Mechanical recycling of adhesive tapes and the use thereof

Abstract

The invention relates to a method for producing a plastic film for use in the production of adhesive elements, comprising the method steps: a) producing or providing an initial composition, comprising one or more old adhesive elements, each comprising: i) at least one carrier layer, comprising one or more thermoplastic materials, and ii) at least one adhesive layer arranged on the carrier layer, comprising an adhesive comprising one or more adhesive-(co)polymers, b) kneading the initial composition in a mixing unit in order to obtain a material mixture comprising the one or more thermoplastic materials and the one or more adhesive-(co)polymers, wherein the kneading takes place at a temperature of T = (TM(i)-10°C) or higher, wherein TM(i) is the melting temperature of the thermoplastic carrier layer material with the highest melting temperature in the initial composition, the proportion of which is 5% or more by mass, relative to the mass of the initial composition, and c) extruding and forming a plastic film from the plastic mixture, wherein the plastic mixture comprises the material mixture.

Description

[0001] Mechanical recycling of adhesive tapes and their use

[0002] Description

[0003] The invention relates to a method for producing a plastic film for use in the production of adhesive elements, a method for producing an adhesive element based thereon, and plastic films and adhesive elements produced by the method. Also disclosed is the use of a material mixture made from adhesive tape waste kneaded at elevated temperatures.

[0004] Joining separate elements is one of the central processes in manufacturing technology. Along with other methods such as welding and soldering, bonding, i.e., joining using an adhesive, is becoming increasingly important. An alternative to the use of formless adhesives, such as those applied from a tube, is so-called adhesive tapes, whose adhesive effect is based on the adhesive masses used. The use of adhesive tapes is associated with many advantages that make this technology ideal for use in many industries, such as the electronics or automotive industries.

[0005] In most cases, such adhesive tapes are multi-component materials that include not only the adhesive but also a carrier layer, usually made of a plastic. Both the adhesives used in the adhesive layer and the plastics used in the carrier layers are often based on fossil resources. In light of growing awareness of the need for more sustainable management and more careful use of fossil resources, this is often perceived as a disadvantage.

[0006] In addition, adhesive tapes for many applications are designed for a single and usually short use, for example as packaging tape or self-adhesive surface protection film, as used in electronic devices, for example. Accordingly, in practice, adhesive tapes often become waste after just one use. In addition to adhesive tape waste that arises as a result of the use of the adhesive tapes, other adhesive tape waste also arises in adhesive tape production. This particularly includes process waste that arises, for example, when cutting adhesive tapes in the edge areas, and which is usually also multi-component materials consisting of a carrier layer and an adhesive, with the adhesive in turn usually comprising several components, in particular (co)polymers and adhesive resins.

[0007] Regardless of how it is generated—be it as previously used adhesive tape or as process waste from adhesive tape production—what all adhesive tape waste has in common is that, to date, this type of waste cannot usually be efficiently recycled. Its multi-component nature, in particular, hampers economic recycling. Accordingly, adhesive tape waste is now mostly incinerated or landfilled ("end of life").

[0008] Taking all the aspects described above into account, it can be concluded that the production of adhesive tapes and their subsequent use generally generates non-recyclable tape waste, the production of which also requires significant amounts of fossil raw materials. This circumstance is often perceived as very detrimental.

[0009] Attempts are known from the state of the art to at least reduce the need for fossil resources in adhesive tape production by using carrier layers that are at least partially made from recycled materials.

[0010] EP 0 839 621 A2 discloses the use of a film for producing an adhesive tape which is self-adhesively coated on at least one side, the film consisting of at least 10% by weight of recycled material which consists of adhesive tapes and / or production residues from their manufacture as well as adhesive tapes after their use, the adhesive tapes each having a carrier in the form of a plastic film.

[0011] A corresponding disclosure can be found, for example, in WO 2014 / 029664 A1. In this case, the carrier material for the carrier layer is manufactured at least partially from recycled plastics during recycling, thus achieving an improved ecological balance. However, the corresponding recycling processes generally require the purest possible starting materials, so that, for example, in PET recycling, the purest possible used PET is used, which may contain only minimal amounts of impurities. Recycling of multi-component materials is generally not possible, so that the corresponding starting materials must first undergo complex separation and / or processing steps.

[0012] The approach described above therefore only addresses one of the aforementioned problems, namely the need for fossil resources for the production of the carrier layer. After coating the carrier layer with a backing layer and thus producing the adhesive tape, the problem described above remains: the corresponding multi-component materials cannot be recycled, or at least not within an economically justifiable time and cost.

[0013] The primary object of the present invention was to eliminate or at least reduce the above-described disadvantages of the prior art.

[0014] In particular, it was the object of the present invention to provide a method for producing a plastic film for use in the production of adhesive elements and a method based thereon for producing corresponding adhesive elements, which enables a more sustainable production of corresponding plastic films and adhesive elements.

[0015] In this respect, it was an object of the present invention that the method to be specified should make it possible to reduce the need for fossil resources in the production of adhesive tape.

[0016] It was a further object of the present invention that the method to be specified should create new possibilities for the recycling of adhesive elements in order to thereby increase the general recyclability of adhesive elements and to reduce the proportion of adhesive elements that must be incinerated or disposed of in landfills.

[0017] Furthermore, it was an object of the present invention that the method to be specified should be able to be carried out as far as possible without the use of substances that are harmful to health and / or the environment.

[0018] Furthermore, it was an object of the present invention that the method to be specified for producing plastic films or adhesive elements should result in high-performance products that should reliably meet even demanding application requirements.

[0019] Furthermore, it was a supplementary object of the present invention to provide corresponding plastic films and adhesive elements that can be produced using the method to be specified, which can be produced in a particularly sustainable manner without having to accept unacceptable compromises in the physico-chemical properties of these products.

[0020] The inventor of the present invention has now discovered that the above-described objects can surprisingly be achieved if, contrary to the existing prejudice that meaningful recycling of materials requires the purest possible separation of the starting materials, adhesive tape waste, rather than multi-component materials, is subjected to a joint recycling process that includes mechanical processing at elevated temperatures, as defined in the claims. Quite surprisingly, the processing of multi-component adhesive tape waste according to the invention results in a non-sticky material mixture that can be very largely homogenized and processed, for example, into granules, which, surprisingly, can also be used in high mass fractions in plastic mixtures for film production.This advantageously makes it possible to efficiently recycle used adhesive tapes and, from the surprisingly non-sticky material mixtures obtained from this recycling, expediently with the addition of certain amounts of virgin plastic, to produce plastic films that possess excellent physicochemical and mechanical properties and can, in particular, be processed in the usual way, for example, stretched. This not only opens up an unexpected opportunity for the time- and cost-efficient recycling of adhesive elements, but also allows the overall demand for fossil resources and the associated CO2 footprint of the adhesive tapes produced in this way to be reduced.

[0021] The plastic films obtained by the process according to the invention are advantageously particularly suitable for use as carrier layers in adhesive tapes, in particular those adhesive tapes which correspond in nature to the adhesive tapes which were previously used as adhesive tape waste in the process according to the invention. Without wishing to be bound by this theory, the inventor assumes that this advantageous suitability for the use of corresponding films in the production of adhesive tapes, in particular in adhesive tapes which correspond in nature to the previously processed adhesive tape waste, is attributable to the presence of domains derived from adhesive in the film produced. It is particularly advantageous to coat the carrier layer with an adhesive which, in terms of its chemical nature, is as similar as possible to the adhesive domains present in the material.

