Plastic strapping band for wrapping one or more objects

Abstract

Method for producing a plastic strapping band (4) for encircling one or more objects, wherein the plastic strapping band (4) has a structure of at least two layers consisting of a core layer (4a) and a functional layer (4b) enclosing this core layer (4a) on at least its broad sides, and wherein the functional layer (4b) is chemically reactive, according to which by means of an extrusion device with at least two die heads the core layer (4a) and the functional layer (4b) are co-extruded, after which further An activating agent is supplied to activate the functional layer (4b), and thereafter the functional layer (4b) is activated only at specific points or in certain areas by a chemical reaction occurring between the functional layer (4b) and the activating agent.

Description

[0001] The invention relates to a method for producing a plastic strapping band for wrapping one or more objects, wherein the plastic strapping band has a structure of at least two layers consisting of a core layer and a functional layer enclosing this core layer on at least its broad sides.

[0002] Plastic strapping is increasingly competing with steel strapping. This is due to its simpler processing, lower price, and the fact that plastic strapping does not damage, or practically does not damage, the strapped objects. However, plastic strapping is at a disadvantage compared to steel strapping in terms of its usable temperature range. For this reason, various approaches have been pursued to increase the temperature stability of plastic strapping. One promising approach is described in EP 2 658 790 B1, in which the plastic strapping is made primarily of polyester and polyolefin with added fiber material. In addition to increased temperature stability, improved relaxation behavior has also been observed.

[0003] Furthermore, plastic strapping bands are also equipped with embossing or narrow grooves and ribs arranged between them, in accordance with the teaching of DE 17 04 986 B2. The plastic strapping band is first stretched and only then profiled. Profiling does not, in itself, orient the molecules of the plastic strapping band longitudinally or transversely. Nevertheless, it results in an accumulation of mass in the longitudinal thickenings. This increases the tensile strength, which is ultimately attributed to the mass orientation of the molecules in the longitudinal thickenings.

[0004] EP 1 129 946 B1 also deals with a plastic strapping band whose surface is embossed. In fact, longitudinal knurling is provided here to stiffen the known plastic strapping band in the longitudinal direction. In this context, very different types of knurling are described, which also lead to an increase in bending stiffness in the longitudinal direction.

[0005] DE 32 06 164 A1 does not deal with plastic strapping bands for wrapping one or more objects. Rather, it describes a process for manufacturing multi-layer sheets made of extrudable plastic. This process uses at least two extruders with slot dies, with which different webs are produced and then fed to a single, common roller assembly.

[0006] The prior art, defined by CH 630 004 A5, relates to a weldable plastic binding tape. Such plastic tapes or strips can be used for a wide variety of lashing and packaging applications. The known binding tape had a substantially rectangular, uniform cross-section made of an oriented crystalline synthetic thermoplastic polymer. Specifically, it consisted of a base layer of the polymer and a flat surface layer adjacent to and bonded to the base layer.

[0007] The surface layer consists of the same polymer, but with a relatively higher average molecular weight than the polymer in the base layer. Furthermore, the weldable binding tape produced in this way exhibits a substantially uniform axial crystalline orientation along the longitudinal direction of the tape across its cross-section. When tape ends are joined, adjacent thinner sections are melted by friction, forming an interface, and fuse together upon cooling under pressure.

[0008] The binding tape according to DE 27 27 356 C2 is produced by equipping a ribbon-shaped core with continuous reinforcing fibers, for example glass fibers, with an outer layer of a thermoplastic resin. The outer layer encases the ribbon-shaped core. The thermosetting resin is formed by crosslinking an unsaturated polyester resin with styrene.

[0009] In a method for banding goods according to DE 39 37 970 A1, the ends to be joined are glued together. For this purpose, an adhesive strip is placed between the ends in question and the adhesive is activated. This is done by heat, moistening, ultrasound, or similar means, depending on the type of adhesive used.

[0010] The state of the art has generally proven its worth in the production of plastic strapping. However, there remains a need to reduce material costs. This is because relatively expensive polyester is predominantly used as the main component in today's standard plastic strapping. While attempts have been made to incorporate recycled material, its proportion cannot be increased indefinitely. At the same time, the requirement to maximize the strength of the plastic strapping while simultaneously preventing longitudinal fraying remains. This is where the invention comes in.

[0011] The invention is based on the technical problem of further developing such a process in such a way that the manufacturing costs are reduced, while maintaining or even increasing strength and overall simplifying handling.

[0012] To solve this technical problem, the invention relates to a method according to claim 1.

