Strong welding seam for film to be used for packaging

Abstract

A packaging film for the packaging of compressed goods and a method for creating such a packaging film using a welding assembly. The packaging film comprising connected layers of film having a first film layer and a second film layer both film layers having a width extending from a first edge to a second edge. The first film layer and the second film layer are connected via a welding seam. The welding seam being arrange along the width and the welding seam having a length exceeding the width.

Description

[0001] Strong welding seam for film to be used for packaging

[0002] Field of the invention

[0003] This invention relates to a packaging film for the packaging of compressed materials and a method of generating such packaging film.

[0004] Background

[0005] Packaging and wrapping of products using film is widely used in many industries. Such packed or wrapped products could be for the building industry and range from building materials such as plaster plates to glass or mineral wool. Other industries such as industries where products are packed under pressure, such as packed mattresses. One of the primary requirements for the packaging of such products is naturally that the material wrapped around the products serves to protect the products until it is purposely broken.

[0006] When wrapping insulation materials, such as glass or mineral wool, the film is often used as a mean for maintaining a compression of normally a stack of insulation objects. The insulation objects are compressed and then wrapped in un-stretched or stretched film, which is joined by welding. The welding is made by a welding assembly comprising two pairs of resilient jaws, between which a knife for cutting the film is placed. Further, between the knife and the resilient jaws two pairs of welding beams for welding the film are positioned. When the objects to be packed have been wrapped in the film, the film is stretched and held between the resilient jaws and at the same time clamped between the welding beams. Hereafter the film is cut and welded at the same time.

[0007] To reduce the production costs, it is desired to reduce the amount of film used per package. This is done by using thinner films in the existing production facilities. However, using thinner film is encumbered with one major problem. Regardless of the film thickness, the thermal stress applied to the stretched film during welding will release the tension present in the film. This will lead the film to creep and consequently lead to a thinning of the film between the resilient jaws and the welding beam. When using thin films, the thinning can reduce the yield strength of the film below the required level or be so severe that the film is reduced to only thin threads. There is therefore a great risk that the packaging process fails or that the finished package is torn or breaks open unintentionally. In the packaging process of insulation wool using film, whether it is in the form of a bag or a tube, the focus is on how the material is handled and how the integrity of the packaging may be maintained.

[0008] Initially, a piece of film, often made from a material like polyethylene, is prepared. This film is known for its flexibility and strength, making it suitable for containing the bulky and pressure-exerting insulation wool. The film is either shaped into a bag or left as a tube, depending on the packaging requirements.

[0009] The compressed insulation wool is inserted into the bag or tube created by the film. The compression of the wool is a key aspect of this process. By reducing its volume, the wool can be more easily handled and transported. However, once inside the film, the compressed wool exerts significant pressure as it tries to expand to its original volume. This exertion of pressure tests the strength and durability of the film, as well as any weld lines or sealed areas.

[0010] The success of this packaging method hinges on the strength and integrity of any sealed areas, be it in a bag or tube format. These areas must withstand the internal pressure of the expanding wool. A failure in any of these sealed areas can lead to the insulation wool breaking through the packaging, which could compromise the safety and effectiveness of the product.

[0011] Consistent quality control and adherence to manufacturing standards are essential throughout this process. The choice of material, the precision in any sealing process, and the handling of the film during the insertion of the wool all play crucial roles in ensuring the efficacy of the packaging. Advances in materials and technology can also contribute to the strength and reliability of the packaging, ensuring the safe and efficient transportation and storage of the insulation wool.

[0012] In essence, whether using a film bag or tube, the process of packaging compressed materials such as insulation wool requires careful attention to the preparation of the material, the handling of the compressed product, and the maintenance of the integrity of the packaging to ensure it effectively contains and protects the insulation material. A summary of the invention

[0013] Numerous objects and advantages, which will be evident from the description of the present invention, are according to a first aspect of the present invention obtained by:

[0014] A packaging film for the packaging of compressed goods, the packaging film comprising connected layers of film, the layers of film comprising a first film layer and a second both film layers having a width extending from a first edge to a second edge, wherein the first film layer and second film layer are connected via a welding seam, said welding seam connecting said first film layer and said second film layer along said width, the welding seam having a length exceeding said width.

[0015] By a film is understood a thin sheet that may be welded by heating. For packaging applications, particularly for large compressed goods like insulation, such foils typically have a width in the range of 800 mm to 3000 mm. Films usable for the creating of packaging film according to the invention may have many different compositions or structures. The film may be made from a single material, e.g. polyethylene, or it may be made from multiple layers, that have been joined by other means than welding, e.g. a coated paper film. Within the context of the present application the terms film and foil will be used interchangeably.

[0016] In some preferred variants the materials used for the packaging films are one or more of the following: HDPE (high density polyethylene), LDPE (low density polyethylene), LLDPE (Linear low density polyethylene), and MDO (Machine Direction Orientation film.