[0022] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0023] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of one embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred plastic films, adhesive elements, and uses emerge from the features of preferred methods.

[0024] To the extent that both specific amounts or proportions of an element and preferred embodiments of the element are disclosed below for an element, for example for the thermoplastic carrier layer plastics or the adhesive (co)polymers, the specific amounts or proportions of the preferably configured elements are also disclosed in particular. Furthermore, it is disclosed that, with the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be preferably configured and, in particular, that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0025] The invention particularly relates to a method for producing a plastic film for use in the production of adhesive elements, comprising the method steps: a) producing or providing a starting assembly comprising one or more used adhesive elements, each comprising: i) at least one carrier layer comprising one or more thermoplastic

[0026] Carrier layer plastics, and ii) at least one adhesive layer arranged on the carrier layer, comprising an adhesive comprising one or more adhesive (co)polymers, b) kneading the starting composition in a mixing unit to obtain a material mixture comprising the one or more thermoplastic carrier layer plastics and the one or more adhesive (co)polymers, wherein the kneading takes place at a temperature of T = (TM ) - 10 °C) or more, wherein T M(i> is the melting temperature of the thermoplastic carrier layer plastic with the highest melting temperature in the initial composition, the mass fraction of which is 2% or more, based on the mass of the initial composition, and c) extruding and forming a plastic film from a plastic mixture, wherein the plastic mixture comprises the material mixture.

[0027] The process according to the invention is used to produce plastic films. These plastic films, in turn, are particularly suitable for use in the production of adhesive elements.

[0028] In process step a), the starting material for the subsequent manufacturing process is first introduced. In practice, this will usually be an initial quantity of adhesive tape waste that is to be recycled in the process according to the invention. The corresponding collection of adhesive tape waste, which can be provided, for example, as collected adhesive tape waste in a container, is referred to in the present invention as the initial assembly in order to clearly identify the entirety of the used adhesive elements.

[0029] The used adhesive elements can, in particular, be previously used adhesive elements, for example, used packaging tapes or protective films removed from electronic devices. In practice, however, the inventor believes that the recycling of previously used adhesive elements will usually be associated with additional difficulties, particularly with regard to the logistical return of corresponding adhesive tape waste from the end user without an appropriate recycling infrastructure, as well as with regard to possible contamination of the adhesive layers with undesirable components, for example, paper and / or cardboard residues in the case of packaging tapes. Accordingly, it is particularly preferred to use process waste from adhesive element production as the starting material, since this can usually be collected directly on site, is free of usage-related contamination, and has a defined material composition.By way of example, a method according to the invention is accordingly provided, wherein the used adhesive elements in the initial composition are selected from the group consisting of process waste from adhesive element production, in particular process waste from adhesive tape production, and used adhesive elements, in particular used adhesive tapes, are preferably selected from the group consisting of process waste from adhesive element production, in particular severed edges of parent rolls from adhesive tape production.

[0030] The old adhesive elements are adhesive elements. In accordance with expert understanding, in practice, these will mostly be adhesive tapes or components of adhesive tapes, for example, process waste. However, other, inherently non-tape-shaped adhesive elements can also be recycled, such as so-called die-cuts or adhesive films. The term "adhesive elements" is used to cover not only adhesive tapes but also these other starting materials that are not tape-shaped.

[0031] According to the above definition, the corresponding starting composition can also be produced in the process. This can be achieved in particular by collecting the process waste that occurs during adhesive tape production, which is obtained by cutting a produced starting adhesive tape, and introducing it into the process according to the invention as a starting composition. This enables particularly efficient integration of recycling into existing production lines. In this preferred case, it is a process according to the invention, additionally comprising, before process step a), the process step: a0) producing a target adhesive element by cutting a starting adhesive composite, wherein old adhesive elements are obtained as process waste during the production of the adhesive tape.

[0032] The waste adhesive elements in the initial assembly can, in principle, be presented in various forms, for example as pieces from process sections or as long strip-like materials. However, with a view to efficient handling, the inventor proposes that at least very long waste adhesive elements should be slightly shredded before further processing in order to be able to be processed efficiently later in a mixing unit. In the inventor's experiments, used adhesive tapes were pre-cut, for example, using a roll cutter. This was essentially done for handling reasons and is not essential to the basic principle of the invention. Rather, it can be seen as an advantage of the method according to the invention that the mixing technique for kneading makes it possible to use even a few large pieces of waste adhesive elements and, in particular, eliminates the need for small-scale pre-shredding.In this respect, however, it is conceivable that, particularly for later large-scale applications and particularly depending on the used adhesive elements to be processed, comminution units could also be used, enabling finer pre-comminution. In this case, for example, it is a process according to the invention, additionally comprising, before process step b), the process step: bO) comminution of the initial assembly with a comminution unit to obtain a comminutioned initial assembly comprising a plurality of used adhesive pieces from the comminutioned used adhesive element(s).

[0033] In this respect, a method according to the invention is preferred, wherein the comminution unit is a cutting device, preferably a shredder or a slitter-cutter, wherein the comminution unit is preferably an automated comminution unit. For the vast majority of cases, a method according to the invention is preferred, wherein the initial assembly comprises a plurality of used adhesive elements, in particular shredded used adhesive elements.

[0034] In the inventor's experiments, a further preferred embodiment was also identified. These experiments demonstrated that it is possible to efficiently recycle an adhesive roll intended for recycling if the used adhesive tape is unwound from this waste adhesive tape roll and fed directly into the mixing unit. This embodiment is particularly suitable for combination with the use of a twin-screw extruder, as disclosed below.

[0035] Many of the adhesive tapes known from the prior art, when stored and handled, include a release liner applied to the adhesive layer. This release liner protects the adhesive layer and, in the case of adhesive tape rolls, is intended to facilitate easy unwinding of the adhesive layer. In used adhesive elements, this release liner will usually no longer be in contact with the adhesive layer. In the case of process waste from adhesive element production, a corresponding release liner will in many cases not yet have been applied at the time the offcuts arise. Furthermore, such a release liner can be removed prior to the process if necessary. Accordingly, the old adhesive elements in the initial assembly will often not include a release liner.However, in the inventor's opinion, it is advantageously possible in the process according to the invention to co-process at least those release liners which themselves consist of a thermoplastic which is also contained in the initial composition as a thermoplastic release layer plastic. This is particularly efficiently possible if the thermoplastic is the carrier layer plastic which has the largest mass fraction in the initial composition. In this case, the process according to the invention is one in which the one or more waste adhesive elements at least partially, potentially predominantly, and in some cases even substantially entirely, comprise a release layer arranged on an adhesive layer, preferably a liner, wherein the release layer comprises a thermoplastic release layer plastic which the carrier layer also comprises.

[0036] In the method according to the invention, the adhesive elements are defined in that they comprise at least one carrier layer and an adhesive layer arranged on the carrier layer. The expression “at least one” expresses that, for example, multi-layer carriers or double-sided adhesive elements, for example double-sided adhesive tapes, can also be included in the initial composition. However, a method according to the invention is particularly relevant in practice in which the one or more old adhesive elements at least partially, preferably predominantly, particularly preferably substantially all, comprise exactly one carrier layer. Additionally or alternatively, a method according to the invention is also particularly relevant in practice in which the one or more old adhesive elements at least partially, preferably predominantly, particularly preferably substantially all, comprise exactly one adhesive layer.