[0013] The invention therefore fundamentally utilizes a plastic strapping band with at least two layers or two layers. This allows the two layers to be equipped with different functions. Typically, the core layer forms the load-bearing element of the plastic strapping band and may, for this purpose, consist predominantly of polyester, optionally polyolefins, and other additives. For example, it is recommended to use a polyester content of at least 80% by weight in the core layer. Furthermore, the polyolefin content may be up to 20% by weight. Other additives can also be used, typically up to a content of 10% by weight.

[0014] The additives can be inorganic or organic, for example, fiber material, as discussed in EP 2 658 790 B1. Other additives are also conceivable, such as known splicing inhibitors based on polystyrene, acrylonitrile butadiene styrene, methyl methacrylate butadiene styrene, etc.

[0015] Reference is made, among other things, to WO 2011 / 160154 A1, which lists suitable splice inhibitors. These can be present – ​​as mentioned – up to a weight fraction of 10 wt% in the core layer.

[0016] In contrast, the functional layer does not play a primary, load-bearing role in the plastic strapping according to the invention in the sense that it provides, or is required to provide, the strength. Rather, the functional layer serves various purposes. For example, it is conceivable that the functional layer could be used to increase the longitudinal splicing resistance of the plastic strapping in question. This could be achieved by incorporating longitudinal grooves and ridges into the functional layer. Such embossing of the functional layer, for the reasons already described, reduces the tendency of the plastic strapping to fray longitudinally.

[0017] Alternatively or additionally, the functional layer can also improve the processing of the plastic strapping according to the invention and, in particular, facilitate the sealing of its ends. For example, it is conceivable that the functional layer primarily ensures the adhesive bonding of the ends of the plastic strapping according to the invention. These ends are typically welded together. The functional layer can then improve the welded joint or increase its strength.

[0018] The functional layer and the additive added during the welding process thus perform a function comparable to that of the filler and hardener in a two-component adhesive. This means that the functional layer reacts chemically with the additive during the welding process in such a way that a particularly high strength is observed in the resulting adhesive bond. This can occur through polyaddition, polycondensation, and / or polymerization.

[0019] Furthermore, it has proven advantageous for the functional layer to regularly have a lower specific density than the core layer. For example, the core layer may have a density of usually more than 1.2 g / cm³. 3 In contrast, the density of the functional layer is significantly lower, reaching values ​​of 0.8 g / cm². 3and less. In practice, this is mainly achieved by designing the functional layer as a plastic foam. This could be a permanently elastic soft foam. A plastically deformable rigid foam is also conceivable. Polyurethane may be used as the base material for the foam in question.

[0020] Despite its low density, the functional layer is able to reduce, for example, the tendency of plastic strapping bands made predominantly of polyester to fray. To achieve this, the functional layer can completely enclose and incorporate the core layer. The core layer is designed to be primarily responsible for the strength of the plastic strapping band according to the invention. The functional layer, on the other hand, can be embossed, so that any tendency of the core layer to fray is reduced, if not completely eliminated, as a result of this embossing. All of this is achieved with significantly reduced material consumption compared to the prior art, for example, according to DE 17 04 986 B2, because the embossing is applied exclusively to the functional layer, which itself is usually designed as a plastic foam layer.In contrast, the core layer is not equipped with an embossing and does not need to be equipped with such an embossing.

[0021] This means that the core layer is largely dimensionally stable during the manufacture and processing of the plastic strapping band according to the invention. In contrast, the functional layer is altered in shape, at least during the processing of the plastic strapping band. As a rule, the core layer and the functional layer are manufactured together, for example, by co-extrusion.

[0022] The plastic strapping produced in this way is then typically stretched. Stretch ratios of typically 1:2 to 1:5 are observed. After stretching, the plastic strapping is typically embossed according to the invention. This embossing process ensures that the plastic strapping according to the invention is equipped with grooves and ribs predominantly in the longitudinal direction to prevent fraying in this direction. The grooves and ribs are incorporated exclusively into the functional layer that completely encloses the core layer. This is easily achieved because the functional layer is typically designed as a plastic foam layer. In contrast, the core layer remains largely dimensionally stable.

[0023] As an alternative to co-extruding the functional layer and core layer, it is also possible to first extrude the core layer and then coat it with the functional layer. For example, the core layer could be passed through an immersion bath in which the functional layer is present as a melt and adheres to the core layer. However, in most cases, the core layer and the functional layer are co-extruded together. This may require a suitably designed extruder head with a double die.

[0024] In addition to the splice-inhibiting effect of the functional layer already described, due to the incorporated grooves and ribs, the functional layer is chemically / physically reactive according to the invention. A chemically reactive design of the functional layer has been described previously. In this case, the functional layer is activated, for example, when the ends of the plastic strapping band according to the invention are welded together using the additive. In this case, the functional layer and the additive react in such a way that a chemical reaction such as polyaddition, polycondensation, or polymerization takes place. As a result, the strength of the resulting joint between the two ends of the plastic strapping band is significantly increased compared to previous methods.

