RU2805853C2 - Method for manufacturing moulded wrapper sheet - Google Patents

Abstract

FIELD: wrapper sheets.

SUBSTANCE: invention relates to a method for producing a moulded wrapper sheet. The wrapper sheet is moulded inside the forming cavity so as to reproduce the shape of the recessed part on it. Moreover, the forming step includes introducing the wrapper sheet into the forming cavity without subjecting it to deformation by stretching at least during the insertion operation phase. Moreover, the moulded sheet contains a plurality of folds, consisting of two or more layers of the specified wrapper sheet, superimposed on each other and in contact with each other. The moulded wrapper sheet is cut along a predetermined profile to form a perimetric edge and produce a moulded wrapper sheet. The cutting step involves the use of a laser generator configured to emit a laser beam and includes exposing the laser beam to the formed sheet and orienting the laser beam to make multiple passes of the laser beam along a predetermined profile. Moreover, the plurality of passes includes a first pass along the first trajectory and at least one additional pass along another trajectory, which is shifted from the first trajectory away from the given profile by a given distance.

EFFECT: increased quality of the finished packaging.

12 cl, 8 dwg

Description

The present invention relates to a method for producing a molded wrapper sheet.

In particular, the method described herein is suitable for producing a molded sheet containing a recessed portion configured to receive a product, such as a food product.

Applications of particular interest in the context of this document address methods in which a sheet of wrapper is subjected to a molding process substantially without any plastic deformation due to stretching.

In these methods, a sheet of wrapper is typically inserted into a forming cavity and positioned adjacent to the surfaces of said cavity so as to be shaped to match the shape of said cavity.

Molding processes of this type are usually carried out under cold conditions, i.e. without heating the wrapper sheet, and on wrapper sheets that contain at least one metal layer, for example, a layer of aluminum foil.

Following the forming step, known methods include a cutting step to cut the wrapper sheet along a predetermined profile.

Currently, this cutting operation is in the vast majority of cases performed using exclusively mechanical means, such as, in particular, punching tools of various types and, in a general sense, cutting knives.

Generally speaking, alternative cutting methods are also known in the industrial packaging industry that involve the use of a laser beam.

It can be noted that laser cutting has a number of advantages over mechanical methods. For example, any change that needs to be made to a cut simply requires resetting the machine rather than changing tools, as is the case with mechanical methods. In addition, it does not use tools that are subject to wear processes and which require continuously programmed replacements.

Despite these advantages, mechanical methods for cutting wrapper sheets continue to be preferred over laser methods.

With specific reference to the methods for producing a molded wrapper sheet as set forth herein, mechanical methods are gaining acceptance because they provide high speeds, optimal performance of the cutting process and preservation of the clean surface of the sheet.

In this regard, the present invention provides a method for manufacturing a molded wrapper sheet, which involves a laser cutting operation of the sheet in accordance with a technology that is such as to obtain significantly superior results compared to known technologies.

In particular, the present invention relates to a method having the characteristics listed in claim 1 of the claims.

Additional features and advantages of the invention will become apparent from the following description with reference to the accompanying drawings, which are shown by way of non-limiting example only and in which:

Fig. 1A, 1B, 1C and 1D show successive steps of the method described herein, in accordance with an example embodiment;

Fig. 2 is a schematic diagram of an example of carrying out a cutting operation in accordance with the method described herein;

Fig. 3 shows a cross-section of a wrapper sheet as well as a cutting technique according to the example shown in FIG. 2;

Fig. 4 shows an example of a molded wrapper sheet produced using the method described herein; And

Fig. 5 shows a detail of a wrapper sheet according to FIG. 4.

In the following description, various specific details are shown in order to provide an in-depth understanding of the embodiments. These embodiments may be provided without one or more of these specific details or using other methods, elements or materials, etc. In other cases, known structures, materials or operations are not shown or described in detail so as not to obscure various aspects of the embodiment.

Reference numerals used herein are for convenience only and, therefore, do not define the scope of protection or the scope of the embodiments.

As stated above, the method described herein relates to the production of a molded wrapper sheet. In particular, with reference to FIG. 4, the method described herein is suitable for producing a wrapper sheet 10 comprising a recessed portion 10A for receiving a product, such as a food product, and a perimeter edge 10C that extends along a predetermined profile K. In preferred embodiments, as in the embodiment shown In an embodiment, sheet 10 may include a substantially flat perimetric projection 10B that surrounds recessed portion 10A and defines a perimetric edge 10C.

With reference to the example shown in FIG. 1, the method described herein includes the steps:

- applying a sheet of wrapper 100 to the processing surface 50 containing the forming cavity 50A;

- molding the wrapper sheet 100 inside the mold cavity 50A so as to form a recessed portion 10A; And

- cutting the wrapper sheet 100 along a given profile K so as to form a perimetric edge 10C.

