WO2004080695A1

WO2004080695A1 - Plastic stretch film, plastic net made therefrom, and method for the production thereof

Info

Publication number: WO2004080695A1
Application number: PCT/EP2004/002468
Authority: WO
Inventors: Harilaos Kavvadias
Original assignee: Mega Plast S.A.
Priority date: 2003-03-12
Filing date: 2004-03-10
Publication date: 2004-09-23
Also published as: DE10310814A1

Abstract

The invention relates to a plastic stretch film (2) that differs in first partial areas, which are also designated as threads (14), extend in a main direction (17) and which are interspaced, and in web surfaces (15),which are located between the threads (14) and which serve as second partial areas. In comparison to the threads (14), these web surfaces (15) are additionally pre-stretched transversal to the main direction (17), and the threads (14) are folded in a manner that is transversal to the main direction (17). An additional film strip (35), which also extends in the main direction, is attached to at least one part of the threads (14). A plastic net can be produced from the plastic stretch film (2) in which rows of holes (16) extending in the main direction (17) are formed in the web surfaces (15).

Description

Plastic stretch film, plastic net made of it and process for its production

The invention relates to a plastic stretch film and a plastic net made therefrom and a method for producing the plastic stretch film.

For packaging pallets, bales of straw, fruit, etc., it is known to use perforated, pre-stretched plastic stretch films in order to enable sufficient stretchability and ventilation of the objects to be packaged. A pre-stretched plastic stretch film is known from EP 0 820 856 A1, in which holes are produced by a thermal stripping process without touching the film.

For other packaging purposes, in particular also for wrapping straw bales, nets have proven to be more suitable, which are usually braided or knotted from individual threads or narrow ribbons. From DE 100 27 527 AI, however, a plastic net is known which can be produced in one piece from a stretch plastic film without various pieces of film being braided, knotted, or the like. be connected to each other. The plastic net has pre-stretched crosspieces and threads running in a main direction, which are cross-folded to increase the tensile strength.

The plastic network known from DE 100 27 527 AI has proven itself extremely well in practice, a further increase in tensile strength being desirable in order to improve the performance characteristics.

In addition, areas of application are known for plastic stretch films in which no ventilation of the wrapped material is desired. Rather, the goods packaged by the film should be sealed airtight. An increase in tensile strength is also desirable for the hole-free plastic stretch films used here.

From EP 0 909 721 AI it is known to use a plastic stretch film with a plurality of reinforcing elements extending in the longitudinal direction of the film, e.g. B. additional film strips to reinforce. The object of the invention is to improve a plastic stretch film and a plastic net which can be produced therefrom such that an increased or at least constant tensile strength is achieved with the same or improved material utilization.

According to the invention the object is achieved by a plastic stretch film according to claim 1 and by a plastic network according to claim 6. A method for producing the plastic stretch film is specified in claim 9. Advantageous further developments of the invention are defined in the dependent claims.

A plastic stretch film according to the invention has, as the first partial areas, a plurality of "threads" which consist of the main film and extend in the main direction and are spaced from one another. The term "thread" was chosen based on DE 100 27 527 AI.

As the second partial areas, web surfaces made of the main film are arranged between the threads, the web surfaces being additionally stretched transversely to the main direction compared to the threads. The threads are folded transversely to the main direction.

This structure is known in principle from DE 100 27 527 AI.

The invention is characterized in that at least one additional film strip, which also extends in the main direction, is attached to at least one part of the threads.

The plastic stretch film, hereinafter also referred to as "film", essentially has to meet two requirements: firstly, the film material should be used in the best possible way, i. that is, the film is stretched as much as possible in order to achieve the lowest possible film thicknesses. On the other hand, the film must also provide the required strength, which, for. B. is determined in relation to the width of a film web.

The functions are divided by the invention: the web surfaces can be pulled out extremely thinly due to the additional stretching in the direction transverse to the main direction in order to achieve optimal material utilization. range, while the threads required to achieve the required tensile strength are considerably reinforced by the additional film strips.

The film strip consisting of an additional film can consist of the same material as the main film of the plastic stretch film itself. Alternatively, it is also possible to select a high-strength film material as the material for the film strip, which has special tensile properties. Since the film strip itself can be very narrow, the material expenditure required for this is relatively low compared to the entire plastic stretch film.

Of course, several film strips can also be attached to a thread or only part of the threads of the plastic stretch film can be reinforced by a film strip.

In a particularly advantageous embodiment of the invention, the film strip is transversely folded together with the thread assigned to it, which improves the connection between the film strip (or the film strip) and the thread. The film strip and the thread assigned to it can overlap one another in several layers due to the transverse folding.

