Security substrate for banknotes, and production method

Abstract

In the method according to the invention, – in a preparation process, secondary fibrous materials are obtained from discarded banknotes and / or banknote waste by means of a dry defibration process, and – the obtained secondary fibrous materials are used at least partly together with primary fibrous materials in a paper production process in order to form the paper layer of the security substrate. The invention also relates to a security substrate (310) for a banknote, having at least one paper layer (320; 332; 15 334) formed from a fibrous material.

Description

[0001] Security substrate for banknotes and manufacturing processes

[0002] The invention relates to a method for producing a security substrate for banknotes, in which at least one paper layer of the security substrate is produced from a fiber material. The invention also relates to a security substrate for a banknote having at least one paper layer obtainable by such a method.

[0003] With almost 600 billion banknotes in circulation, cash is currently the world's most widely used means of payment. Against this backdrop, questions about the environmental friendliness of cash use and ways to increase the sustainability of banknotes are becoming increasingly important.

[0004] One promising way to increase the sustainability of banknotes is to use recycled raw materials in banknote production. However, so-called "end-of-life" banknotes cannot currently be used for banknote paper production. At the end of their life cycle, banknotes are destroyed using cutting processes (shredding) and cut into small pieces. These are unsuitable for the production of new banknote paper for several reasons. For example, banknotes are often heavily soiled, and the fibers of the banknote shreds are not in the individual form required for paper production. In addition to the soiling, the banknote shreds are also inherently contaminated by printing ink and security features typical of banknotes. Finally, banknote shreds exhibit high wet strength and physical stability, which make their use in paper production very difficult.Based on this, the invention is based on the object of improving the sustainability of banknotes and other security documents, and in particular of enabling the use of used banknotes in the paper production of paper layers of a security substrate.

[0005] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0006] The invention provides a method for producing a security substrate for banknotes, in which at least one paper layer of the security substrate is produced from a fiber material. In a processing process, secondary fibers are obtained from used banknotes and / or banknote waste, such as edge trimmings, by dry fiberization. The obtained secondary fibers are then used proportionally together with primary fibers in paper production to form the paper layer of the security substrate.

[0007] The secondary fibers preferably constitute up to 70%, preferably between 5% and 50%, and particularly preferably between 5% and 30% of the fiber material used in paper production. The percentages of secondary fibers are based on weight percent.

[0008] The primary fibers preferably comprise cotton fibers, but can alternatively or additionally also comprise alternative fibers, particularly sisal, hemp, flax, or cellulose fibers. In an advantageous process, the used banknotes and / or banknote waste are pre-shredded into shreds during the processing process prior to dry fiberization. Alternatively, complete banknotes can also be fed directly into the dry fiberization without pre-shredding.

[0009] Preferably, the used banknotes, banknote waste, or pre-shredded scraps are dry-shredded in a shredding unit with a mechanical air-flow impact mill. A mechanical air-flow impact mill is preferably used in which a plurality of grinding elements rotate on one or more levels around a vertical axis of rotation. The material to be shredded is advantageously fed centrally into the grinding element, and the material to be shredded is then centrifugally moved between the rotor and stator.

[0010] During the preparation process, the dry-fibered paper material is advantageously further broken down into individual fibers in a flaker. Fluff is generally referred to as an agglomeration of fibers. Since the fibers contained in fluff are not available for paper production, the quality of the dry-fibered end product is determined not only by the length and integrity of the individual fibers, but also by the remaining fluff content.

[0011] The dry-fibered paper material is cleaned and freed from foreign substances during the processing process.

[0012] In the processing process, the used banknotes and / or banknote waste are advantageously split into secondary fiber materials with individual fibers whose length is more than 70%, in particular more than 85%, more than 90% or even more than 95% of the original length.

[0013] The proportion of individual fibres in the secondary fibres obtained by the processing process is advantageously more than 80%, in particular more than 85%, more than 90% or even more than 95%.