Preferably, the wrapper sheet 100 contains at least one layer made of a metallic material, such as aluminum.

In particular, the wrapper sheet 100 may be formed from a sheet of aluminum foil coated on the outside (relative to the location in the finished package) with a layer of paint that imparts a predetermined color and/or decoration and/or image on the outer surface of the sheet. The opposite side, that is, the inner surface (relative to the location in the finished package), can be covered with a layer of heat-sealable material. The aluminum foil sheet may have a thickness ranging from 1 to 500 μm, optionally from 3 to 300 μm, and preferably from 5 to 50 μm (1 μm=1∙10 ^-6 m). Alternatively, the wrapper sheet 100 may have a multilayer structure comprising at least one layer of polymeric material. For example, the wrapper sheet 100 may be formed from a sheet having a multilayer film structure consisting of multiple layers of polymeric material. Preferred polymeric materials are, for example, polypropylene, polyethylene, polyester, polyamide, etc. A sheet of plastic material suitable for this application may generally have a thickness of less than 140 μm, in particular less than or equal to 50 μm. Sheet 100 may also contain a heat-sealable material, such as a heat-sealable varnish.

In some embodiments, sheet 100 may be a multilayer structure comprising at least one layer of polymeric material in conjunction with a metal layer. For example, sheet 100 may consist of a sheet of metallized plastic material (eg, polypropylene - PP) with a metal coating thickness ranging from 10 to 500 A (1A=1∙10 ^-10 m).

Generally speaking, in the method described herein, the forming step involves forming the sheet 100 without substantially subjecting it to any plastic deformation by stretching.

With reference to FIG. 1A and 1B, said molding step comprises:

- placing a sheet of wrapper 100 on the processing surface 50 and over the forming cavity 50A;

- inserting the forming element 52 into the forming cavity 50A, pushing the wrapper sheet 100 into the cavity 50A and placing it flush against the cavity surface 50A.

At the end of this step, the sheet 100 takes a shape corresponding to the shape of the surface 50A', in the form of that part which is inserted into the cavity 50A; this portion forms the recessed portion 10A.

This molding step can be carried out under cold conditions, i.e. without applying heat to the wrapper sheet. Alternatively, the wrapper sheet may be heated to cause it to deform to achieve the shape intended for said recessed portion 10A.

This forming step creates a plurality of folds 110 in the wrapper sheet 100.

These folds are formed due to the fact that the forming step is carried out essentially without any deformation due to stretching of the sheet, simply as a result of changing its position from the flat position shown in FIG. 1A to the position defined by the mold cavity 50A shown in FIG. 1B.

The folds 110 are formed by fold lines oriented transversely relative to the top view boundary of the recessed portion 10A, each fold being formed by at least two folds disposed on each other and in mutual contact, connected together by a corresponding fold line.

The fold 110 itself is in turn in contact, through one of its two folds, with an underlying layer of wrapper sheet 100. Thus, each fold 110 may have three or more layers of material superimposed on each other.

It should be noted that in some applications, in particular when using a wrapper sheet made of plastic material, this molding operation can be carried out in accordance with the ideas of the PCT patent application WO2018/146577A1, registered in the name of this applicant, which provides for the sealing of these folds to secure the sheet in the form taken inside the forming cavity.

In some applications, it is also possible, if necessary, to somehow deform the sheet slightly by stretching.

As stated above, the method described herein involves a cutting operation in which a laser beam B is used to cut a sheet of wrapper 100 along a predetermined profile K.

The cutting operation may be carried out by a processing head 60 equipped with a conventional type laser generator suitable for performing functions that will be described below. Said laser generator may be, for example, a fiber laser, a yttrium aluminum garnet laser (YAG laser), or a carbon dioxide laser (CO ₂ laser), and may be either a pulsed laser or a continuous wave laser. Operating parameters of the processing head 60, such as the wavelength of the laser beam or the focal length, can be selected in accordance with conventional criteria known for laser processing based on the requirements of specific applications.

Generally speaking, as is known, laser cutting involves directing a laser beam onto a sheet of wrapper and continuously orienting it so that its point of incidence on the sheet moves along a predetermined profile provided for the specified edge to be obtained.

The energy transmitted by the laser beam to the sheet causes a sublimation phenomenon at the point of impact, so that the material goes from a solid state directly to a gaseous state.

In accordance with the method described herein, the cutting operation involves performing multiple passes of the laser beam along a given profile K, which include:

- the first pass of the laser beam, which is carried out along the first trajectory P1; And

- at least one additional pass, which is carried out along another trajectory Pn, which is shifted relative to the first trajectory P1 in the direction away from the given profile K.

Said additional pass or passes of the laser beam have/have the function of removing material from the wrapper sheet 100 which, at the end of the first pass, still connects the molded sheet 10 containing the recessed portion 10A to the remaining 100' of the sheet 100.