[0025] In fact, the functional layer with the additive can cure at room temperature, similar to the resin and hardener in a two-component adhesive. However, elevated temperatures are typically used, set in conjunction with the plastic welding process. Temperatures of typically 100°C to 200°C have proven effective. Fundamentally, the adhesive bond can also be created using the functional layer without additional heating, simply by bringing the additive to the joint and initiating the described reaction.

[0026] As previously explained, the functional layer is activated with the help of the activating agent or additive. The functional layer and the activating agent or additive perform a function comparable to that of the resin and hardener in a two-component adhesive.

[0027] In this context, a further possibility according to the invention is that the functional layer is activated only at specific points or in certain areas. In fact, the invention recommends that the functional layer be activated at least at the ends to be joined. In this way, the two ends to be joined are coupled particularly firmly.

[0028] The result is a described method for manufacturing a plastic strapping band which, first and foremost, offers significant cost advantages. This is primarily due to the fact that material consumption, particularly of expensive polyester, can be significantly reduced compared to previous methods. In fact, in the plastic strapping band according to the invention, only the core layer consists predominantly of polyester, for example, in a weight fraction of up to 80%. In contrast, the functional layer, which completely or partially encloses the core layer, is made of a cost-effective plastic such as polyurethane. Since a plastic foam is advantageously used at this point, further advantages are observed, for example, with regard to the weight of the plastic strapping band thus produced.

[0029] This is because the plastic foam layer or functional layer typically has a density that is significantly below 0.8 g / cm³. 3 is located. This means that the functional layer partially replaces polyester or polyolefin with a density of more than 1.2 g / cm³. 3 , which explains the weight saving.

[0030] Furthermore, the functional layer suppresses or counteracts the tendency of the plastic strapping to splice, and in particular the tendency of the core layer. For this purpose, the functional layer is equipped with longitudinal grooves and ribs. These can be easily incorporated into the functional layer because it is advantageously made of a plastically deformable rigid foam, for example, polyurethane. In addition, the functional layer enables a particularly strong bond between the ends of the plastic strapping. According to the invention, the activating agent is added to the functional layer for this purpose, advantageously in the area of ​​the ends to be joined. As a result, a chemical reaction occurs between the functional layer and the activating agent or additive, similar to a two-component adhesive.

[0031] All of this can be set up so that the curing reaction starts at room temperature. Typically, the resulting joining process of the ends is supported by an additional plastic welding. However, this is not mandatory.

[0032] Consequently, a plastic strapping band is provided that can be produced more cost-effectively than previously observed plastic strapping bands, namely through its implemented two-layer construction. Despite this particularly cost-effective design, comparable strengths to conventional plastic strapping bands are observed. All this is achieved with a simultaneously reduced weight and the additional possibility of significantly increasing the strength of the joint between the two ends when strapping objects, compared to previous methods. This is because the friction welding typically used at this point in the prior art sometimes leads to structural changes in the plastic in the area of ​​the ends to be joined. These changes are avoided by the invention because the bond is primarily created through the reaction of the functional layer with the activating agent.This is where the main advantages lie.

[0033] The invention will now be explained in more detail with reference to a drawing that illustrates only one embodiment; the drawing shows: Fig. 1 a plant for the production of the plastic strapping band according to the invention and Fig. 2 the plastic strapping band according to the invention in section.

[0034] In the Fig. Figure 1 shows an extrusion device 1 equipped with an extruder screw 2 and an extruder hopper 3. The raw materials for the production of the plastic strapping band 4 are stored in the extruder hopper 3 at the outlet of the extruder screw 2 and fed to the extruder screw 2. The extruder hopper 3 therefore contains the extrudate.

[0035] After extrusion of the plastic strapping band 4 at the exit end of the extruder screw 2, it first passes through a water bath 5. Following the water bath 5, a first stretching unit 6 and a second stretching unit 7 are provided. The second stretching unit 7 is also equipped with an oven 8, through which the plastic strapping band 4 is passed during the second stretching process. During the stretching process, the plastic strapping band 4 exiting the extruder screw is stretched to a total length of 1:2 to 1:5. This means that the plastic strapping band 4 exiting the extruder screw 2 is stretched to two to five times its original length in the first and second stretching units 6 and 7, respectively.

