Lid for closing a cup
A lid ( 2 ) for closing a cup ( 1 ) along a peripheral sealing edge ( 10 ) and a method for producing such a lid. The lid includes at least one aluminum film and an optionally multi-layered plastic layer which is co-extruded onto the aluminum film and has a closed predetermined tearing line ( 3 ). The plastic layer is made of plastic based on polyethylene (PE) or plastic based on polypropylene (PP), and the predetermined tearing line is introduced into the plastic layer preferably by means of a CO 2 laser. The predetermined tearing line ( 3 ) may be provided directly in the region of the sealing edge ( 10 ).
1. A process for producing a lid for closing a cup along a circumferential sealing rim, where lid material for producing the lid comprises at least one aluminum foil and one or more layers of polymer film coextruded onto the at least one aluminum foil, with at least one layer of the polymer film comprising either polyethylene polymer or polypropylene polymer and configured to form an inner surface of the lid, the process comprising:
conveying the lid material past a laser; wherein the lid material is in a form of a continuous sheet, the lid material is sliding on an appropriate support, and the polymer film is facing the laser;
focusing a laser beam from the laser on a point within the polymer film and above the aluminum foil when viewed from a side of incidence of the laser, such that the laser beam is focused to a diameter of from about 150 μm to about 350 μm; and
introducing a cohesive line of weakness into the polymer film using the focused laser beam, wherein the introduced cohesive line of weakness is introduced in a portion of the polymer film that will face an interior of the cup, and wherein the cohesive line of weakness does not expose the aluminum foil.
2. The process of claim 1 , wherein focusing includes focusing the laser beam to a diameter of about 210 μm.
3. The process of claim 1 , wherein focusing includes focusing the laser beam such that the focal point is at a depth in the range from about 75% to about 90% of a thickness of the layer being treated by the laser when viewed from a side of incidence of the laser.
4. The process of claim 1 , wherein focusing includes focusing the laser beam such that the focal point is at a depth in the range from about 80% to about 85% of a thickness of the layer being treated by the laser when viewed from a side of incidence of the laser.
5. The process of claim 1 , wherein the laser beam has a wavelength in the range from about 10.2 μm to about 10.8 μm.
6. The process of claim 1 , wherein the laser is selected to produce a laser beam having an energy of from about 100 W to about 450 W.
7. The process of claim 1 , wherein the laser is selected to produce a laser beam having an energy of about 300 W.
8. The process of claim 1 , further comprising selecting an appropriate conveying speed for producing a desired cohesive line of weakness, where the appropriate conveying speed is dependent upon one or more of the composition of the layers to be weakened, the thickness of the layers to be weakened, and the desired degree of weakening.
9. The process of claim 1 , further comprising selecting a conveying speed that results in a point of incidence of the laser beam on the surface of the lid material to be moving across the lid material surface at a speed in the range from about 5 mm/s to 50 mm/s.