[0037] It can be seen as an advantage of the method according to the invention that it can be used for a wide range of typical adhesive elements. An example of a method according to the invention is one in which the carrier layer has an average thickness in the range of 20 to 120 μm, preferably in the range of 40 to 100 μm, particularly preferably in the range of 60 to 80 μm. Additionally or alternatively, an example of a method according to the invention is one in which the adhesive layer has an average thickness in the range of 10 to 40 μm, preferably in the range of 20 to 30 μm.

[0038] In the vast majority of cases, the carrier layer will be a carrier film. However, based on the inventor's experiments, old adhesive elements can also be used whose carrier layer is formed by a foamed carrier material or a textile fabric made of plastic fibers. An example of this is a method according to the invention, wherein the carrier layer is selected from the group consisting of carrier films, plastic foams, and textile fabrics, in particular woven fabrics, nonwovens, or nonwovens, with the carrier layer particularly preferably being a carrier film. According to the invention, the at least one carrier layer comprises at least one thermoplastic, which in the context of the present invention is referred to as the carrier layer plastic for the purpose of the clearest possible identification.In accordance with the expert's understanding, this is thus a plastic carrier layer, for example a plastic film, on which the adhesive layer of the adhesive element is arranged. Such plastic films nowadays are usually high-performance materials, which in addition to the actual polymer, can in many cases also comprise further additives, so that corresponding carrier layers in many cases do not consist entirely of the carrier layer plastic. However, the person skilled in the art understands that in practice, the carrier layers usually consist predominantly of the corresponding thermoplastic carrier layer plastics, and this is also preferred for the process according to the invention.Accordingly, a method according to the invention is preferred, wherein the carrier layer consists of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially completely, of the one or more thermoplastic carrier layer plastics, based on the mass of the carrier layer.

[0039] The inventor has succeeded in identifying particularly suitable materials for the carrier layer of the reusable old adhesive elements, with which excellent results can be achieved in the process according to the invention, in particular in combination with poly(meth)acrylate-based and / or rubber-based adhesives, as disclosed below. Particularly in the recycling of polypropylene-based carrier materials with corresponding adhesives, excellent processability has been achieved, resulting in a high-performance mixed material. First, a process according to the invention is preferred, wherein the one or more thermoplastic carrier layer plastics are selected from the group consisting of polyesters and polyolefins, preferably polyolefins.Particularly preferred is a process according to the invention wherein the one or more thermoplastic carrier layer materials are selected from the group consisting of polyethylene terephthalate, polyethylene, and polypropylene, preferably polypropylene. At least theoretically, it is possible for the carrier layer to comprise a mixture of several thermoplastic carrier layer materials, for example, polyethylene and polypropylene. From a manufacturing perspective and with a view to the industrially relevant plastic films regularly used in the manufacture of adhesive elements, however, it is particularly preferred to use carrier layers that are as pure as possible, for example, carrier layers consisting essentially of polyethylene or polypropylene, since, in the inventor's opinion, this facilitates, in particular, the selection of optimal processing parameters during kneading.Accordingly, a method according to the invention is preferred, wherein the carrier layer comprises a thermoplastic carrier layer plastic with a mass fraction of 90% or more, preferably 95% or more, particularly preferably 99% or more.

[0040] The adhesive layer arranged on the carrier layer comprises an adhesive. In accordance with the understanding of one skilled in the art, it is possible for the adhesive layer to comprise other components in addition to the adhesive, in particular insoluble fillers, for example particulate inorganic compounds or macroscopic fillers such as fibers or hollow microspheres. Within the scope of the present invention, these fillers are not included in the adhesive when calculating mass fractions. Fortunately, however, the process according to the invention is relatively tolerant of certain proportions of filler being introduced into the plastic film subsequently produced via the adhesive layer. However, the inventor considers it particularly advantageous if the adhesive layer consists as largely as possible only of the adhesive and, accordingly, for example, low filler contents are set in the adhesive layer.Consequently, a process according to the invention is preferred, wherein the adhesive layer consists of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially completely, of the adhesive composition, based on the mass of the adhesive layer.

[0041] According to the invention, the adhesive comprises one or more (co)polymers, which in the context of the present invention are referred to as adhesive (co)polymers for the purpose of clear identification. In the vast majority of cases, the adhesive will also comprise adhesive resins. This advantageously makes it possible to design the adhesive with advantageous adhesive properties, in particular pressure-sensitive adhesiveness. Such pressure-sensitive adhesiveness is preferred for many adhesive applications, so that many starting materials for the process according to the invention will comprise a pressure-sensitive adhesive, which can be advantageously processed particularly well in the process according to the invention. A process according to the invention in which the adhesive is a pressure-sensitive adhesive is therefore also particularly preferred.

[0042] According to expert understanding, a pressure-sensitive adhesive is an adhesive that possesses pressure-sensitive adhesive properties, i.e., the ability to form a permanent bond with a substrate even under relatively light pressure. Such pressure-sensitive adhesive tapes can usually be removed from the substrate after use without leaving any residue and are generally permanently tacky even at room temperature. This means that they exhibit a certain viscosity and tackiness, allowing them to wet the surface of a substrate even under light pressure. The tackiness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive.Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive capacity described above. It is assumed that with corresponding pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are necessary in particular to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.To characterise the degree of elastic and viscous components, the storage modulus (G') and the loss modulus (G") are usually used, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed, for example, in WO 2015 / 189323. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive and thus a pressure-sensitive adhesive if, at a temperature of 23°C in the deformation frequency range from 10° to 10. 1 rad / sec G' and G“ each at least partly in the range of 10 3 up to 10 7 Pa lie.

[0043] The inventors have thus succeeded in specifying preferred mass fractions for the adhesive (co)polymers and the corresponding adhesive resins. Preferred is a process according to the invention wherein the combined mass fraction of adhesive (co)polymers in the adhesive is in the range from 20 to 90%, preferably in the range from 30 to 80%, particularly preferably in the range from 40 to 70%, based on the mass of the adhesive. Additionally or alternatively, preferred is a process according to the invention wherein the adhesive comprises one or more adhesive resins, such as rosin or terpene-phenol resins, preferably in a combined mass fraction in the range from 10 to 50%, preferably in the range from 15 to 45%, particularly preferably in the range from 20 to 40%, based on the mass of the adhesive.

[0044] For those skilled in the field of adhesive technology, it is easily possible to distinguish adhesive (co)polymers, which are sometimes also referred to as film-forming (co)polymers, from tackifier resins. The distinction is made in particular on the basis of the average molar masses, which for typical adhesive (co)polymers are significantly higher than those of typical tackifier resins. The weight-average molar mass Mw of the adhesive (co)polymers, measured by GPC, is typically 100,000 g / mol or more, preferably 150,000 g / mol or more, particularly preferably 200,000 g / mol or more. The weight-average molar mass Mw of the tackifier resins, measured by GPC, is typically 30,000 g / mol or less, preferably 20,000 g / mol or less, particularly preferably 10,000 g / mol or less.

[0045] The weight-average molecular weight Mw values ​​refer to the determination by gel permeation chromatography (GPC). The determination is carried out on 100 μl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A PSS-SDV column, 5 μm, 10 3 Ä, 8.0 mm * 50 mm (information here and below in the order: type, particle size, porosity, inner diameter * length; 1 Ä = 10 -10 m). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä with 8.0 mm x 300 mm columns each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed for polyacrylates against PMMA standards (polymethyl methacrylate calibration) and for other materials (resins, elastomers) against PS standards (polystyrene calibration).

