BAG FOR FOOD

Abstract

A packaging bag for foods/food products comprises at least a front part and a back part, which are connected to one another in the two lateral edge regions over at least one side fold or at least one side seam in each case and between which a bag pocket is formed with an upper open end and a lower closed end, especially which is formed by the fact that the front part, at a lower fold or seam, is turned over toward the back onto the back part, wherein the entire packaging bag has a left and a right bag part, the two of which are connected together along an overlapping region extending between the lower and the upper end, wherein in the overlapping region or laterally adjacent to this, at least one weakening line is provided, at which the two bag parts can be separated from one another.

Description

FIELD OF THE INVENTION

The present invention relates to a bag. More particularly this invention concerns a bag intended to hold food.

BACKGROUND OF THE INVENTION

A typical packaging bag for foods has at least a front part and a back part, which are connected to one another in the two lateral edge regions over at least one side fold or at least one side seam in each case and between which a bag pocket is formed with an upper open end and a lower closed end, wherein the entire packaging bag has a left bag part and a right bag part, the two of which are connected together along an overlapping region extending between the lower and the upper end, especially which extends congruently over the entire height of both the front side and the back side.

In such a packaging bag, for example, the lower closed end may be formed in that the front part, at a lower fold or a lower seam toward the back, is wrapped around the back part and for example is fastened to it by gluing or welding.

Packaging bags for foods of this type are known in the prior art, for example in an embodiment in which a left bag part is formed from a clear film and a right bag part is formed from a paper material or vice versa. Such bags offer the advantage, for example, that a food packed in such a packaging bag is clearly recognizable from the outside despite secure accommodation in the bag.

However, bags of this type have the drawback that a food packed in them, e.g., a sandwich, usually can only be removed through the opened end, while on the other hand such a bag cannot be torn open in a defined manner.

To be sure, it is also known in the prior art, in order to facilitate defined opening, that weakening lines, especially in the form of perforations, may be created in such a packaging bag; in such cases, however, it is often found that despite the provision of a weakening line, a bag does not necessarily tear on this weakening line during a tearing process, especially if the person who is using it does not definitively produce an initial tear site at the location of the weakening line, which would then tear further along this weakening line.

With such bags, even if they have a weakening line, careless tearing can have unwanted consequences, especially completely uncontrolled tearing open of the bag, and thus even entail the risk that the food packed therein will fall out in an uncontrolled manner.

OBJECT AND SUMMARY OF THE INVENTION

In view of this background it is the goal of the invention to further develop bags of the initially mentioned type, made of a left and a right bag part by connecting the two parts, in such a manner that even in the case of an uncontrolled or unintended tearing process these permit defined removal of part of the total packaging bag, especially in such a manner that the food continues to be surrounded securely and hygienically by the remaining part of the bag and can be held in the hand, but it is possible to eat the food after part of the bag has been removed.

The directional statements used here relate to a bag position in which the open end of the bag is positioned at the top.

According to the invention, this task is accomplished in that in a packaging bag of the initially-mentioned type, in the overlapping region or laterally adjacent to this, at least one weakening line is provided, at which the two parts of the bag can be separated from one another. Preferably such a weakening line extends in the same way as the overlapping area and parallel to it, i.e., completely over the total height from the bottom end to the top end on both the front and the back part.

Thus within the framework of the invention described, a packaging bag for foods is defined as a packaging bag of this type that is suitable and intended for accommodating foods or food products, and thus the materials thereof are suitable and approved for this area of application.

One essential aspect of an embodiment of the invention is based on the fact, which is utilized here, that the overlapping of the two parts of the bag in the initially-mentioned overlapping region results in reinforcement of the material, essentially through the fact that the layer of the material of the left bag part is connected to a layer of the material of the right bag part, and thus a thicker and stronger material aggregation always results here than in the other areas of the packaging bag, in which in each case the material is present only in a single thickness.

If it is thus provided that a weakening line in parallel extension to the extension of the weakening line of the overlapping region on a packaging bag is used, it is highly probable that even an uncontrolled tearing process will not cause tearing of the material that extends between the two bag parts beyond the overlapping region, since these two bag parts are separated from one another by the material reinforcement in the overlapping region and are reinforced in this overlapping region, so that with a high degree of probability the tearing process will take place exactly along the weakening line provided, for example a perforation line, without the tear extending beyond the overlapping region.

