A magnetic anti-counterfeiting label and a preparation method thereof

Abstract

This invention discloses a magnetic anti-counterfeiting label and its preparation method, comprising: (1) dispersing cobalt nanorods in a dispersion solvent to obtain a cobalt nanorod dispersion; (2) dispersing the cobalt nanorod dispersion in oleic acid to obtain a cobalt nanorod-oleic acid dispersion; (3) dropping the cobalt nanorod-oleic acid dispersion onto the surface of deionized water to spread and form a magnetic film; after the magnetic film stabilizes, transferring the magnetic film to the surface of a substrate and drying it under an inert atmosphere to obtain a magnetic functional layer; (4) coating a protective layer on the surface of the magnetic functional layer and die-cutting it to obtain a magnetic anti-counterfeiting label. This invention modifies the surface of cobalt nanorods with oleic acid and solves the agglomeration problem by "oleic acid solution-water surface spreading". The cobalt nanorods spread on the water surface to form a magnetic film with a random structure. The random magnetic structure prepared by this invention is non-replicable, and the process is simple, low-cost, and suitable for large-scale production. It can be widely used in commodity anti-counterfeiting traceability and document security marking.

Description

Technical Field

[0001] This invention relates to the fields of magnetic material application and anti-counterfeiting technology, and in particular to a magnetic anti-counterfeiting label and its preparation method. Background Technology

[0002] Magnetic anti-counterfeiting labels, with their unique scanning method based on magnetic field recognition devices, have built a unique anti-counterfeiting identification system. This system not only ensures the accuracy of anti-counterfeiting verification but also enhances the reliability of anti-counterfeiting based on their specific technical characteristics. As a result, they have been widely used in the field of anti-counterfeiting.

[0003] Magnetic materials can respond to changes in external magnetic fields, exhibiting magnetization and demagnetization. This characteristic gives magnetic technology a unique advantage in the field of anti-counterfeiting. Magnetization refers to the process by which the magnetic domains within a magnetic material align uniformly under the influence of an external magnetic field, thus generating magnetism. Demagnetization, on the other hand, occurs when the external magnetic field disappears, causing the magnetic domains to become disordered, and the magnetism to weaken or disappear. These properties allow magnetic materials to be used to store information, which can then be read using specific devices.

[0004] Common methods for preparing magnetic anti-counterfeiting labels include direct printing, material lamination, physical embedding, and advanced microfabrication. Magnetic fiber / film composite methods involve pre-forming magnetic materials into fibers or films and then laminating them onto a substrate, enabling linear detection features and dynamic effects. Sandwich structures / transfer methods are commonly used for high-end documents such as banknotes, including security thread embedding, but these processes are complex. Micro-magnetic code technology represents the pinnacle of magnetic anti-counterfeiting, using semiconductor processes to create miniature magnetic patterns, but this method is costly.

[0005] The direct printing method involves mixing fine powder of magnetic materials (such as ferrite or reduced iron powder) with binders (resins, oil-based / water-based solvents) and additives (dispersants, stabilizers). This mixture is then ground to create a uniform and stable magnetic ink. Finally, screen printing, gravure printing, or offset printing is used to print the magnetic ink onto specific locations on a substrate, forming the designed magnetic pattern or code. For example, Chinese patent document CN 116606569 B discloses a magnetic anti-counterfeiting ink composition comprising at least the following components by weight percentage: core-shell magnetic material 0.1–40 wt%; binder 1–95 wt%; pigment 0–30 wt%; and additives 0–70 wt%, with a percentage greater than 0. This magnetic anti-counterfeiting ink can be applied to coatings or ink-coded anti-counterfeiting systems.

[0006] With economic development, there is an increasing demand for a simple, convenient, and low-cost method for preparing anti-counterfeiting labels. Cobalt nanorods, as a highly promising magnetic anti-counterfeiting material, possess outstanding characteristics such as high magnetic saturation strength and strong magnetic response signal, which can significantly improve the anti-counterfeiting sensitivity and recognition accuracy of labels, perfectly meeting the core requirements of high-end anti-counterfeiting. However, the strong magnetism of cobalt nanorods easily leads to magnetic dipole agglomeration in common solvents (such as tetrahydrofuran and n-hexane), forming aggregates of uneven size, which cannot be directly used for the large-scale preparation of labels.

