Biodegradable support for security elements, security element made of said support and method of manufacture of said support and security element

Abstract

The present invention describes a biodegradable support suitable for the production of security elements that can be used in the production of security papers and their manufacturing method.

Description

[0001] BIODEGRADABLE SUPPORT FOR SECURITY ELEMENTS, SECURITY ELEMENT MADE OF SAID SUPPORT AND METHOD OF MANUFACTURE OF SAID SUPPORT AND SECURITY ELEMENT

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to a biodegradable support for security elements, a security element made of said support and a method of manufacturing said support and said security element .

[0005] In particular, the present invention refers to the technical field of so-called security threads intended to be incorporated or applied to paper supports. STATE OF THE ART

[0006] Security supports, especially security threads are known to be state of the art and widely used in combination with supports such as paper or the like .

[0007] Patent IT1296098B1 / EP0914970A2, for instance, describes the construction of a security thread with optical and magnetic information to combat document forgery. This application, filed in 1997 and now freely available, represents the state of the art as regards the product "security thread for security papers". Some of the materials and processes involved in the production of security documents are reviewed in the peer-reviewed literature [Rafiei, A.; Karimi, A.; Bodaghi, M., Sustainability 2023, 15, 3736; Haihua Wang and Liyu Sun, Accounts of Materials Research 2021, 2(1), 1-6; Prime, E. and Solomon, D., Angew. Chem. Int . Ed., 2010, 49, 3726-3736].

[0008] The plastic material currently used as a support for the manufacture of security threads and holographic strips is part of the family of petroleum-derived polyesters . The films used have mechanical and chemical properties suitable for mass production processes, such as the printing of ferromagnetic inks, the coating of solvent-based adhesives and primers, vacuum deposition of metal oxides and / or metals.

[0009] Since the aforementioned elements, after their production, are incorporated or applied to paper supports, the processing waste and the products themselves, at the end of their useful life, constitute a waste that is difficult to recycle. The methods commonly used for disposal are as follows:

[0010] - Combustion at high temperatures by incinerators in order to avoid the formation of dioxins;

[0011] - Mechanical separation of the plastic material from the paper and subsequent disposal on separate supply chains.

[0012] Document WO2016 / 067285 Al describes the production of biodegradable co-extruded films using polymers such as PLA, PBS, PBSA and PCL. In particular, the main application that is claimed is an increase in the barrier properties (e.g. against oxygen) common in the packaging world. There is no information on the use of these materials in industrial areas wherein techniques such as printing and coating of inks, metallization, etc. are used.

[0013] In the 2020 article by Barletta et al. (J Appl Polym Sci.2021; 138:app50236) talc-reinforced PLA and PBS blends are considered in a broader analysis to study crystallinity and the modification of mechanical and thermal properties following the addition of nucleating agents such as EBS and PDLA. Again, in the article the authors carry out an analysis of the change in properties without demonstrating the use of the materials in a real industrial application. Patent application WO2019 / 122195A1 "Biodegradable fabric and use of such fabric" describes a fabric comprising layered composite filaments, wherein the layered composite filaments comprise at least one first biodegradable polymer layer and at least one second biodegradable polymer layer adhering to each other.

[0014] In the known art described above, mixtures of biodegradable polymers are cited for the production of biodegradable supports for security elements and security elements comprising such supports that do not have the characteristics of chemical, thermal and mechanical resistance adequate for the processes currently used for the manufacture of security elements such as, for instance and in particular, a "security thread for security papers". In particular, PLA has adequate mechanical characteristics, but thermal characteristics and resistance to chemical solutions (acetone, ethyl acetate, etc.) are not adequate; PBS has good resistance to chemical solutions (acetone, ethyl acetate, etc.), but does not have adequate mechanical and thermal characteristics; mixtures of PLA and PBS, suitably combined, may have partially adequate mechanical characteristics and resistance to chemical solutions, but do not have suitable thermal characteristics .

[0015] The purpose of this invention is to develop a biodegradable support for security elements and a method of its production, as well as a security support and in particular a security thread comprising that support in combination with additional layers and a method of manufacturing said security support which will enable the existing limits to be overcome at the state of the art . In particular, the present invention aims at the realization of a biodegradable support for security elements that is suitable to be processed as a security thread in paper forming plants, with compostability characteristics compatible with pulping processes commonly used in the paper industry.

[0016] DESCRIPTION OF THE INVENTION

[0017] The invention achieves the above purposes with a biodegradable support for security elements, said support consisting of a multi-component film comprising: a first layer of said multi-component film which consists of polybutylsuccinate PBS in the range 40-60% by weight and polylactic acid PLA in the range 60-40% by weight and a second layer of said multi-component film which consists of a predominant or greater part of polybutylsuccinate PBS, in particular in the range 60- 80% by weight and for a part in a smaller quantity than the quantity of PBS, of polylactic acid PLA, in particular in the range 40-20% by weight.

[0018] According to a further characteristic, additives consisting of one or more of the additives listed in the following list are added to said first and / or second layer: one or a combination of inorganic nucleating agents such as clays, silicon oxide, titanium oxide, talc and boron nitride; one or more organic nucleating agents such as N,N'-ethylene bis-stearamide (EBS) and D— and L-lactide stereo complexes (PDLA and PLLA).

[0019] Still according to a further characteristic, said biodegradable support according to one or more of the previous embodiments, one or more additional layers of material superimposed on each other can be associated and to one or both sides of said substrate said layers being selected from the following list: inks, oxides, metals, magnetic materials, adhesives, protective layers or a combination thereof.

[0020] The invention also concerns a security element comprising said biodegradable support and said security element having a multilayer structure with two opposite faces facing outwards and wherein said security element comprises two of said biodegradable supports made according to one or more of the forms or embodiments described above or in the following description, said two biodegradable supports being coupled together directly or by interposing one or more additional layers of material along the faces of the corresponding second layer of said first and second layers constituting the biodegradable support .