[0014] In a preferred embodiment, the process forms a paper layer having a basis weight of 30 g / m 2 or more, preferably 65 - 120 g / m 2 and particularly preferably from 85-100 g / m 2 Furthermore, the paper layer advantageously has one or more, preferably all of the following properties: a tear length of at least 6000 m, a longitudinal breaking strength of 5 - 8.2 kN / m, a transverse breaking strength of 2.0 - 4 kN / m, a wet strength of at least 35%, a double fold number of at least 3500, a longitudinal tear resistance of 670 - 785 mN, a transverse tear resistance of 770 - 900 mN, and a bursting strength of 320 - 375 kPa.

[0015] As a security substrate, the method preferably produces a paper substrate made of one or more paper layers or a composite substrate made of at least one paper layer and at least one plastic layer.

[0016] The invention also includes a security substrate for a banknote comprising at least one paper layer formed from a fiber material, obtainable by a method of the type mentioned above. The paper layer has a basis weight of 30 g / m 2 or more, preferably 65 -120 g / m 2 and particularly preferably from 85-100 g / m 2and furthermore has one or more, preferably all of the following properties: a tear length of at least 6000 m, a longitudinal breaking strength of 5 - 8.2 kN / m, a transverse breaking strength of 2.0 - 4 kN / m, a wet strength of at least 35%, a double fold number of at least 3500, a longitudinal tear resistance of 670 - 785 mN, a transverse tear resistance of 770 - 900 mN, and a bursting strength of 320 - 375 kPa.

[0017] The proportional use of used banknotes in the production of banknote paper significantly improves the sustainability of the cash cycle.

[0018] The reuse of used banknotes also provides a cost advantage in banknote destruction. Currently, banknotes must be destroyed at the end of their life cycle, which involves considerable effort and strict security requirements to prevent unauthorized access and to guarantee that the destroyed banknotes are irretrievably destroyed. The used banknotes used in the present invention are not only securely destroyed by shredding into individual fibers, but also form a valuable secondary raw material for the production of new banknote paper, instead of becoming waste that would otherwise have to be disposed of.

[0019] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0020] Shown are: Fig. 1 a diagram to explain a method according to the invention, and

[0021] Fig. 2 in (a) schematically shows a banknote with a security substrate according to the invention in plan view, and in (b) to (d) various advantageous embodiments of the security substrate of (a) in cross section.

[0022] In order to improve the sustainability of the cash cycle, end-of-life banknotes are to be partially reused in the paper production process for the manufacture of banknote paper.

[0023] According to the invention, in a novel processing process, secondary fibers 20 are obtained from discarded banknotes 10 by dry fiberization. These secondary fibers can be used in paper production in proportion together with primary fibers and optionally other additives. For the processing of discarded banknotes 10, the procedure can be as follows, for example, with reference to Fig. 1.

[0024] First, used banknotes 10 are pre-shredded in a pre-shredder 100, for example to a size of approximately 2 x 2 cm 2 or less. Alternatively, the banknotes can be fed directly into the dry shredding process without pre-shredding.

[0025] The resulting banknote shreds 12 are then dry-fibered in a shredding unit 110. For this purpose, the shredding unit 110 advantageously comprises a mechanical air-flow fine impact mill 112 with a peripheral grinding track, in which grinding elements rotate on several levels about a vertical rotation axis and in which the banknote shreds 12 are moved from bottom to top by an air stream against the force of gravity.

[0026] The shredding of the banknote shreds 12 occurs primarily through collisions between the shreds and the grinding elements, the impact surfaces, and the apparatus walls caused by the turbulent air currents. The impact stress, together with a compressive-shear stress in the grinding gap and a stress in the turbulent air flow, leads to the shreds becoming defibrated. It has been shown that with such an air-flow fine impact mill, even high-strength paper products, such as the shreds 12 of discarded banknotes 10, can be gently shredded into almost uncut individual fibers. Further details and advantageous embodiments of a suitable air-flow fine impact mill 112 can be found in the document DE 102015223333 A1, the disclosure content of which is incorporated into the present application in this respect.In the next process step, the dry-fibered paper material is briefly suspended in a 120 pulper and dissolved in water to a point where it can be pumped. This can be done in a continuous or discontinuous pulper in the consistency range of up to 8% (low consistency range) or in the consistency range of 8-15% (medium consistency range). Deinking chemicals are added to the paper suspension in the 120 pulper, in particular NaOH to adjust a pH value of 10-11, hydrogen peroxide to assist ink removal and prevent alkali graying, and water glass (sodium silicate) as a solvent for printing inks and a stabilizer for oxidative bleaching with peroxide. Surfactants such as alkylbenzenesulfonates or alkyl sulfates, as well as complexing agents such as EDTA (ethylenediaminetetraacetic acid) or DTPA (diethylenetriaminepentaacetic acid), can also be used.