This material is, in particular, formed by hidden layers of the sheet, which appear only after the first pass of the laser beam.

This predominantly occurs in said folds 110, which, as stated, may contain three or more layers of material superimposed on each other.

The first pass of the laser beam will affect the top layer, and subsequent passes will affect the layers below.

Each additional pass of the laser beam is carried out along a corresponding trajectory, which does not coincide with the trajectory carried out in the previous pass, but is slightly shifted from it in the direction away from the given profile K.

Preferably, this offset is equal to a distance less than or equal to the diameter of the laser beam.

In particular, according to preferred embodiments, said cutting operation comprises n additional passes of the laser beam, which are carried out along n corresponding additional paths offset from the path of the previous pass away from a given profile K by corresponding distances dn corresponding to corresponding fractions of the diameter of the laser beam . The sum of the distances dn is less than the diameter of the laser beam.

The number n of passes can, for example, be in the range from 2 to 10. The distances dn can be less than or equal to half the diameter of the laser beam.

It should be noted that the laser beam operates with operating parameters, in particular operating power, which are such that in each individual pass the beam is capable of affecting only one layer of the sheet.

In preferred embodiments, the laser beam power is less than 500 W.

In fig. 2 and 3 show an example of a cutting operation of a sheet 100 on which a recessed portion 10A has already been formed along a predetermined profile K.

The operation shown involves three successive passes of the laser beam along a given profile K, which are carried out along the corresponding trajectories P1, P2, P3, located at an increasingly increasing distance, starting from the first pass to the third pass, from the given profile K (Fig. 3).

The shown trajectories P1, P2, P3 show the positions taken by the center of the laser beam (relative to the beam cross-section) when the beam moves along profile K.

The trajectory P1 of the first pass continues in such a way that the laser beam is directed tangentially to the given profile K and therefore remains along the entire trajectory along the profile K.

Trajectory P2 continues in a direction parallel to trajectory P1 and is displaced from it by a distance d1 equal to half the diameter of the laser beam. This distance is maintained throughout the entire length of the trajectory along profile K.

Similarly, the path P3 continues parallel to the path P2 and is located even further from the path P1. In particular, the path P3 is located at a distance d2 from the path P2, which is equal to one fourth of the diameter of the laser beam. This distance is maintained throughout the length of this trajectory. The distances d1 and d2 are given as an example only.

It can be noted that since the distances d1 and d2, and accordingly also their sum, are smaller than the diameter of the laser beam, the different passes of the laser beam have overlap areas between the corresponding areas A1, A2, A3 they cover (Fig. 3). In particular, an overlap zone Aʽ is provided, which is common to all three areas covered by the three passes of the laser beam.

In fig. 3 shows the action of the laser beam during individual passes in the area of the sheet 100 in which the fold 110 and, respectively, three layers 101, 102, 103 are located, superimposed on each other.

In fig. The 3 shaded rectangles formed on different layers of the sheet represent parts of these layers that are gradually removed after different passes of the laser beam.

As shown in FIG. 3, the first pass along the path P1 causes a portion 101I of the first layer 101 to be removed.

The second pass along the path P2 in turn causes the removal of a portion 102I of the second layer 102 in the overlap region between the area A1 covered in the first pass and the area A2 covered in the second pass, and further removal of a portion 101II of the first layer 101 in the remaining portion of the area A2, covered by the second pass.

Finally, the third pass along the P3 path causes:

- removing part 103I of the third layer 103 in the overlap area Aʽ, common to three areas A1, A2 and A3, covered by three passes of the laser beam;

- removing part 102II of the second layer 102 in the overlap area between the area A2 covered by the second pass and the area A1 covered by the first pass; And

- removing part 101III of the first layer 101 for the remaining part of the area covered by the third pass.

In zone Aʽ, the material of all three layers 101, 102 and 103 is removed and thus the final cut of the sheet 100 is obtained. In the example shown, each pass of the laser beam removes exactly one layer of the sheet. This choice is made to make the solution easier to understand. One skilled in the art will appreciate that individual passes may also remove only a portion of one layer of the sheet, or remove the entire layer plus a portion of the underlying layer, as required by specific applications. In any case, in the above method, the final cutting of the sheet is achieved only after multiple passes of the laser beam.

Based on the above, it should be noted that the author of this application was able to verify that laser cutting of the wrapper sheet in this manner can guarantee the final cutting of the sheet and at the same time also preserve the surface characteristics of the sheet along the edge 10C that is obtained as a result of the cutting operation.

This can be explained by the fact that the laser beam is designed to act in a limited area, as a result of which many of the above passes are necessary, and also by the fact that these passes are not carried out along the same path, but along different paths.