[0021] According to a further characteristic, the external face of each first layer of the biodegradable support opposite that of adhesion to said second layer and to the additional biodegradable support element of said two biodegradable supports is coated, completely or only for some areas of said face and with a predetermined distribution design, with a metallization layer.

[0022] According to a further characteristic, an additional compatibilization layer is coupled to said metallization layer by an adhesive for the adhesion of a layer of paper to which said security element is intended to be coupled.

[0023] According to a further characteristic of the security element, according to one or more of the characteristics described above, one or more intermediate layers are provided between the reciprocal coupling faces of said two support elements.

[0024] According to a characteristic, said intermediate layers are made, on the face of one of the two coupled biodegradable supports that are facing each other, of one or more layers applied by printing and which comprise at least one layer consisting of graphic elements, optionally in colour, and / or at least one layer comprising ferromagnetic elements which are distributed according to designs reproducing pre- established codes, while the face of the second biodegradable support facing said first biodegradable support is coupled to a layer of thermo-adhesive glue.

[0025] According to an embodiment, the security element may consist of two intermediate elements respectively comprising one of the two biodegradable supports coupled to one or more additional layers, said two intermediate elements being laminated together to form the complete security element, being:

[0026] - one of said two intermediate elements, consisting of said first biodegradable support, with said metallization layer applied to the external face of the first layer on the entire surface or on part of said surface of said face and / or the additional compatibility layer with the adhesives for the adhesion of the paper or other material of the product to which the security element is intended to be applied and with, applied to the external face of the second layer of said two layers forming the biodegradable support, one or more layers applied by printing and comprising at least one layer consisting of graphic elements, optionally in colour, and / or at least one layer comprising ferromagnetic elements which are distributed according to designs reproducing pre- established codes;

[0027] - the other of the two intermediate elements, consisting of said second biodegradable support, having on the external face of the first layer of the two layers that make up said biodegradable support a metallization layer on the entire surface or on part of said surface of said face and / or the additional compatibility layer with the adhesives for the adhesion of the paper or other material of the product to which the element is intended to be applied and on the face of the second biodegradable support facing said first biodegradable support a layer of thermo-adhesive glue for the adhesion of said second support to said first support with the two outer faces of the two second layers of the corresponding biodegradable support facing each other.

[0028] In an embodiment, the metallization layer of the external face of the first layer that forms the biodegradable support (s) may alternatively consist of one of the materials indicated in the following list : aluminium, chromium, copper, silicon, metal oxides such as ZnS, SiO2, TiO2.

[0029] Said metallization layer can have different thicknesses and according to a preferred embodiment the thickness of said metallization layer is in the range from 50 to 500 nm.

[0030] As a material for the realization of the aforementioned thermo-adhesive layer of reciprocal coupling of the two biodegradable supports, it is possible to provide a thermo-adhesive glue based on epoxy and / or acrylic and / or polyurethane polymers, preferably activated at a temperature between 40°C and 90°C.

[0031] According to an embodiment, the outer face of the first layer of at least one or each of the biodegradable supports is further coated with a layer of adhesives, in particular based on polyvinyl-acetate (PVA) and / or polyvinyl chloride (PVC) and / or acrylates, or the like.

[0032] The invention also concerns a method for the creation of a biodegradable support comprising the characteristics according to one or more of the embodiments described, said method comprising: a first production step of granules, or pellets, consisting of mixtures of the pre-established components of material for said first and second layers of the biodegradable support, in which step said granules or pellets for said first and second layers are produced separately for each of said two layers; a second production step by co-extrusion from said granules or pellets of said first and second layers in a coupled condition.

[0033] According to an embodiment of the method, the production step of the granules or pellets consisting of mixtures of material components for said first and second layer of the biodegradable support respectively involves the following steps: mixing those components of the mixture of materials for said first layer in one extruder and for said second layer in a different extruder; extrusion of said mixture of materials separated by the mixture of materials of said first and second layer respectively and in the form of a continuous thread; formation of pellets from each of those continuous threads consisting of the mixture of materials for the first layer and the second layer respectively by cutting said thread into short segments.

[0034] Depending on yet another characteristic which is provided in combination with one or more of the previous embodiments or characteristics, the method may provide for a cooling step of the extruded threads before the cutting step of said threads into granules or pellets.

[0035] In an embodiment that can be envisaged in combination with one or more of any of the previous executive or characteristic forms, the material components provided for the formation of the pellets for the manufacture of said first layer are fed to the extruder in the following quantities: PBS granules in the range from 40 to 60% by weight, PLA granules in the range from 60 to 40% by weight, optionally added with powder fillers consisting of boron nitride in the range from 1 to 2% by weight, clay in the range from 4 to 6% by weight, while the material components provided for the formation of pellets for the manufacture of said first layer are fed to the extruder in the following quantities: PBS granules in the range from 60 to 80% by weight and PLA granules in the range from 40 to 20% by weight and optionally added with boron nitride powder fillers in the range from 1 to 2% by weight.

[0036] According to an embodiment that can be provided in combination with one or more of any of the previous embodiments or characteristics of said method, the extruder is a screw extruder, preferably twin-screw and the rotation speed is selected in the range from 20 to 50 rpm, while the extruder cylinder is heated to a temperature between 180° and 250°C. According to a characteristic of the method, which is provided in combination with one or more of any of the previous executive or characteristic forms, the cooling temperature of the extruded thread before cutting into granules is between 2 and 6°C.

[0037] According to a further characteristic that is provided in combination with one or more of any of the previous embodiments or characteristics, the granules, i.e. the pellets obtained from the cutting pitch of said threads, have a length in the range from 1 to 5 mm, while the diameter of the threads and therefore of the granules is in the range from 1 to 5 mm.

[0038] With reference to the co-extrusion step of said first and second layers from granules, or pellets, in particular obtained according to one or more of the previous embodiments and / or one or more characteristics of the production step of mixtures in granular form for the manufacture of the respective layers, said step comprises the following steps; the feeding of the granules or pellets composed respectively of the mixture of material components for said first and second layers to a separate extruder, optionally single-screw, and the simultaneous extrusion of said two layers from the respective mixture of material components fed by the corresponding extruder to a corresponding drawing mouth of a co-extrusion die.

