Ultrasonic sealing jaw and method for ultrasonic sealing

1. Ultrasonic sealing jaw ( 1 ) for sealing portions of plastic film to a tube so as to form a sealing engagement of the portions of plastic film around the circumference of the tube, the sealing jaw ( 1 ) comprising a concave film-tube welding portion ( 7 ) for receiving the tube covered by the plastic films, the film-tube welding portion ( 7 ) being adapted to form the film-tube attachment, and, adjacent to at least one side of the concave portion ( 7 ) of the sealing jaw ( 1 ), characterised in that the sealing jaw comprises a substantially flat film-film welding portion ( 3 , 4 ) for engaging the plastic film and sealing adjacent portions of plastic film to each other in an area adjoining the tube, said film-film welding portion ( 3 , 4 ) defining a top plane ( 10 ) of the sealing jaw ( 1 ), and the film-film welding portion ( 3 , 4 ) comprises along the edge towards the film-tube welding portion ( 7 ) at least one recess with a surface ( 11 ) so as to form a cavity ( 12 ) with an opening towards the film-tube welding portion ( 7 ).

2. Sealing jaw according to claim 1 , wherein the surface ( 11 ) of the recess extends from a first point A located at the film-tube welding portion ( 7 ) at a level h below the top plane ( 10 ) to a second point B located in the top plane ( 10 ) at a distance L from the first point A in a direction away from the film-tube welding portion ( 7 ) and parallel to the top plane ( 10 ), wherein the point A defines the intersection of the surface ( 11 ) of the recess with the film-tube welding portion ( 7 ) and point B defines the intersection of the surface ( 11 ) of the recess with the top plane ( 10 ).

3. Sealing jaw according to claim 2 , wherein L is at least 0.1 mm, alternatively at least 0.2 mm preferably at least 0.3 mm, most preferably at least 0.5 mm and L is less than 10 mm, alternatively less than 5 mm, preferably less than 3 mm.

4. Sealing jaw according to claim 2 , wherein h is between 0.01 mm and 0.3 mm, alternatively between 0.01 mm and 0.15 mm, preferably between 0.01 mm and 0.1 mm.

5. Sealing jaw according to claim 1 , wherein the distance between the surface ( 11 ) of the recess and the top plane ( 10 ) is largest at the opening towards the film-tube welding portion ( 7 ) as seen in the direction perpendicular to the top plane ( 10 ).

6. Sealing jaw according to claim 5 , wherein the surface ( 11 ) of the recess monotonously approaches the top plane ( 10 ) as seen in the direction from the film-tube welding portion ( 7 ) towards the film-film welding portion ( 4 ).

7. Sealing jaw according to claim 2 , wherein the surface ( 11 ) of the recess comprises a step edge with a level difference d at point B, a first area ( 11 b ) extending from the step edge to an intermediate point P, the first area ( 11 b ) being substantially parallel to the top plane ( 10 ) at a distance d thereto, and a second area ( 11 a ) extending from the intermediate point P to point A at the film-tube welding portion ( 7 ), wherein the distance of the second area ( 11 a ) to the top plane ( 10 ) gradually increases from the level difference d at the intermediate point P to level h at point A, wherein level h is larger than level difference d.

8. Sealing jaw according to claim 7 , wherein the second area ( 11 a ) is a plane that is inclined towards the film-tube welding portion ( 7 ) by an angle α with respect to the top plane ( 10 ), wherein the angle α is between 0.05 degrees and 20 degrees, alternatively between 0.2 degrees and 10 degrees, preferably between 0.5 and 5 degrees.

9. Sealing jaw according to claim 1 , wherein a film-film welding portion ( 3 , 4 ) is provided on either side of the film-tube welding portion ( 7 ).

10. Sealing jaw according to claim 9 , wherein both film-film welding portions ( 3 , 4 ) comprise at least one recess so as to form a cavity ( 12 ) with an opening towards the film-tube welding portion ( 7 ).

11. Sealing jaw according to claim 1 , wherein the film-film welding portion comprises at least one depression ( 16 , 18 , 28 ).

12. Sealing jaw according to claim 1 , wherein the film-film welding portion as seen in a direction perpendicular to the top plane has a first leg ( 20 ) along the edge towards the film-tube welding portion ( 7 ) and at least a second leg ( 21 , 22 ) connected to the first leg ( 20 ) and pointing away from the film-tube welding portion ( 7 ).

13. Apparatus for ultrasonic sealing of portions of plastic film in sealing engagement around a tube, the apparatus comprising cooperating sealing jaws ( 1 , 2 ) configured to close around the tube and the portions of plastic film, so as to apply a pressure to the plastic film, and means for transferring ultrasonic energy to the plastic film and/or tube through at least one of the sealing jaws ( 1 , 2 ), characterised in that at least one of the sealing jaws ( 1 , 2 ) is a sealing jaw according to claim 1 .