[0017] Preferably, MDO made from polyethylene which has been heated and stretched during the manufacturing process before any welding steps have occurred, are used for the packaging film. MDO has the benefit of increased strength due to the pre-stretching process where the film is stretched to the point of deformation, meanwhile such treatment encumbers the welding process as the flexibility of the MDO is lost along the stretching direction, which affects the contraction of the film due to the heating of the welding process.

[0018] The first film layer and the second film layer being connected by the welding seam may be made from the same material. The first film layer and the second film layer being connected by the welding seam may be made from different types of films. By a compressed material is understood any material, product or group of products that may be temporarily compressed during packaging and which will resiliently return to an intended shape upon release from the packaging. The compressed material may for example be insulation wool, a foam matters or multiple single-use diapers. Packaging films to be used for packaging of compressed goods need to be capable of withstanding the pressure applied by the material which expands against the packaging film once it has been sealed inside.

[0019] It is understood that the packaging film of the present invention may also be used for other purposes than the packaging of compressed goods, e.g. the packaging of noncompressed goods or plastic bags such as shopping bags. In particular bags used for transportation of goods where ethe applied stress may vary depending on the used may also subject the packaging film to requirements of stress resistance and high strength.

[0020] By the width of the film layers is understood the shortest distance between a first edge and a second edge of the film in the direction where the welding seam is to connect the first film layer and the second film layer. It is to be understood that the length of the welding seam exceeding the width is relevant relating to the dimensions of the final product. Hence, the welding seam may be created connecting part of two film layers and be cut subsequently, without the seam spanning the entirety of the film layers as long as it spans the width of the final packaging film. In other words, the requirements of the length of the welding seam exceeding the width may also be seen as relevant for a specific section of a longer film, such that the length of the welding seam in the direction of the width of the section exceeds the width of the section. Hence, a linear welding seam exceeding the width simply by being at an angle relative to the width of the section, e.g. a diagonal welding seam, does not follow this requirement, but a welding seam made up of multiple connected pieces being angled in varying directions will, e.g. a zigzagging shape of the welding seam. Furthermore, the invention should not be seen as restricted to a first film and a second film having the same width beyond the section of the welding seam. Even if the final product may be cut to provide the same length the connected first and second film may, e.g. originate from rolls of film material having different lengths.

[0021] A benefit of the length of the welding seam exceeding the width of the film layers is that the strength of the welding seam is increased such that it is more resistant to stress. During the process of creating a welding seam the film is heated with a welding band to a temperature that is above the melting point of the film such that the first film layer and the second film layer will merge. When the film melts the structure of the film will change, especially in the longitudinal direction, i.e. along the course of the welding band, making the welding the weakest point of the packaging film. Increasing the width of the welding seam will not increase the strength as the weakest point occurs at the transition from the non-welded film to the welded film regardless of the subsequent width of the welding seam. The longer welding seam will increase the strength of the welding seam as it increases the region of which the applied stress is distributed.

[0022] Increasing the length of the welding seam beyond the length of the linear welding seam known in the art may be achieved by changing the shape and / or design of the welding band used to create the welding seam and thus also the shape of the resulting welding seam.

[0023] According to a further embodiment of the first aspect of the invention, the course of the welding seam having one or more segments being transverse to the width.

[0024] In other words, the welding seam has one or more segments which are arranged at an angle less than ninety degrees relative to the first and second edge. In a preferred variant the welding seam comprises at least two segments being angled relative to each other.

[0025] According to a further embodiment of the first aspect of the invention, the welding seam has a serpentine shape, such as a sine shape or a meandering shape.

[0026] Having a welding seam with multiple segments being angled relative to each other and / or being arranged with a serpentine shape ensures that the welding seam has a length exceeding the width of the film. Furthermore the change of welding direction along the course of the welding seam occurring causes the direction of shrinkage or creep of the film due to the heat of the welding to vary whereby the direction of the stress applied during the welding process is distributed.

[0027] In particular for MDO films where pre-stretching has been performed in one direction, this direction is particularly vulnerable during welding. Hence, traditional welding seams are always created to have a course perpendicular to the direction of the pre-stretch of an MDO film. The meandering shape of the welding seam ensures that for the majority of the course of the welding seam is not parallel to the direction of the pre-stretching, regardless of the direction of the seam whereby the welding seam can be more freely arranged along various edges of the film.

[0028] According to a further variant of the first aspect of the invention, the welding seam has a serpentine shape being periodic and being arranged such that the welding seam extends further along the direction of the width than perpendicularly to the width for each period of the serpentine shape. In other words the length of the half period exceeds the length of the amplitude.

[0029] According to a further embodiment of the first aspect of the invention, the welding seam comprises multiple parallel segments, at least one of the parallel segments comprises stippling.

[0030] By the welding seam comprising multiple parallel segments is understood that for at least a section of the welding seam comprises at least two welding lines arranged in a parallel manner. Such parallelly arranged welding lines may be linear lines or they may follow an different course, such as a serpentine course.

