METHOD FOR CLOSING A MESH BAG AND BAG OBTAINABLE BY MEANS OF SAID METHOD

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for closing a mesh bag comprising applying an ancillary closing element around a transversely collected portion of the bag, tightly girdling the same. The invention also relates to a bag obtainable by means of said method.

BACKGROUND OF THE INVENTION

Mesh bags are widely known. The use of mesh bags is widespread, for example, to package fruit and vegetable products, which require to be packaged in breathable bags for better preservation.

One way of closing an open end of a bag may be to gather the body of the bag transversely, forming a transversely collected longitudinal portion thereof, and using an ancillary closing element to tightly embrace, tighten or girdle said previously collected portion preventing same from expanding again, thus keeping the end of the bag closed. This method of closing an open end of a bag can be used to close mesh bags in automated bag making, filling and closing processes, although it exhibits a number of drawbacks.

Closing an open end of a mesh bag with an ancillary closing element must be distinguished from those solutions consisting of performing a closing seam. For example, it is known in the prior art to attach two opposite sides of the mesh bag and bond said opposite sides by melting or other means, forming a transverse closing seam in the bag. When bonding by melting or other bonding means, sheets or strips which are placed outside the bag, applied to one or both sides of the bag to be bonded may also be used. Where the formation of the sealing seam involves melting material, a portion of the molten material may be from one or more of these sheets; and where the formation of the sealing seam is carried out by other means, the sheet or sheets may include adhesive substances for this purpose, such as substances with adhesive properties.

Known ancillary closing elements include metal straps, or straps with at least a metal core, adhesive tapes and clips.

As for the clips, they are generally clamp-shaped. For example, patent documents ES 2076889; ES 2058717; and EP 287627 all disclose clamp-shaped clips comprising two arms joined and hinged together, the clip being able to adopt an open position, which allows the transversely collected portion of a bag to be closed to be arranged between the arms; and a closed position, in which the arms are joined together, flattening the transversely collected portion of the bag arranged between said arms.

Although these clips may generally provide less secure closure than straps and adhesive tapes for closing mesh bags, their use is of interest because they can be made entirely of the same plastic material as the mesh of the bag or, at least, the material of the clip and that of the mesh may share the same category of selective waste collection, such that both can be deposited in the same collection container without having to unlink the clip from the bag.

In utility model document ES1305762 a clip is disclosed such as those described above but which presents some improvements intended to increase the closing security of the mesh bag on which said clip is applied, specifically, to try to prevent the mesh from slipping through the arms of the clip, or to prevent the clip from slipping in relation to the mesh, when the mesh is subjected to a force or forces, that is, when the mesh is pulled, which in use can occur due to the effect that gravity exerts on the mass of the products housed in the bag when the position of the bag is suddenly reversed or when the mesh is pulled strongly to lift or move the full bag.

This phenomenon of the mesh slipping relative to the ancillary closing element, or vice versa, is a cause for concern regardless of the nature of the ancillary closing element used, as it can occur with ancillary closing elements such as metal strapping, adhesive tape or a clip, especially in bags containing relatively bulky products or quantities of product the total weight of which is several kilograms.

Moreover, it is of interest to reduce the manufacturing costs of the finished bags, the amount of material used to manufacture these ancillary closing elements being a measure to be taken into account. The less material is used, the cheaper the ancillary closing element will be, but it will offer poorer performance in terms of withstanding pulls on the mesh.

There is also concern about changing the usual configurations of ancillary closing elements in such a way that they become difficult to handle during automated bag closing processes; or that they increase the execution time of a closing operation; or that they make said operation more expensive because complex tools are required or that they cause production stoppages due to lack of precision, need for replacement or maintenance, among others.

DESCRIPTION OF THE INVENTION

In order to improve the performance offered by closing a mesh bag by applying an ancillary closing element on a transversely collected portion of the bag, tightly girdling the same, the implementation of the method according to claim 1 is proposed.

