014] In the embodiment according to the invention it is further specified that the first counter roll has a first surface with a first hardness and the second counter roll has a second surface with a second hardness, wherein the first hardness is greater than the second hardness. The hardnesses can be determined using suitable hardness testing methods, for example according to Rockwell, Brinell or Vickers. When selecting the suitable hardness testing method, the material of the surfaces in particular must be taken into account. As mentioned, the first penetration depth is less than the second penetration depth. The second penetration depth is dimensioned such that the needles can penetrate into the second surface of the second counter roll. In order to keep penetration and the resulting wear of the needles to a minimum, the second hardness is less than the first hardness.

[0015] According to a further embodiment, the first penetration depth can be selected such that the needles do not penetrate the film. In this case, the needles do not penetrate the first counter roller, so that the abrasion of the first counter roller can be kept particularly low. The operating time of the counter roller is correspondingly long.

[0016] In a further developed embodiment, - at least the needle roller or - at least the first counter roller and / or the second counter roller are adjustably mounted by means of an adjustment device. As a result, the first penetration depth and the second penetration depth can be flexibly adapted to the respective application. The first penetration depth and the second penetration depth determine the contact pressure with which the film is pressed against the needle roller. The second penetration depth also determines the diameter of the resulting holes. With a harder film material and a greater film layer thickness, a different contact pressure may be required than with a softer film material and a thinner film to achieve the desired perforation result.

[0017] In a further developed embodiment, the first counter roll can have a closed first surface. A closed surface can be understood as a surface that has no significant depressions, as a result of which the film rests against the first counter roll without interruption or almost without interruption. This allows a particularly high and evenly distributed contact pressure to be exerted on the film.

[0018] In a further embodiment, the second counter roll can have an open second surface into which the needles can be immersed. The open second surface can be provided, for example, with a brush roll. Due to the open surface, the second counter roll offers enough space into which the needles can be inserted without causing significant abrasion of the second counter roll and increased wear of the needles inserted into the second counter roll. The open surface provided by the brush roll can be designed such that it has a lower second hardness than the first hardness of the first surface of the first counter roll.

[0019] It has been shown that the first contact pressure required to press the needles into the film is significantly greater than the second contact pressure required to push the needles further into the film and pierce them. Therefore, it is not a disadvantage that the second counter rollers can only exert a lower and more unevenly distributed counter pressure on the film.

[0020] A further developed embodiment can be characterized in that - the needle roller, and / or - the first counter roller, and / or - the second counter roller can be driven or is driven by a drive unit.

[0021] The film is fed to the device by means of a feed unit, which is designed in such a way that the film is also moved. The film is therefore guided through the device at a specific web speed. At least one of the rollers, in particular the needle roller, is set in motion by means of the drive unit. The needle roller can be driven in such a way that the needles at their free ends have a circumferential speed that corresponds to the web speed and consequently there is no or only very little relative movement of the needles with regard to the feed direction of the film. The needles are therefore moved synchronously with the film. In this case, the load on the film resulting from the drive of the non-driven rollers is reduced.

[0022] However, it may also be desirable to move the needles at a peripheral speed slightly higher than the web speed. This can cause the holes to be slightly torn and enlarged. The tips of the needles cut slightly into the film. As a result, a small tear is visible at the edge of the hole. With some films, the hole can otherwise close almost completely after perforation. According to a further embodiment, the device can - between an open position in which the film can be inserted into the device, and - a closed position is adjustable in which the film can be perforated, whereby - in the open position, the needle roller, the first counter roller and the second counter roller are arranged so that a passage channel is formed through which the film can be passed for insertion.

[0023] The resulting feed-through channel is not intended as a physical assembly, but rather as a free space through which the film can be fed for insertion. It is advisable to design the device so that the feed-through channel runs vertically. This allows the film to be fed quickly and easily through the rollers using the force of gravity in the open position, without any contact between the film and the rollers. This prevents any resulting damage to the film.

[0024] In a further embodiment, it may be appropriate that the device - a shielding unit for shielding the needle roller and / or - has a housing in which the needle roller, the first counter roller and the second counter roller are arranged.