[0036] The oven 8 at the second stretching unit 7 ensures that the molecular orientation of the polymer chains in the material, achieved during stretching, remains unchanged. Following the two stretching units 6 and 7, the plastic strapping band 4 is then embossed. For this purpose, an embossing unit 9 is provided, which is equipped with an embossing roller 10 and a counter roller or counter-pressure roller 11 that interacts with the embossing roller 10.

[0037] The plastic strapping band 4 is composed, as shown in the cross-sectional view, of Fig. 2 made up of two layers. That is, the plastic strapping band 4 is characterized by a two-layer structure consisting of a core layer 4a and a functional layer 4b that encloses the core layer 4a on at least its broad sides. In the exemplary embodiment, this can be seen from the Fig. 2, that the functional layer 4b completely encloses the core layer 4a and incorporates its interior.

[0038] The core layer 4a and the functional layer 4b are produced together in the extrusion device 2, or rather in the extruder screw 2 therein, i.e., co-extruded. For this purpose, the extrusion device or extruder screw 2 has a correspondingly designed double die on the outlet side, which has a die for the core layer 4a in the center and another die for the functional layer 4b surrounding the center. The core layer 4a may be made of up to 80 wt.% polyester and up to 20 wt.% polyolefins. However, it is also possible that up to 90 wt.% polyester and up to 10 wt.% polyolefins, or even other compositions, are used here. In contrast, the functional layer 4b in the exemplary embodiment is made of polyurethane. In fact, a polyurethane foam, or more generally a plastic foam, is used here. A plastically deformable rigid foam has proven to be particularly advantageous.

[0039] The plastic foam or polyurethane foam for the production of functional layer 4b can be produced by filling the extruder hopper 3 with appropriate chemical foaming agents. At the temperature required for extrusion, this causes the chemical foaming agents to foam in the extruder screw 2, resulting in the slot die extruding the plastic foam layer or polyurethane foam to create functional layer 4b.

[0040] Instead of the described co-extrusion of the core layer 4a and the functional layer 4b, it is also possible for the functional layer 4b to encase the core layer 4a using an immersion bath. In this case, for example, instead of the water bath 5, a suitably designed immersion bath might be used, through which the core layer 4a is passed. After exiting the immersion bath, the functional layer 4b encases the core layer 4a as described.

[0041] During the final embossing in the embossing device 9, the core layer 4a largely retains its shape. That is, the core layer 4a is designed to be largely dimensionally stable. In contrast, the functional layer 4b is designed to be deformable, at least during processing. That is, with the aid of the embossing device 9, grooves 12 and ribs 13 are introduced into the functional layer 4b, as shown in the sectional view according to the Fig.Figure 2 shows that the distribution of the grooves 12 and ribs 13 is indeed mirror-symmetrical and usually also uniform compared to a mirror plane that horizontally divides the plastic strapping 4 in cross-section. Furthermore, the design is usually such that the grooves 12 and ribs 13 are located on the respective broad sides of the plastic strapping 4. This prevents any fraying in the longitudinal direction of the plastic strapping 4.

[0042] Furthermore, the functional layer 4b can be chemically reactive. For this purpose, an activating agent may be supplied to the functional layer 4b in the area of ​​a closure device (not shown in the exemplary embodiment). This closure device may be a hand-operated machine or a component of a strapping device. In any case, the activating agent is regularly supplied in the closure device, which joins and couples the two ends of the plastic strapping band 4 after the objects have been wrapped. That is, the functional layer 4b is activated at least at the ends of the plastic strapping band 4 that are connected to each other.

Claims

[1] Method for producing a plastic strapping band (4) for wrapping one or more objects, wherein the plastic strapping band (4) has a structure of at least two layers consisting of a core layer (4a) and a functional layer (4b) enclosing this core layer (4a) on at least its broad sides, and wherein the functional layer (4b) is chemically reactive, according to which by means of an extrusion device with at least two die heads the core layer (4a) and the functional layer (4b) are co-extruded, after which further An activating agent is supplied to activate the functional layer (4b), and thereafter the functional layer (4b) is activated only at specific points or in certain areas by a chemical reaction occurring between the functional layer (4b) and the activating agent. [2] Method according to claim 1, characterized by, that the functional layer (4b) completely encloses the core layer (4a) and incorporates it within its interior. [3] Method according to claim 1 or 2, characterized by , that the core layer (4a) is predominantly dimensionally stable during manufacture and processing. [4] Method according to any one of claims 1 to 3, characterized by , that the functional layer (4b) is designed to be shape-changeable, at least during processing. [5] Method according to any one of claims 1 to 4, characterized by , that the functional layer (4b) is imprinted. [6] Method according to any one of claims 1 to 5, characterized by , that the functional layer (4b) is activated at least at interconnected ends.

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