[0031] By at least one of the parallel segments of the welding seam comprising stippling is understood that at least one of the parallelly arranged welding lines is stippled for at least part of its course. By a welding line being stippled is understood that it is pointwise welded along its course, such that there are intermittent line segments and line openings.

[0032] In a preferred variant, all of the parallel segments of the welding seam comprises stippling, the stippling being arranged in a staggered manner.

[0033] By the stippling being arranged in a staggered manner is understood that the there is overlap between the line segments of neighbouring welding lines, such that a continuous and closed welding seam is created by the stippled lines together.

[0034] The length of the line segments and / or line openings of a stippling may vary along the course of a welding line and / or for each of the adjacent welding lines. Another object of the present invention is to provide a welding assembly for the production of packaging material having strong welding seams.

[0035] According to a second aspect of the present invention, the above objects and advantages are obtained by:

[0036] A welding assembly for producing a welding seam of a packaging film, the welding assembly comprising a lower jaw, the lower jaw comprising a welding support, a resilient member and cutting means, an upper jaw, the upper jaw comprising an upper welding beam and at least a first welding band, said first welding band being configured such that the length of said first welding band exceeds the length of the cutting means, whereby the welding seam created by the welding band will exceed the width of the packaging film created using the welding assembly.

[0037] According to a further variant of the second aspect of the invention, the first welding band has a serpentine shape.

[0038] A welding band having a serpentine shape may be used to create a welding seam having a serpentine shape such as a meandering shape, a zigzag shape or a sinusoidal shape, whereby it is ensured that the length of the welding seam will exceed the width of the film being sealed by the welding seam.

[0039] According to a further embodiment of the second aspect of the invention, the first welding band comprising a first sub-band and a second sub-band arranged adjacently.

[0040] By sub-bands adjacently arranged are understood welding bands arranged along the same beam of an upper jaw of a welding assembly in such a manner that both subbands will contribute to the same welding seam. Such a configuration may for example be beneficial for the creation of welding seams comprising multiple welding lines. In some variants the first welding band may comprise three or more sub-bands.

[0041] According to a further embodiment of the second aspect of the invention, the first subband and said second sub-band are configured to be independently operable.

[0042] By the first sub-band and the second sub-band being configured to be independently operable is understood that during the welding procedure they may operate having separate setting, e.g. different currents run through each sub-band such that they operate at different welding temperatures, or they may be operated at different times, e.g. the welding performed by the first sub-band occurring or beginning before the welding performed by the second sub-band.

[0043] According to a further variant of the second aspect of the invention, the welding assembly comprises both a first welding band and a second welding band being arranged on a first and a second beam of the upper jaw. Such arrangement enables the welding of two welding seams simultaneously. In preferred variants the first welding band and the second welding band are arranged on opposite sides of the cutting means such that welding seams may be made from the same film layers and partake in the creation of two separate packaging films.

[0044] According to a further preferred embodiment of the invention, a longitudinal portion of the first film layer overlaps a longitudinal portion of the second film layer to form an overlapping region, and the welding seam connects the first and second film layers within said overlapping region. This arrangement provides a stronger weld by increasing the material interface and structural integrity at the seam, making it more resistant to failure under pressure from compressed goods.

[0045] Another object of the present invention is to provide a method for generating a packaging material from film.

[0046] According to a third aspect of the present invention, the above objects and advantages are obtained by:

[0047] A method for generating packaging material from film, the method comprising connecting a first film layer and a second film layer both film layers having a width extending from a first edge to a second edge. The layers are connected via a welding seam along at least a section of the width wherein the welding seam has a length exceeding the width.

[0048] According to a further embodiment of the third aspect of the invention, the method comprising the steps of arranging and aligning at least a first film layer and a second film layer such that a first edge of said first film layer and a first edge of said second film layer are parallel, before connecting the film layers are connected by welding.

[0049] According to a further embodiment of the third aspect of the invention, the method comprising the step of cutting the connected layers of film along the width of the connected layers.

[0050] According to a further variant of the third aspect of the invention, the method comprising the step of cutting the first film layer and the second film layer before the first film layer and the second film layer are connected by the welding process.

[0051] According to a further variant of the third aspect of the invention, the method comprising preheating of a welding band.

[0052] According to a further embodiment of the third aspect of the invention, the welding seam being created by welding at a temperature within the range of of 150-200 degrees Celsius.

[0053] Description of figures

[0054] Fig. 1a - 1f illustrates a method of welding according to prior art.

[0055] Fig. 2 illustrated a welding seam according to prior art.

[0056] Fig. 3 illustrates an enhanced welding seam according to the present invention.

[0057] Fig. 4a - 4c illustrates exemplary shapes of welding seams according to the present invention.

[0058] Fig. 5a - 5d illustrates exemplary shapes of welding seams according to the present invention.

[0059] Fig. 6a and 6b illustrate a modified welding assembly for performing a welding shape according to the present invention. Fig. 7 illustrates a cross-sectional view of an embodiment showing overlapping film layers.