[0046] When using poly(meth)acrylate-based adhesives, it is advantageously also possible to keep the content of tackifier resins low and, if necessary, even to dispense with them entirely. In this case, a process according to the invention is involved, wherein the one or more adhesive (co)polymers are selected from the group consisting of poly(meth)acrylates, wherein the mass fraction of tackifier resins in the adhesive is 5% or less, preferably 1% or less, particularly preferably 0.1% or less, based on the mass of the adhesive.

[0047] The inventor has recognized in his own experiments that poly(meth)acrylate-based and rubber-based adhesives and corresponding adhesive elements are particularly well suited for processing in the process according to the invention and exhibit particularly advantageous recyclability. In particular, the combination of the corresponding adhesives with thermoplastic carrier layers made of polyester or polyolefin, especially polypropylene, offers significant advantages, resulting in high-performance material blends and corresponding plastic films with excellent physicochemical properties. Corresponding poly(meth)acrylate-based or rubber-based adhesive tapes are commercially available from numerous suppliers, with the nature of the adhesive used usually being evident from the product information.Preference is given to a process according to the invention, wherein the one or more adhesive (co)polymers are selected from the group consisting of poly(meth)acrylates and rubbers, preferably selected from the group consisting of rubbers, particularly preferably selected from the group consisting of natural rubber and synthetic rubbers, very particularly preferably selected from the group consisting of styrene-containing block copolymers, particularly preferably styrene-isoprene-styrene block copolymer and / or styrene-butadiene-styrene block copolymer.

[0048] According to the inventor's assessment, a used adhesive element that is particularly suitable for recycling is obtained when an adhesive composition, which comprises natural rubber and an adhesive resin as an adhesive (co-)polymer, is combined with a polypropylene-based carrier layer.

[0049] In the context of the present invention, the term "poly(meth)acrylates" encompasses, in accordance with the expert understanding, polyacrylates and polymethacrylates as well as copolymers of these polymers. Poly(meth)acrylates may contain minor amounts of monomer units that are not derived from (meth)acrylates. Accordingly, in the context of the present invention, a "poly(meth)acrylate" is understood to mean a (co)polymer whose monomer base consists of a mass fraction of 70% or more, preferably 90% or more, particularly preferably 98% or more, of monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters, based on the mass of the monomer base.

[0050] Among the rubber-based adhesive elements, synthetic rubber-based adhesive elements in particular have proven to be particularly efficiently recyclable, although in the opinion of the inventors, natural rubber can also be used additionally or alternatively. Particular preference is given to a process according to the invention wherein the adhesive comprises synthetic rubber, preferably styrene-containing block copolymers, particularly preferably styrene-isoprene-styrene block copolymer and / or styrene-butadiene-styrene block copolymer, preferably in a combined mass fraction of 20% or more, preferably 30% or more, particularly preferably 40% or more, based on the mass of the adhesive. Additionally or alternatively, preference is given to a process according to the invention wherein the adhesive comprises natural rubber, preferably in a combined mass fraction of 20% or more, preferably 30% or more, particularly preferably 40% or more, based on the mass of the adhesive.

[0051] Particularly when processing used adhesive elements, residues may still be present on the adhesive layers, for example, remnants of paper or cardboard. Accordingly, it is at least theoretically conceivable that the initial composition comprises other components in addition to the used adhesive elements. However, the person skilled in the art readily understands that for essentially all embodiments, it is preferred that the initial composition consists predominantly, and preferably essentially entirely, of used adhesive elements, since this enables particularly efficient recycling and prevents any interference with the inventive process from any interfering components.Advantageously, a corresponding process is particularly easy to implement, particularly in an industrial context when recycling process waste, which again demonstrates that the process according to the invention is particularly preferred for processing such used adhesive elements from process waste. Thus, a process according to the invention is preferred, wherein the starting composition consists of 80% or more, preferably 90% or more, particularly preferably 95% or more, and most particularly preferably essentially completely, of the one or more used adhesive elements, based on the mass of the starting composition.

[0052] Based on their own experiments, the inventors assume that it is at least in principle possible to use various old adhesive elements in the starting composition, which differ, for example, in terms of the thermoplastic carrier layer plastic in the carrier layer and / or the adhesive (CO)polymers, so that material mixtures in the starting composition are also possible. In the inventor's opinion, however, such a mixing of different materials in the starting composition not only complicates the selection of the optimal processing temperature in the subsequent mixing step, but will also likely result in a mixed material whose physicochemical properties are very difficult to precisely adjust, making it more suitable for less demanding applications.In the inventor's opinion, it is preferable for essentially all embodiments to process the same type of used adhesive elements wherever possible. For example, with regard to both processability and the uniformity of the physicochemical properties of the plastic films produced, it is preferable if, for example, rubber-based adhesive tapes with a polypropylene carrier are processed separately from poly(meth)acrylate-based adhesive tapes with a PET carrier in order to obtain the purest possible rubber / PP or poly(meth)acrylate / PET blend materials, which can then be used particularly efficiently in the production of the corresponding starting adhesive tapes.This process of the method according to the invention can also be implemented particularly efficiently when process waste is used, which allows for the compilation of adhesive tape waste that is as pure as possible. Therefore, a process according to the invention is preferred, wherein the waste adhesive elements in the initial composition comprise 50% or more, preferably 70% or more, particularly preferably 90% or more, and most particularly preferably substantially all, the same carrier layer and / or the same adhesive layer, preferably the same carrier layer and the same adhesive layer, based on the mass of the initial composition.

[0053] The skilled person understands that an advantageous initial composition, for example, a container full of adhesive tape offcuts from adhesive tape production, will consist essentially of thermoplastic carrier layer plastics and adhesives, apart from minor components such as fillers or plastic additives. Since the material mixtures produced in the process according to the invention are later intended to be used in plastic mixtures for film production, the inventor proposes that the proportion of thermoplastic carrier layer plastic should not be chosen too low, so that high degrees of substitution remain possible when mixing with fresh plastics and, in other words, the resulting material mixture still has a distinct plastic character.However, given the typical coating of plastic substrates with adhesive, since prior separation of the adhesive is not desired, the proportion of thermoplastic substrate materials in the initial composition cannot be chosen arbitrarily high, so that in practice a minimum adhesive content will be present. The inventor has succeeded in specifying particularly coordinated mass fractions and ratios for these mass fractions, with which advantageous material mixtures can be obtained.A process according to the invention is preferred, wherein the combined mass fraction of thermoplastic carrier layer plastics in the starting composition is in the range from 50 to 90%, preferably in the range from 55 to 80%, particularly preferably in the range from 60 to 70%, based on the mass of the starting composition, and / or wherein the combined mass fraction of adhesive in the starting composition is in the range from 10 to 50%, preferably in the range from 20 to 45%, particularly preferably in the range from 30 to 40%, based on the mass of the starting composition.Additionally or alternatively, a process according to the invention is preferred, wherein in the starting composition the quotient of the combined mass fraction of thermoplastic carrier layer plastics divided by the combined mass fraction of adhesive is in the range from 0.9 to 5, preferably in the range from 1.0 to 4, particularly preferably in the range from 1.1 to 3, very particularly preferably in the range from 1.2 to 2.5, based on the mass of the starting composition.