The tearing process here can be particularly supported in cases in which a packaging bag of the type according to the invention is filled through the upper end with a food, for example a sandwich, and then closed, for which purpose for example an upper cover flap can be provided in that the upper edge of the back part projects beyond the upper edge of the front part and this cover flap can then, as an extension of the back part, be lapped over the opening onto the front part.

For example, a closed bag according to the invention can be torn opened especially easily if it is held so that the one bag part is gripped with the hand, for which purpose the bag can first be rotated by about 90° in order to grasp the other bag part with all the fingers of one hand and separate it from the bag part held in the other hand by means of a tearing process.

A packaging bag of the initially-mentioned type can provide the previously-mentioned advantages, for example, on one hand of reinforcement of the material in the overlapping region mentioned, and on the other hand, weakening of the material by a weakening line, even if both parts of the bag are made from the same material in terms of all material properties, thus for example both parts of the bag are made of paper or a composite paper material or of plastic or a composite plastic material.

For example, a packaging bag made of two identical materials to be sure has an essentially uniform external appearance, but has realized the initially-mentioned advantages realized in terms of the adjacent or even nested reinforcement and weakening areas.

In another alternative embodiment it may also be provided that different materials are used for the two parts of the bag. For example, one part of the bag may be made of plastic, especially a transparent film, and the other part of the bag of paper. The respective materials in each case may also be composites made of several layers.

In another embodiment it may also be provided that both parts of the bag are to be made of paper, but of different thicknesses and/or types of paper. Alternatively, likewise both parts of the bag may be made of plastic, for example, transparent film, but likewise of different thicknesses and/or types.

A preferred further embodiment is produced especially when the right and left parts of the bag are selected to be made of different materials in terms of thickness and/or type, wherein it can thus be provided that the at least one weakening line is arranged in the weaker material, especially in the thinner and/or less tear-resistant material, between these two materials of the two bag parts.

Thus a packaging bag of this type according to the invention achieves a higher tear resistance in the one bag part with the already more tear-resistant material and especially in the overlapping region of the two materials, where through the material reinforcement by overlapping, an even higher tear strength is achieved relative to the single-layer material, and then furthermore a pronounced weakening is achieved in that the weakening line at which the tearing process is to be performed is arranged in the weaker, especially easier to tear material of the two materials.

Here also it may then be preferred that the weakening line is arranged in the overlapping region of the two bag parts, but preferably in that case such that it is arranged on the side adjacent to a connecting line or a joint line, at which the two bag parts are connected together, e.g., by gluing, welding, embossing or similar process steps.

Especially in the case of the above-mentioned embodiment, but even if the materials of the two bag parts are identical or differ only insubstantially in terms of the tear strength and consequently in the case of any conceivable pairs of materials for the two bag parts, it may be provided that the weakening line is arranged in the material which is overlapped at the front edge by the other material, thus looking at the front part in the material lying toward the back.

Here a further embodiment can provide that the weakening line is arranged in the overlapping region below the overlapping material. A weakening line arranged in this way is thus covered by the overlapping material, which offers protection to the weakening line and for example can be especially advantageous if a weakening line is designed as a perforation.

In such a case, through the overlapping of the weakening line, the weakening line is closed toward the outside, so that for example liquids such as oils, fats or gravies or other coatings of foods, even if they penetrate the perforation line, cannot reach the outside.

In the embodiment such that a weakening line is arranged immediately adjacent to the side of the overlapping region in at least one of the two bag parts, thus extending parallel to the overlapping region between the upper and the lower end, especially both on the side of the front part and on the side of the back part, it is understood that preferably the distance between the weakening line and the overlapping region is smaller than the width of the overlapping region, in particular smaller than 10 mm, particularly preferably smaller than 5 mm.

Here the overlapping region is basically defined as the region in which the materials of the two bag parts overlap, thus a double layer of the packaging bag is present in this region. An overlapping region is thus delimited with respect to both parts of the bag by the edge of the respective other bag part.

Weakening lines in the sense of the invention can be produced in any manner whatsoever that is suitable for producing a linear weakening of the bag part to define a tearing line. Typically this is accomplished for example by the formation of a perforation in the material of at least one of the two bag parts in or closely adjacent laterally to the overlapping region. Likewise for example the possibility exists for providing not a perforation but a thinning of the material to weaken the material at the thinned points and promote tearing there.