[0025] Both the housing and the shielding serve to ensure the operational safety of the device. The shielding unit prevents a person from accidentally coming into contact with the needle roller and thereby injuring themselves. The housing can be designed so that an opening flap can only be opened in the open position and when the machine is stationary to access the rollers.

[0026] One embodiment of the invention relates to a method for perforating web-shaped films, in particular plastic films, with a device according to one of the preceding claims, comprising the following steps: - pressing in the needles of the needle roller in the first effective area with a first penetration depth, and - Pressing in the needles of the needle roller in the second effective area with a second penetration depth, whereby - the first penetration depth is less than the second penetration depth and - the film remains on the needle roller when moving from the first effective area to the second effective area.

[0027] The technical effects and advantages that can be achieved with the proposed method essentially correspond to those discussed for the present device. In summary, it should be noted that, according to the proposed method, the perforation is carried out in two stages. This results in holes with equal or approximately equal diameters, while simultaneously minimizing needle wear and abrasion of the counter-rollers.

[0028] It should be noted that the film remains on the needle roller as it moves from the first active zone to the second active zone. The needles inserted into the film in the first active zone remain there at least until they have passed through the second active zone.

[0029] With further training, the procedure may include the following steps: - Feeding the film to the needle roller at a web speed, - Driving the needle roller by means of the drive unit in such a way that the needles at their free ends are moved synchronously with the film or faster than the film.

[0030] The needle roller, the first counter roller and the second counter roller do not need to be actively driven, but are set in rotation due to the friction acting between them and the film.

[0031] According to this method design, the needle roller can be driven so that the needles move synchronously with the film. In this case, the stress on the film resulting from the drive of the non-driven rollers is reduced.

[0032] However, it may also be desirable to move the needles at a peripheral speed higher than the web speed. As already described, this can cause the holes to tear slightly and enlarge.

[0033] Exemplary embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 a schematic representation of an embodiment of the device for perforating web-shaped films in a closed position, Fig. 2 a basic diagram to explain the penetration depths, and Fig. 3 which in Fig. 1 illustrated embodiment of the device in an open position.

[0034] In Fig. 1 shows an embodiment of a device 10 according to the invention for perforating web-shaped films 12 based on a schematic representation in a closed position. The device 10 comprises a housing 14 which encloses a cavity 16 in which a rotatably mounted needle roller 18 with a plurality of needles 20 distributed around its circumference, a rotatably mounted first counter-roller 22 and a rotatably mounted second counter-roller 24 are located. The needle roller 18, the first counter-roller 22 and the second counter-roller 24 are adjustable relative to one another by an adjusting device 26. The adjusting device 26 is symbolically represented by elongated holes which run horizontally in the needle roller 18 and the second counter-roller 24 and vertically in the first counter-roller 22, along which the rollers 18, 22, 24 can be moved.However, this does not mean that, for example, the first counter roller 22 can only be adjusted vertically. Rather, the rollers 18, 22, 24 can be mounted, for example, with a bearing in the manner of a cross slide, allowing both vertical and horizontal adjustment.

[0035] The first counter roll 22 has a closed first surface 28, which in the illustrated embodiment is provided with a rubber coating 29, which imparts a first hardness H1 to the first surface. The second counter roll 24 has an open second surface 30, which is provided with bristles 32. The second surface 30 has a second hardness H2, which is lower than the first hardness H1.

[0036] The needle roller 18 is driven by a drive unit 34. Furthermore, the device 10 has a guide device 36 with which the film 12 can be guided through the device 10. The guide device 36 comprises a first pair of guide rollers 38 and a second pair of guide rollers 40. During production, the not yet perforated film 12 can be wound onto a supply roll, which can be rotatably mounted in or near the device 10. The film 12 can then be pulled off the supply roll using the guide device 36. Accordingly, the perforated film 12 can be wound onto a take-up roll. Neither the supply roll nor the take-up roll are shown.

[0037] The guide device 36 is designed such that it can move the film 12 through the device 10 at a web speed. For this purpose, the second pair of guide rollers can be driven. The direction of movement is indicated by the arrow P.

[0038] The first counter roller 22 forms a first active area 42 with the needle roller 18. The second counter roller 24 forms a second active area 44 with the needle roller 18. The guide device 36 is designed such that the film 12 is guided, with respect to the direction of movement, first through the first active area 42 and then through the second active area 44. In this case, the film 12 first comes into contact with the first counter roller 22.

