Welding Method for a Multilayer Composite Having a Barrier Layer

Abstract

The invention relates to a welding method for material webs which each consists of a multilayer composite having a barrier layer and are connected to each other via a sealing seam. In order to provide a welding method by means of which sealing seams can be produced which, on the one hand, meet the highest demands on strength and, on the other hand, prevent light, in particular UV light, from penetrating into the product to be packaged, according to the invention, the sealing seems are produced by leading two sealing surfaces of two tools together, wherein the material webs are arranged between the sealing surfaces and the sealing seam is produced having two seams lying beside each other, a main seam and a secondary seam and, during the production of the main seam, the two sealing surfaces exert a main welding pressure on the material webs and, during the production of the secondary seam, the two sealing surfaces exert a secondary welding pressure on the material webs, wherein the secondary welding pressure is lower than the main welding pressure, at least in some sections, and, in the secondary processing step, at least one of the two sealing surfaces is structured.

Claims

1. A method of producing a sealing seam connecting two material webs of a multilayer composite with a barrier layer, wherein the two material webs are positioned between sealing surfaces of a first and a second tool (1, 2) in such a way that the portions of the material web, that are to be connected together, lie upon each other and between the sealing surfaces, the two tools (1, 2) are moved towards each other so that the two sealing surfaces for producing the sealing seam are pressed towards each other, wherein the first tool is an ultrasonic sonotrode (1) which is excited with an ultrasonic vibration while the two sealing surfaces are pressed towards each other and the sealing seam is produced with two mutually juxtaposed seams, a main seam and a secondary seam, wherein the sealing surfaces are so selected that in a main processing portion the maximum spacing between the two sealing surfaces is less than the maximum spacing between the two sealing surfaces in a first secondary processing portion, wherein the main processing portion and the secondary processing portion are in mutually juxtaposed relationship so that in the production of the main seam the two sealing surfaces exert a main welding pressure on the material webs and in the production of the secondary seam the two sealing surfaces exert a secondary welding pressure on the material webs, wherein the secondary welding pressure is at least portion-wise less than the main welding pressure, wherein the secondary seam produced by the secondary processing portion faces towards a product which is to be enclosed in the material webs and the main seam produced by the main processing portion faces away from the product to be enclosed in the material webs, wherein during the welding operation the material webs remain in their position and in the secondary processing portion at least one of the two sealing surfaces has structure elements.

2. A method according to claim 1 characterised in that the sealing surfaces are so selected that besides the main processing portion a second secondary processing portion is provided in opposite relationship with the first secondary processing portion, wherein the maximum spacing between the two sealing surfaces in the second secondary processing portion is greater than the maximum spacing between the two sealing surfaces in the main processing portion.

3. A method according to claim 1 characterised in that the structure elements are in the form of a truncated pyramid.

4. A method of utilizing a welding tool having a sealing surface which intended to come into contact with a material to be processed, wherein the sealing surface is of a width b, for carrying out the method according to claim 1, characterised in that the sealing surface has a main portion extending in the longitudinal direction and a first secondary portion extending in the longitudinal direction, wherein the main portion (7) and the first secondary portion (8) adjoin each other, wherein the first secondary portion (8) is at least partially set back with respect to the main portion (7) in opposite relationship to the direction of a normal vector on the sealing surface by a distance a>0 mm.

5. A method according to claim 4 characterised in that the sealing surface has a second secondary portion (9), wherein the main portion (7) and the second secondary portion (9) adjoin each other so that the first secondary portion (8) and the second secondary portion (9) are positioned on opposite sides of the main portion (7), wherein the second secondary portion (9) is at least partially set back with respect to the main portion (7) in opposite relationship to the direction of a normal vector on the sealing surface by a distance a>0 mm.

6. A method according to claim 4 characterised in that the total first secondary portion (9) is set back with respect to the main portion (7) in opposite relationship to the direction of a normal vector on the sealing surface by a distance a>0 mm.

7. A method according to claim 4 characterised in that the distance a>0.002 mm.

8. A method according to claim 4 characterised in that the distance a is less than 0.5 mm.

9. A method according to claim 4 characterised in that the welding tool is an ultrasonic sonotrode (1) or a counterpart tool (2) for an ultrasonic sonotrode.