Instead of focusing their efforts solely on perfecting the ancillary closing elements, the inventors have conceived of acting on the mesh, specifically conditioning the same so that it interacts with the ancillary closing element in such a way that it improves the retention of the closing element, specifically, to ensure that the mesh does not slip through the closing element girdling the mesh or vice versa, that the closing element does not slip relative to the mesh, when the mesh is stretched.

The proposed method comprises, in a known manner, applying an ancillary closing element around a transversely collected portion of the mesh bag, tightly girdling the same, thereby determining on a first side of the closing element a storage portion of the bag and on a second side of the closing element, adjacent thereto, a mesh bundle.

In essence, the method is characterised in that the method further comprises the operation of bonding packed yarns of said mesh bundle together to form at least one bulge that acts as a retainer, which prevents the mesh bundle from passing from the second side to the first side of said ancillary closing element by abutting against the closing element.

If the transversely collected portion of the bag is an end portion of the bag, the mesh bundle will be a tail of the closed bag.

The mesh bundle may be temporarily bonded to a mesh storage or aggregation, which can be used to make another bag in series. In this case, when the mesh bundle is cut to separate the same from the mesh storage or aggregation, the mesh bundle will become a tail of the closed bag. Said cut may be made before, during or after the operation of bonding the yarns of the mesh bundle.

In practice, the bulge or bulges formed in the mesh bundle improve the retention of the ancillary closing element, specifically, it prevents the mesh bundle from slipping between the ancillary closing element that girdles the mesh towards the side of the ancillary closing element where the storage portion of the bag is located or vice versa, it prevents said ancillary closing element from slipping through the mesh bundle, in either case causing the unwanted opening of the bag when the mesh bundle is a tail of the bag.

The invention contemplates that the bonding together of the packed yarns of the mesh bundle can be carried out in different ways. In one variant, the bond is produced by melting the material from which the mesh yarns are made; said melting can be achieved by applying pressure and temperature to the mesh bundle or in another manner, for example, by applying ultrasound.

The material from which the yarns are made also includes the material from which a coating of the yarns may be made. Such a material may be, by way of example only, an adhesive, and the adhesive material may be a heat-activatable adhesive.

In any case, the bond proposed by the invention is not a bond intended to close the bag, that is, the bonding of packed yarns of the mesh bundle together would not be sufficient in itself to ensure the secure closure of the bag, that is, in a way that would resist the usual pulling of the mesh that occurs during the normal handling of the finished bag, for example during its transport, storage, suspension, etc.

Since the bond proposed to be used in the invention is not a bond intended to close the bag, the operation does not require long execution times. This means that the time required for the operation of bonding the packed yarns of the aforementioned mesh bundle together to form at least one bulge that acts as a retainer will not entail a bottleneck in the manufacturing process. In fact, the execution time of the operation of bonding the packed yarns of said mesh bundle together may be equal to or less than the time required to apply the ancillary closing element around the transversely collected portion of the bag and, therefore, if this operation is carried out at the same time as the ancillary closing element is applied to the bag, the implementation of the method according to the invention does not imply a reduction in productivity.

Revealingly, the method of the invention is compatible with the interposition, between the mesh and the ancillary closing element, of an external element such as a portion of a label, thus linking the label to the mesh.

Typically, a neck, or narrow, portion of the label is juxtaposed to a longitudinal portion of the mesh comprising the transversely collected portion of the mesh so that said neck portion of the label is pressure-trapped between the mesh and the ancillary closing element when the latter surrounds, tightens or girdles the said transversely collected portion of the bag. Usually, said neck portion of the label extends towards a wider main portion of the label, which is the bearer of the information of interest and which is sufficiently far from the neck portion so that a deformation of the neck portion due to the effect of the tightening to which it is subjected by the ancillary closing element does not alter the shape of the main portion of the label.

Consequently, applying an ancillary closing element around a transversely collected portion of the mesh bag by tightly girdling the same does not exclude this application being with interposition, between the mesh and the ancillary closing element, of an external element such as a label portion or the like.

As will be explained in greater detail later, in a variant of the invention the operation of bonding packed yarns of said mesh bundle together to form at least one bulge that acts as a retainer is carried out with a tool comprising at least one head that is applied under pressure to one side of the mesh bundle.