The film strip is fastened to the thread by adhesion or by means of an adhesive.

The connection of the film strip to the thread is improved if the two elements are additionally pressed together after the joining. As a result, the film strip is pressed into the thread.

In the above description, it was initially assumed that the web surfaces are closed and thus a hole-free plastic stretch film is given.

In a particularly advantageous further development of the invention, a plastic net is produced with the plastic stretch film according to the invention, in which perforations extending in the main direction in each case in the web surfaces rows are formed. The web surfaces themselves are then reduced to connecting webs that connect the respective threads to one another.

The rows of holes are advantageously stretched in the main direction after the holes have been created, so that the holes in the main direction have enlarged dimensions compared to the holes originally produced.

Accordingly, in a further advantageous embodiment of the invention, the rows of holes are also stretched transversely to the main direction, so that they also have enlarged dimensions in the direction transverse to the main direction compared to the holes originally produced. In this way, the holes can be significantly enlarged by the additional stretching, which consequently also leads to the enlargement of the plastic network with unchanged use of material. The result is a significantly improved material utilization without the strength being impaired, since the strength is maintained or even improved by the additionally applied film strips.

In the method according to the invention for producing the plastic stretch film, a film web made of a stretch film material is first provided, which is then stretched transversely to the main direction in the so-called second partial regions of the stretch film to produce web surfaces. Areas remain between the web surfaces which are not stretched transversely and which are referred to as first partial areas or threads.

Then one or more film strips are fed from an additional film and applied along the main direction to one or more threads in the first partial areas of the main film between two web surfaces. Then the threads are folded together with the film strips and finally pressed together.

In a particularly advantageous further development of the invention, the method according to the invention makes it possible to produce a plastic net, for which purpose rows of holes are introduced into the second partial regions along the main direction before the transverse expansion of the second partial regions. The holes in the rows of holes can be cut into the plastic stretch film are introduced, such as. B. described in EP 0 820 856 AI.

These and other advantages and features of the invention are explained in more detail below using an example with the aid of the accompanying figures. Show it:

1 shows a schematic side view of the entire system for producing the plastic stretch film or plastic network according to the invention;

Pig. 2 shows a schematic view of a device for transverse stretching of the web surfaces;

3 shows a schematic spatial view of a forming area of a device for cross-folding the threads;

4 shows a section through the forming area;

Fig. 5 is a plan view of the plastic stretch film after the transverse expansion of the web surfaces.

Fig. © is a schematic, not to scale, sectional view through the plastic stretch film before the transverse folding of the threads;

7 shows a plan view of the plastic stretch film after the threads and film strips have been stretched transversely;

8 shows a plan view corresponding to FIG. 5 of the plastic stretch film, but with holes for producing a plastic network;

Fig. 9 is a schematic plan view of the plastic network after its completion.

Fig. 1 shows a schematic side view of the entire system for producing a plastic stretch film according to the invention. A broadband, pre-stretched plastic stretch film 2 made of LLDPE polyethylene (low density or very low density) is continuously drawn off from a supply roll 1. The plastic stretch film 2 can also consist of any other polyethylene film material (for example high density) or a polymer. The plastic stretch film can have 2 different colors and be transparent or opaque. Any combination is conceivable.

In a perforating device 3, holes can be produced in the plastic stretch film 2 by means of a method known from EP 0 820 856 A1. First, however, the production of a plastic stretch film 2 without holes will be described, so that the generation of the holes for producing a plastic network will only be discussed later.

After leaving the perforating device 3 (not required here), the plastic stretch film 2 is guided through a longitudinal stretching device 4 known per se and consisting of a pair of rollers.

Then it reaches a device described in detail in DE 100 27 527 AI for pre-stretching web surfaces in a direction transverse to the main direction (hereinafter called transverse stretching device 5). Since the transverse stretching device 5 has already been described in detail in DE 100 27 527 AI, the following brief explanation with reference to FIG. 2 is sufficient:

The transverse stretching device 5 shown in a top view in FIG. 2 has a first roller 6 and a second roller 7.

Rolling bodies 8 and steel disks 9 are placed on the first roller 6. The roller bodies 8 are coated on their radial outside with rubber 10.

The second roller 7 also has roller bodies 11 which are fastened either as individual elements on the second roller 7 or as one piece. The rolling elements 11 form recesses 12, the number of which corresponds to the number of steel disks 9. The radial peripheral surfaces of the roller body 11 are also covered by rubber layers 13. As can be seen in FIG. 2, the first roller 6 and the second roller 7 are arranged with respect to one another in such a way that their rubber layers 10, 13 and thus their roller bodies 8, 11 touch and roll against one another. As a result, the steel disks 9 engage in the associated recesses 12.