10. A method according to claim 4 characterised in that the first secondary portion (8) has structure elements.

11. A method according to claim 4 characterised in that the distance a is less than <0.05 mm.

12. A method according to claim 4 characterised in that the distance a is less than <0.01 mm.

13. A method according to claim 4 characterised in that the structure elements are in the form of a truncated pyramid.

14. A method according to claim 4 characterised in that the distance a>0.004 mm.

Description

[0037] Further advantages, features and possible uses of the present invention will be apparent from the description hereinafter of a preferred embodiment of a welding tool which is used for the method according to the invention, and the accompanying Figures in which:

[0038] FIG. 1 shows a perspective view of an embodiment of a welding tool which is used for the method according to the invention,

[0039] FIG. 2 shows a perspective partial sectional view through the embodiment of the FIG. 1 welding tool,

[0040] FIG. 3 shows a plan view of the sealing surface of the welding tool, and

[0041] FIG. 4 shows a sectional view through the welding tool.

[0042] FIG. 1 shows a perspective view of an embodiment of a welding tool used for carrying out the method according to the invention. The welding tool has a sonotrode 1 connected by way of an amplitude transformer 5 to a converter 4. The converter 4 converts an electric ac voltage into a mechanical ultrasonic vibration. For that purpose the converter 4 has a series of piezoelements. The mechanical ultrasonic vibration produced by the converter 4 is modified in terms of the amplitude of the vibration by means of the amplitude transformer 5. That vibration is performed by the sonotrode 1. The complete ultrasonic vibration system comprising the sonotrode 1, the amplitude transformer 5 and the converter 4 is held in a holder 3 which has as little effect as possible on the vibration characteristic of the vibration system.

[0043] The sonotrode 1 has a sealing surface directed downwardly in FIG. 1. Arranged in opposite relationship to the sealing surface of the sonotrode 1 is a counterpart tool 2 also having a sealing surface which is oriented upwardly in FIG. 1 so that the two sealing surfaces, namely the sealing surface of the sonotrode 1 and the sealing surface of the counterpart tool 2, are opposite.

[0044] To produce sealing seams the material webs to be connected together are disposed between the sonotrode 1 and the counterpart tool 2. The sonotrode 1 can then be moved together with the ultrasonic vibration system in the direction of the counterpart tool 2 so that the material webs come into contact both with the sealing surface of the counterpart tool 2 and also with the sealing surface of the sonotrode 1. As a result an ultrasonic vibration is exerted on the material web by the sonotrode, which leads to local fusing of the individual material webs and interconnection thereof.

[0045] FIG. 2 shows a perspective sectional view through the sonotrode 1 and the counterpart tool 2.

[0046] It will be seen that the sonotrode 1 has a structured sealing surface facing towards the counterpart tool 2. That structured surface can comprise for example truncated pyramids.

[0047] The sealing surface of the counterpart tool 2 comprises a main portion 7 extending in the longitudinal direction. In the illustrated embodiment the main portion 7 is flat, that is to say it does not have any structuring whatsoever. Arranged on both sides of the main portion 7 is a respective secondary portion 8, 9. In the illustrated example a structure has been introduced into the secondary portions 8, 9, that is to say the surface facing towards the sonotrode 1 has been portion-wise set back or recessed.

[0048] The result of this is that welding of material webs between the sealing surface of the sonotrode 1 and the sealing surface of the counterpart tool 2 is effected with a greater force in the region of the main portion 7 than in the region of the secondary portions 8, 9. Particularly when a multilayer paper composite with a barrier layer, like for example an aluminium layer is used, damage to the aluminium layer can occur in the region of the main portion 7, with the result that air can there pass into the packaging bag. As however there are secondary portions 8, 9 which allow welding with a lesser force no damage to the aluminium layer occurs in the region of the secondary portions 8, 9 so that light and in particular UV light cannot penetrate through the portions of the sealing seam, which have been produced by means of the secondary portions 8, 9.

[0049] FIG. 3 once again shows the sealing surface structure of the counterpart tool 2 as a plan view. Here too it is possible to see the main portion 7 which is flat while the secondary portions 8, 9 are structured. In the illustrated example V-shaped grooves have been introduced into the surface at a right angle relative to each other so that this gives a truncated pyramid structuring. The orientation of the grooves is so selected that they include an angle of 45° with the longitudinal direction.

[0050] FIG. 4 shows a further sectional view through the counterpart tool 2. It will be seen here that the entire sealing surface, that is to say also the top side of the truncated pyramids of the structured secondary portions 8, 9 have been set back relative to the plane of the main portion 7 by a distance a. For the purposes of illustration the distance a is shown here in greatly exaggerated form. In actual fact however it has been found that the distance a can be in the range of 0.005 mm to 0.01 mm to achieve the effect.

LIST OF REFERENCES

[0051] 1 Sonotrode [0052] 2 Counterpart tool [0053] 3 Holder [0054] 4 Converter [0055] 5 Amplitude transformer [0056] 7 Main portion [0057] 8, 9 Secondary portions