Said head can provide heat or be a source of ultrasound emission.

If the application of the ancillary closing element on the transversely collected portion of the mesh bag is carried out with the interposition of an external element, such as a label or the like, between the mesh and the ancillary closing element, which does not completely surround the mesh bundle, the head can be applied on the side of the mesh bundle coinciding with the lateral area of the bundle that is not surrounded by the external element.

This may result in a reduction in the time required for the operation of bonding together packed yarns of said mesh bundle.

As will be explained in more detail later, the operation of bonding the packed yarns of the aforementioned mesh bundle together may or may not mean bonding all of the yarns that make up the mesh bundle.

The fact that the bonding of all the yarns is not required, which means reducing operation times, is significant.

The method according to the invention comprises the operation of bonding packed yarns of the mesh bundle together to form at least one bulge that acts as a retainer. A bulge is understood to be a more or less compact mass or body that aggregates or gathers material from several yarns, which is not necessarily an elevation on the surface of the bundle and which may, therefore, be an internal bulge.

The size of the bulge or bulges will depend on the number of packed yarns of the mesh bundle that are bonded together, which in turn may depend on the time or other parameters involved in the bonding operation, such as the temperature or the intensity of the ultrasound when the bond is formed by melting the material from which the mesh yarns or a coating of said yarns are made.

The tooling used to form the package or packages may be configured to give a specific shape to the bulge or bulges. For example, and as explained later, in the case of using as an ancillary closing element a clamp-shaped clip with two arms which, by proximity, flatten the longitudinal collected portion of the mesh, the tooling can be configured to form a bulge whose shape develops in a main direction which is transverse to the mesh bundle, this is, extends across a width dimension of the mesh bundle, in a direction at an angle α with respect to the direction followed by the mesh in its transversely collected portion captured between the arms of the clamp. An angle α may be an angle greater than 20°, preferably greater than 30°, more preferably greater than 50° and most preferably about 90°.

In an embodiment, the bulge extends across the full width, from one side to the other, of the mesh bundle.

The method according to the invention comprises applying an ancillary closing element over a transversely collected portion of the mesh bag, tightly girdling the same. The way in which the mesh is collected may vary, without affecting the achievement of the invention.

Thus, the mesh may be twisted, concentrated, constricted, puckered, folded, constrained or compressed in any manner sufficient to enable the ancillary closing element to be applied around the mesh tightly girdling the transversely collected portion of the mesh.

The method according to the invention comprises the operation of bonding packed yarns of the mesh bundle together to form at least one bulge that acts as a retainer. As previously mentioned, this operation may be prior to, simultaneous with or subsequent to the application of the ancillary closing element around the transversely collected portion of the mesh bag.

Another aspect of the present invention is a mesh bag obtainable according to the method that is also the object of the invention.

The bag is a mesh bag having at least one transversely collected portion which is, specifically, an end portion and around which an ancillary closing element is applied which keeps said transversely collected portion pressed, with or without interposition of an external element, tightly girdling the same, thereby determining on a first side of the ancillary closing element a storage portion of the bag and on a second side of the ancillary closing element, adjacent thereto, a tail of the bag formed by a mesh bundle, at least a portion of the packed yarns of which are bonded together forming at least one bulge that acts as a retainer, which prevents by abutment with the ancillary closing element that the latter can slide along the entire tail of the bag formed by the mesh bundle, unintentionally opening said bag.

In a variant of the invention, the ancillary closing element is made of the same material as the mesh of the bag or at least the material of the ancillary closing element and that of the mesh of the bag share the same category of selective waste collection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show graphically and realistically, respectively, the result of implementing the method according to the invention, using as an ancillary closing element a particular clip, which is clamp-shaped;

FIG. 3 schematically illustrates the direction that a bulge formed by the union of packed yarns of the mesh bundle on a second side of the ancillary closing element can follow with respect to a general direction adopted by the transversely collected portion of the mesh bag captured by the ancillary closing element, the particular clip in the example; and

FIGS. 4 and 5 realistically show the result of implementing the method according to the invention, using an adhesive tape and a metal strap as ancillary closing elements, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The invention is exemplified in FIGS. 1 and 2 with an ancillary closing element 1 in the form of the particular clip 1.1 described in Utility Model ES1305762, the content of which is included by reference, therefore only briefly described herein.