[0027] Optionally, coarse cleaning devices 130 can be connected directly downstream in order to separate coarse flat components such as PET films and the like from the paper material.

[0028] In a deflaker 140, the dry-fibered paper material is further separated into individual fibers. The proportion of flakes, i.e., fiber agglomerates, represents an important quality criterion for the ultimately obtained secondary fiber stock. Perforated disc, strip, labyrinth, or toothed disc deflakers can be used as deflakers 140. The acceleration and deceleration of the stock suspension creates impact forces that further break down the flakes into individual fibers.

[0029] In order to remove foreign particles such as film parts or other surface contaminants, the suspension is cleaned using pressure sorting 150, for example perforated baskets or slotted baskets.

[0030] Subsequently, the printing inks are separated from the fibers and removed from the pulp in a flotation cell 160. The pre-cleaned suspension is simultaneously introduced into the flotation cell 160 with compressed air. The hydrophobic printing ink foam attaches to the air bubbles and is drawn to the surface. Polyelectrolytes are advantageously used as flocculants. The resulting foam is removed from the surface of the flotation cell 160 with a scoop or suction device 162. After flotation, the cleaned pulp is neutralized and thickened and conveyed to a bleaching bath 170 for further treatment.

[0031] In the bleaching bath 170, the thickened fiber stock is oxidatively bleached using hydrogen peroxide (H2O2) / sodium dithionite (Na2S2O4) or other suitable bleaching processes.

[0032] The secondary fiber 20 obtained as the final product after bleaching is then used proportionally together with primary fiber 30 for the production of banknote paper 200. Blends with cotton noils or alternative fibers such as sisal, hemp, flax, and cellulose are also possible.

[0033] The secondary fiber 20 can also be used in the production of impregnated or precoated banknote paper. It can also be advantageously used in the production of paper layers for hybrid or composite papers.

[0034] To maintain good mechanical properties of the resulting paper layers, the proportion of secondary fiber in the fiber material used for paper production should not exceed 50%. Particularly good results are achieved with a fiber content between 5% and 30%.

[0035] Figure 2 shows (a) a banknote 300 with a security substrate 310. Figures 2(b) to 2(d) show the security substrate 310 in various configurations of the banknote 300 in cross-section along line BB of Figure 2(a). In the configuration of Figure 2(b), the security substrate is a pure paper substrate 320. The banknote paper of the paper substrate 320 is manufactured according to the method described above from a fiber material comprising approximately 25% secondary fiber obtained from discarded banknotes by dry defibration.

[0036] The paper substrate 320 has a basis weight of 30 g / m 2 or more, preferably 65 -120 g / m 2 and particularly preferably from 85-100 g / m 2and has the following properties, particularly in the latter area weight range: a tear length of at least 6000 m, a longitudinal breaking strength of 5 - 8.2 kN / m, a transverse breaking strength of 2.0 - 4 kN / m, a wet strength of at least 35%, a double fold number of at least 3500, a longitudinal tear resistance of 670 - 785 mN, a transverse tear resistance of 770 - 900 mN, and a bursting strength of 320 - 375 kPa.

[0037] In the embodiment of Fig. 2(c), the security substrate is a composite substrate 330 having an inner paper layer 332 and two outer plastic layers 334. The banknote paper of the inner paper layer 332 is produced according to the method described above from a fiber material which comprises 15% to 25% of secondary fibers obtained by dry defibration from discarded banknotes and which also has the advantageous properties mentioned above.