In another embodiment of the invention it can also be provided that a weakening line is formed by a linear, releasable connection along which the bag parts are connected in the overlapping region, for example by gluing, welding or embossing. Such a weakening line lies in the overlapping region.

An embodiment of this type has the advantage that during the manufacturing of a packaging bag of this type no manufacturing step need be provided for producing a weakening line in addition to the step of connecting the two bag parts.

For example, such a releasable connection that thus extends along the overlapping region extends in this and connects the two overlapping regions of the bag parts can be made by a noncontinuous line of adhesive consisting of a plurality of individual adhesive dots or individual adhesive line sections. As a result, regions thus form along the connecting line within the overlap at which connection of the overlapping regions occurs, as well as regions at which the two bag parts loosely overlap one another.

In another embodiment an adhesive line can also be made from an adhesive, especially a weak adhesive, which permits the nondestructive separation of one part of the bag from the other. Here a weak adhesive is thus defined as an adhesive that permits this above-mentioned nondestructive separation. For example it may involve a pressure-sensitive adhesive similar to those known for sticky note pads, and which guarantees an adequate level of adherence between the two bag parts at the time of packaging of a food, but permits the reliable separation of one bag part from the other during the opening process. In this case it is preferable to use an adhesive which is approved in the food sector and/or for utensils.

It may also be provided to make a connecting line out of several embossing sites that are arranged in linear succession to one another, at which the overlapping components are respectively embossed into one another. For example here the material of one bag part can be passed in an embossing step through the material of the other bag part to create the connection of the overlapping bag parts in the overlapping region. Additional alternatives include an interrupted weld seam made from a plurality of individual weld points or weld line sections, or a weak weld connection in the above-mentioned sense (analogous to the adhesive) can be produced.

It is preferably ensured in all these above-mentioned embodiments that the linear releasable connection can be released with a tearing force that is smaller than a force needed to destroy the material of each of the two bag parts. In this way it is ensured that in a tearing process in which one of the two bag parts is pulled relative to one another, in all probability the two bag parts will separate from one another at the releasable connection without the occurrence of tearing within the material of one of the two bag parts.

In a further preferred embodiment variant that can be combined with all of the previously mentioned embodiments, and especially that can be used independent of the choice of materials for the two bag parts, it may be provided that the overlapping region, especially one edge of the overlapping region or a connecting line arranged in the overlapping region of the two bag parts or a weakening line that is arranged in the overlapping region or immediately adjacent to it, is arranged at 45% to 55% of the width of the packaging bag, especially at exactly 50% of the width.

Thus in each case the optionally selected above-described element (overlapping region, edge, connecting line or weakening line) preferably extends essentially centrally relative to the width of the packaging bag, resulting in a packaging bag that is essentially divided in half into a left and a right bag part which can be separated from one another by one of the previously described mechanisms.

It is regarded as particularly advantageous here if the overall width of a packaging bag is selected such that this is larger, for example at least 50% larger, than the food product to be packaged in it, so that during a packaging process, the food product can essentially be positioned in one of the two bag parts, then the bag is closed, for example by wrapping around an optionally provided cover flap, wherein then a person can hold the packaging bag in such a way that the packaging bag with the food product, for example a sandwich, in it is grasped with one hand and the empty other part of the bag in a particularly large area with the other hand, so that this bag part is grasped over abroad area and can be subjected to a tensile force relative to the other part of the bag, which causes the tearing of the bag according to one of the previously described mechanisms.

To guarantee secure packaging of the contents in a packaging bag it may also be provided that the back part, to reinforce the lower, closed end, has a lower fold that is located within the fold or seam of the front part, with which the front part is wrapped around the back part. As a result, a multilayered structure of the material is formed in the lower end region of the bag, and thus reinforcement [is achieved].

In the upper region of the packaging bag, which preferably has a closing flap, in that the upper edge of the back part is made higher than the upper edge of the front part, based on the division of the packaging bag in terms of its width into a left and a right bag part it may be provided that in the cover flap in one of the two bag parts on one side of the overlapping region, optionally in both bag parts on both sides of the overlapping region, an opening is provided, for example a punched-out area, which is stuck to a sticker from the side of the back part that interacts with its adhesive surface through the recess or the punched-out area.