[0007] Therefore, how to solve the aggregation problem of cobalt nanorods, and at the same time utilize their surface properties to achieve orderly dispersion and form a functional layer with a unique anti-counterfeiting structure, has become a key technical bottleneck to unlock the large-scale application of cobalt nanorods in magnetic anti-counterfeiting labels, and also provides a core direction for research and development in related fields. Summary of the Invention

[0008] This invention provides a magnetic anti-counterfeiting label and its preparation method. It offers a novel method for preparing magnetic anti-counterfeiting labels that is simple to operate and low in cost, and solves the problem of agglomeration of ferromagnetic materials with strong magnetism.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing a magnetic anti-counterfeiting label includes the following steps:

[0011] (1) Cobalt nanorods are dispersed in a dispersion solvent to obtain a cobalt nanorod dispersion;

[0012] (2) The cobalt nanorod dispersion was dispersed in oleic acid to obtain a cobalt nanorod-oleic acid dispersion;

[0013] (3) Cobalt nanorod-oleic acid dispersion was dropped onto the surface of deionized water and spread to form a magnetic film; after the magnetic film was stabilized, the magnetic film was transferred to the surface of the substrate and dried under an inert atmosphere to obtain a magnetic functional layer.

[0014] (4) A transparent protective layer is coated on the surface of the magnetic functional layer, and the magnetic anti-counterfeiting label is obtained after die cutting.

[0015] This invention modifies the surface of cobalt nanorods with oleic acid, utilizing the hydrophobic properties of the oleic acid ligands on the cobalt nanorod surface. An "oleic acid solution-water surface spreading" process solves the aggregation problem, allowing the cobalt nanorods to spread on a water surface to form a randomly structured magnetic thin film. This film is then transferred to a substrate surface, dried, and finally coated with a protective layer and laminated to obtain a magnetic anti-counterfeiting label. The randomly structured magnetic structure prepared by this invention is non-replicable, and the process is simple, low-cost, and suitable for large-scale production. It can be widely used in product anti-counterfeiting traceability and document security marking.

[0016] The magnetic anti-counterfeiting label of the present invention has magnetic features and its pattern shape is unique, which cannot be accurately copied by manual means, thus fundamentally improving the anti-counterfeiting level of the label and effectively resisting counterfeiting.

[0017] Cobalt nanorods possess high magnetic saturation strength and strong magnetic response signals, resulting in highly sensitive magnetic anti-counterfeiting labels. Cobalt nanorods can be commercially available products or prepared in-house.

[0018] Preferably, the method for preparing the cobalt nanorods includes:

[0019] Under inert gas protection, cobalt source, ruthenium source and base are added to solvent and stirred; then heated to 100-200℃ at a rate of 1-5℃ / min and held for 1-15 min; after cooling to below 80℃, black powder is collected with a magnet, washed and cobalt nanorods are obtained, and the cobalt nanorods are dispersed in dispersion solvent.

[0020] The cobalt source is cobalt laurate, the ruthenium source is ruthenium trichloride, the alkali is sodium hydroxide, and the dispersing solvent is tetrahydrofuran and / or n-hexane.

[0021] Preferably, the mass ratio of cobalt source to ruthenium source is 67-71:1.

[0022] Preferably, during the heating process, the reaction solution is stirred at a speed of 300-600 r / min.

[0023] In step (1), the magnetism, particle size and morphology of cobalt nanorods can be changed by adjusting the heating rate, heating temperature and holding time, so as to generate more unreplicable magnetic patterns.

[0024] Preferredly, heat to 150-170℃ at a rate of 1-5℃ / min and hold for 5-12 min.

[0025] Preferably, in step (1), the concentration of the cobalt nanorod dispersion is 0.1-0.2 mol / L.

[0026] Preferably, in step (2), the volume ratio of cobalt nanorod dispersion to oleic acid is 1:3-7.

