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DE-102024133170-A1 - Method for producing a plastic film with a local material weakening arrangement using ultrasound

DE102024133170A1DE 102024133170 A1DE102024133170 A1DE 102024133170A1DE-102024133170-A1

Abstract

A method for producing a plastic film (48) provided with a local material weakening arrangement (12) comprises the following steps: i. Providing an ultrasonic tool arrangement (25) comprising at least one sonotrode (26(i)) and at least one anvil (30) as ultrasonic tools (28, 32) with mutually approachable and mutually removable cooperating action formations (33, 35), wherein at least one ultrasonic tool (28, 32) has a structure action formation (33) which has a complementary shape with respect to the shape of at least one section of the local material weakening arrangement (12), ii. Inserting a plastic film blank (22) into a working gap (24) between the ultrasonic tools (28, 32), iii. Reducing a working gap width (W) to a first working gap final width (w) which is less than the film thickness (D) of the plastic film blank (22), iv. Activating at least one sonotrode (26(i)) at least during step iii. of working gap reduction, and v. Increasing the working gap width (W) to a second working gap end width (W max ) which is larger than the film thickness (D) of the plastic film blank (22).

Inventors

  • Andreas Michalsky

Assignees

  • HUHTAMAKI FLEXIBLE PACKAGING GERMANY GMBH & CO. KG

Dates

Publication Date
20260513
Application Date
20241113

Claims (10)

  1. Method for producing a plastic film (48) provided with a local material weakening arrangement (12), wherein the material weakening arrangement (12) has a defined shape, the method comprising the following steps: i. providing an ultrasonic tool arrangement (25) comprising at least one sonotrode (26(i)) and at least one anvil (30) as ultrasonic tools (28, 32) with mutually approachable and mutually removable cooperating active formations (33, 35), wherein at least one ultrasonic tool (28, 32) has a structure-active formation (33) which has a complementary shape with respect to the shape of at least one section of the local material weakening arrangement (12), ii. inserting a plastic film blank (22) into a working gap (24) between the ultrasonic tools (28, 32), iii. iv. Reducing a working gap width (W) to a first working gap final width (w) which is less than the film thickness (D) of the plastic film blank (22), iv. Activating the at least one sonotrode (26(i)) or maintaining an activation state of the at least one sonotrode (26(i)) during step iii. of reducing the working gap width, v. Increasing the working gap width (W) to a second working gap final width (W max ) which is greater than the film thickness (D) of the plastic film blank (22).
  2. Procedure according to Claim 1 , characterized in that the first working gap end width (w) is greater than zero, so that a material weakening (13) introduced into the plastic film blank (30) by approaching the cooperating active formations (33, 35) does not completely penetrate the plastic film blank (22) in the thickness direction (TD) of the plastic film blank (22).
  3. Procedure according to Claim 1 or 2 , characterized in that the method comprises the following further steps: vi. advancing the plastic film blank (22) and vii. repeating steps iii. to v.
  4. Procedure according to Claim 3 , characterized in that at least one ultrasonic tool (28, 32) is a rotatable ultrasonic tool (28, 32) and the method comprises a step of rotating the at least one rotatable ultrasonic tool (28, 32).
  5. Procedure according to Claim 4 , characterized in that a rotational movement of the at least one rotatable ultrasonic tool (28, 32) is a continuous rotational movement.
  6. Procedure according to one of the Claims 3 until 5 , characterized in that a feed movement of the plastic film blank (22) is a continuous feed movement.
  7. Procedure according to Claim 3 , characterized in that the relative movement to reduce the working gap width (W) in step iii. is exclusively a translational relative movement towards each other.
  8. Procedure according to Claim 4 or after Claim 7 , characterized in that a feed movement of the plastic film blank (22) is a clocked feed movement.
  9. Method according to one of the preceding claims, characterized in that the amplitude of an ultrasound-induced micro-movement of an active formation (33, 35) and its origin to the respective other active formation (33, 35) are selected such that the structure-active formation (33) is located outside the plastic material of the plastic film blank (22) at one dead point of its ultrasound vibration movement and has penetrated the plastic material at the other dead point.
  10. Procedure according to Claim 9 , characterized in that the ultrasonic vibration movement of the ultrasonic tools (28, 32) at least partially, preferably completely, causes steps iii. and v.