[0060] Detailed description of the invention

[0061] Figs. 1 a- 1 f show cross-sectional views of a welding assembly 100 during various steps of the method of creating a welding seam of a film 10. The welding assembly 100 comprises holding means, welding means, cutting means and accumulation means. The holding means comprises an upper jaw 102 and a lower jaw 104. The lower jaw 104 comprises a resilient member 105, arranged to face the upper jaw 102 such that the two protrusions of the upper jaw 102 can form a recess or groove by indenting the resilient member 105 upon contact between the upper jaw 102 and the lower jaw 104. The upper and lower jaws 102, 104 can be moved vertically up and down whereby is understood that upward movement moves the upper jaw 102 further from the lower jaw 104 while it corresponds to moving the lower jaw 104 towards the upper jaw 102, while downward movement conversely moves the upper jaw 102 towards the lower jaw 104 and the lower jaw 104 away from the upper jaw 102. The upper and lower jaws 102, 104 are arranged to receive a film 10 between them. The welding means of the welding assembly 100 comprises a welding beam 106 and a welding support 108. The welding beam 106 is flanked on both sides by upper jaw 102 and the welding support 108 is arranged to be flanked on both sides by the lower jaw 104. The welding support 108 can be moved vertically up and down, independently of the lower jaw 104. This movement can be enabled by accumulation means (not shown), such as a pneumatic cylinder. The welding beam 106 can be moved vertically up and down relative to the upper jaw 102, this relative movement being limited to the clearance 118 (illustrated by the double-headed arrow) of the upper jaw 102; for illustrative purposes, the clearance 118 is only depicted in figure 1a. The welding beam 106 comprises a first welding band 107 and a second welding band 109, which can be heated e.g. by directing a current therethrough. The welding beam 106 and the welding support 108 may be moved vertically such that they are brought together whereby the film 10 is clamped between the first welding band 107 and the welding support 108 and between the second welding band 109 and the welding support 108, respectively. The contact point between the first welding band 107 and the film 10 when the welding assembly 100 is in the clamped position is denoted the first welding point 122. The contact point between the second welding band 109 and the film 10 when the welding assembly 100 is in the clamped position is denoted the second welding point 123. It is to be understood that while the terminology welding point 122, 123 is used, the first and second weld bars 107, 109 extend along the length of the welding assembly 100, such that they span the width of the film 10. The welding assembly 100 further comprises cutting means 110 comprising a blade for cutting the film 10. The cutting means 110 can be moved vertically up and down independently of the welding support 108. The width of both the jaws 102, 104, the welding beam 106, and the welding support 108 span at least the width of the film, but do not have to be continuous. The blade of the cutting means 110 may spans at least the width of the film 10 such that it may cut units of packaging film from a larger film layer. In other variants the cutting means 10 may be shorter than the width such that the welding assembly may be used repeatedly along the same direction each pass creating a section of a welding seam along a packaging film. Before the welding takes place, a length of the film is passed by the welding assembly 100 such that the final product, e.g. a packaged good or a bag, will obtain the intended length, subsequently the film 10 is clamped in position, welded and cut along the width of the film such that an end welding seam is created along the width of the film 10.

[0062] In one embodiment the film 10 is welded using the welding assembly 100 according to the following method. The method relates to the joining of at least a first and a second film layer. The at least two film layers can originate from the same roll of film, e.g. by the film being folded, or they may originate from two different rolls of film. For the sake of simplicity the at least two film layers are depicted and referenced as one film 10. The film 10 used can be un-stretched or pre-stretched. A pre-stretched film concerns a film that has been stretched to such an extent that it is plastically deformed. The prestretched film cannot be stretched any further without breaking it.

[0063] As illustrated in Fig. 1a, the film 10 is directed or led in between the upper jaw and the welding beam 106 on one side and the lower jaw 104 and the and the welding support 108 on the other side the components having been arranged for form a space therebetween for the placement of the film 10. As depicted in Fig. 1a, the welding beam 106 is positioned vertically higher than the jaws of the upper jaw 102. The welding support 108 is directed upwards towards the first and second welding bands 107, 109, whereby the film 10 is clamped at the first and second welding points 122, 123, see figure 1b. This upward movement of the welding support 108 could be enabled by using accumulation means (not shown), such as actuating a pneumatic cylinder. Once the film 10 is clamped, the upper jaw 102 and thereby also the welding beam 106 are moved downwards towards the lower jaw 104 and the resilient member 105. The downwards movement of the welding beam 106 may e.g. be actuated by reducing pressure of the pneumatic cylinder (accumulation mean) of the welding support 108 or by fully removing the pressure. As illustrated in Fig. 1c the film 10 is thusly held between both upper and lower jaws 102, 104 at the first and second holding points 124, 125, i.e. at the resilient member 105 and the upper jaw 102 as well as being clamped between the welding beam 106 and the welding support 108 at the first and second welding points 122, 123. Thus, accumulated film 10 is held between the first holding point 124 and the first welding point 122 on one side as well as between the second welding point 123 and the second holding point 125 on the other side. The film 10 being thusly confined will typically fold taking e.g. an S- or Z-shape. As illustrated in Fig. 1d , once the film 10 has been secured between the upper and lower jaws 102, 104, the film 10 is cut by moving the cutting means 110 upwards. During this step the film 10 is also welded at the first and second welding points 122, 123. Due to the heat, the accumulated film 10 on both sides of each of the welding points 122, 123 is drawn or crept towards that welding point 122, 123, this is called welding creep. If the film 10 is pre-stretched (plastically deformed or stretched being an MDO film), the film 10 will be particularly vulnerable to welding creep at the respective first and second welding points 122, 123 in the direction of the pre-stretch. In order to provide the best possible welding, the welding support 108 can be pressed against the welding bands 107, 109 during and after welding, which may be done by activating the pneumatic cylinder of the welding support 108. By applying such pressure the risk of breaking or tearing the film due to forces across the film caused by the welding is decreased.