14. Apparatus according to claim 13 , wherein ultrasonic energy (U 1 ) with a first frequency (Uf 1 ) is applied to the plastic film and/or the tube through a first sealing jaw ( 1 ) and ultrasonic energy (U 2 ) with a second frequency (Uf 2 ) is applied to the plastic film and/or the tube through a second sealing jaw ( 2 ) cooperating with the first sealing jaw ( 1 ) simultaneously.

15. Method for ultrasonic sealing of portions of plastic film ( 41 , 42 ) to a tube ( 30 ) so as to form a sealing engagement of the portions of plastic film ( 41 , 42 ) around the circumference of the tube ( 30 ) and sealing the portions of plastic film ( 41 , 42 ) together in an area adjoining the tube, the method comprising the steps of

arranging the tube ( 30 ) between the portions of plastic film ( 41 , 42 ),

engaging the portions of plastic film ( 41 , 42 ) by means of cooperating sealing jaws ( 1 , 2 ), thereby clamping the plastic film ( 41 , 42 ) around the tube ( 30 ) in concave film-tube welding portions ( 7 , 8 ) of the sealing jaws ( 1 , 2 ) and pressing abutting portions of plastic film ( 41 , 42 ) against each other by means of substantially flat film-film welding portions ( 3 , 4 , 5 , 6 ) adjoining the film-tube welding portions ( 7 , 8 ) of the sealing jaws ( 1 , 2 ),

applying a clamping force (F 1 , F 2 ) to the sealing jaws ( 1 , 2 ) in a direction substantially perpendicular to the film-film welding portions ( 3 , 4 , 5 , 6 ), thereby exerting a pressure on the plastic film ( 41 , 42 ) in contact with the sealing jaws ( 1 , 2 ), and,

by means of the sealing jaws ( 1 , 2 ), applying ultrasonic energy (U 1 , U 2 ) to the layers of plastic film ( 41 , 42 ) and/or tube ( 30 ) during an exposure time,

characterised in that

the film-film welding portions ( 3 , 4 , 5 , 6 ) comprise at least one proximal region ( 3 b , 4 b , 5 b , 6 b ) extending from a first point A at the film-tube welding portion ( 7 , 8 ) to a second point B a distance L away from the film-tube welding portion, and at least one distal region ( 3 a , 4 a , 5 a , 6 a ) extending from point B in a direction away from the film-tube welding portion, wherein the pressure exerted on the plastic film by the at least one proximal region ( 3 b , 4 b , 5 b , 6 b ) is reduced with respect to the pressure exerted by the at least one distal region ( 3 a , 4 a , 5 a , 6 a ).

16. Method according to ultrasonic sealing of portions of plastic film ( 41 , 42 ) to a tube ( 30 ) so as to form a sealing engagement of the portions of plastic film ( 41 , 42 ) around the circumference of the tube ( 30 ) and sealing the portions of plastic film ( 41 , 42 ) together in an area adjoining the tube, the method comprising the steps of

arranging the tube ( 30 ) between the portions of plastic film ( 41 , 42 ),

engaging the portions of plastic film ( 41 , 42 ) by means of cooperating sealing jaws ( 1 , 2 ), thereby clamping the plastic film ( 41 , 42 ) around the tube ( 30 ) in concave film-tube welding portions ( 7 , 8 ) of the sealing jaws ( 1 , 2 ) and pressing abutting portions of plastic film ( 41 , 42 ) against each other by means of substantially flat film-film welding portions ( 3 , 4 , 5 , 6 ) adjoining the film-tube welding portions ( 7 , 8 ) of the sealing jaws ( 1 , 2 ),

applying a clamping force (F 1 , F 2 ) to the sealing jaws ( 1 , 2 ) in a direction substantially perpendicular to the film-film welding portions ( 3 , 4 , 5 , 6 ), thereby exerting a pressure on the plastic film ( 41 , 42 ) in contact with the sealing jaws ( 1 , 2 ), and,

by means of the sealing jaws ( 1 , 2 ), applying ultrasonic energy (U 1 , U 2 ) to the layers of plastic film ( 41 , 42 ) and/or tube ( 30 ) during an exposure time,

characterised in that

the film-film welding portions ( 3 , 4 , 5 , 6 ) comprise at least one proximal region ( 3 b , 4 b , 5 b , 6 b ) extending from a first point A at the film-tube welding portion ( 7 , 8 ) to a second point B a distance L away from the film-tube welding portion, and at least one distal region ( 3 a , 4 a , 5 a , 6 a ) extending from point B in a direction away from the film-tube welding portion, wherein the pressure exerted on the plastic film by the at least one proximal region ( 3 b , 4 b , 5 b , 6 b ) is reduced with respect to the pressure exerted by the at least one distal region ( 3 a , 4 a , 5 a , 6 a ), wherein at least one of the sealing jaws ( 1 , 2 ) is a sealing jaw according to claim 1 .