FIG. 2 also schematically shows the path of the plastic stretch film 2 brought up in plan view, as can also be seen in FIG. 1. The plastic stretch film 2 is passed between the first roller 6 and the second roller 7 in such a way that first sub-regions 14 (hereinafter also referred to as "threads") are each held by the rubber layers 10, 13, while second sub-regions 15 located therebetween (also as Web surfaces designated) come initially to the recesses 12.

In FIG. 3, holes 16 have already been drawn in, which are arranged in the form of rows of holes in a main direction 17 of the plastic stretch film 2 along the web faces 15. The description of the holes 16 and their manufacture will be given later.

With the further rotation of the rollers 6, 7, the web surfaces 15 reach the effective area of the steel disks 9 and are pressed deep into the recesses 12, as is shown by the deformed plastic stretch film 18 in FIG. 2.

As a result, the web surfaces 15 are stretched in the transverse direction, which significantly increases the width of the entire band of the plastic stretch film 2. For example, it is possible to produce an 80 cm wide band from an originally 50 cm wide band. The effect of the widening is shown schematically in FIG. 2 by the wider band 19 of the plastic stretch film 2.

After the plastic stretch film in the longitudinal stretching device 4 and the transverse stretching device 5 has been stretched in the longitudinal and transverse directions, it has the structure shown schematically in FIG. 5. The threads or first partial regions 14 then alternate with the web surfaces or second partial regions 15 lying between them. While the web surfaces 15 have been stretched transversely, the threads 14 in the transverse stretching device 5 are remained undeformed since they were held between the rubber layers 10, 13 of the rollers 6, 7.

Immediately after leaving the transverse stretching device 5, the plastic stretch film 2 enters a device for transverse folding of the threads 14 (hereinafter called transverse folding device 20). The transverse folding device 20 is also described in detail in DE 100 27 527 AI, so that a detailed explanation is unnecessary.

The transverse folding device 20 consists of a first pair of rollers 21, a second pair of rollers 22 and a forming area 23 arranged between them. The first pair of rollers 21 is formed by the rollers 6, 7 of the transverse stretching device 5. The first and the second pair of rollers 21, 22 stretch the plastic stretch film 2 and press it against the one in the main direction 17, i. H. Direction of movement of the plastic stretch film 2 curved forming area 23.

The forming area 23 is explained in more detail with reference to FIGS. 3 and 4, FIG. 3 showing the forming area 23 in a spatial view and FIG. 4 a section through the forming area 23.

The forming area 23 has a curved guide plate 24, over which the plastic stretch film 2 is guided. On the guide plate 24, the z. B. can be formed by a curved sheet metal, in a first section 25 one of the number of web surfaces 15 in the transverse direction corresponding number of guide rails 26 is attached. In the course of the first section 25, the distance between the guide rails 26 decreases.

4 shows a schematic section through the forming area 23. Each of the guide rails 26 is then formed by an elongated tube 27 which is held on the guide plate 24 with supports 28. In a second section 29 adjoining the first section 25, the guide rails 26 merge into shaped ribs 30 (FIG. 3). The ribs 30 are described in detail in DE 100 27 527 AI, so that a further explanation is unnecessary.

As already stated, the plastic stretch film 2 is pressed against the guide plate 24 stopped by means of the pairs of rollers 21, 22 taut. The plastic stretch film 2 runs over the guide rails 26 such that the threads 14 are in the spaces between the guide rails 26, i.e. in contact with the guide plate 24, while the webs 15 arch over the guide rails 26, as is also shown in FIG. 4 is recognizable.

Since the guide rails 26 approach more and more in their course, the threads 14 are pushed together, which ultimately leads to folds running in the longitudinal direction (main direction 17). Because of the lateral folding effect, one speaks of a transverse folding.

The unfolding effect is further increased after leaving the guide rail 26 in the first section 25 by the shaped ribs 30 in the second section 29. The webs 15 of the plastic stretch film 2 are guided over the respective backs of the shaping ribs 30, while the threads 14 located in the spaces between the shaping ribs 30 are increasingly folded together. In this way, z. B. reduce a 16 mm wide thread at the beginning to a width of only 2 mm. The good adhesive effect of the material of the plastic stretch film 2 ensures that the thread 14 can be easily knotted together.

1 also shows a tape feed device 31.