In such instances it may be particularly preferred to arrange this recess or punch-out in the stronger or more tear-resistant material out of the two materials of the two bag parts, insofar as different materials are selected, or independently of the material selection, in the bag part that surrounds the food/food product following the tearing off of the other bag part and keeps it ready to eat.

In that the sticker interacts with an adhesive surface through the punch-out or the recess in general, a cover flap can be fastened adhesively over the open end of the front part following the turnover or the fold-over. In this variant of the bag, even after part of it is torn off, the package remains securely closed by way of the remaining adhesive.

In another, particularly preferred embodiment it may be provided that the sticker on its nonadhesive back side has a coating, especially an adhesive-repellent coating, which may be is provided to be contacted by the adhesive surface of an additional packaging bag stacked onto the [first] packaging bag, so that a stack of packaging bags can be formed by the stacking of packaging bags of this type in accordance with the invention, wherein the adhesive surface of each of the bags is protected by the adhesive-repellent coating of a bag located beneath it or, depending on the viewpoint, above it, until the bag is removed from the stack and used for packaging.

Such a packaging bag of this type according to the invention is thus to be classified as particularly hygienic, without requiring an additional removable protective film for the adhesive surface.

In a further embodiment that can be combined with all other embodiments, it may be provided that a side fold or one of two side folds that connect the front part and the back part on the side s, in particular the side fold of the bag part which surrounds a food/food product after removal of the other bag part and/or has the adhesive recess in the cover flap and/or is made of paper or the stronger of the two materials, projects beyond the upper edge of the front part.

This has the advantage that when the cover flap is lapped over onto the front part, this projecting side fold region is also lapped over and reinforces the sides of the packaging bag according to the invention (when positioned upright with the opening at the top), or after tearing off the other part of the bag and tipping over the remaining part of the bag to eat a food/food product surrounded by this, produces reinforcement in a lower region, then on the bottom.

The packaging bag according to the invention or the remaining bag part of the packaging bag according to the invention thus has better tightness, which is important specifically in the case of foods/food products that contain sauces. The stability is also increased, so that the remaining bag part can be placed on a table without problems, when the side fold, which then forms the base, is slightly swung open.

In one embodiment the front part of the side fold can stand out to the upper edge of the back part and thus correspond in height to the height of the back part.

Preferably on the other hand it may be provided that the part of the side fold projecting beyond the upper edge of the front part has a length that corresponds to 20% to 80%, preferably 30% to 60%, more preferably 45% of the length of the cover flap or the distance of the upper edges of the front part and the back part. Such a length is sufficient for stabilizing and improving the tightness without excessively stiffening the cover flap.

A side fold that connects the front part and the back part in the region in which the front part and the back part are connected to this side fold has approximately a W shape in cross-section. In the area of the side fold in which this projects over the edge of the front part, the side folds lacks the connection to the front part and thus [to] one of the W-branches of the previously-mentioned W-shape.

The side fold has one fold part that is connected to the front part and one fold part that is connected to the back part. In the unopened state of a bag according to the invention, these fold parts lie one on top of the other. These two fold parts can each have exactly the same width, which corresponds to half of the total width of the side fold.

In a further development of the above-mentioned embodiment(s), it may also be provided that beginning from an upper common edge of the two fold parts of the side folds which is located between the upper edge of the front part and the upper edge of the back part (for example, at the previously-mentioned length of 20% to 80%, preferably 30% to 60%, more preferably 45%), only the fold part of the side fold that is connected to the back part, especially in a reduced width, continues in the direction toward the upper edge of the back part, especially exactly to the upper edge of the back part or below. In this embodiment with reduced width, therefore, the fold part that is connected to the back part has a notch.

BRIEF DESCRIPTION OF THE DRAWING

Exemplified embodiments of the invention will be described in the following, referring to the figures in which:

FIGS. 1-3 are various side views of the bag according to the invention; and

FIGS. 4 and 5 are perspective view of two embodiments of the bag according to the invention.

DETAILED DESCRIPTION

FIGS. 1-3 shows several perspective views of a packaging bag of the type according to the invention with a front part 1 and a back part 2, wherein the front part 1 and the back part 2 are connected together over a side fold, i.e., a folded material part 3 on both left and right sides, and thus form a pocket closed toward the bottom and open toward the top in which a food can be placed.