[0039] According to a further characteristic, the co- extrusion step of the first and second layers of the biodegradable support according to one or more of the previous embodiments and / or characteristics comprises a final cooling step and a subsequent winding step in the reel. According to one characteristic, the die is configured to produce co-extruded films with an overall thickness in the range 10 to 20 μm.

[0040] According to a characteristic that can be provided in combination with one or more of the previous embodiments and / or characteristics described above, the heating temperature of the extruder cylinders is preferably in the range from 180 to 250°C.

[0041] Again, according to a characteristic which can be provided in combination with one or more of the previous embodiments and / or characteristics previously described, preferably the screw of the single-screw extruders rotates at a rotation speed in the range from 10 to 40 rpm.

[0042] Again, according to a characteristic, which can be provided in combination with one or more of the previous embodiments and / or characteristics described above, the cooling temperature is preferably in the range 40 to 70°C.

[0043] The invention also concerns a method for the manufacture of a security element, such as in particular a so-called security thread or similar according to one or more of the embodiments described above for a security element and said method involving the coupling of a first security support to a second security support, said first and second security supports being made according to one or more of the embodiments described above and having one or more of the characteristics described above, said biodegradable supports being coupled to each other by chemical / physical adhesion with the faces consisting of the respective second layer facing each other and with the interposition between them of one or more additional layers and said first and second biodegradable supports providing for the coating with one or more additional layers of the faces of the same which are made up of the external sides of the respective first layer.

[0044] According to an embodiment of the method for the manufacture of said security element, the following steps are provided: the application of a metallization layer on the entire surface or on part of the external face of the first layer of each of said first and second biodegradable supports, said face being the one opposite to the face of direct or indirect mutual adhesion of said two biodegradable supports; a subsequent step of application of a compatibility layer, or adhesion of said metallization layer to a layer of adhesive for paper or for other materials for the application of said security element; a printing application step on the face of the second layer of the first of the two biodegradable supports of graphic elements, optionally in colour, said graphic elements presenting one or more pre- established drawings; a further subsequent step of application of ferromagnetic elements according to one or more pre- established distribution drawings for the constitution of codes on said layer of graphic elements; an application step on the face of the second of said two biodegradable supports which is aimed towards said first biodegradable support of a layer of thermo- adhesive glue for adhesion to the face of said first biodegradable support provided with the layer consisting of said graphic elements applied by printing and / or the layer consisting of said ferromagnetic elements; the hot coupling of the first biodegradable support with the aforementioned additive layers to said second biodegradable support with the aforementioned additive layers and with said first support and said second support in a position facing each other.

[0045] According to an embodiment, the method provides for the completion of a metallisation layer in whole or in part of the surface of the outer face of the two biodegradable supports by applying and / or deposing at least one layer consisting of one of the following materials: aluminium, chromium, copper, silicon or a combination thereof, or by coating with metals or oxides selected by the group comprising ZnS, SiO2, TiO2or by coating with solvent-based systems, such as esters or ketones, containing dispersed metal elements.

[0046] According to a characteristic, said metallization layer is applied with a thickness in the range 50 to 500 nm.

[0047] According to an embodiment, said compatibilization layer consists of a material based on mixtures of epoxy polymers and / or melamine resins and / or urethane polymers.

[0048] Again, according to a characteristic of the aforementioned method, the thermo-adhesive layer is made of a material based on epoxy and / or acrylic and / or polyurethane polymers, which can be activated at a temperature between 40°C and 90°C.

[0049] For the production of security elements, such as threads or bands, said security element deriving from the co-extrusion steps of the biodegradable supports from those of subsequent coupling to one or more additional layers and to that of reciprocal hot coupling of the two biodegradable layers, provides for the cutting of said support element into bands or threads having a predetermined thickness and a predetermined width .

[0050] These bands or threads are advantageously wound onto reels or spools for use in paper forming plants, wherein the outer faces of the security element are coupled to at least one layer of paper respectively.

[0051] Thanks to the characteristics of the invention described above, the drawbacks relating to the recyclability and / or biodegradability of the security elements are overcome.

[0052] In particular, conflicting needs are optimized and concerning the materials that confer the characteristics of compostability and therefore contribute to making the security element suitable to be processed in pulping processes for the treatment of paper in order to produce recycled papers, with the needs dictated by the specific function of the security element and therefore the characteristics relating to behaviour in the event of thermal stress and mechanical resistance that are required to make the security element workable with the manufacturing processes of the same and also of the products to which said security element is intended to be coupled. These thermal and mechanical properties are also necessary to make the security element sufficiently resistant to the corresponding stresses to which the product to which the security element is coupled and therefore the security element itself is subjected.

[0053] The use of biodegradable support for security elements according to the present invention therefore makes it possible to effectively recycle these security elements and the paper supports wherein they are embedded by pulping processes.

[0054] In addition, the above also shows the advantages related to an efficiency of waste management processes during the production steps.

[0055] An example of a recycling process involves the treatment of a paper product containing the security thread made in accordance with the present invention and which is therefore suitable for parcelling and subsequently pulping (repulping process) using the systems commonly used in the paper industry.

[0056] In a preferred configuration of this recycling process, the thread / paper laminate is treated by an aqueous solution based on sodium hydroxide (NaOH) and by an aqueous solution based on sodium hydroxide (NaOH) and sodium persulphate (Na2S2O8). The concentration of sodium hydroxide (NaOH) in the first solution is in the range 2-10% by weight. In the second solution, the concentration of sodium hydroxide (NaOH) is in the range 2-10% by weight and the concentration of sodium persulfate (Na2S2O8) is in the range 10-30% by weight. The process times, which vary between 5 and 20 hours, depend on the concentrations, temperatures and stirring speeds of the baths. At the end of the process, the biodegradable plastic support is totally dissolved, and the resulting paper material can be used for the production of paper supports with lower added value. To ensure a better diffusion of the solution within the paper support, it is preferable and advantageous to subject the latter to a preventive process of fragmentation (shredding) which will allow the disposal of banknotes at the end of their life to be treated in total security.

