Weld Seam, Method and Device for Connecting Plastics Films by Thermal Joining, and Use of a Blow-Forging Press

Abstract

Weld seam, method and device for connecting plastic films (10) by thermal joining, wherein the plastic films (10) are connected between welding jaws (2, 4) along a weld seam (12). According to the invention, the device comprises a pair of unheated welding jaws (2, 4) between which the plastic films (10) are arranged parallel to each other for thermal joining. A device for impulse generation (30) applies an impact impulse to one of the welding jaws (2, 4) with a penetration time into the plastic films (10) of less than 10 ms with a first intensity (Fi1). The impact impulse acts on the plastic films (10), wherein a heating in the material caused by deformation is produced and the weld seam (12) is formed in an effective area of the welding jaws (2, 4); use of a blow-forging press.

Claims

1. A weld seam for connecting plastic films (10), produced by thermal joining between welding jaws (2, 4), characterized in that an impact impulse, a stroke movement of at least one of the welding jaws (2, 4) perpendicular to the film layer, with a penetration time of at least one of the welding jaws (2, 4) into the plastic films (10) of less than 10 ms, acts on the unheated plastic films (10) arranged in parallel between a pair of unheated welding jaws (2, 4), the impact impulse having at least a first intensity (F.sub.i1) by which the weld seam (12) is formed, the plastic melted by the impact impulse being restricted to the weld seam (12).

2. The weld seam according to claim 1, wherein the width thereof is between half and twice the thickness of each of the plastic films (10).

3. The weld seam according to claim 1, which is formed as a longitudinal seam (12) that connects the plastic film (10) in the area of opposing edges and forms a film tube (14) from the plastic film (10).

4. The weld seam according to claim 3, which is formed as at least one transverse seam (12) that closes the film tube at at least one end and produces a tubular bag (16).

5. The weld seam according to claim 3, wherein the impact impulse acts on the plastic films (10) with a second intensity (F.sub.i2), whereby after the weld seam (12) has been produced, it is separated along a dividing line and welded plastic films (10) remain on both sides of the dividing line.

6. The weld seam according to claim 1, wherein a shrink film is used as the plastic film (10).

7. The weld seam according to claim 1, wherein the weld seam (12) is designed as at least one weld point (12) and a plurality of weld points (12) arranged in a row connect the plastic films (10).

8. A method for connecting plastic films (10) by thermal joining between welding jaws (2, 4), wherein the plastic films (10) are connected along a weld seam (12), characterized in that an impact impulse, a stroke movement of at least one of the welding jaws (2, 4) extending perpendicularly to the film layer, with a penetration duration of at least one of the welding jaws (2, 4) into the non-preheated plastic films (10) arranged parallel to one another, is shorter than 10 ms, acts on the plastic films (10) with at least a first intensity (F.sub.i1), causes a heating in the material due to deformation and forms the weld seam (12).

9. The method according to claim 8, wherein in a step preceding the impact impulse, the plastic films (10) are pressed against each other between the pair of welding jaws (2, 4) with a pre-tensioning force F.sub.v and then the impact impulse acts on the plastic films (10) at least through one of the driven welding jaws (2, 4) or at least through one of the welding jaws (2, 4).

10. The method according to claim 8, wherein the impact impulse is effected with a second intensity (F.sub.i2) instead of the first intensity (F.sub.i1), wherein the second intensity (Fi2) is higher than the first intensity (F.sub.i1), so that immediately after the joining, a separation of the plastic films (10) within and along the weld seam (12) occurs.

11. The method according to claim 8, wherein the mechanical drive of the welding jaws (2, 4) is effected directly or the indirectly transmitted impact impulse is effected by spring force, a drop weight, a magnetic drive or a cam disk drive.

12. The method according to claim 8, wherein the impact impulse is applied by the upper welding jaw (2) or by both welding jaws (2, 4) acting against each other

13. The method according to claim 12, wherein the welding jaws (2, 4) acting against each other are part of a continuous, high-speed process.