[0027] In a cobalt nanorod-oleic acid dispersion, if the concentration of cobalt nanorods is too high, the distance between the cobalt nanorods is too close, and the magnetic attraction between them is too strong, which makes it difficult for the cobalt nanorods to disperse after being dropped onto the water surface. If the concentration of cobalt nanorods is too low, the distance between the cobalt nanorods is too far, and the magnetic attraction between them is too weak, which makes it difficult for the cobalt nanorods to form a non-replicable pattern after being dropped onto the water surface.

[0028] Preferably, the aspect ratio of the cobalt nanorods is 1.5-20:1.

[0029] In step (3), the spreading container can be any volume of vessel, and before spreading, the vessel should be placed on a horizontal experimental platform and left to stand for 10-15 minutes to ensure that there are no air bubbles on the water surface.

[0030] Preferably, in step (3), the volume of the oleic acid dispersion of cobalt nanorods added per square centimeter of deionized water surface is 5-10 μL.

[0031] If too much liquid is added, a large, dense film will form on the water surface, preventing the formation of a unique, unreproducible pattern. If too little liquid is added, the density of the unique, unreproducible pattern will be low, or no unique, unreproducible pattern may even be formed. The substrate is a plastic film; the thickness of the plastic film is 50-100 μm.

[0032] Furthermore, the substrate is a PET (polyethylene terephthalate) film.

[0033] Step (4) includes: using 3D printing technology to coat the surface of the magnetic functional layer with a light-curing resin that has transparent and flexible properties, and irradiating it with an ultraviolet lamp for 1-10 minutes to form a protective layer.

[0034] The photocurable resin is a commercially available photocurable resin with transparent and flexible properties.

[0035] Preferably, the thickness of the protective layer is 5-50 μm.

[0036] Preferably, the other side of the substrate is laminated with an adhesive layer, which can be adhered to the surface of a specific object.

[0037] The present invention also provides a magnetic anti-counterfeiting label, comprising a substrate and a magnetic functional layer and a protective layer sequentially attached to the surface of the substrate, which is prepared by the above-described preparation method.

[0038] In the magnetic functional layer of the magnetic anti-counterfeiting label of the present invention, cobalt nanorods are randomly distributed, and this pattern is random and unreplicable. Coating the surface of the magnetic functional layer with a protective layer makes the label wear-resistant.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The preparation method of the present invention can effectively solve the problem of magnetic material agglomeration and has excellent dispersibility. Cobalt nanorods naturally form randomly distributed magnetic structures during the spreading process on the water surface. The structure is affected by various random factors such as environmental conditions and intermolecular forces during spreading. Its microstructure and magnetic distribution are unique and cannot be accurately replicated by artificial means, which fundamentally improves the anti-counterfeiting level of the label and can effectively resist counterfeiting.

[0041] (2) The preparation process of the present invention is simple and low cost. The entire preparation process does not require complex equipment and precise control conditions. It can be completed through simple steps such as solution dispersion, water surface spreading, and transfer drying. Moreover, the cobalt nanorods used can be commercially available products or made by simple processes. The raw material cost is low, which lowers the threshold for large-scale production and is suitable for large-scale industrial applications.

[0042] (3) The magnetic anti-counterfeiting label of the present invention has wide applicability and flexible application scenarios. The substrate is made of plastic film such as PET, which has good flexibility and adaptability and can be made into different shapes and sizes according to actual needs; and the other side of the substrate can be laminated with an adhesive layer, which is convenient to stick on the surface of various commodities, certificates and other objects, and is suitable for various fields such as anti-counterfeiting traceability of commodities and security marking of certificates. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of the magnetic anti-counterfeiting label of the present invention;

[0044] Figure 2 This is a physical image of the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 1;

[0045] Figure 3 This is a schematic diagram of the random distribution pattern of the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 1;

[0046] Figure 4 This is a hysteresis loop diagram of the magnetic anti-counterfeiting label in Example 1;

[0047] Figure 5 These are transmission electron microscope images of the cobalt nanorods in Example 1;

[0048] Figure 6 This is a physical image of the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 2;

[0049] Figure 7 This is a schematic diagram of the random distribution pattern of the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 2. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0051] The magnetic anti-counterfeiting label structure of the present invention is as follows: Figure 1 As shown, it includes a PET substrate 1, a magnetic functional layer 2 and a protective layer 3 sequentially attached to the surface of the PET substrate, and an adhesive layer 4 attached to the other surface of the PET substrate 1.