[0057] These and other characteristics of the invention and its advantages will be more clearly shown by the following description of some of the illustrated embodiments and with reference to the attached figures wherein: LIST OF FIGURES

[0058] Figure 1 shows a schematic example of a plant for the production of pellets consisting of the mixture of material components provided for respectively the first layer and the second layer of the biodegradable support consisting of the multilayer film according to the present invention.

[0059] Figure 2 shows a plant for the co-extrusion of the multilayer film that constitutes the biodegradable support according to the present invention.

[0060] Figure 3 shows a schematic example of a detail of a biodegradable support according to the present invention.

[0061] Figure 4 shows two views respectively of the two opposite outer faces of a biodegradable support according to Figure 3 and two cross-sections of said biodegradable support .

[0062] Figure 5 shows a first intermediate element comprising a support element according to the present invention and its functional layers.

[0063] Figure 6 shows a second intermediate element comprising a support element according to the present invention and its functional layers

[0064] Figure 7 shows a security element according to the present invention consisting of the coupling by mutual adhesion of the intermediate elements according to figures 4 and 5.

[0065] Figure 8 shows the graph related to the thermogravimetric analysis (TGA) of the biopolymer- based support. Onset = 328°C. Degradation T (PLA) = 346°C. Degradation T (PBS) = 373°C. Residue = 3.88%.

[0066] Figure 9 shows the graph relating to the thermogravimetric analysis (TGA) of a 12-micron film of PET material. Onset = 403.7 °C. Degradation T = 428.4 °C Weight loss = 87%.

[0067] Figure 10 shows the graph of the differential scanning calorimetric analysis (DSC) of the biopolymer- based support . Recorded thermal events: glass transition temperature (PBS): ~ -32°C; glass transition temperature (PDA): ~ 56°C; melting point (PBS): ~104°C, ~112°C; melting temperature (PDA): ~ 151°C

[0068] Figure 11 shows the contact angle values on both sides of the PET-based film and the biopolymer-based film.

[0069] Figure 12 shows the graph relating to the analysis of the deformation temperature under load of a PET film, of the bilayer without boron nitride (Bilayer) and of the bilayer with 1% boron nitride (BilayerBN). DETAILED DESCRIPTION OF THE EXAMPLES AND FIGURES Figure 3 shows schematically a biodegradable support according to the present invention, which consists of a multi-component film comprising at least two layers 101 and 102 which are made and coupled together by co-extrusion.

[0070] Figure 3 shows the division into two layers in a completely illustrative way and does not correspond to reality. In fact, as will appear later from figures 4C and 4D, the co-extrusion process generates an interpenetration of the mixtures of material components that characterize the two layers with each other.

[0071] The two layers 101 and 102 consist of two compostable plastic-based mixtures to which additives are added that optimize the thermal and mechanical properties of these two mixtures.

[0072] With reference to a preferred example of the present invention, a first layer 101 consists of a mixture of polybutylsuccinate PBS and polylactic acid PLA. In particular, polybutylsuccinate PBS is present in a quantity corresponding to a value in the range from 40 to 60% by weight, while polylactic acid PLA is provided in a quantity corresponding to a value in the range from 60 to 40% by weight, said two quantities being selected in such a way that the sum of their value does not exceed the value of 100% by weight.

[0073] The second layer 102 of the film is composed mostly of polybutylsuccinate PBS in particular, for instance with a quantity corresponding to a value in the range 60 to 80% by weight and a minority of polylactic acid PLA, for instance, with a quantity corresponding to a value in the range 40 to 20% by weight, said two quantities being selected in such a way that the sum of their value does not exceed the value of 100% by weight.

[0074] In order to optimize the thermal and mechanical properties of the film consisting of the two co-extruded layers 101, 102, additives with specific functionalities are added, such as, by way of example but not limited to, nucleating agents, such as inorganic nucleating agents such as clays, silicon oxide, titanium oxide, talc and boron nitride; and / or organic nucleating agents, such as N,N'-ethylene bis-stearamide (EBS)], and D— and L-lactide stereo complexes (PDLA and PLLA).

[0075] Thanks to the particular composition of the first and second layers and the fact that these layers are co-extruded, the biodegradable support shows, as will also be described in greater detail below, mechanical and chemical / physical characteristics suitable for the construction of security elements, such as in particular security threads for security papers, or the like. Since, for instance, the security thread is generally made up of the coupling of multi-component films, the two layers covered by the present invention are designed in such a way that one is suitable for being inside and the other outside the set of layers coupled together and forming a complete security element .

[0076] The characteristics of the biodegradable support described above, give it characteristics of compostability and biodegradability or recyclability and characteristics relating to the response to thermal and mechanical stresses that make it usable in the manufacturing processes of security elements and their application to paper or other materials without any loss of performance compared to the supports present at the state of the art, but on the contrary overcoming the limitations of the aforementioned state of the art supports highlighted above.

[0077] With reference to figures 3 and 4, these show respectively the faces indicated by A and B of a biodegradable support and which constitute the external faces of the same of layer 101 and layer 102 respectively. The term external refers to the film that constitutes the support itself, while as will become clearer later when this support is used for the manufacture of a security element comprising two biodegradable supports coupled together, the B faces of the two biodegradable supports are facing each other and are located inside the security element, while the A faces of the two biodegradable supports coupled together face the outside of the security element .

[0078] With reference to figures 4A and 4B, these show respectively images acquired by scanning electron microscope (SEM), the conformation of face A and face B of the biodegradable support, i.e. of the two co- extruded layers 101, 102. From the images, it is evident that the filler is greater in the second co-extruded layer that shows the B face. Images 4C and 4D show two cross-sections according to a plane perpendicular to the extension of the biodegradable support and from which the interpenetration of said two co-extruded layers is evident .