[0054] In this respect, the person skilled in the art will understand that the total mass fraction of thermoplastics in the starting composition will be higher than the above-mentioned proportion of the thermoplastic carrier layer plastics, given that the adhesive (co)polymers are also generally thermoplastic. An example in this respect is a process according to the invention wherein the combined mass fraction of thermoplastics, i.e. in particular of thermoplastic carrier layer plastics and adhesive (co)polymers, in the starting composition is 75% or more, preferably 85% or more, particularly preferably 95% or more, based on the mass of the starting composition. In process step b), the starting composition is kneaded at elevated temperatures. The material mixture produced in process step b) accordingly comprises the thermoplastic carrier layer plastics and the adhesive.This process step takes place in a mixing unit, whereby in the inventors' experiments the use of a stamp kneader, also referred to as an internal mixer, proved particularly advantageous for homogenizing the initial composition. Accordingly, a process according to the invention is preferred, wherein the mixing unit is a stamp kneader. Such a stamp kneader, sometimes also referred to as a stamp mixer, in most cases comprises a closed mixing chamber with at least two, usually counter-rotating rotors, which are designed to mix the components fed into the stamp kneader. The mixing chamber of the stamp kneader is accessible via an inlet opening that can be closed with a stamp, whereby the typically pneumatically or hydraulically operated stamp forces the components fed into the mixing chamber through the rotors in order to achieve mixing of these components.Due to the combined action of the ram and rotors, the material to be mixed is exposed to particularly high shear forces within the ram kneader, whereby high temperatures are also achieved particularly effectively in ram mixers.

[0055] In addition to the use of a stamping kneader, the inventor's experiments have also shown the use of a twin-screw extruder to be particularly advantageous, particularly when processing strand-shaped waste adhesive elements, which can, for example, be unwound directly from a waste adhesive roll, although twin-screw extruders are also suitable for processing shredded waste adhesive elements. Accordingly, a method according to the invention is preferred, wherein the mixing unit is a twin-screw extruder, preferably a conical twin-screw extruder. Melting and homogenization / mixing then take place in the twin-screw extruder. At the end of the twin-screw extruder, strand granulation to form plastic granules can then take place, for example. In the inventor's opinion, it is essential that the shear forces exerted by the mixing unit are combined with an elevated temperature.The inventor has found that the minimum temperature to be used is determined by the properties of the thermoplastic carrier layer. Accordingly, the minimum temperature for kneading the starting composition in the context of the present invention is determined by the melting temperature T. Mof the thermoplastic carrier layer plastic at normal pressure, which is specified here in °C. The person skilled in the art will understand that in the vast majority of cases, and particularly for preferred initial compositions, essentially only one thermoplastic carrier layer plastic will be present, so that the temperature during kneading can be adjusted to its melting point.When using old adhesive elements that have multiple thermoplastic carrier layers in the carrier layer and / or when using several different old adhesive elements with different carrier layers in the initial composition, the inventor believes that the temperature should be adjusted to the thermoplastic carrier layer plastic that has the highest melting point in the initial composition and is present in a sufficiently large mass fraction that its complete melting is also necessary for process-related reasons. For example, the processing of an initial composition that consists of more than 99.5% of a thermoplastic carrier layer plastic with a melting temperature of 135°C and contains 0.5% of a higher-melting plastic can be adjusted to the melting temperature of 135°C.

[0056] For the most extensive melting of such starting compositions, a process according to the invention is preferred, wherein T M (i> is the melting temperature of the thermoplastic carrier layer plastic with the highest melting temperature in the initial composition, whose mass fraction is 1% or more, preferably 0.5% or more, particularly preferably 0.1% or more, based on the mass of the

[0057] Starting composition. A process according to the invention is particularly preferred, wherein T M (i> is the melting temperature of the thermoplastic carrier layer plastic with the highest melting temperature in the initial composition.

[0058] The melting temperature of adhesive (co)polymers used in adhesives is generally below the highest melting temperatures of thermoplastic carrier layer plastics. In other words, this is a process according to the invention, wherein the one or more adhesive (co)polymers are thermoplastic adhesive (co)polymers, wherein the melting temperature of the adhesive (co)polymers is lower than T M (i). This also applies analogously to other components of typical adhesives, in particular the adhesive resins and plasticizers used.

[0059] From the above definition that the temperature used during kneading can be up to 10 °C below the melting temperature TM WIt is clear that, particularly when using powerful mixing units and strong shear forces, complete melting of the polymer components of the starting composition is not necessarily required, and a reaction close to the melting point may be sufficient. However, it is particularly preferred to keep the processing temperature essentially at TM Wor even higher. If the temperature used for kneading is set essentially to the melting temperature of the thermoplastic carrier layer plastic with the highest melting temperature that is present to a noticeable extent, it follows that the starting composition, apart from any fillers or any small contents of higher-melting carrier layer plastics, can be melted essentially completely, thereby enabling advantageous homogenization and a particularly efficient process control during kneading. In other words, this is a process according to the invention, wherein the kneading in process step b) is carried out such that at least the polymeric components, preferably all components, of the

[0060] Initial composition is melted in the mixing unit.

[0061] With regard to the temperature during kneading, a process according to the invention is particularly preferred, wherein the kneading in process step b) is carried out at a temperature of T = (TM W - 5 °C) or more, preferably T = T M (i> or more, particularly preferably T = (TM W + 5 °C) or more, very preferably of T = (TM ) + 10 °C) or more, especially particularly preferably of T = (T M (i> + 20 °C) or more.

[0062] In the inventors' opinion, excessively hot processing should be avoided in order to prevent unnecessary damage such as polymer degradation, especially with long residence times in the mixing unit. Additionally or alternatively, a process according to the invention is preferred, wherein the kneading in process step b) is carried out at a temperature in the range of T = (T M (i> - 10 °C) to (TM W + 50 °C), preferably in the range of (T M (i> - 5 °C) to (T M(i> + 45 °C), particularly preferably in the range of T = T M (i) to (TM W + 40 °C).

[0063] An example of a process according to the invention is one in which the relevant thermoplastic carrier layer plastic with the highest melting temperature in the starting composition is polyethylene, wherein the kneading in process step b) takes place at a temperature of 130°C or more, preferably 135°C or more. An alternative example is one in which the relevant thermoplastic carrier layer plastic with the highest melting temperature in the starting composition is polypropylene, wherein the kneading in process step b) takes place at a temperature of 165°C or more, preferably 175°C or more.

[0064] In practice, the time required for kneading will depend primarily on the physicochemical properties of the material mixture, the performance of the mixing unit, and the set temperature. According to the inventor's assessment, a typical method according to the invention is one in which the kneading in process step b) takes place for a time t in the range of 0.8 to 7 minutes, preferably in the range of 0.9 to 5 minutes, particularly preferably in the range of 1 to 3 minutes.

[0065] Based on the material mixtures contained in the experiments, it was found that, depending on the used adhesive tapes, a completely homogeneous material mixture cannot be obtained in the vast majority of cases. However, this is advantageously not absolutely necessary for subsequent processing into a plastic film. Rather, the process according to the invention produces, in particular, material mixtures comprising a plurality of material domains made of the respective thermoplastic carrier layer plastics or adhesive (co)polymers and, optionally, the adhesive resins. However, these are distributed as evenly or finely dispersed as possible in the material mixture during kneading, so that the resulting material mixture has the most uniform macroscopic properties possible.A preferred method according to the invention is one in which the material mixture comprises a plurality of material domains made of thermoplastic carrier layer plastic, wherein the material domains made of thermoplastic carrier layer plastic are preferably evenly distributed in the material mixture, and / or wherein the material mixture comprises a plurality of material domains made of adhesive (co)polymers, wherein the material domains made of adhesive (co)polymers are preferably evenly distributed in the material mixture. The use of commercially available compatibilizers can be helpful to improve the fine distribution and thus the material properties.