[0038] In the embodiment of Fig. 2(d), the security substrate is a composite substrate 340 with an inner plastic layer 342 and two outer paper layers 344. The banknote paper of the outer paper layers 344 is produced according to the method described above from a fiber material which comprises approximately 15% of secondary fiber materials obtained by dry defibration from discarded banknotes and which also have the advantageous properties mentioned above.

Claims

Patent claims 1. A method for producing a security substrate for banknotes, in which at least one paper layer of the security substrate is produced from a fiber material, characterized in that secondary fiber materials are obtained from used banknotes and / or banknote waste in a processing process by dry defibration, and the secondary fiber materials obtained are used proportionally together with primary fiber materials in the paper production in order to form the paper layer of the security substrate.

2. Process according to claim 1, characterized in that the secondary fiber materials constitute a proportion of up to 70%, preferably a proportion of between 5% and 50%, and particularly preferably between 5% and 30% of the fiber material used in paper production.

3. Process according to claim 1 or 2, characterized in that the primary fibers comprise cotton fibers and / or alternative fibers, in particular sisal, hemp, flax or cellulose fibers.

4. Method according to at least one of claims 1 to 3, characterized in that the used banknotes and / or banknote waste are pre-shredded into shreds in the processing process before the dry defibration or are fed directly into the dry defibration without pre-shredding.

5. Method according to at least one of claims 1 to 4, characterized in that the used banknotes, the banknote waste or the pre-shredded shreds are dry-fibered in a fiberizing unit with a mechanical airflow fine impact mill, preferably in a fiberizing unit with a mechanical airflow fine impact mill, in which a plurality of grinding elements on two or more levels rotate about a vertical axis of rotation and the ground material is moved from bottom to top by an air flow against the force of gravity.

6. Method according to at least one of claims 1 to 5, characterized in that the dry-fibered paper material is further broken down into individual fibers in a flaker in the processing process.

7. Method according to at least one of claims 1 to 6, characterized in that the dry-fibered paper material is cleaned and freed from foreign substances in the processing process.

8. Method according to at least one of claims 1 to 7, characterized in that the used banknotes and / or the banknote waste are split in the processing process into secondary fiber materials with individual fibers whose length is more than 70%, in particular more than 85%, more than 90% or even more than 95% of the initial length.

9. Method according to at least one of claims 1 to 8, characterized in that the proportion of individual fibers in the secondary fiber materials obtained by the processing process is more than 80%, in particular more than 85%, more than 90% or even more than 95%.

10. Method according to at least one of claims 1 to 9, characterized in that a paper layer is formed which has a basis weight of 30 g / m 2 or more, preferably 65 -120 g / m 2 and particularly preferably from 85-100 g / m 2 and furthermore has one or more, preferably all of the following properties: a tear length of at least 6000 m, a longitudinal breaking strength of 5 - 8.2 kN / m, a transverse breaking strength of 2.0 - 4 kN / m, a wet strength of at least 35%, a double fold number of at least 3500, a longitudinal tear resistance of 670 - 785 mN, a transverse tear resistance of 770 - 900 mN, and a burst strength of 320 - 375 kPa.

11. Method according to at least one of claims 1 to 10, characterized in that a paper substrate made of one or more paper layers or a composite substrate made of at least one paper layer and at least one plastic layer is produced as the security substrate.

12. Security substrate for a banknote with at least one paper layer formed from a fiber material, obtainable by the process according to one of claims 1 to 10, wherein the paper layer has a basis weight of 30 g / m 2 or more, preferably 65 -120 g / m 2 and particularly preferably from 85-100 g / m 2 and furthermore has one or more, preferably all of the following properties: a tear length of at least 6000 m, a longitudinal breaking strength of 5 - 8.2 kN / m, a transverse breaking strength of 2.0 - 4 kN / m, a wet strength of at least 35%, a double fold number of at least 3500, a longitudinal tear resistance of 670 - 785 mN, a transverse tear resistance of 770 - 900 mN, and a burst strength of 320 - 375 kPa.

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