The front part 1 and the back part 2 each extend over the entire width of the bag, but as is recognizable here, based on its width, it is divided approximately in the center into a left bag part and a right bag part, wherein each of the two bag parts, left and right, has a share of a front part 1a and a back part 2a or front part 1b and a back part 2b.

Here it can be provided in an embodiment that the right side bag part, formed from front part 1b, side fold 3b and back part 2b, is made of a different, e.g., more tear-resistant material than the left side bag part consisting of the front part 1a, the side fold 3a and the back part 2a.

Regardless whether the two bag parts are made of different or the same material, an overlapping region 4 is shown cross-hatched here in FIGS. 1 and 3, where the left and right side bag parts overlap adjacent to one another and are fastened together in this overlapping region 4, e.g., by gluing, welding, or embossing. Such an overlapping region 4 can generally have, for example, a width in the range of 5 to 20 mm.

In this embodiment, immediately adjacent on the left, i.e., here preferably at a distance in the range of less than 5 mm, to form a weakening line, a perforation 5 is provided in the left-hand part of the bag both on the front 1a and on the back 2a, wherein this perforation 5 is arranged such that it is provided in the overlapped material, thus in the material of the left bag part 1a here, which in the overlapping region 4 is covered by the right-hand bag part 1b on the front side and thus in a top view lies at the back on the front side.

Here, the extents of the overlapping region and the weakening line 5 are made parallel to one another and are each formed from the lower to the upper extremal ends of the front part 1 and the back part 2.

FIGS. 1-3 also show that here, relative to the right-hand, especially more tear-resistant bag part in its cover flap, which is formed in the back part 2b by a higher top edge compared to the front part, a punch-out 6 is provided, which has an adhesive sticker placed behind it from the back side, so that the adhesive surface of the adhesive sticker can act through the punch-out 6. In the perspective view of FIG. 3 it is recognizable that after turning over the cover flap 7, a closed packaging bag according to the invention, which accommodates a food product, is produced by adhesion of the cover flap to the front part.

By grasping the left part of the bag here and holding tightly to the right bag part on the front and back parts respectively, the tearing process can be initiated, in which the left part of the bag is torn away from the right part of the bag at the weakening line 5 immediately adjacent to the overlapping region 4. Here with a high degree of certainty the tear will be produced on the side in front of the overlapping region, since because of the double material layer this [overlapping region] has a high degree of reinforcement and thus a high tear strength, and therefore the tearing process is started and completed in the area of the weakening line lying alongside this.

It is recognizable here in FIGS. 1-3 that the overlapping region 4 and the weakening line 5 are arranged approximately in the center based on the width of the packaging bag. Here the distance between these two regions is of determining significance for the effect according to the invention and the interplay between the weakening line and the overlapping area, but less so the central positioning relative to the width. The distance is preferably selected to be less than 10 mm, particularly preferably less than 5 mm, optionally even in the range of 1 mm, whereas the positioning of the weakening line, overlapping region or an edge of the overlapping region or a connecting line provided therein falls in the range of 45% to 55% of the width.

FIG. 4 shows a further development of the packaging bag according to FIG. 1 with all of the details described there, wherein here in addition the side fold 3b (on the right in FIG. 4), which is assigned to the bag part 1b/2b with the recess 6 in the cover flap, projects beyond the edge 1c of the front part 1.

Here the two fold parts 3b′ and 3b″, which are connected to the back part and the front part respectively, together form an upper edge 3c of the side fold 3b, which is located between the upper edge of the front part 1 and the back part 2, e.g., in the range of 30% to 60% of the distance between the edges 1c, 2c of the front part 1 and the back part 2. In the area of the projecting length 3d, the fold part 3b″, which is connected with the front part 1 beneath this, has no connection to the front part 1.

FIG. 5 shows another further development, in which as in FIG. 4 a common upper edge 3c of the two fold parts 3b′ and 3b″ is formed, which as before is located between the upper edge 1c of the front part 1 and the upper edge 2c of the back part 2.

Beyond this common upper edge 3c of the two fold parts 3b′ and 3b″, only the fold part 3b′ continues upward; this has a connection to the back part 2.

Here the execution is such that the part of the fold part 3b′ projecting beyond the common edge 3c is of a reduced width, especially relative to the total width of the fold part 3b′, which is shown in FIG. 3 between the vertical broken fold lines. The fold part 3b′ thus has a notch above the upper common edge 3c.