14. A device for connecting plastic films (10) by thermal joining, wherein the plastic films (10) are connected between welding jaws (2, 4) along a weld seam (12), characterized in that the device (1) comprises a pair of unheated welding jaws (2, 4) between which the unheated plastic films (10) are arranged parallel to each other for thermal joining, wherein a device for impulse generation (30) generates an impact impulse, a stroke movement of at least one of the welding jaws (2, 4) perpendicular to the film layers with a penetration time of at least one of the welding jaws (2, 4) into the plastic films (10) of less than 10 ms, having at least a first intensity (F.sub.i1) into at least one of the welding jaws (2, 4), wherein the impact impulse acts on the plastic films (10), a heating in the material of the plastic films (10) caused by deformation is produced and the weld seam (12) is formed in an effective area of the welding jaws (2, 4).

15. The device according to claim 14, wherein the welding jaws (2, 4) are pressed against each other by means of a device for applying a prestressing force (F.sub.v) before the impact impulse is applied.

16. The device according to claim 14, wherein the pair of welding jaws (2, 4) consists of at least a first welding jaw (2) with an active area having a profiled cross-section (6).

17. The device according to claim 16, wherein the pair of welding jaws (2, 4) comprises a second welding jaw (4) with a flat active area (6) or with a profiled cross section (6), wherein the profiled cross-section (6) is formed as a radius R1, or wherein the profiled cross-section (6) is formed as a flat profile with a width a, which is limited by two radii R2 or wherein the profiled cross-section (6) is wedge-shaped at an angle to the flat effective area of the second weldinq jaw (4), the wedge tip of which is formed as a radius R3.

18. (canceled)

19. (canceled)

20. (canceled)

21. The device according to claim 14, wherein the pair of welding jaws (2, 4) is inserted into a high-speed, continuous web running process with continuous feed.

22. The device according to claim 21, wherein the first and/or the second welding jaw (2, 4) is designed as a rolling tool (42), as a tool that pivots towards the active zone or as a tool that is intermittently carried along with the web during the welding process.

23. (canceled)

24. (canceled)

25. The use of a blow-forging press (20) as a drive mechanism for a device according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The invention is explained in more detail below, based on the description of examples of the design and their representation in the associated drawings. The following show:

[0058] FIG. 1: a schematic view of a process sequence of the method according to the invention for connecting plastic films by thermal joining;

[0059] FIG. 2: a schematic perspective view of an embodiment of a welding jaw according to the invention with an active area with a cross-section profiled as a radius;

[0060] FIG. 3: a schematic perspective view of an embodiment of a welding jaw according to the invention with an active area with a cross section profiled as a radius, limited by two radii;

[0061] FIG. 4: a schematic perspective view of an embodiment of a welding jaw according to the invention with an active area with a cross section profiled at a flat angle;

[0062] FIG. 5: a schematic perspective view of an embodiment of a first welding jaw according to the invention with an active area with a flat-profiled cross-section;

[0063] FIG. 6: a schematic perspective view of an embodiment of a second welding jaw according to the invention with a flat working area;

[0064] FIG. 7: a schematic view of an embodiment of a blow-forging press in two views;

[0065] FIG. 8: a schematic side view of an embodiment of a continuous web running process;

[0066] FIG. 9: a schematic view of a further embodiment of a continuous web running process;

[0067] FIG. 10: a schematic perspective view of an embodiment of a weld seam according to the invention on a film tube;

[0068] FIG. 11: a schematic perspective view of an embodiment of weld seams according to the invention on a tubular bag;

[0069] FIG. 12: a schematic side view of an embodiment of an apparatus according to the invention in a joining-separating combination and

[0070] FIG. 13: a schematic enlarged view of a joining-separating combination with joined plastic films and a separated area.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] FIG. 1 shows a schematic view of a process sequence of the method according to the invention for connecting plastic films 10 by thermal joining. The process sequence is shown in three steps, starting from the left. First, a first welding jaw 2 is moved over the feed distance s.sub.z to the surface of the plastic films 10 in the direction of the arrow until an active area 6, 6 touches the plastic films 10. The two plastic films 10 to be joined by a weld seam are thereby lying on the surface of the second welding jaw 4.

[0072] In a second step, the first welding jaw 2 is pressed against the plastic films 10 with a pre-tensioning force F.sub.v. In the third step, the impulse force F.sub.i is applied under the pre-load created in this way, which leads to the formation of the weld 12.

[0073] In the embodiment of the method according to the invention shown, the plastic films 10 remain connected to each other in the area of the weld seam 12. However, by selecting a higher impulse force F.sub.i, the plastic films 10 can also be separated at the weld seam 12, so that two plastic films are present that are connected to each other by the weld seam 12, but are transversely separated in the area of the weld seam 12.