[0066] A particular advantage of the process according to the invention is that the production of the material mixture by kneading is surprisingly possible without the addition of additional chemicals, thus resulting in a purely thermomechanical reaction. Those skilled in the art will understand that the above-disclosed compositions of preferred starting compositions can be directly transferred to the composition of the preferred material mixture.Accordingly, a method according to the invention is preferred, wherein the combined mass fraction of thermoplastic carrier layer plastics in the material mixture is in the range from 50 to 90%, preferably in the range from 55 to 80%, particularly preferably in the range from 60 to 70%, based on the mass of the material mixture, and / or wherein the combined mass fraction of adhesive in the material mixture is in the range from 10 to 50%, preferably in the range from 20 to 45%, particularly preferably in the range from 30 to 40%, based on the mass of the material mixture.Additionally or alternatively, a method according to the invention is preferred, wherein in the material mixture the quotient of the combined mass fraction of thermoplastic carrier layer plastics divided by the combined mass fraction of adhesive is in the range from 0.9 to 5, preferably in the range from 1.0 to 4, particularly preferably in the range from 1.1 to 3, very particularly preferably in the range from 1.2 to 2.5, based on the mass of the material mixture.

[0067] In this respect, the person skilled in the art will understand that the total mass fraction of thermoplastics in the material mixture will be higher than the above-specified proportion of the thermoplastic carrier layer plastics, given that the adhesive (co)polymers are also generally thermoplastic. An example of this is a process according to the invention, wherein the combined mass fraction of thermoplastics, i.e., in particular, of thermoplastic carrier layer plastics and adhesive (co)polymers, in the material mixture is 75% or more, preferably 85% or more, particularly preferably 95% or more, based on the mass of the material mixture.

[0068] Also additionally or alternatively preferred is a process according to the invention wherein the material mixture comprises natural rubber, preferably in a combined mass fraction in the range from 0.5 to 30%, preferably in the range from 1 to 20%, particularly preferably in the range from 5 to 15%, based on the mass of the material mixture. Also additionally or alternatively preferred is a process according to the invention wherein the material mixture comprises synthetic rubber, preferably styrene-containing block copolymers, particularly preferably styrene-isoprene-styrene block copolymer and / or styrene-butadiene-styrene block copolymer, preferably in a combined mass fraction in the range from 0.5 to 30%, preferably in the range from 1 to 20%, particularly preferably in the range from 5 to 15%, based on the mass of the material mixture.

[0069] Even if it is particularly advantageous, with a view to time- and cost-efficient process management, to only implement the initial composition in the mixing unit, the process according to the invention advantageously also offers the possibility of adding further additives during the kneading process, which serve, for example, to adjust the physicochemical properties of the resulting material mixture. For this purpose, a process according to the invention is preferred, wherein the material mixture comprises one or more additives, wherein the additives are preferably selected from the group consisting of anti-aging agents, which are commercially available, for example, under the trade names Irganox 1010 or Irgafos 168, UV stabilizers, dyes, plasticizers, compatibilizers, and processing aids, wherein the additives are preferably added in the mixing unit.

[0070] The material mixture obtained in process step b) is then extruded in process step c) and formed into a plastic film. The skilled person understands that the material mixture should be transferred from the mixing unit to the extruder in a suitable manner, whereby the skilled person can choose a transfer method suitable for him and the equipment available to him. According to the inventors' assessment, in the vast majority of cases the material mixture will be cooled downstream of the mixing unit and converted into an easily handleable solid form, which is particularly useful if the material mixture is also to be combined with other thermoplastic materials in the plastic mixture. In this case, processing into an easily handleable form as a bulk material is particularly useful, which can be efficiently mixed with other plastic granules and fed into an extruder.For essentially all embodiments, a method according to the invention is accordingly preferred, additionally comprising, after method step b), the method step: b2) processing the material mixture to obtain a plastic granulate, wherein the plastic mixture comprises the plastic granulate.

[0071] This plastic granulate, like the material mixture itself, can also be referred to as plastic recyclate or recycled adhesive tape. Those skilled in the art will understand that the term "plastic granulate" is to be interpreted broadly within the scope of the present invention and, in addition to the form of typical granules, also encompasses, for example, other pourable, particulate, or coarse-grained materials as well as flakes. The functional requirement is, in particular, that the plastic granulate is suitable for feeding into a typical extruder. Such processing, particularly on a laboratory scale, can consist, for example, in the material mixture discharged from the mixing unit being formed into a sheet between cooling rollers, and flakes or cubes being cut from this sheet.

[0072] In process step b2) of the preferred process according to the invention, the material mixture obtained in the mixing unit will, in particular, be extruded and granulated in the subsequent large-scale application to obtain plastic granules consisting of the material mixture, provided no further components are added in the extruder. Thus, a preferred process according to the invention is particularly preferred for industrial application, wherein the processing of the material mixture in process step b2) is carried out by extrusion and granulation.

[0073] It can be seen as an advantage of the process according to the invention that for the implementation of this process step b2), typical extrusion processes and devices can be used, which are widely known from the field of the plastics processing industry, wherein in particular such processes and devices can be used which would also serve for the granulate production for the thermoplastic carrier layer plastics that were contained in the carrier layers of the old adhesive elements. With regard to the extrusion temperature, a process according to the invention is preferred, wherein the extrusion takes place at a temperature TE in the range of 120 to 240 °C, preferably in the range of 130 to 220 °C, particularly preferably in the range of T E = T M (i) to (TM W+ 60 °C). Granulation can be carried out using conventional methods and devices known from the prior art. In process step c) of the process according to the invention, a plastic film is formed from an extruded plastic mixture which comprises the material mixture, for example in the form of plastic granules. An example of this is an inventive process wherein the plastic film is a cast film or a blown film. An example of this is additionally or alternatively an inventive process wherein the plastic film is a single-layer or multi-layer carrier film, preferably a single-layer one. It can be seen as an advantage of the process according to the invention that methods and devices can be used for forming the plastic film which are also used in the prior art for film production from corresponding thermoplastic carrier layer plastics.

[0074] The plastic mixture comprises the material mixture, for example, in the form of plastic granules. While it is at least theoretically possible, especially with high contents of thermoplastic carrier layer plastic in the material mixture, that the plastic mixture consists essentially of the material mixture, the inventors believe that such plastic films are more suitable for relatively undemanding applications, i.e., for applications in which, for example, compromises can be made in the mechanical properties of the plastic films.

[0075] In the vast majority of cases, it is preferred that the material mixture be mixed with other thermoplastics, in particular those freshly produced from fossil resources (also referred to as "virgin material"). In the context of the present invention, the material used for mixing with the material mixture is referred to as a thermoplastic material for the purpose of clear differentiation, but in accordance with the understanding of those skilled in the art, it itself comprises thermoplastics. The same applies to the thermoplastic material as was disclosed above for the carrier layer, for example, that it preferably consists predominantly of thermoplastics and, in this respect, thermoplastic materials that are as pure as possible are preferred over mixed thermoplastics.Accordingly, a process according to the invention is preferred, wherein the plastic mixture in process step c) is obtained by mixing the material mixture, preferably in the form of plastic granules, with a thermoplastic material which consists of 95% or more, preferably 98% or more, particularly preferably 99% or more, of one or more thermoplastics, based on the mass of the thermoplastic material.