[0079] With reference to Figures 1 and 2, they show, respectively, a plant for the production of the mixtures to be used for the subsequent co-extrusion of the biodegradable support as described above and for the manufacture of said biodegradable support by co- extrusion of said mixtures of material provided for said two layers 101 and 102.

[0080] The preparation of the mixtures of the material components provided for the aforementioned two layers 101 and 102, in granular form, is carried out by means of a double screw extrusion and a pellet cutting system. The materials are fed in the following quantities:

[0081] For the preparation of the mixture intended for the production of the first layer 101, PBS granules are fed in a quantity with a value in the range 40 to 60% by weight, PLA granules in a quantity with a value in the range from 60 to 40% by weight and powder fillers consisting of, for instance but not limited to, boron nitride in the range 1 to 2% by weight, clay in an amount in the range 4 to 6% by weight .

[0082] Separately, for the preparation of the material mixture for the second layer, PBS granules are predominantly fed to the extruder, e.g. in the range 60 to 80% by weight while PLA granules are used in a lesser proportion for instance, in a quantity in the range 40 to 20% by weight and powder fillers, for instance boron nitride, in an amount in the range 1 to 2% by weight.

[0083] The plant illustrated in figure 1 and suitable for mixing the aforementioned components and cutting into granular form is indicated with 1 and comprises:

[0084] - a twin-screw extruder with heated cylinder 2.

[0085] - a water bath for cooling the melt 3

[0086] - a device designed to cut extruded material in granular form 4.

[0087] In a preferred example, the cutting takes place in such a way as to form segments of extruded thread having lengths in the range 1 to 5 mm in length.

[0088] The production of the two mixtures takes place in distinct steps and in a completely similar way.

[0089] The resin granules of the mixture for the first layer 101 and the mixture for the second layer 102 are fed into extruder 2 through hopper 2A in the percentages specified above. The powder fillers of the first or second mixture are fed into extruder 2 through hopper 2B in the percentages specified above.

[0090] During operation, the 2C twin screw rotates at a speed in the range 20-50 rpm and the sections of the extrusion cylinders 21, 22, 23, 24 and 25 are heated to an operating temperature in the range 180°-250°C.

[0091] The circular section thread (diameter in the range 1-5 mm) of the first or second melted mixture, coming out of the 2D "die" placed at the end of extruder 2, is collected, immersed in the cooling water of tank 3 and directed towards the apparatus responsible for cutting the material in granular form (4) by rollers 31, 32 and 33.

[0092] The cooling water temperature is in the range 2- 6°C.

[0093] The cooled thread is collected by roller 4A which rotates at a speed in the range 5-13 rpm and cut into granular form by the toothed roller 4B which rotates in the opposite direction to 4A at the speed suitable for obtaining granules in the length range 1-5 mm.

[0094] The granules thus produced are accumulated at the collection station.

[0095] The plant described above concerns a first step of the method of making the biodegradable support according to the present invention and which is related to the production of mixtures in granular form.

[0096] Figure 2 shows a scheme of a plant for the production of the biodegradable support from the granules of material produced in the first step in the form of a multicomponent film co-extruded and wound in a reel.

[0097] Said plant 5 is used for the production of co- extruded films with a thickness of 8-20 μm fed by two single-screw extruders 6, 7 and equipped with:

[0098] - a co-extrusion die 8

[0099] - a collection system with three cooled cylinders 9 - a coil winder 10

[0100] The pellets consisting of the mixture for the first layer (PBS in the range 40-60% by weight, PLA in the range 60—40% by weight and filler in the range 1—7% by weight) are fed into the single screw extruder 6 through the hopper 6A.

[0101] The pellets consisting of the mixture for the second layer (PBS in the range 60-80% by weight, PLA in the range 40-20% by weight and filler in the range 1- 7% by weight) are fed into the single-screw extruder 7 through the hopper 7A.

[0102] During operation, the screw 6B rotates at a speed in the range 10-40 rpm and the sections of the extrusion cylinders 61, 62, 63 and 64 are heated to an operating temperature in the range 180°-250°C.

[0103] During operation, the screw 7B rotates at a speed in the range 10-40 rpm and the sections of the extrusion cylinders 71, 72, 73 and 74 are heated to an operating temperature in the range 180°-250°C.

[0104] The first melted mixture, coming out of extruder

[0105] 6, feeds the co-extrusion die 8 through the connector 8A heated to an operating temperature in the range 180°- 250°C.

[0106] The second melted mixture, coming out of extruder

[0107] 7, feeds the co-extrusion die 8 through connector 8B heated to an operating temperature in the range 180°- 250°C.

[0108] Inside the 8C co-extrusion block, the melts are distributed in such a way that, at the exit of the same, the mixture for the first layer constitutes side A and the mixture for the second layer the side B of the co- extruded fiIm . The co-extruded film, thus constituted, is collected and cooled by rollers 91 and 92 and directed towards the winder 10 by roller 93. The rollers are cooled to an operating temperature in the range 40-70°C and rotate at a speed in the range 3-10 m / min and in the direction shown in Fig. 2.

[0109] The cooled co-extruded film is collected by the reel winder 10 which rotates at a speed in the range 3- 10 m / min.

[0110] As will appear from the following description, to said first and second layers 101, 102 can be associated by means of printing, lamination, vacuum deposition, etc. additional layers of materials with specific functionalities such as inks, oxides, metals, magnetic materials, adhesives, etc.

[0111] An example of application for the production of a security element and in particular of a security thread to be applied to paper substrates or other materials is shown in figures 5 to 7.

[0112] In a preferred configuration, the security element and in particular the security thread is made by coupling two biodegradable supports, each consisting of a co-extruded film as described above and to which additional layers are added as shown by way of example in figures 5 and 6.

[0113] The A-side of the first and second biodegradable supports consisting of a co-extruded film 100 are, for instance, partially or completely coated with a metallization layer 110. The metallization layer can be applied by vacuum technologies or printing techniques.

[0114] In a preferred example, such a metallization layer is obtained by deposition of a layer of aluminium or chromium or copper or silicon. According to an embodiment, the thickness of said metallization layer is in the range from 50 to 500 nm.