[0052] Example 1

[0053] This embodiment provides a method for preparing a magnetic anti-counterfeiting label. The method uses long rod-shaped cobalt nanorods as the magnetic component and an 8μm thick photocurable resin as the protective layer. Specifically, it includes the following steps:

[0054] (1) Preparation of cobalt nanorods: Under nitrogen protection, 2.73 g of cobalt laurate, 0.039 g of ruthenium trichloride and 0.225 g of sodium hydroxide were added to 75 mL of 1,4-butanediol and mechanically stirred at 300 r / min for 15 min until the raw materials were completely dissolved. Then, the mixture was heated to 150 ℃ at a rate of 5 ℃ / min and kept at that temperature for 12 min. After cooling to below 80 ℃, the black powder was magnetically collected using a permanent magnet with a magnetic field strength ≥ 0.5 T. The powder was washed 5 times with ethanol (each time the amount of ethanol used was 3-5 times the volume of the powder). Finally, the powder was transferred to a tetrahydrofuran or n-hexane solution for storage. The concentration of cobalt nanorods in the tetrahydrofuran or n-hexane dispersion was 0.12 mol / L.

[0055] (2) Dispersion and film preparation of cobalt nanorods: Take the cobalt nanorod-tetrahydrofuran dispersion from step (1), add oleic acid at a volume ratio of 1:5 between the cobalt nanorod dispersion and oleic acid, and sonicate for 3 min using an ultrasonic disperser to obtain a cobalt nanorod-oleic acid dispersion. Drop the dispersion onto the surface of deionized water at a depth of 2-3 cm to spread it and form a magnetic film. The drop volume of the cobalt nanorod-oleic acid dispersion is 5 μL per square centimeter of deionized water surface. After the film has stabilized for 10 min, vertically insert a 50 μm thick polyethylene terephthalate (PET) substrate into the water, slowly rotate it to contact the magnetic film, and then remove the magnetic film. After transfer, dry it in a nitrogen atmosphere at 60 ℃ for 10 min to obtain a magnetic functional layer.

[0056] (3) Label forming: 3D printing technology is used to coat the surface of the magnetic functional layer with a light-curing resin with a thickness of 8 μm. The self-adhesive layer is then laminated onto the other side of the PET substrate, and the magnetic anti-counterfeiting label is obtained after die cutting.

[0057] The distribution pattern of cobalt nanorods in the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 1 is as follows: Figure 2 and Figure 3 As shown, the distribution pattern is random and cannot be replicated.

[0058] The hysteresis loop of the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 1 is as follows: Figure 4 As shown, it has good magnetic properties.

[0059] Example 2

[0060] This embodiment provides a method for preparing a magnetic anti-counterfeiting label. The method uses short, rod-shaped cobalt nanorods as the magnetic component and a 10 μm thick photocurable resin as a protective layer. The drop volume of the cobalt nanorod-oleic acid dispersion is 10 microliters per square centimeter of deionized water surface. The specific steps include:

[0061] (1) Preparation of cobalt nanorods: Under nitrogen protection, 2.73 g of cobalt laurate, 0.039 g of ruthenium trichloride and 0.225 g of sodium hydroxide were added to 75 mL of 1,4-butanediol and mechanically stirred at 300 r / min for 15 min until the raw materials were completely dissolved; then heated to 170 ℃ at a rate of 5 ℃ / min and held for 5 min; after cooling to below 80 ℃, the black powder was magnetically collected by a permanent magnet with a magnetic field strength ≥ 0.5 T, washed 5 times with ethanol (each time the amount of ethanol was 3-5 times the volume of the powder), and finally the powder was transferred to tetrahydrofuran or n-hexane solution for storage; the concentration of cobalt nanorods in the tetrahydrofuran or n-hexane dispersion was 0.12 mol / L;