The clip 1.1 is made of plastic material, is flexible and is made in a single piece.

The clip 1.1 comprises two arms 2, 3 each connected to a connecting bridge 4 by means of a respective lightened portion of material 4.1, each determining a respective joint.

This particular configuration, based on two joints, one for each arm 2, 3, helps to better control the bending deformation of the material from which the clip 1.1 is made when the arms 2, 3 of the clip are suddenly pushed closer together, specifically to move the same from an open position that they adopt by default to the closed position shown in FIG. 1.

The arms 2, 3 of the clip 1.1, in a conventional manner, have respective compression means which, when the arms 2, 3 are brought together, will cooperate to close by flattening a longitudinal collected portion from the mesh bag arranged between said arms; the arms 2, 3 being also provided, at their distal end, with respective complementary retention elements suitable for their mutual latching when the arms 2, 3 are brought together and the clip 1.1 is arranged in the closed position, avoiding its accidental or unwanted opening.

The bag 100 is a mesh bag made of the same or similar plastic as the clip 1.1. Therefore, the set formed by the bag and the clip can be disposed of in the same selective collection container. In other words, it is not necessary to remove the clip from the bag to dispose of each one in a corresponding container, according to the material of which the bag and the clip are made, respectively.

FIGS. 1 and 2 show graphically and realistically, respectively, the result of closing the mesh bag 100 by applying the clip 1.1 around a transversely collected portion 9 of the bag located at one end thereof, tightly girdling the same, thereby determining on a first side of the clip 1.1 a storage portion 100a of the bag, which is only partially shown, and on a second side of the clip 1.1, adjacent thereto, a tail of the bag formed by a mesh bundle 100b, all following the method according to the invention comprising the operation of bonding packed yarns of said mesh bundle 100b together to form at least one bulge 20 that acts as a retainer, which prevents by abutment with the clip 1.1 the entire tail of the bag from passing from the second side to the first side of said clip 1.1.

The contribution of the operation of bonding the packed yarns of the mesh bundle 100b together for improving the retention of the ancillary closing element 1, in this example constituted by the clip 1.1, and preventing the unwanted opening of the mesh bag, is verified by carrying out tests on market mesh bags, specifically on tubular bags, following a test protocol using self-manufactured equipment, which simulates the handling of a bag by the consumer.

Essentially, said test protocol consists of holding the tested bags closed with the clip 1.1 by their bottom and in an inverted position, holding them with a clamp that is hung or connected to a vertical cylinder with variable pressure regulation that exerts a succession of pulls at different pressures. The cylinder contracts and expands every two seconds, increasing the pressure by half a bar every five pulls, with the succession of pulls beginning at a pressure of 1.5 bar. When the contents of the bag fall out due to the opening of the bag, the number of pulls made so far is noted down.

The following is a non-limiting example of the number of pulls/cycles that the tested mesh bags withstood, with content distributed in the form of discrete balls, simulating fruit or vegetables, closed with a clip 1.1 similar to that in FIG. 1 and sized according to z=4 mm; y=16 mm; and x=9.2 mm, without breaking/opening, the clip being mainly made of REPSOL ALCUDIA 5703L HDPE material.

In all cases, the operation of bonding packed yarns of the mesh bundle together has been carried out using a tool with a single active head, specifically a hot head with a rectangular attack surface having 12 mm×2.5 mm size, applied under pressure on one side of the tail of the bag formed by the mesh bundle to be molten and bonding packed yarns of the mesh bundle together, the results where n is the number of trials being shown; MAX is the maximum number of pulls that can be withstood before the ancillary closing element detaches; MIN is the minimum number of pulls that can be withstood before the ancillary closing element detaches; PROM is the average number of pulls withstood; and Welding time indicates, if there is a value associated with this field, the duration of the operation of bonding together packed yarns of the mesh bundle.