The strip feed device 31 has a supply roll 32 on which an additional film 33 is wound. The additional film 33 can consist of the same material as the plastic stretch film 2 from the supply roll 1. But it is also possible that the additional film 33 consists of a higher quality, in particular a higher strength plastic material, such as. B. HDPE. The additional film 32 is cut into a plurality of narrow film strips 35 in a cutting device 34. The width of the film strips 35 is dimensioned such that they are not wider than the threads 14 of the plastic stretch film 2 serving as the main film if the threads 14 have not yet been folded transversely.

The number of film strips 35 can be selected depending on the requirements for the film product to be produced. So it is possible that as many film strips are produced as the plastic stretch film 2 has first partial areas, that is to say threads 14. This ratio between threads 14 and film strips 35 is freely variable. With lower strength requirements, it will be sufficient to feed even a few film strips 35.

The film strip 35 can on the one hand from flat, z. B. from the strip feeder 31 cut strips. Of course, it is also possible to feed the strips directly, that is to say they are already cut to size, without further cutting them by the cutting device 34. Alternatively, it is also possible to design the strips 35 as narrow tubes. The hoses have the advantage of particularly high strength.

The film strips 35 are deflected via a guide device 36 in such a way that they are brought tangentially to the main film (plastic stretch film 2) in the first section 25 of the forming area 23 of the transverse folding device 20 and lie on the threads 14. The film strips 35 are then pressed together transversely in the ribs 30 with the threads 14.

6 schematically shows a section through the plastic stretch film 2 in a region of the forming area 23 in which the film strips 35 have already been applied to the threads 14 but have not yet been subjected to transverse compression or folding by the shaped ribs 30. The sectional view in Fig. 6 is not to scale. In particular, the thickness of the film 2 was considerably exaggerated in relation to the width in order to emphasize the different dimensions. So z. B. recognizable that the web surfaces 15 have a smaller thickness than the threads 14 due to their transverse expansion. In each case a film strip 35 is placed on a thread 14 in each case.

As can be seen in FIG. 1, the film strips 35 are pulled together with the plastic stretch film 2 through the forming area 23. Since the film strips 35 are on the threads 14, they are folded together with the threads 14 in the transverse direction or squeezed and kneaded. The entire plastic stretch film 2 is then pressed together in the pair of rollers 22, which in particular the connection between the film strips 35 and the threads 14 improved.

The film strips 35 thus adhere to the threads 14 by being pressed in or squeezed. The cohesion is particularly high if the film strips 35 in the forming area 23 are also folded into the threads 14 by their transverse folding.

In order to ensure sufficient strength, it is also possible to attach the film strips 35 to the threads 14 with the aid of adhesive.

FIG. 7 schematically shows the plastic stretch film of FIG. 6 after leaving the forming area 23 or the second pair of rollers 21.

As shown in Fig. 1, the plastic stretch film 2 is guided over several pairs of rollers 37 and stretched further in the longitudinal direction. A heating device can also be integrated in the roller pairs 37 in order to bring about an equalization of tensions and a normalization or stabilization within the plastic stretch film 2. The plastic stretch film is then stretched again in a stretching device 38 formed by two rollers before it is wound up into a roll 40 in a winding device 39.

As has already been described several times, it is also possible to use the plastic stretch film according to the invention to produce a plastic network with particularly favorable strength properties and high material utilization.

For this purpose, holes 16 are produced in the plastic stretch film 2 in the perforating device shown in FIG. 1, which holes can be seen in plan view in FIG. 2. The thermal radiation method described in EP 0 820 856 A1 is suitable for producing the holes. The holes 16 are arranged in the main direction 17 in the web surfaces 15 extending rows of holes. In the transverse direction, the holes can be at the same height or have an offset to one another, such as, for. B. shown in Fig. 8.

In the process known from EP 0 820 856 A1 for producing the holes, hot metal tips are moved into the vicinity of the plastic stretch film 2, causing holes to burst open at the hottest points and a film bead forms around the holes. The holes 16 are generally circular. Alternatively, it is also possible to make holes with other shapes, e.g. B. square or rectangular. In addition to hot metal tips, it is also possible to make the holes with the aid of directed infrared radiation, a gas burner with one or more flames and by irradiation with a laser. All of these methods have in common that the holes are produced contactlessly by thermal action. It is also possible to create the holes - with any cross-section - by other classic manufacturing processes, such as. B. by punching, punching, piercing the film, etc.

Regardless of the initial shape of the holes 16, the longitudinal and transverse elongation of the holes in the final product will result in a substantially quadrangular (rectangular) shape.