For the above reasons, the method described herein is particularly advantageous for applications with printed wrapper sheets (i.e. sheets coated with a layer of ink), since it is possible to maintain the print layer also along the perimeter edge of the sheet resulting from cutting, thus significantly improving the quality of the finished packaging.

In applications in which the wrapper sheet 100 contains, in combination, a layer of polymeric material and a layer of metallic material, the cutting step may involve the use of two laser beams of different wavelengths: one to process the layer of polymeric material, the other to process the metallic layer. For example, a CO ₂ laser can be used to process a layer of polymer material, and a fiber laser or YAG laser can be used to process a metal layer.

Preferred methods of using two laser beams are described in patent application EP 352308A1, registered in the name of this applicant.

Of course, without prejudice to the spirit of the present invention, details of construction and embodiments may differ, even significantly, from those shown herein by way of unrestricted example only, without departing from the scope of the invention as defined by the appended claims.

Claims (12)

1. A method for producing a molded wrapper sheet (10) comprising a recessed portion (10A) and a perimetric edge (10C) extending along a predetermined profile (K), said method comprising the steps of: applying the wrapper sheet (100) to a processing surface (50) containing a shaping cavity (50A); and molding said wrapper sheet (100) within said mold cavity (50A) so as to reproduce thereon the shape of said recessed portion (10A), said molding step comprising inserting said wrapper sheet (100) into said mold cavity (50A) without subjecting it to deformation by stretching at least during the phase of said insertion operation, said molded sheet (100) comprising a plurality of folds (110) consisting of two or more layers superimposed and in contact with each other of said wrapper sheet (100); cutting said molded wrapper sheet (100) along said predetermined profile (K) to form said perimetric edge (10C) and obtain said molded wrapper sheet (10); characterized in that said cutting step involves the use of a laser generator (60) configured to emit a laser beam (B) and includes exposing said laser beam (B) to said molded sheet (100) and orienting said laser beam to effect a plurality of passes of said laser beam along said specified profile (K), wherein said plurality of passes includes: a first pass of said laser beam, which is carried out along a first path (P1); and at least one additional pass of the specified laser beam, which is carried out along another trajectory (P2, P3, ..., Pn), which is shifted from the specified first trajectory (P1) in the direction away from the specified specified profile (K) by a given distance ( d1, d2) so that the laser beam, which moves along said other path (P2, P3, ..., Pn), is able to act on the underlying layer of the molded sheet (100), which still connects said molded sheet (10) with the rest (100ʽ) of said wrapper sheet (100) and which appears on the side where said laser generator is located as a result of said first pass of said laser beam. 2. The method according to claim 1, characterized in that said distance (d1, d2) is less than or equal to the diameter of said laser beam. 3. The method according to claim 1 or 2, characterized in that said at least one additional pass includes n passes, which are carried out along n corresponding trajectories (P2, P3, ..., Pn), shifted relative to the trajectory of the previous pass in the direction to the side from said specified profile (K) to corresponding distances (d1, d2, dn) corresponding to corresponding fractions of the diameter of said laser beam, wherein the sum of said distances (d1, d2, dn) of said n additional passes is less than the diameter of said laser beam. 4. The method according to any of the previous paragraphs, characterized in that the introduction of the specified sheet into the specified forming cavity includes: providing the presence of a forming element (52), which interacts with the specified forming cavity (50A); applying said wrapper sheet (100) to said processing surface (50) and over said forming cavity (50A); and moving said forming element (52) into said forming cavity (50A), pushing said wrapper sheet (100) into said cavity (50A) through said element (52). 5. A method according to any of the previous claims, characterized in that said molded sheet (10) comprises a peripheral projection (10B) which extends around said recessed portion (10A) and forms said perimetric edge (10C), said cutting step including orienting said laser beam along a predetermined profile (K) which is located at a predetermined distance from said recessed portion (10A) so as to form said peripheral protrusion (10B). 6. Method according to any of the previous claims, characterized in that said wrapper sheet (100) contains at least one layer of metallic material, preferably an aluminum sheet. 7. The method according to claim 6, characterized in that one side of said sheet is covered with a layer of paint. 8. The method according to claim 7, characterized in that the opposite side of said sheet is covered with a layer of heat-sealable material. 9. Method according to any of the previous claims, characterized in that said wrapper sheet (100) has a multilayer structure containing at least one layer of polymeric material. 10. The method according to claim 9, characterized in that said wrapper sheet contains a heat-sealable layer, for example, a heat-sealable varnish. 11. Method according to claim 9 or 10, characterized in that said wrapper sheet (100) has a multilayer structure containing a layer of polymeric material in connection with a metal layer. 12. The method of claim 11, wherein said cutting step involves exposing said laser beam to said metal layer and exposing said layer of polymeric material to another laser beam having a different wavelength.

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