It follows from the results in Table 1, where

• • 80-57-R4-1925:80-yarn polyethylene (PE) mesh, 1.9 mm×62.5 micron yarn, 4.5 grams per linear meter weight, 57 cm mesh tube diameter,
  • that in all cases the operation of bonding the packed yarns of the mesh bundle together contributes by a factor of ×4 to the increase in the number of pulls that the bag can withstand without opening, even when the time invested in the operation is only 0.3 s.

Similar tests were repeated with other mesh configurations, this time even with the interposition of an external element—in the form of a label tail made of PE being 12 mm wide and 600 gauge (150 microns) thick-interposed between the ancillary closing element and the mesh, wherein:

• • 80-57-R4-2220: 80-yarn PE mesh, 2.2 mm×50 micron yarn, 3.7 grams per linear meter weight, 57 cm mesh tube diameter.
  • 92-57-R4-1925: 92-yarn PE mesh, 1.9 mm×62.5 micron yarn, 5.2 grams per linear meter weight, 57 cm mesh tube diameter.
  • 104-57-R4-1920: 104-yarn PE mesh, 1.9 mm×50 micron yarn, 4.8 grams per linear meter weight, 57 cm mesh tube diameter.
  • 72-57-R4-1925: 72-yarn PE mesh, 1.9 mm×62.5 micron yarn, 4.2 grams per linear meter weight, 57 cm mesh tube diameter.

It is clear from the results in Table 2 that in all cases the operation of bonding packed yarns of the mesh bundle together contributes to an increase in the number of pulls that the bag can withstand without opening, even when the time spent on the operation is only 0.2 s.

It can be seen from the results in Table 3 that in all cases the operation of bonding packed yarns of the mesh bundle together continues to contribute to an increase in the number of pulls that the bag can withstand without opening, even when the pressure exerted on the mesh bundle is reduced to 0.2 Kg/mm, which in practice means bonding together only a portion of the packed yarns of the aforementioned mesh bundle.

The bulge 20 formed by the bonding of packed yarns of the mesh bundle becomes a more or less compact mass or body that aggregates or gathers material from several yarns, which is not necessarily an elevation on the surface of the bundle and which can, therefore, be an internal bulge.

When the method according to the invention is carried out by selecting a conventional metal strap or adhesive tape for the ancillary closing element, the formation of a bulge or bulges by bonding packed yarns of the mesh bundle also improves the retention capacity.

FIGS. 4 and 5 realistically show the result of implementing the method according to the invention, using as ancillary closing element 1 an adhesive tape 1.2 and a metal strap 1.3, respectively. In both cases, the same tools and conditions were used to ensure that the bonding of packed yarns of the tail of the bag formed by the mesh bundle together as described above in relation to the tests in Tables 1 to 3.

It can be observed in FIGS. 2, 4 and 5 the characteristic notch produced in the mesh bundle using a single active head as a tool, in the case of the examples a hot head that bonds yarns of the mesh bundle, specifically by melting the material of which said yarns are made, applied to one side of said bundle, the head having a width dimension that exceeds the width dimension of the mesh bundle.

It can also be observed in FIGS. 2, 4 and 5 that, the transversely collected mesh portion being partially surrounded by an external element, specifically a label tail, the head has been applied to the side of the mesh bundle coinciding with the lateral area of the bundle that is not surrounded by the label tail. In this way, the temperature of the head is transmitted directly to the yarns of the mesh bundle, without physical interposition of the label tail that partially surrounds said mesh bundle.

It is also observed, especially in FIGS. 2 and 4, the result of using an active head configured and/or positioned with respect to the mesh bundle such that the bulge 20 formed is transverse to the mesh bundle and in an angle direction a with respect to the general direction adopted by the collected portion of mesh imprisoned by the ancillary closing element 1, all as intended to be schematically illustrated in FIG. 3. In the exemplary embodiments illustrated, this angle α is approximately 90°.