[0039] In the first effective area 42, the first counter roller 22 presses the film 12 against the needle roller 18 in such a way that the needles 20 are pressed into the film 12 with a first penetration depth T1. The first penetration depth T1 is determined in particular from the Fig. 2. The first penetration depth T1 is selected such that the needles 20 are pressed into the film 12 but do not penetrate the film 12. Consequently, the needles 20 do not come into direct contact with the first surface 28 because at least a portion of the film 12 remains between the needles 20 and the first surface 28. Alternatively, the first penetration depth T1 can be selected such that the needles 20 just penetrate the film 12 without dipping into the first surface 28. The first surface 28 is therefore not pierced by the needles 20 or is pierced only to a very limited extent, so that the abrasion of the first surface 28 can be kept low. The first hardness H1 is selected such that the contact pressure required for this can be applied to the film 12 without any significant compression of the first surface 28. The first hardness H1 is also selected so that the abrasion of the first surface 28 is kept low.

[0040] After leaving the first effective area 42, the needles 20 pressed into the film 12 remain in the film 12 until they have passed through the second effective area 44. There, the film 12 is pressed against the needle roller 18 by the second counter roller 24 such that the needles 20 are pressed into the film 12 with a second penetration depth T2 and pierce the film 12. The second penetration depth T2 is selected such that the holes thus created have the desired diameter. In this respect, the desired diameter of the holes is set by adjusting the second counter roller 24. As mentioned, the second counter roller 24 has an open second surface 30 with the second hardness H2, which is formed by the bristles 32. The bristles 32 form empty spaces into which the needles 20 can penetrate without significantly damaging the bristles 32. The needles 20 themselves are also subject to hardly any significant wear.In this respect, no excessive abrasion is generated here either.

[0041] Both the first penetration depth T1 and the second penetration depth T2 can be defined as the distance of the free end of the respective needle 20 to the surface of the film 12 through which the needle 20 penetrates into the film 12. In Fig. 2, this is the lower surface of the foil 12. As can be seen particularly from the Fig. 2, the second penetration depth T2 is greater than the first penetration depth T1.

[0042] After the film 12 has passed through the second effective area 44, it is guided out of the device 10 by the guide device 36, whereby the needles 20 are removed from the film 12. The perforated film 12 can then be wound onto the aforementioned take-up roll (not shown) for further use.

[0043] As mentioned, the device 10 is located in Fig. 1 in a closed position. In Fig. 3, the device 10 can be seen in an open position, in which the first counter-roller 22 and the second counter-roller 24 are arranged at a distance from the needle roller 18 such that a straight through-channel 46 is formed, which runs between the needle roller 18 and the first counter-roller 22 and between the needle roller 18 and the second counter-roller 24. The first counter-roller 22, the second counter-roller 24 and the needle roller 18 are arranged such that the through-channel 46 runs parallel to the direction of action of the weight force g. The film 12 can therefore be introduced from above into the through-channel 46 and guided through it by utilizing the weight force g. The free end of the film 12 can then be threaded into the second guide roller pair 40. The device 10 can then be brought into the closed position, so that the Fig. 1. The adjustment between the open position and the closed position can be performed using the adjustment device 26. However, a further adjustment unit, not shown here, can also be provided for this purpose. In this case, the adjustment device 26 limits the fine adjustment of the first counter-roller 22, the second counter-roller 24, and the needle roller 18 relative to one another in order to set the desired contact pressure and the diameter of the holes.

[0044] Both in Fig. 1 as well as in Fig. 3 shows a shielding unit 48, which prevents a person from accidentally coming into contact with the needle roller 18 and thereby being injured. The shielding unit 48 is rotatably mounted in the housing 14 and can be moved away from the needle roller 18 when access to the needle roller 18 is necessary. A safety device (not shown) can be provided to ensure that the shielding unit 48 can only be moved when the needle roller 18 is stationary. Fig. 3, the shielding unit 48 is in a closed position, which is defined so that when threading into the second foil pair 40, the foil 12 cannot touch the needle roller 18. If the threading is carried out manually, the shielding unit 38 also prevents the person concerned from coming into contact with the needle roller 18 and thereby injuring themselves. Fig.1, the shielding unit 48 is shown in an operating position in which the first counter-roller 22 and the second counter-roller 24 can be moved close enough to the needle roller 18 to form the first active area 42 and the second active area 44. Furthermore, the shielding unit 48 largely covers the needle roller 18 to minimize the risk of injury.