[0076] In the inventors' opinion, analogous to the above considerations regarding the mixing of used adhesive elements with different carrier layers made of different thermoplastic carrier layer materials in process step c), it is particularly preferred to use the material that is also the dominant thermoplastic carrier layer material in the material mixture as the thermoplastic. For the particularly preferred processes according to the invention, in which used adhesive elements with a carrier layer made of a thermoplastic that is as pure as possible are used, this means that the thermoplastic of the thermoplastic material corresponds precisely to this thermoplastic carrier layer material of the carrier layer.A method according to the invention is therefore particularly preferred, wherein the one or more thermoplastics of the thermoplastic material are selected from the group consisting of thermoplastics which are contained in the material mixture, preferably selected from the group consisting of the three thermoplastic carrier layer plastics which are contained in the material mixture with the highest mass fraction, wherein the one thermoplastic of the thermoplastic material is particularly preferably the thermoplastic carrier layer plastic which is contained in the material mixture with the highest mass fraction.

[0077] Particularly when the material mixture contains relatively large proportions of the thermoplastic carrier layer plastic and only comparatively low requirements are placed on the properties of the plastic film to be produced using the process according to the invention, very high mass fractions of the material mixture can also be provided in the plastic mixture. However, the inventors have succeeded in identifying particularly suitable mass fractions for the proportion of the material mixture in the plastic mixture, with which films can be advantageously obtained that have excellent properties and are thus also suitable for demanding applications. The corresponding proportions are particularly matched to the proportions of the thermoplastic carrier layer plastic in the material mixture described above as preferred.Particularly preferred is a process according to the invention, wherein the mass fraction of the material mixture in the plastic mixture is in the range from 2.5 to 80%, preferably in the range from 5 to 70%, particularly preferably in the range from 20 to 60%, very particularly preferably in the range from 30 to 50%, based on the mass of the plastic mixture.

[0078] It can be considered an advantage of the process according to the invention that the plastic films produced, despite being manufactured from at least partially recycled materials, can be processed using the stretching methods known from the prior art to optimize the mechanical properties. Accordingly, a process according to the invention is also preferred, additionally comprising the process step: e) stretching the plastic film to obtain a stretched plastic film, preferably a monoaxially or biaxially stretched plastic film.

[0079] The concept of a mono-axially or bi-axially oriented carrier layer is known to those skilled in the art. Depending on the process used to establish the corresponding orientation, those skilled in the art also refer to biaxially or mono-axially stretched materials. During mono- or bi-axial stretching, a plastic film, for example a cast or blown film, is heated inline during film production or offline in a separate process by means of rollers or in a heat channel to a temperature above the glass transition temperature Tg, in particular more than 20 °C above Tg, but below the melting temperature Tm of the film material. The stretching takes place, for example, between two or more rollers rotating at increasing speeds. The temperature control during stretching should be very constant and homogeneous.The stretching factor for mono-axial stretching in the machine direction is, for example, in the range from 1:4 to 1:8 and the stretching factor in the transverse direction for bi-axial stretching is, for example, in the range from 1:4 to 1:6.

[0080] The invention also relates to a method for producing an adhesive element, comprising the method steps of the method according to the invention for producing a plastic film, as well as the step: q) coating the plastic film with an adhesive mixture to obtain the adhesive element. In the method according to the invention for producing an adhesive element, the plastic film obtained from the method according to the invention for producing a plastic film is coated with an adhesive mixture, wherein the conventional coating methods known from the field of technology for producing adhesive elements can advantageously be used, for example coating from solution, dispersion, or melt, to which reference is made here.

[0081] In the above definition of the process for producing an adhesive element, the term "adhesive mixture" is used to allow a linguistic distinction from the adhesive compositions used in the process according to the invention. However, the skilled person will understand that corresponding adhesive mixtures are also adhesive compositions in the language of the skilled person, to which the above statements apply accordingly.

[0082] In light of the above, to obtain particularly advantageous adhesive elements, it is particularly preferred to use a composition as the adhesive mixture that corresponds to the adhesive mass of the used adhesive tapes processed in the production of the plastic film. In other words, if, for example, the plastic film is produced from used adhesive tapes containing styrene-isoprene-styrene block copolymers and a certain amount of adhesive resin in the adhesive mass, it is particularly preferred to provide the same composition of styrene-isoprene-styrene block copolymers and adhesive resin for the adhesive mixture.Without wishing to be bound by this theory, the inventors assume that it is the high chemical compatibility of the adhesive mixture with the corresponding material domains in the coated plastic film, which have been created from the corresponding adhesive mass, that contributes to the advantageous properties of the adhesive elements produced by the process according to the invention.

[0083] The invention further relates to a plastic film produced or producible by the method according to the invention. The invention also relates to an adhesive element, in particular an adhesive tape, preferably produced or producible by the method according to the invention for producing an adhesive element, comprising a plastic film according to the invention as a carrier layer and at least one adhesive layer arranged on the carrier layer, comprising an adhesive mixture.

[0084] Also disclosed is the use of a material mixture of at a temperature of T = (TMW - 10 °C) or more kneaded adhesive tape waste in the production of plastic film for use in adhesive tapes to reduce the consumption of fossil resources.

[0085] In the following, the invention and preferred embodiments of the invention are further explained and described with reference to experiments.

[0086] A. Production of samples

[0087] A1 Production of a material mixture from old adhesive tape:

[0088] By carrying out the process steps a), b0) b) and b2) of the process according to the invention, two different material mixtures in the form of flakes were first produced.

[0089] In the initial compilation, waste rolls or other waste resulting from the production of adhesive tapes, such as edge trimmings from old adhesive tape, are used as old adhesive elements.

[0090] Specifically, for the two different material mixtures, which are referred to below as “Recyclate A” and “Recyclate B”, used rolls of adhesive tape were used, which were sold under the trade name tesa 64294 (85 pm MOPP film coated with 22 g / m 2 a resin-based natural rubber pressure-sensitive adhesive) or under the trade name tesa 64286 (45 pm MOPP film coated with 20 g / m 2 a synthetic rubber SIS pressure-sensitive adhesive containing an adhesive resin) are commercially available.

[0091] The corresponding waste tape rolls were each cut into small pieces using a bale cutter. These pieces were then mixed in a GK5E mixer from HF Mixing Group at an increasing temperature for 1 minute, reaching a final temperature of 172 °C, and homogenized as far as possible.

[0092] The corresponding waste tape rolls were each cut into small pieces using a bale cutter. These pieces were then mixed in a GK5E mixer from HF Mixing Group at an increasing temperature for 1 minute, reaching a final temperature of 172 °C, and homogenized as far as possible.

[0093] The resulting mass, which appeared essentially homogeneous to the naked eye, was discharged from the mixing unit and rolled in a hot state on a rolling mill into a plate, which was then cut into flakes with an edge length of 5 mm in a strip cutter.

[0094] A2 Production of plastic films

[0095] To produce plastic films E1 to E4, the flakes of "Recyclate A" or "Recyclate B" are blended with a thermoplastic material made of a heterophasic polypropylene copolymer (HECO PP; trade name: Profax SV258; company: LyondellBasell). These blends are then extruded using a Collin E30 single-screw extruder and formed into plastic films. For this purpose, the plastic blends were melted and formed into a flat film via a slot die on a rolling mill with a chill roll (trade name: TeachLine; company: Collin).

[0096] As comparative example V1, a film was produced in an analogous manner whose plastic mixture consisted exclusively of the heterophasic polypropylene copolymer (HECO PP; trade name: Profax SV258; company: LyondellBasell).