[0064] Once the film 10 has been cut and welded the cutting means 110 may be retracted by lowering it back towards the welding support 108, see Fig. 1e. Finally the film 10 may be unclamped from the upper and lower jaws 102, 104 by lowering the welding support 108 and the raising the upper welding beam 106, see Fig. 1f. The now cut and welded film may then be removed from the welding assembly.

[0065] The steps of the method described can vary both in terms of how they are performed and the sequence of them. Thus, the film may be accumulated in many other ways between the first and second holding points 124, 125 and the first and second welding points 122, 123, using different accumulation means. Alternative ways of carrying out the accumulation may be by moving the holding means and the welding means according to another method or sequence of steps. The film could also be preaccumulated before it is led in between the holding and the welding point. The accumulation means could also be an element or apparatus that conveys film towards the welding point, e.g. when the welding means clamps the film and before the film is held in the holding point by the holding means.

[0066] Fig. 2 is a conceptual illustration of a welding and welding seam 20 created by traditional welding methods known in the art. The welding seam 20 fastens a first film layer 11 and a second film layer 12 to each other. While the first film layer 11 and second film layer 12 are in Fig. 2 shown to be attached only along the welding seam 20 it is to be understood that welding seams 20 may be present along multiple edges, may be used to close and cut off a film tube and or may be arranged to close off a film bag having packaged material contained therein optionally being compressed at the time of welding whereupon it may expand to fill out the space and potentially cause stretching of the film 10.

[0067] For solutions known in the art as illustrated in Fig. 2, the welding seam 20 is a straight line spanning the width w of the film 10 as the first film layer 11 and the second film layer 12 have the same width w. The straight welding seam 20 is arranged substantially perpendicular to the first edge 15 and the second edge 16 of the film 10 whereby the welding seam 20 is substantially parallel to the cut edge 17. Thus, welding seams 20 of the prior art have a length L being the same as the width w of the film 10.

[0068] Fig. 3 is a conceptual illustration of an embodiment of a welding and welding seam 20 according to the present invention. For all embodiments of the invention the welding seam 20 has a length along the course of the welding seam 20 being longer than the width w of the film 10. The welding seam 20 is arranged to extend from a first edge

[0069] In the embodiment illustrated in Fig. 3 the welding seam 20 takes the shape of a sine wave. A sinusoidal shape is particularly advantageous as it increases the seam length smoothly, without creating sharp angles or corners that could act as stress concentration points and potential weak spots in the final package. As will be discussed in the following the welding seam 20 according to the invention may take various shapes resulting in the length L of the welding seam 20 exceeding the width of the film 10. In some preferred embodiments the welding seam 20 may comprise a periodic pattern with even or varying amplitudes, see Figs. 4a-4b. For such periodic patterns they preferably have their nodes located along the line that would extend perpendicularly from the first edge 15 to the second edge 16 of the film, i.e. the straight line along which a welding seam according to the prior art would follow, in other words that line is the zero-point of their amplitudes.

[0070] Figs. 4a-4c illustrate various meandering or serpentine patterns being exemplary embodiments of sections of the welding seam 20 taking various forms. The figures illustrates only part of the full width w of the film 10 along part of the cut edge 17 and it is to be understood that the shown patterns may repeat for the full width such that it extends from the first edge to the second edge (not shown) of the film 10. The particular cut-off point and / or shape at the first and second edge (not shown) of the film may vary depending on the specific embodiment and alignment of the film 10 in the welding assembly and the width of the film 10 relative to the jaws of the welding assembly. In some preferred embodiments the first and second welding pars of the welding assembly a wider than the width of the film whereby the shape of the welding seam 20 at the first and second edge depends on the relative difference in the widths of the film 10 and the welding bands.

[0071] Fig. 4a illustrates a welding seam 20 having a sinusoidal wave shape. As is evident form the illustration and being a mathematical necessity the length L’ of the section of the welding seam 20 exceeds the width w’ of the section of the film 10.