[0045] Analogously, the housing 14 can have an opening flap (not shown) that can open and close access to the cavity 16. The safety device can be configured such that the opening flap only opens access when the needle roller 18, the first counter roller 22, and the second counter roller 24 are stationary. List of reference symbols 10 Device 12 slides 14 housings 16 Cavity 18 Needle roller 20 needles 22 first counter roller 24 second counter roller 26 Adjustment device 28 first surface 29 Rubber coating 30 second surface 32 bristles 34 Drive unit 36 Guide device 38 first pair of guide rollers 40 second pair of guide rollers 42 first effective range 44 second effective range 46 Feed-through channel 48 Shielding unit g weight force H1 first hardness H2 second hardness P Arrow T1 first penetration depth T2 second penetration depth

Claims

[1] Device (10) for perforating web-shaped films (12), in particular plastic films, comprising - a rotatably mounted needle roller (18) with a number of needles (20), - a rotatably mounted first counter-roller (22), with which the film (12) can be brought into contact with the needle roller (18) in a first effective area (42) such that the needles (20) are pressed into the film (12) with a first penetration depth (T1), and - a rotatably mounted second counter roller (24), with which the foils (12) can be brought into contact with the needle roller (18) in a second effective area (44) such that the needles (20) are pressed into the foil (12) with a second penetration depth (T2), wherein the first penetration depth (T1) is less than the second penetration depth (T2), characterized by , that - the first counter roll (22) has a first surface (28) with a first hardness (H1) and - the second counter roll (24) has a second surface (30) with a second hardness (H2), wherein - the first hardness (H1) is higher than the second hardness (H2). [2] Device (10) according to claim 1, characterized by that the first penetration depth (T1) is selected so that the needles (20) do not penetrate the film (12). [3] Device (10) according to one of claims 1 or 2, characterized by , that - at least the needle roller (18) or - at least the first counter-roller (22) and / or the second counter-roller (24) are adjustably mounted by means of an adjusting device (26). [4] Device (10) according to one of the preceding claims, characterized by that the first counter roller (22) has a closed first surface (28). [5] Device (10) according to one of the preceding claims, characterized bythat the second counter roller (24) has an open second surface (30) into which the needles (20) can dip. [6] Device (10) according to one of the preceding claims, characterized by , that - the needle roller (18), and / or - the first counter roller (22), and / or - the second counter roller (24) can be driven or is driven by means of a drive unit (34). [7] Device (10) according to one of the preceding claims, characterized by that the device (10) - between an open position in which the film (12) can be inserted into the device (10), and - a closed position in which the film (12) can be perforated, whereby - in the open position, the needle roller (18), the first counter roller (22) and the second counter roller (24) are arranged so that a through-channel (46) is formed through which the film (12) can be passed for insertion. [8] Device (10) according to one of the preceding claims, characterized by that the device (10) - a shielding unit (48) for shielding the needle roller (18) and / or - a housing (14) in which the needle roller (18), the first counter roller (22) and the second counter roller (24) are arranged. [9] Method for perforating web-shaped films (12), in particular plastic films, with a device (10) according to one of the preceding claims, comprising the following steps: - pressing in the needles (20) of the needle roller (18) in the first effective area (42) with a first penetration depth (T1), and - pressing in the needles (20) of the needle roller (18) in the second effective area (44) with a second penetration depth (T2), wherein - the first penetration depth (T1) is less than the second penetration depth (T2) and - the film (12) remains on the needle roller (18) when moving from the first effective area (42) to the second effective area (44). [10] Method according to claim 9, comprising the following steps - feeding the film (12) to the needle roller (18) at a web speed, - Driving the needle roller (18) by means of the drive unit (34) such that the needles (20) are moved at their free ends synchronously with the film (12) or faster than the film (12).

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