Fig. 8 shows a plan view of the plastic stretch film with holes 16 after leaving the transverse stretching device 5. As can be seen, the holes have their shape and thus dimensions compared to the originally z. B. circular holes 16 changed. Due to the transverse expansion, but also due to the longitudinal expansion in the main direction 17 caused in the transverse stretching device 5 or in the longitudinal stretching device 4, the circular hole shape changes into a rather square one. With increased longitudinal expansion, it is also possible for the holes 16 to have a rectangular contour.

FIG. 9 shows - likewise in a schematic plan view - the plastic net as the end product, the threads 14 being reinforced by the film strips 35 in each case. Instead of the closed web surfaces 15 provided in the unperforated plastic stretch film according to FIG. 7, only webs 41 remain in the plastic network shown in FIG. 9, which connect the threads 14 and thus the film strips 35 to one another in the transverse direction.

Due to the very narrow threads 14 and the reinforcement by the film strips 35, very good longitudinal extensibility is achieved. The threads 14 and the plastic network have a high strength in the longitudinal direction, which reliable operation even with automatic winding machines, for. B. for wrapping straw bales. The width of the end product, ie the finished plastic film 2 or the plastic network produced therefrom, can be set as desired. Widths of 1 m or 1.50 m have proven to be suitable. In particular for wrapping hay or straw bales, which usually have a width of 1.10 m, a width of the end product of 1.20 m to 1.80 m can also be expedient in order to achieve reliable wrapping. After leaving the transverse stretching device 5, the width of the plastic stretch film 2 is naturally larger {z. B. 1.80 m) than in the starting product on the supply roll 1 (1.50 m). The width of the plastic stretch film 2 is reduced again by the transverse folding in the transverse folding device 20, for. B. to 1.20 m, so that the end product also has a width of about 1.20 m and is well suited for wrapping straw bales.

Claims

claims

1. stretch plastic film, with a main film (2), the main film (2) comprising: as first partial areas, a plurality of threads (14) extending in a main direction (17) and spaced from one another and consisting of the main film; and as second partial areas between the threads (14), web surfaces (15) consisting of the main film, the web surfaces (15) being additionally stretched transversely to the main direction (17) compared to the threads (14); and the threads (14) are folded transversely to the main direction (17); characterized in that at least one additional film strip (35), which also extends in the main direction, is attached to at least some of the threads (14).

2. Plastic stretch film according to claim 1, characterized in that the film strip (35) together with the thread (14) assigned to it is cross-folded.

3. Plastic stretch film according to claim 1 or 2, dadurek gekennseieh- that the film strip (35) and the thread (14) assigned to it overlap one another in several layers due to the transverse folding.

4. Plastic stretch film according to one of claims 1 to 3, characterized in that the film strip (35) is attached to the thread (14) by adhesion or by means of an adhesive.

5. Plastic stretch film according to one of claims 1 to 4, characterized in that the film strip (35) and the thread (14) assigned to it are pressed together.

6. Plastic network of a plastic stretch film according to one of claims 1 to 5, characterized in that in the web faces (15) each in the main direction (17) extending rows of holes (16) are formed.

7. Plastic network according to claim 6, characterized in that the rows of holes after the holes (16) are stretched in the main direction (17), so that the holes in the main direction (17) have enlarged dimensions compared to the originally created holes (16).

8. Plastic network according to claim 6 or 7, characterized in that the rows of holes with the web faces are stretched transversely to the main direction (17), so that the holes (16) transversely to the main direction have enlarged dimensions compared to the holes originally produced (16).

9. A method for producing a plastic stretch film according to one of claims 1 to 5, with the steps

Providing a film web made of a pre-stretched main film (2) made of a stretch film material;

Stretching second partial areas of the main film (2) transversely to the main direction to produce web surfaces (15);

Feeding at least one film strip (35) from an additional film (33);

Applying the film strip (35) along the main direction to a thread (14) in a first partial area of the main film (2) between two web surfaces (15);

Transverse folding of the thread (14) with the film strip (35);

Press the entire main film (2) with the film strip (35).

10. The method according to claim 9, characterized in that a plurality of film strips (35) on a thread (14) or on a plurality of parallel spaced threads (14) are applied.

11. The method according to claim 9 or 10, characterized in that rows of holes (16) are introduced along the main direction (17) in the second partial areas before the stretching of the second partial areas.

12. The method according to any one of claims 9 to 11, characterized in that the holes (16) of the rows of holes are made by a thermal process in the plastic stretch film (2).

13. The method according to any one of claims 9 to 12, characterized in that the plastic stretch film (2) after the introduction of the rows of holes (16) and before stretching the second partial areas in the main direction (17) is stretched.