[0074] FIG. 2 shows a schematic perspective view of an embodiment of a first welding jaw 2 according to the invention, with a profiled cross-section designed as a radius R1, which forms a profiled active area 6. For a film thickness of 70 m, the preferred radius R1=4 to 10 mm, wherein a good material bond at the weld and a tight weld seam are achieved.

[0075] FIG. 3 shows a schematic perspective view of a design of a welding jaw 2 according to the invention with a flat profiled cross-section, limited by two radii R2, which forms an effective area 6. For a film thickness of 70 m, the preferred radius R2=1 to 4 mm and the flat profile has a width a=0.1 to 0.5 mm.

[0076] FIG. 4 shows a schematic perspective view of a design of a welding jaw 2 according to the invention with a flat-angled profiled cross-section, which forms an effective area 6. The tip of the angle has a radius R3. For a film thickness of 70 m, the preferred radius R3=4 to 10 mm and the preferred angle =2 to 5.

[0077] FIG. 5 shows a schematic perspective view of a design of a first welding jaw 2 according to the invention with an active area 6 with a flat cross-section. A mounting hole 8 is used to insert a clamping bolt, which is not shown here, with which the first welding jaw 2 is attached to a welding jaw holder 26 (see FIG. 7) of a machine that applies the pre-tensioning force F.sub.v and the impulse force F.sub.i to the first welding jaw 2.

[0078] FIG. 6 shows a schematic perspective view of a design of a second welding jaw 4 according to the invention with a flat active area 6. This is attached to a welding jaw holder 28 (see FIG. 7).

[0079] FIG. 7 shows a blow-forging press 20 in two views, which is used to carry out the sealing process according to the invention. It is particularly advantageous that such a blow-forging press 20 can be operated without electrical power and purely manually if it is designed as a spring-loaded blow-forging press according to the example shown. The force required for the feed movement over the feed distance s.sub.z, as well as for the pre-tensioning force F.sub.v and the impulse force F.sub.i, is applied by the operator via an operating lever 24.

[0080] As shown in FIG. 1, the weld 12 is produced between the second welding jaw 4, on which the plastic films 10 rest, and the first welding jaw 2, which is fastened in a first welding jaw holder 26. To do this, the operating lever 24 is moved and the first welding jaw holder 26 is moved towards the second welding jaw holder 28 by means of a feed device 32 until the first welding jaw 2 inserted in the first welding jaw holder 26 touches the plastic films 10.

[0081] By further movement of the operating lever 24, the required pre-tensioning force F.sub.v is applied and, after continued movement of the operating lever 24, wherein a spring is tensioned, the impulse force F.sub.i is applied to the plastic films 10 by triggering the impulse generation 30. The weld 12 is thus produced in the area of an active zone between the first welding jaw 2 and the second welding jaw 4. The return stroke of the second welding jaw holder 26 and thus of the associated welding jaw by countermovement of the operating lever 24 leads to the release of the sealed, welded plastic films 10.

[0082] Depending on the desired result and the set level of the impulse force F.sub.i, the sealed plastic films 10 can be additionally and simultaneously separated in the area of the weld seam 12 and along the latter. This can be advantageous, for example, if a package, a tubular bag, is to be closed by the weld seam 12 and at the same time separated from a subsequent package.

[0083] FIG. 8 shows a schematic side view of a continuous web running process in which each of the plastic films 10 to be welded runs off a supply roll 40. In the device 1 for connecting plastic films 10 by thermal joining, the plastic films 10 pass between the first welding jaw 2 and the second welding jaw 4, where the weld seam 12 (not yet formed in the illustration) is produced. However, precautions must be taken to ensure the continuity of the web running process, even during the application of the prestressing force in particular, but also of the impact impulse. This can be realized, for example, by a cyclically synchronized movement of the device 1 or by a web buffer storage after the supply roll 40 and before the device 1.

[0084] FIG. 9 shows a further embodiment of a continuous web running process in a schematic side view. The prestressing force is applied by prestressing rollers 42, between which the plastic film 10 passes. A device for impulse generation 30, in particular a percussion gear, acts on one or both of the pre-tensioning rollers 42, so that the impact impulse is indirectly introduced into the plastic film 10 and the weld seam 12 is produced.