However, in another embodiment (not shown), the fold part 3b′ can also project upward over its entire width.

In the embodiments shown here the top edge 3e of the fold part 3b′ is at the same level as the upper edge 2c of the back part, but in another embodiment (not shown) it may also be lower, at a height between the common upper edge 3c of both fold parts 3b′/3b″ and the upper edge 2c of the back part 2.

Claims

1. The invention relates to a packaging bag for foods/food products, comprising at least a front part and a back part, which are connected to one another in the two lateral edge regions over at least one side fold or at least one side seam in each case and between which a bag pocket is formed with an upper open end and a lower closed end, especially which is formed by the fact that the front part, at a lower fold or seam, is turned over toward the back onto the back part, wherein the entire packaging bag has a left and a right bag part, the two of which are connected together along an overlapping region extending between the lower and the upper end, wherein in the overlapping region or laterally adjacent to this, at least one weakening line is provided, at which the two bag parts can be separated from one another.

2. The packaging bag according to claim 1, wherein the two bag parts are made from materials of one of the following pairs:

one bag part of plastic, especially transparent film, and the other of paper.

both bag parts of paper, but of different thicknesses and/or kinds.

both bag parts of plastic, but of different thicknesses and/or kinds.

both bag parts of the same material in terms of all material properties.

3. The packaging bag according to claim 1, wherein the at least one weakening line is arranged in the weaker, especially the thinner and/or less tear-resistant material, of the two materials.

4. The packaging bag according to claim 1, wherein the weakening line is arranged in the material that is overlapped by the other material in the front part.

5. The packaging bag according to claim 4, wherein the weakening line is arranged in the overlapping area under the overlapping material.

6. The packaging bag according to claim 4, wherein a weakening line is arranged in one of the bag parts immediately adjacent to the side of the overlapping area, especially at a distance from the overlapping area of up to a maximum of 10 mm, particularly preferably up to a maximum of 5 mm.

7. The packaging bag according to claim 4, wherein a weakening line is formed by a linear releasable connection, along which the bag parts are connected in the overlapping area, especially are glued or welded or embossed.

8. The packaging bag according to claim 7, wherein the releasable connection is formed by

an interrupted adhesive line consisting of a plurality of individual adhesive dots or individual adhesive line segments

an adhesive line consisting of an adhesive, especially a weak adhesive, which permits the nondestructive separation of one bag part from the other

a line consisting of several embossed sites at which the bag parts are pressed into one another

an interrupted weld seam consisting of several individual weld points.

9. The packaging bag according to claim 1, wherein

the overlapping region, especially an edge of the overlapping region or

a line connecting the two bag parts, arrange in the overlapping region, or

a weakening line is arranged at 45 to 55% of the width of the packaging bag, especially at 50% of the width.

10. The packaging bag according to claim 1, wherein the back part, to reinforce the lower, closed end, has a lower fold that lies in the fold/seam of the front piece, with which the front piece is lapped over onto the back piece.

11. The packaging bag according to claim 1, wherein the upper edge of the back part projects beyond the upper edge of the front part and forms a cover flap that can be flapped over onto the front part.

12. The packaging bag according to claim 1, wherein in the cover flap, in one of the two bag parts, especially in the bag part made of the thicker or more tear-resistant material of in the bag part that surrounds a food/food product after removal of the other bag part, an opening, especially a punch-out is arranged, which has a sticker stuck onto it from the side of the back part, the adhesive surface of which [sticker] peeks through the opening/punch-out with its adhesive surface.

13. The packaging bag according to claim 11, wherein the sticker, on its nonadhesive back side, has an adhesive-repellent coating, especially onto which the adhesive surface of an additional packaging bag stacked on the packaging bag is adheres to form a stack of packaging bags.

14. The packaging bag according to claim 1, wherein a side fold or one of two side folds, especially the side fold of the bag part that

after removal of the other bag part, surrounds a food/food product, and/or

contains the adhesive-coated opening in the cover flap and/or

is made of paper or the stronger of the two materials projects beyond the upper edge of the front part.

15. The packaging bag according to claim 11, wherein the part of the side fold projecting beyond the upper edge of the front part has a length that corresponds to 20% to 80%, preferably 30% to 60%, more preferably 45%, of the length of the cover flap or the distance of the upper edges from the front part and back part.