[0072] Various embodiments of welding seams 20 having a wave shape fall within the scope of the invention, e.g. having various periods P and / or amplitudes A. Preferably the period of the waveshape fall within the range of 1-20 mm more preferably 1-10 mm yet more preferably 2-5 mm. The amplitude may preferably fall within the range of 1-20 mm more preferably 1-10 mm yet more preferably 2-5 mm.

[0073] Fig. 4b illustrates a welding seam 20 having a zigzag shape of angled welding seam lines. It is to be understood that while the theoretical shape illustrated are sharply pointed zigzag structures, in practice the welding process where the film is melted, causes blurring of the lines such that tips may be rounded.

[0074] In some preferred embodiments the dimensions of amplitude and period fall within the ranges described for the embodiment of Fig. 4a. Preferably the angle b of neighbouring lines of the zigzag welding seam fall within the range of 25-150 degrees, preferably between 45-135 degrees yet more preferably between 70-110 degrees.

[0075] While the zigzag pattern illustrated in Fig. 4b is symmetric it is to be understood that all angles of the welding seam need not be the same, e.g. the angle may alternate between neighbouring peak and / or between the peaks and valleys.

[0076] Fig. 4c is an exemplary illustration of a welding seam 20 having more varied structuring than what is shown in the previous embodiments. This is but one illustration of the fact that period and amplitude may vary along the course of the welding seam.

[0077] The dimensions of the meandering or serpentine welding seam patterns are for all embodiments designed to obtain a suitable trade-off between increasing the length of the welding seam sufficiently to obtain an increased welding strength, avoiding that too sharp peaks cause weak points when force is applied to the welding seam while the dimensions are large enough that the remain well-defined during the welding procedure where the melting of the film causes blurring and / or merging of the structures.

[0078] It is understood that the distance d between the cut edge 17 and the point of the welding seam 20 closest to the cut edge 17 may vary for different embodiments of the invention. A trade-off between minimising the amount of excess film between the welding seam and the cut edge while ensuring that the distance is sufficient that there is no risk of tears or puncturing of the welding seam may be preferrable. Furthermore, the minimum distance may be limited by the need for a required film buffer to ensure that the film integrity is not damaged due to the shrinkage during the welding process, The distance d may fall within the range of 1-100 mm, preferably within the range of 1- 20.

[0079] Figs. 5a-5d illustrate various exemplary embodiments of welding seams 20 in accordance with the invention where the length of the welding seam 20 is increased by including multiple stippled lines arranged adjacently. By a stippled line is understood a line along the course of which there are intermittent line segments 25 and line openings 26. It is to be understood that while the stippled lines of the welding seam 20 of Fig. 5a is illustrated as spaced apart this is for illustrative purposes and in practice the adjacent lines and length of the stippled sections of the welding seam 20 are such that they will when melded merge whereby a closed welding seam is created along the width of the section of the film. Fig. 5c illustrates the concept of how a closed welding seam 20 may be formed by stippled lines adjacently spaced. It is to be understood that while the illustrations of Figs. 5a-5d include line segments having sharp edges and corners these too will smear / be rounded during the welding process during which the film melts.

[0080] Fig. 5a illustrates a segment of a welding seam 20 having a length longer than the width of the section of the film. The embodiment illustrated in Fig. 5a comprises a first stippled line 21 and a second stippled line 22 arranged adjacently in a parallel manner. The stippling of the first stippled line 21 and the second stippled line 22 is arrange din a staggered manner such that every line piece of the first stippled line 21 overlaps a line piece of the second stippled line 22. Such staggering ensures that a closed welding seam 20 is created, i.e. such that there will be no leak between the opposite sides of the welding seam 20. The length of the segment of the welding seam 20 is increased compared to a straight welding seam 20 known in the art, by the amount of the overlap of the line pieces of the first stippled line 21 and the second stippled line 22.

[0081] Fig. 5b shows an example the option of having multiple adjacently arranged welding lines one of which is stippled while the other is continuous along its course. In the illustrated embodiment a first solid line 2T is a linear welding line being continuous along its course is arranged parallel to an adjacent second stippled line 22. The first and second lines 21 , 22 are arranged such that they will merge during welding when the foil is melted whereby a single welding seam 20 the length of which is longer than the width of the section of the foil at least on the side of the welding seam 20 facing away from the cut edge 17.

[0082] In a preferred embodiment having a continuous welding line, at least the welding line furthest from the cut edge 17 will be stippled. The welding line furthest from the cut edge 17 is the welding line which will be facing toward the region where goods will most commonly be packaged or held by the packaging foil and thus it will be the part of the welding seam 20 which will be subjected to most stress. Hence, it is along this part of the welding seam 20 that it is necessary that the length exceeds the width.

[0083] Fig. 5c illustrates that more than two adjacently spaced stippled lines may be used for the welding seam 20. The embodiment shown in Fig. 5c comprises a first 21 , second 22 and third 23 stippled line parallelly arranged adjacent to each other. As described previously using the example of the embodiment having only two stippled lines, the stippled lines are arranged such that the welding seam 20 is leak tight.