[0085] FIG. 10 shows a schematic perspective view of an embodiment of a weld seam 12 according to the invention on a film tube 14. This can advantageously be used as a sleeve packaging, wherein the film tube 14 is pushed over a package. It is particularly advantageous if the film tube 14 consists of a shrink film that shrinks when heated and fits tightly and smoothly as a shrink sleeve to the wrapped packaging.

[0086] The particular advantages of the method according to the invention become apparent in such an application, since the weld seam 12 does not impair the surrounding areas of the shrink film by heating. While in known welding processes the heat flow from the (also comparatively wide) weld into the surrounding plastic film leads to unsightly, undesirable and even after shrinking still visible deformations, especially wrinkling, and thus an aesthetically deficient result, the invention can avoid these disadvantages. The weld seam 12 is very narrow and, as explained above, avoids thermal impairment of the plastic film 10 adjacent to the weld seam 12, which remains smooth in the area of the weld seam 12 and also retains its full shrink capacity.

[0087] FIG. 11 shows a schematic perspective view of an embodiment of the weld seams 12 according to the invention on a tubular bag 16. This comprises a film tube 14, as shown in FIG. 10, which is sealed at both ends. This is usually done on the second side after filling with a packaged product. At the same time, the tubular bag 16, which is closed by a top seam, the upper weld seam 12, is separated from the film web by means of a joining-separating combination, while a further bottom seam, the lower weld seam 12 of the next tubular bag 16, is produced.

[0088] A shrink film can also be used for this application, in particular to wrap a box, wherein the wrapping lies tightly against the box after shrinking. Here too, the advantage is that an attractive appearance can be achieved by very narrow, clean and non-distorted weld seams 12.

[0089] FIG. 12 shows a schematic side view of a design of a device 1 according to the invention in a joining-separating combination, i.e. that immediately after the welding or practically at the same time, the plastic films 10 are separated directly in the center of the already very narrow weld 12. This is particularly clear in the enlarged view in FIG. 13. The device 1 comprises the welding jaws 2, 4, shown after the return stroke, which releases the joining and separating point.

[0090] FIG. 13 shows a schematic enlarged view of a joining-separation combination with joined plastic films 10 and a separated area where the part protruding beyond the weld 12 is separated within the weld 12. The very narrow weld 12 can be seen.

[0091] The material next to the weld 12 is not thickened, which already makes it clear that no excess material from the plastic films 10 is melted and displaced, as is the case with other prior-art heat-sealing processes. It can also be seen that the heat-affected zone 13, whose boundary with the unaffected plastic film 10 is shown by a dashed line, is limited to the weld 12, the joining zone, and leaves the surrounding areas of the plastic films 10 unaffected.

[0092] FIG. 14 shows a schematic enlarged view of a joint with joined plastic films 10, without separation at the weld 12, so that the plastic films 10 extend on both sides of the weld 12. The very low weld 12 with the height H at the joint zone, the fused plastic films 10, can also be seen. The material next to the weld 12 is also not thickened, which makes it clear that no excess material from the plastic films 10 is melted and displaced. Rather, the heat-affected zone 13 is confined to the area of the weld seam 12 and neither the plastic films 10 nor any area outside the plastic films 10, for example a heat-sensitive packaged product inside a package, is affected by unwanted heating.

LIST OF REFERENCE NUMERALS

[0093] 1 Device [0094] 2 First welding jaw [0095] 4 Second welding jaw [0096] 6, 6 Effective area [0097] 8 Mounting hole [0098] 10 Plastic film [0099] 12 Weld seam, joining zone, longitudinal seam, transverse seam, weld spot [0100] 13 Heat-affected zone [0101] 14 Tubular film [0102] 16 Tubular bag [0103] 20 Blow-forging press [0104] 22 Stand [0105] 24 Operating lever [0106] 26 First welding jaw holder [0107] 28 Second welding jaw holder [0108] 30 (Device for) impulse generation [0109] 32 Feed device [0110] 40 Supply roll [0111] 42 Rolling tool, pre-tensioning roller [0112] a Effective width [0113] R1 First effective range radius [0114] R2 Second effective range radius [0115] R3 Third effective range radius [0116] F.sub.v Preload force [0117] F.sub.i Impact force, intensity of the impact [0118] s.sub.z Feed distance [0119] H Height of joining zone (weld seam)