[0115] Other embodiments may comprise the application of a coating of metals or metal oxides such as, for instance, but not limited to, ZnS, SiO2, TiO2or the coating of water-based or solvent-based systems, containing metal elements in dispersion. This metallization layer 110 can be roll-to-roll, i.e. continuous or contain graphic elements, logos or glyphs and is subsequently covered by layer 120 based on mixtures of epoxy polymers and / or melamine resins and / or urethane polymers, designed to ensure good adhesion of the underlying metal layer with the layer of glue for a material of an application support of said security element, such as, but not limited to, paper and whose substrate will be deposited after the coupling step of said two biodegradable supports, i.e. the co-extruded films that form the same.

[0116] As shown in figure 5, the B side of the first biodegradable support, i.e. the co-extruded film that constitutes it, is printed, for instance, with solvent- based systems such as esters, ketones and preferably ethyl acetate suitable for printing color graphic elements 130, and with solvent-based systems containing a dispersion of ferromagnetic elements 140, suitable for the reproduction of codes.

[0117] As shown in figure 6, the B side of the second biodegradable support, i.e. the co-extruded film that constitutes this support, is coated with thermo- adhesive glue 150 which is, for instance, based on epoxy and / or acrylic and / or polyurethane polymers and said thermo-adhesive glue can be activated at a temperature between 40°C and 90°C. The security element, i.e. the complete security thread, is made by hot coupling by heating the aforementioned layer of thermo-adhesive glue 150 of the B sides of the aforementioned biodegradable supports to the aforementioned activation temperature according to figures 5 and 6 as shown in figure 7.

[0118] Subsequently, in order to allow optimal adhesion to the paper or other types of supports, the external sides of the set of layers coupled together are coated with adhesives as indicated with 160.

[0119] For the production of security bands or threads, the material for the security element thus obtained is subsequently cut into threads and wound on special spools suitable for use in paper formation plants or other substrates to which the application of these security elements is envisaged.

[0120] At the end of its useful life, the paper product containing the security thread thus created is suitable for fragmentation (shredding) and subsequently pulping (repulping process) using the systems commonly used in the paper industry.

[0121] A preferred configuration is described in detail above.

[0122] In order to establish the characteristics of the biodegradable support, i.e. the co-extruded film from which it is made, a co-extruded film was made as described above.

[0123] Table I shows the characteristics related to the measurement according to ASTM D 882 of Young's modulus, yield strength (Tensile Stress) and related deformation (Tensile Strain) relative to a film co-extruded with a first mixture consisting of PLA and PBS in a weight ratio of 1:1, with the addition of a clay filler and BN at a concentration between 5 and 1 % by weight of the total and a second mixture consisting of PLA and PBS in a weight ratio of 3:7, with the addition of a BN filler at a concentration of 1% by weight of the total.

[0124] Table I

[0125] Table II shows the values of Young's modulus, yield strength (Tensile Stress) and related strain (Tensile Strain) for the material currently used for the production of security thread, i.e. PET. The measurements were also performed according to ASTM D 882.

[0126] Table II

[0127] The differences in terms of strength and elasticity between the values reported in tables I and II, being of the same order of magnitude, show that for the film co-extruded according to the present invention it is allowed to be used by adjusting the working parameters of the security thread production machines.

[0128] The thermal properties of the sample under investigation were examined by means of thermogravimetric analysis (TGA) and differential calorimetric scanning (DSC). In this way it was possible to identify the main thermal events (e.g. degradation temperature, glass transition temperature and melting temperature) .

[0129] The TGA curve is shown in Fig.8, and it is possible to observe that the sample has two degradation peaks around 346°C, relative to PLA, and around 373°C, relative to PBS.

[0130] The TGA curve was also performed on the reference PET with a thickness of 12 μm, as shown in Fig. 9. The other main thermal events of the biodegradable support were analyzed through DSC analysis as shown in Fig. 10. The glass transition temperature (55-60°C) and melting temperature (150°C) are consistent with the known properties of PLA. In order to further characterize the co-extruded film that forms the biodegradable support according to the present invention, transmittance and opacity measurements were performed on the samples of said biodegradable support with different thicknesses and on the reference sample consisting of PET, the results of which are reported in Table III.

[0131] Table III

[0132] Table III shows that the transmittance values of the co-extruded film are comparable to the reference sample (PET), while its opacity (haze), although higher, does not affect the functionality of the product .

[0133] In order to characterize the printability of the samples, wettability measurements were carried out on the two sides of the co-extruded film and compared with the values obtained with the reference sample whose results are shown in the graph in figure 11.

[0134] The above graph shows that the contact angle of the co-extruded film is in the range from 75° to 80°, in line with the values of the reference sample (PET).

[0135] In order to evaluate the compatibility of the mixtures used and the feasibility of the extrusion process, "melt flow index" measurements were carried out on each side of the co-extruded film and are reported in Table IV.

[0136] Table IV

[0137] The images acquired by scanning electron microscope (SEM) of Figure 4 C and D show an adequate interpenetration between the two layers, respectively formed by the mixtures for the first and second layer of the biodegradable support and indicated with mixture 1 and 2 in table IV, confirming the values reported in Table IV.

[0138] In order to get a more detailed idea of the thermal resistance of the materials in question, stress deflection tests were carried out (in particular "deflection temperature under load" tests). Fig. 12 shows the curves for PET, the co-extruded film without boron nitride (Bilayer) and the co-extruded film with 1% boron nitride (BilayerBN) respectively.

[0139] The trend of the curves shows how the materials in question have a different mechanical behaviour as the temperature increases. In particular, considering a reference temperature of 100°C, the PET material undergoes a deformation of 20.15 μm, the co-extruded film (bilayer) with 1% boron nitride of 808 μm and the co-extruded film (bilayer) without boron nitride of 3823 μm. The presence of a small percentage of boron nitride favours the thermal resistance of the co- extruded film, allowing the use of the co-extruded film without particular process problems.