[0097] The composition of the plastic mixtures is documented in Table 1.

[0098] Table 1 - Composition of the plastic mixtures, all data in mass fractions

[0099] The production of plastic films E5 to E8 is essentially analogous to the production of plastic films E1 to E4, although the films are produced with a higher initial thickness and stretched inline, i.e. directly in the film production process, on a stretching unit (company: Collin) in the machine direction with a factor of 1:6.

[0100] As comparative example V2, a film was again produced in an analogous manner, the plastic mixture of which consisted exclusively of the heterophasic polypropylene copolymer (HECO PP; trade name: Profax SV258; company: LyondellBasell).

[0101] The composition of the plastic mixtures is documented in Table 2.

[0102] Table 2 - Composition of the plastic mixtures, all data in mass fractions

[0103] B. Tests carried out:

[0104] One or more of the following tests were performed on the samples manufactured as described above. The measurements were performed (unless otherwise stated) at a test temperature of 23 ± 1 °C and 50 ± 5% relative humidity. Mechanical tests:

[0105] The mechanical properties are determined in a tensile / elongation test. The tensile strain behavior is determined using Type 2 test specimens (rectangular, 150 mm long and, if possible, 15 mm wide test strips) according to DIN EN ISO 527-3 / 2 / 300 at a test speed of 300 mm / min, a clamping length of 100 mm, and a preload of 0.3 N / cm. Samples are cut with sharp blades to determine the data.

[0106] Unless otherwise stated, tensile elongation behavior is tested in machine direction (MD). Tensile strength is measured in N / mm 2and the elongation at break is expressed in %. The modulus of elasticity is determined from the force-strain curve at low strain. The test results, especially the elongation at break, are statistically validated by a sufficient number of measurements.

[0107] Tear resistance:

[0108] Tear strength is the force in N / cm required to tear a specimen according to a specified method. Measurement is performed according to DIN EN ISO 6383-2:2004 (Part 2: Elmendorf method (ISO 6383-2:1983)). A rectangular specimen is used. The test results are also statistically validated by a sufficient number of measurements.

[0109] Shredding test:

[0110] For the shredding test, the test specimen is first exposed to Corona (30 kW / m 2) and coated with a pressure-sensitive adhesive (solvent-based natural rubber pressure-sensitive adhesive containing 40% adhesive resin). The test specimen is then bonded to PS plates, and the bonded specimens are subsequently stored for 24 hours at 40°C. This is followed by reconditioning at room temperature (climate-controlled laboratory conditions) for 2 hours, and finally, the specimen is stored in a freezer at -10°C for 24 hours. The tape is then peeled off in the freezer at a 180° angle, first slowly and then quickly. The assessment is made visually to determine whether and at what speed splicing of the adhesive tape (backing) occurs. Tensile impact strength:

[0111] The tensile impact strength of the film is determined according to DIN EN ISO 8256:2005-05 on specimens measuring 15 mm wide and 27 mm long. For longitudinal tensile impact strength, the specimens are cut parallel to the machine direction, and the crack propagation is therefore perpendicular to the machine direction.

[0112] The arithmetic mean of 10 measurements is given in each case.

[0113] C. Results

[0114] The results of the tests are summarized in Tables 3 and 4 below. Table 3 - Results of the tests - Part 1

[0115] The mechanical properties of the flat films with recycled content E1 to E4 are surprisingly comparable to those of the film made from 100% virgin polymer. The examples demonstrate that the addition of up to 75% recycled content has essentially no adverse effect on the film's properties. Table 4 - Results of the tests conducted - Part 2

[0116] * the measured values ​​show a very large scatter, which could be an indication of inhomogeneity in the mixture.

[0117] The mechanical properties of the monoaxially oriented films with recycled content E5 to E8 are comparable to those of the film made from 100% virgin polymer. However, experiments indicate that with a high recycled content, for example, 75%, the strength of the film decreases noticeably due to the high rubber content from the pressure-sensitive adhesive. However, the rubber content from the pressure-sensitive adhesive leads to a significant improvement in the application test (reduction in shredding).

Claims

Claims 1. A method for producing a plastic film for use in the production of adhesive elements, comprising the method steps: a) producing or providing a starting composition comprising one or more used adhesive elements, each comprising: i) at least one carrier layer comprising one or more thermoplastic carrier layer plastics, and ii) at least one adhesive layer arranged on the carrier layer, comprising an adhesive comprising one or more adhesive (co)polymers, b) kneading the starting composition in a mixing unit to obtain a material mixture comprising the one or more thermoplastic carrier layer plastics and the one or more adhesive (co)polymers, wherein the kneading is carried out at a temperature of T = (T M <i) - 10 °C) oder mehr erfolgt, wobei T M(i> is the melting temperature of the thermoplastic carrier layer plastic with the highest melting temperature in the initial composition, the mass fraction of which is 2% or more, based on the mass of the initial composition, and c) extruding and forming a plastic film from a Plastic mixture, wherein the plastic mixture comprises the material mixture.

2. The method according to claim 1, wherein the waste adhesive elements in the initial composition are selected from the group consisting of process waste from adhesive element production and used adhesive elements.

3. The method according to claim 1 or 2, wherein the carrier layer is selected from the group consisting of carrier films, plastic foams and textile fabrics.

4. The method according to any one of claims 1 to 3, wherein the one or more thermoplastic carrier layer plastics are selected from the group consisting of polyesters and polyolefins, preferably selected from the group consisting of polyethylene terephthalate, polyethylene and polypropylene.

5. The method according to any one of claims 1 to 4, wherein the one or more adhesive (co)polymers are selected from the group consisting of poly(meth)acrylates and rubbers, and / or wherein the one or more adhesive (co)polymers are selected from the group consisting of natural rubber and styrene-containing block copolymers.

6. The method according to claim 5, additionally comprising, after method step b), the method step: b2) processing the material mixture to obtain a plastic granulate, wherein the plastic mixture comprises the plastic granulate.

7. The method according to any one of claims 1 to 6, wherein the combined mass fraction of thermoplastic carrier layer plastics in the starting composition is in the range from 50 to 90%, based on the mass of the starting composition, and / or wherein the combined mass fraction of adhesive in the starting composition is in the range from 10 to 50%, based on the mass of the starting composition.

8. The method according to any one of claims 1 to 7, wherein the kneading in step b) is carried out at a temperature of T = (T M (i> - 5 °C) or more.

9. The method according to any one of claims 1 to 8, wherein the plastic mixture in method step c) is obtained by mixing the material mixture with a thermoplastic material which consists of 95% or more of one or more thermoplastics, based on the mass of the thermoplastic material.

10. The method according to claim 9, wherein the one or more thermoplastics of the thermoplastic material are selected from the group consisting of thermoplastics contained in the material mixture.

11. The method according to any one of claims 1 to 10, wherein the mass fraction of the material mixture in the plastic mixture is in the range of 2.5 to 80%, based on the mass of the plastic mixture.

12. The method according to any one of claims 1 to 11, additionally comprising the method step: e) stretching the plastic film to obtain a stretched plastic film.

13. A method for producing an adhesive element, comprising the method steps of the method for producing a plastic film according to one of claims 1 to 12, and the step: q) coating the plastic film with an adhesive mixture to obtain an adhesive element.

14. Plastic film produced or producible by the process according to one of claims 1 to 12.

15. Adhesive element comprising as carrier layer a plastic film according to claim 14 and at least one adhesive layer arranged on the carrier layer, comprising an adhesive mixture.

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