Description

The present invention relates to a method for producing a plastic film, in particular a plastic lid film for push-through packaging, provided with a local material weakening arrangement. The material weakening arrangement has a defined shape. The material weakening arrangement is typically a linear arrangement whose line extends across the surface of the plastic film, particularly the lid film, and penetrates the film to a certain depth in the thickness direction. The material weakening arrangement generally has a relatively long linear extension, usually to ensure that the plastic film can be punctured at any given location. "Puncture" in this context refers to a local tearing or bursting of the plastic film, which occurs, for example, during the use of a push-through package formed with the plastic film as a lid film. This happens when a packaged rigid product is pressed against the surface of the plastic film or lid film facing it, thereby locally exceeding the film's strength limit. The material weakening arrangement is incorporated into the plastic film to reduce this strength limit to a manageable level. Due to the large overall length of the material weakening arrangement and its distribution over at least a large portion of the surface of the plastic film, particularly the lid film, a local reduction in the strength limit is located so close to any possible point of contact with the packaged rigid product that the applied force, regardless of the specific point of contact, is sufficient to cause the film to open at the location of the material weakening arrangement. Push-through packaging is also known as "blister packaging" in the relevant industry. The material weakening arrangement can be a continuous, long weakening that changes direction multiple times, or it can comprise a multitude of separate, shorter weakenings that work together to form the arrangement. The individual weakenings of the arrangement can intersect to create particularly weakened areas of the plastic film at their intersection points. Such a plastic film as a lid film is in the US 2008/0230432 A1 with a thickness of 6 to 50 µm. The known lid film has a material weakening arrangement comprising a multitude of material weakenings which, in order to protect the product packaged in the push-through packaging formed with the lid film, do not completely penetrate the lid film in its thickness direction. The US 2008/0230432 A1 The document discloses two possible methods for forming such a material weakening arrangement: laser cutting and a so-called "kiss-cut" method, i.e., a punch cutting process with a mechanical blade, in which the blade entering the film material to be weakened does not completely penetrate the film material. The aforementioned methods currently represent the standard procedures for producing locally weakened plastic or lidding films. While laser cutting allows for highly customized design of the material weakening arrangement, it is relatively expensive. Cutting with a mechanical blade is considerably more cost-effective for larger quantities of lidding film relative to the surface area produced, but it leads to less consistent results in the weakened product. Due to material elasticity and unpredictable fluctuations in adhesion between the blade, which has penetrated the lidding film blank, and the blade's surface of the plastic material, the dimensions of mechanically introduced material weakenings in the lidding film blank can vary significantly, particularly in the thickness direction. Furthermore, undesirable propagation of the cut material weakening as a tear when the blade is withdrawn from the plastic material adhering to it can sometimes occur. From the DE 10 2013 225 042 A1 is a known ultrasonic processing device for welding and cutting materials. The sonotrode of the from the DE 10 2013 225 042 A1 The known device can be designed as a rotating roller. Likewise, a rotatable anvil as a counter-tool for the sonotrode is known from this publication. The object of the present invention is to provide an improved method for producing a locally weakened plastic film, in particular as a lidding film for push-through packaging. The present invention solves this problem by means of a method having all the features of claim 1. Such a method comprises the following steps: i. Providing an ultrasonic tool arrangement comprising at least one sonotrode and at least one anvil as an ultra sonic tools with cooperating active formations that can be approached and removed from each other, wherein at least one ultrasonic tool has a structure-active formation which has a complementary shape with respect to the shape of at least one section of the local material weakening arrangement, ii. Inserting a plastic film blank into a working gap between the ultrasonic tools, iii. Reducing the working gap width to a first final working gap width, which is less than the film thickness of the plastic film blank, iv. Activating the at le