[0084] Fig. 5d is an exemplary embodiment of a welding seam 20 made up of a first and a second stippled line each of which follows a meandering pattern in the form of a sine wave. The first 21 and second 22 stippled lines are arranged parallelly to each other. As for the previously described embodiments the line pieces are arranged such that a closed welding seam 20 is created, i.e. the welding seam is leak tight. Such embodiments of the welding seam 20 comprising both stippled lines and a meandering shape further increases the length of the welding seam 20 relative to the width of the film.

[0085] In some embodiments of the invention having multiple stippled lines, the lines pieces are all of equal length. The line pieces may preferably be evenly distributed along the course of the welding seam. The line pieces of adjacently arranged stippled lines may be arranged such that the overlap of each line piece is within the range of 10-40 % of the length of the line piece.

[0086] In other embodiments, such as the one illustrated in Fig. 5d the line pieces of the stippled lines may be of varying length and / or unevenly distributed along the course of each of the stippled lines.

[0087] It is to be understood that the illustrated examples are purely exemplary and more variations fall within the scope of the invention. For example, welding seams comprising both a meandering shape and stippling may have carefully designed placement of the stippled line segments, e.g. such that the rounded peaks of a wave are all within a first stippled line while the middle sections of the waveshape are all part of the second stippled line.

[0088] Embodiment of the welding seam comprising stippled lines may be produced using a single welding band for each welding seam or they may be created using multiple welding bands, e.g. a welding band for each stippled line of the welding seam. For embodiments using multiple welding bands they may contact the film simultaneously or subsequently such that different stippled lines of the welding seam are welded sequentially. Alternatively multiple welding bands may contact the film simultaneously but current may be driven through each welding band sequentially such that the heating and welding happens sequentially. Furthermore, embodiments of the welding line being created at separate times may be created using different temperatures.

[0089] Figs. 6a shows the lower jaw 104 of a welding assembly along with welding seams 20 created when welding a first film layer 11 and a second film layer 12 together along a cut edge 17. For illustrative purposes both a new welding seam 20 according to the present invention (left side of the figure) and a traditional welding seam 20’ according to the prior art (right side of the figure) are shown. As illustrated a welding assembly may comprise different shapes / types of welding bands for the first welding band 107 and the second welding band 109 creating different welding seams 20, e.g. having different shapes may be created using the same welding assembly. In preferred embodiments of the invention the welding assembly is configured to provide a first welding band 107 and a second welding band 109 both being arranged to create welding seams 20 according to the invention. In preferred embodiments the first welding band 107 and the second welding band 109 are of the same type. The first and second welding bands 107,109 may be of the same type but be arranged differently, e.g. such that they are mirrored with respect to each other.

[0090] The situation illustrated in Figs. 6a and 6b are after the welding seams 20, 20’ have been created and the film 10 has been cut and released from the welding assembly.

[0091] Fig. 6b shows a close-up of a part of Fig. 6a more clearly revealing the shapes of the first and second welding bands 107, 109 and the welding seams 20, 20’ they have been used to create.

[0092] The welding assembly 100 may be configured to be used for the method of creating welding seams 20 comprising steps similar to those described for the prior art in relation to Figs. 1 a-1f. As previously mentioned the steps described in relation to Figs. 1 a-1f may be performed in various orders. In a preferred variant according to the invention, the first and second film layers 11 , 12 are firstly clamped at the holding points whereupon the first and second film layers 11 , 12 are cut before the welding seams are created. The welding support 108 may move up and clamp the film layers 11 ,12 at the welding points such that the film being clamped both at the holding points and at the welding points. Once the film is clamped at both of these points, the components of the welding assembly may be arranged such that the spacing between the first holding point and the first welding point is decreased whereby a buffer of film is created such that the film is not stressed during the creation of the welding seam as the film creeps and / or contracts during the heating, melting and solidification of the film. Similarly the spacing between the second holding point and the second welding point may be decreased to create an equivalent buffer effect. In a preferred embodiment the welding support 108 moves downward to release the film at the welding points before the perpendicular spacing of the welding points relative to the holding points are increased in the horizontal direction, i.e. before the respective welding bands are moved further from the resilient member in the horizontal direction. This order of movement minimises the stress applied to the created welding seams before they are cooled.

[0093] In a preferred embodiment one or both of the welding bands 107, 109 are spring loaded enabling them to elongate during the welding procedure. The welding bands 107, 109 may be made from any suitable conducting material. In a preferred embodiment the welding bands 107, 109 are made from nickel-plated copper.

[0094] In a preferred embodiment, when the welding assembly is operated the welding bands will maintain an elevated basic temperature, before a welding seam is created the welding bands will be pre-heated to a temperature which remains below the melting point of the film to be welded. During the welding procedure the temperature of the welding bands is raised, such that they may melt the film. Once the welding seam has been created the temperature of the welding bands is once more reduced to the basic temperature.

[0095] The conditions of the welding depend on both the material of the film, the thickness of the film and the ambient condition sunder which the welding assembly is operated.