[0140] In a further example of characterization, a security thread has been made by adding the following layers to the co-extruded film that constitutes a biodegradable layer according to the present invention: an aluminium metallization layer 110; layers of protective materials 120; ferromagnetic ink 140; thermo-adhesive glues in layers 150 and 160.

[0141] The resistance of the security thread made with the materials and processes covered by the present invention to substances was verified by immersion in the solutions shown in Table V for a residence time of 30 min.

[0142] Table V

Claims

CLAIMS1. A biodegradable support for security elements, said support consisting of a multi-component film comprising: a first layer (101) of said multi-component film which is composed of Polybutylsuccinate PBS in the range 40-60% by weight and Polylactic acid PLA in the range 60-40% by weight and a second layer (102) of said multi-component film which is composed of a predominant or greater part of polybutylsuccinate PBS, in particular in the range 60- 80% by weight and a part in a smaller quantity than the quantity of PBS, of polylactic acid PLA, in particular in the range 40-20% by weight.

2. The biodegradable support according to claim 1, wherein said first and second layers are made by co- extrusion.

3. The biodegradable support according to claims 1 or 2, wherein additives selected from the following list are added to said first and / or second layer: one or a combination of inorganic nucleating agents such as clays, silicon oxide, titanium oxide, talc and boron nitride; one or more organic nucleating agents such as N,N'—ethylene bis-stearamide (EBS) and D- and L-lactide stereo complexes (PDLA and PLLA).

4. The biodegradable support according to one or more of the preceding claims, wherein said biodegradable support can be associated with one or more additional functional layers of materials superimposed on each other and on one or both sides of said substrate said functional layers being selected from the following list: inks, oxides, metals, magneticmaterials, adhesives, protective materials or combinations thereof.

5. A security element comprising the biodegradable support in accordance with one or more of the preceding claims 1 to 4, which is a multi-layer structure with two opposite faces (A) facing outwards and wherein said security element comprises two of said biodegradable supports (100) said two biodegradable supports (100) being coupled together directly or by the interposition of one or more additional layers (130, 140, 150) of material along the faces of the corresponding second layer (102) of said first and second layers (101, 102) which constitute the biodegradable support .

6. The security element according to claim 5, wherein the outer face (A) of each first layer (101) of the biodegradable support opposite to face (B) of adhesion to the additional biodegradable support of said two biodegradable supports is coated, either completely or only for certain areas of said face (A) and with a predetermined distribution design, with a metallization layer (110).

7. The security element in accordance with claim 5 or 6, wherein an additional compatibilization layer is coupled to said metallization layer by an adhesive of an adhesion layer of a layer of paper to which said security element is intended to be coupled.

8. The security element according to one or more of the preceding claims 5 to 7, wherein one or more intermediate layers are provided between the faces (B) of mutual coupling of said two biodegradable supports (100).

9. The security element according to claim 8, wherein those intermediate layers consist of one ormore layers applied by printing on the face (B) facing inwards of the second layer (102) forming a first of the two biodegradable supports coupled together and facing the second of those two biodegradable supports (100), consisting of one or more layers applied by printing and comprising at least one layer (130) consisting of graphic elements, optionally in colour, and / or at least one layer (140) comprising ferromagnetic elements which are distributed according to designs reproducing pre-established codes, while face (B) of the second biodegradable support facing said first biodegradable support is coupled to a layer of thermo-adhesive glue (150).

10. The security element according to one or more of the preceding claims 5 to 9, characterised by the fact that the security element may consist of two intermediate elements each comprising one of the two biodegradable supports (100) coupled to one or more additional layers, two intermediate elements being laminated together to form the complete security element, being:- one of the two intermediate elements consisting of the first biodegradable support (100) with the metallization layer (110) applied to the outer face (A) of the first layer (101) on the entire surface or part of said surface of said face (A) and / or the additional compatibility layer (120) with the adhesives for the adhesion of the paper or other material of the product to which the security element is intended to be applied and with the face (B) of the second layer (102) of said two co-extruded layers (101, 102) forming the biodegradable support (100), one or more layers applied by printing and comprising at least one layer (130)consisting of graphic elements, optionally in colour, and / or at least one layer (140) comprising ferromagnetic elements which are distributed according to designs reproducing pre-established codes;- the other of the two intermediate elements, consisting of said second biodegradable support, has on the outer face (A) of the first layer (101) of the two co-extruded layers (101, 102) which constitute said biodegradable support (100), a metallization layer (110) on the entire surface or part of said surface of said face (A) and / or the additional compatibility layer (120) with the adhesives for the adhesion of the paper or other material of the product to which the security element is intended to be applied and on the face (B) of the second biodegradable support facing said first biodegradable support a layer (150) of thermo-adhesive glue for the adhesion of said second biodegradable support to said first biodegradable support the two faces (B) of the two biodegradable supports which are facing each other.

11. The security element according to one or more of the preceding claims 5 to 10, wherein the metallization layer of the outer face (A) of the biodegradable supports may consist alternatively of one of the materials listed below: aluminium, chromium, copper, silicon, metal oxides such as ZnS, SiO2, TiO2.

12. The security element according to one or more of the preceding claims, wherein said metallization layer (110) has a thickness that is in the range 50 to 500 nm.

13. The security element according to one or more of the preceding claims 5 to 12, wherein the material for the production of said thermo-adhesive layer (150)of mutual coupling of the two biodegradable supports (100) consists of a thermo-adhesive glue based on epoxy and / or acrylic and / or polyurethane polymers, preferably which can be activated at a temperature between 40°C and 90°C.

14. The security element according to one or more of the preceding claims 5 to 13, wherein the outer face (A) of at least one or more of the biodegradable supports (100) is additionally coated with a layer (120) of adhesives, in particular based on polyvinyl acetate (PVA) and / or polyvinyl chloride (PVC) and / or acrylates, or the like.