[0096] The basic elevated temperature of the welding bands may be within the range of 50-75 degrees Celsius.

[0097] The pre-heating temperature of the welding bands may be within the range of 75-125 degrees Celsius.

[0098] The welding temperature of the welding bands may be within the range of 150-200 degrees Celsius. The welding time may be within the range of 800-1500 ms.

[0099] The cooling time after welding may be within the range of 800-1500 ms.

[0100] In a further preferred embodiment, illustrated conceptually in Fig. 7, the strength of the welding seam (20) is enhanced by arranging the film layers in an overlapping configuration before welding. As shown, a longitudinal portion of the first film layer (11) is disposed on top of a longitudinal portion of the second film layer (12) to form an overlapping region (18). The welding seam (20) is then created within this overlapping region (18).

[0101] This lap joint configuration provides a greater surface area for the weld and increases the effective material thickness at the seam, resulting in a significantly stronger and more durable connection. This is particularly beneficial for packaging highly compressed goods that exert substantial pressure on the weld. This arrangement can be used with any of the welding seam shapes described herein, including the straight, serpentine, or stippled welding seams. This corresponds to the method step of arranging the film layers to form an overlapping region (18) before connecting them by welding.

[0102] List of references

[0103] Below is a list of reference signs used in the detailed description of the present disclosure and in the drawings referred to in the detailed description of the present disclosure. w Width of the film layer w’ Width of the section of the film L Length of the welding seam

[0104] L’ Length of the welding seam along the section of the film d Shortest distance between cut edge and the welding seam b Angle of zigzag

[0105] 10 Film

[0106] 11 First film layer

[0107] 12 Second film layer

[0108] 15 First edge

[0109] 16 Second edge

[0110] 17 Cut edge

[0111] 18 Overlapping region

[0112] 20 Welding seam

[0113] 21 First stippled line 2T First solid line 22 Second stippled line

[0114] 23 Third stippled line

[0115] 25 Line segment

[0116] 26 Line opening

[0117] 100 Welding assembly

[0118] 102 Upper jaw 104 Lower jaw

[0119] 105 Resilient member

[0120] 106 Upper welding beam 107 Welding band

[0121] 108 Welding support 109 Welding band

[0122] 110 Cutting means

[0123] 118 Clearance 120 Direction of movement

[0124] 122 Welding point

[0125] 123 Welding point

[0126] 124 Holding point

[0127] 125 Holding point

Claims

CLAIMS1. A packaging film for the packaging of compressed goods, said packaging film comprising connected layers of film comprising a first film layer and a second film layer both film layers having a width extending from a first edge to a second edge, wherein said first film layer and said second film layer are connected via a welding seam, said welding seam connecting said first film layer and said second film layer along said width, said welding seam having a length exceeding said width.

2. A packaging film according to claim 1, wherein the film has a width in the range of 800 mm to 3000 mm.

3. A packaging film according to claim 1-2, wherein the welding seam has a sinusoidal shape.

4. A packaging film according to claim 1-3, the course of said welding seam having one or more segments being transverse to said width of the film layers.

5. A packaging film according to claim 1-4, said welding seam having a serpentine shape, such as a sine shape or a meandering shape.

6. A packaging film according to any of the preceding claims, said welding seam comprising multiple parallel segments, at least one of said parallel segments comprising stippling.

7. A packaging film according to any of the preceding claims, wherein a longitudinal portion of the first film layer overlaps a longitudinal portion of the second film layer to form an overlapping region, and wherein the welding seam connects the first and second film layers within said overlapping region.

8. A welding assembly for producing a welding seam of a packaging film according to any of the preceding, said welding assembly comprising a lower jaw, said lower jaw comprising a welding support, a resilient member and cutting means, an upper jaw, said upper jaw comprising an upper welding beam and at least a first welding band, said first welding band being configured such that the length of said firstwelding band exceeds the length of said cutting means, whereby the welding seam created by said welding band will exceed the width of the packaging film created using said welding assembly.

9. The welding assembly according to claim 6, said first welding band comprising a first sub-band and a second sub-band arranged adjacently.

10. A method for generating packaging material from film, said method comprising connecting a first film layer and a second film layer both film layers having a width extending from a first edge to a second edge, wherein said layers are connected via a welding seam along at least a section of said width wherein said welding seam has a length exceeding said width.

11. The method according to claim 8, said method comprising the steps of arranging and aligning at least a first film layer and a second film layer such that a first edge of said first film layer and a first edge of said second film layer are parallel, before connecting said film layers are connected by welding.

12. The method according to claim 10 or 11, further comprising arranging the first film layer and the second film layer to form an overlapping region where a longitudinal portion of the first film layer is disposed on a longitudinal portion of the second film layer, wherein the connecting of the film layers by the welding seam occurs within said overlapping region.

13. The method according to any of the claims 10-12, said method comprising the step of cutting the connected layers of film along the width of said connected layers.

14. The method according to any of the claims 10-13, said welding seam being created by welding at a temperature within the range of of 150-200 degrees Celsius.

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