15. A method for making a biodegradable support according to one or more of claims 1 to 4, said method comprising: a first production step of granules, or pellets, consisting of mixtures of the material components predetermined for said first and second layers (101, 102) of the biodegradable support (100), in which step said granules or pellets for said first and second layers (101, 102) are produced separately for each of said two layers (101, 102); a second production step by co-extrusion from said granules or pellets of said first and second layers (101, 102) in a coupled condition.

16. The method according to claim 15, wherein the production step of the granules or pellets consisting of mixtures of material components respectively for said first and second layers (101, 102) of the biodegradable support (100) involves the following steps:mixing of those components of the mixture of materials for the first layer (101) in an extruder (2) and for the second layer in a different extruder (2); separated extrusion of said mixture of materials for the mixture of materials of said first and second layer respectively (101, 102) in the form of a continuous thread cooled in the range 2 to 6°C before cutting said threads into granules or pellets; pellets formation from each of those continuous threads, consisting respectively of the mixture of materials for the first layer and the second layer (101, 102) by cutting said thread into short segments.

17. The method in accordance with one or more of the preceding claims 15 to 16, wherein the material components intended for the formation of the pellets for the manufacture of said first layer (101) are fed to the extruder in the following quantities: PBS granules in the range 40 to 60% by weight, PLA granules in the range 60 to 40% by weight, optionally powder fillers consisting of a combination of inorganic nucleating agents such as clays, silicon oxide, titanium oxide, talc and boron nitride, one or more organic nucleating agents such as N,N'-ethylene bis- stearamide (EBS) and D— and L- lactide stereo complexes (PDLA and PLLA) in the range 1 to 6% by weight, while the material components provided for the formation of pellets for the manufacture of said second layer are fed to the extruder in the following quantities: PBS granules in the range 60 to 80% by weight and PLA granules in the range 40 to 20% by weight and optionally powder fillers consisting of a combination of inorganic nucleating agents such as clays, silicon oxide, titanium oxide, talc and boron nitride, one or moreorganic nucleating agents such as N,N'-ethylene bis- stearamide (EBS) and D— and L-lactide stereo complexes (PDLA and PLLA) in the range 1 to 6% by weight .

18. The method according to one or more of the preceding claims 15 to 17, wherein the extruder is a screw extruder, preferably twin-screw and the rotational speed is selected in the range 20 to 50 rpm, while the extruder cylinder is heated to a temperature between 180° and 250°C.

19. The method according to one or more of the preceding claims 15 to 18, wherein the granules, i.e. pellets obtained from the cutting pitch of said threads, have a length in the range 1 to 5 mm, while the diameter of the threads and therefore of the granules is in the range 1 to 5 mm.

20. The method according to one or more of the preceding claims 15 to 19, wherein said co-extrusion step of the biodegradable support comprises the following steps: feeding the granules or pellets composed respectively of the mixture of material components for said first and second layers to a separate extruder, optionally single-screw, and the simultaneous extrusion of these two layers from the respective mixture of material components fed by the corresponding extruder to a corresponding drawing mouth of a co-extrusion die.

21. The method according to claim 20, wherein the co-extruded films have an overall thickness in the range 8 to 20 μm.

22. The method according to one or more of the preceding claims 15 to 21, wherein the heating temperature of the extruder cylinders is in the range 180 to 250°C.

23. The method according to one or more of the preceding claims 15 to 22, wherein the cooling temperature is in the range 40 to 70°C.

24. The method for the manufacture of a security element according to one or more of the preceding claims 5 to 14, said method involving the coupling of a first support (100) to a second support (100), said biodegradable supports being coupled to each other by chemical / physical adhesion with the faces (B) consisting of the respective second layer (102) facing each other and with the interposition of one or more additional layers between them (130, 140, 150) and said first and second biodegradable support (100) providing for the coating with one or more additional layers of the faces (A) of the same which are made up of the external sides (101).

25. The method according to claim 24, wherein the following steps are provided: the application of a metallization layer (110) to the entire surface or part of the same external face (A) of each of said first and second biodegradable supports (100), whose face (A) is the opposite face (B) of reciprocal adhesion, direct or indirect, of said two biodegradable supports (100); a subsequent step of application of a compatibility or adhesion layer (120), of said metallization layer to a layer of adhesive for paper or for other materials for the application of said security element; a step of printing on the face (B) of the first of the two biodegradable supports of graphic elements (130), optionally in colour, said graphic elements presenting one or more pre-established drawings;a further step of application of ferromagnetic elements (140) according to one or more pre-established distribution drawings for the constitution of codes on said layer (130) of graphic elements; a step of application on face (B) of the second of said two biodegradable supports which is facing said first biodegradable support of a layer (150) of thermo- adhesive glue for adhesion to face (B) of said first biodegradable support provided with the layer (130) consisting of said graphic elements applied by printing and / or the layer (140) consisting of said ferromagnetic elements; the hot coupling (150) of said first biodegradable support with the above-mentioned additional additive layers (130, 140) to said second biodegradable support with the aforementioned additive layers (150) and with said first support and said second support in a position facing upwards with the faces (B) facing each other.

26. The method according to one or more of the preceding claims, wherein a step is provided to create the full or partial metallisation layer (110) of the surface of the outer face (A) of the two biodegradable supports by deposition of at least one layer consisting of one of the following materials: aluminium, chromium, copper, silicon or a combination thereof, or by coating with metals or oxides selected from the group comprising ZnS, SiO2, TiO2or by coating with water-based or solvent-based systems, containing metal elements in dispersion .

27. The method according to one or more of the preceding claims 24 to 26, wherein said compatibilization layer (120) consists of a materialbased on mixtures of epoxy polymers and / or melamine resins and / or urethane polymers.

28. The method according to one or more of the preceding claims, wherein the thermo-adhesive layer (150) consists of a material based on epoxy and / or acrylic and / or polyurethane polymers, which can be activated at a temperature between 40°C and 90°C.

29. The method according to one or more of the previous claims 24 to 29, wherein the security elements are in the form of threads or bands, said security element being subjected to a cutting step in a plurality of bands or threads having a predetermined thickness and a predetermined width, these bands or threads being wound in coils or spools.

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