[0062] (2) Dispersion and film preparation of cobalt nanorods: Take the cobalt nanorod-tetrahydrofuran dispersion from step (1), add oleic acid at a volume ratio of 1:5 between the cobalt nanorod dispersion and oleic acid, and sonicate for 3 min using an ultrasonic disperser to obtain a cobalt nanorod-oleic acid dispersion. Drop the dispersion onto the surface of deionized water at a depth of 2-3 cm to spread it and form a magnetic film. The drop volume of the cobalt nanorod-oleic acid dispersion is 10 μL per square centimeter of deionized water surface. After the film has stabilized for 10 min, vertically insert a 50 μm thick polyethylene terephthalate (PET) substrate into the water, slowly rotate it to contact the magnetic film, and then remove the magnetic film. After transfer, dry it in a nitrogen oven at 60 ℃ for 10 min to obtain a magnetic functional layer.

[0063] (3) Label forming: A 10 μm thick layer of photocurable resin is coated on the surface of the magnetic functional layer using 3D printing technology. The self-adhesive layer is then laminated onto the other side of the PET substrate, and the magnetic anti-counterfeiting label is obtained after die cutting.

[0064] The distribution pattern of cobalt nanorods in the magnetic functional layer of the magnetic anti-counterfeiting label prepared in Example 2 is as follows: Figure 6 and Figure 7 As shown, the distribution pattern is random and cannot be replicated.

[0065] The magnetic material distribution pattern in the magnetic functional layer of the magnetic anti-counterfeiting label prepared by this invention is highly random and disordered, and the distribution patterns prepared in the same batch are completely different, making it unreplicable.

[0066] In addition, a vibrating sample magnetometer (VSM) can be used to test the magnetic properties of magnetic anti-counterfeiting labels. In addition to judging authenticity based on appearance, the authenticity of the anti-counterfeiting label can also be judged by whether the label is magnetic and whether the hysteresis loop is consistent. This improves the anti-counterfeiting performance and reduces the difficulty of production, thereby effectively preventing counterfeiting.

[0067] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a magnetic anti-counterfeiting label, characterized in that, Includes the following steps: (1) Cobalt nanorods are dispersed in a dispersion solvent to obtain a cobalt nanorod dispersion; (2) The cobalt nanorod dispersion was dispersed in oleic acid to obtain a cobalt nanorod-oleic acid dispersion; (3) Cobalt nanorod-oleic acid dispersion was dropped onto the surface of deionized water and spread to form a magnetic film; after the magnetic film was stabilized, the magnetic film was transferred to the surface of the substrate and dried under an inert atmosphere to obtain a magnetic functional layer. (4) A transparent protective layer is coated on the surface of the magnetic functional layer, and the magnetic anti-counterfeiting label is obtained after die cutting.

2. The method for preparing the magnetic anti-counterfeiting label according to claim 1, characterized in that, The method for preparing the cobalt nanorods includes: Under inert gas protection, cobalt source, ruthenium source and base are added to solvent and stirred; then heated to 100-200℃ at a rate of 1-5℃ / min and held for 1-15 min; after cooling to below 80℃, black powder is collected with a magnet, washed and cobalt nanorods are obtained, and the cobalt nanorods are dispersed in dispersion solvent.

3. The method for preparing the magnetic anti-counterfeiting label according to claim 2, characterized in that, Heat to 150-170℃ at a rate of 1-5℃ / min and hold for 5-12 minutes.

4. The method for preparing the magnetic anti-counterfeiting label according to claim 1, characterized in that, In step (1), the concentration of the cobalt nanorod dispersion is 0.1-0.2 mol / L.

5. The method for preparing the magnetic anti-counterfeiting label according to claim 4, characterized in that, In step (2), the volume ratio of cobalt nanorod dispersion to oleic acid is 1:3-7.

6. The method for preparing the magnetic anti-counterfeiting label according to claim 1 or 5, characterized in that, In step (3), the volume of oleic acid dispersion of cobalt nanorods added per square centimeter of deionized water surface is 5-10 μL.

7. The method for preparing the magnetic anti-counterfeiting label according to claim 1, characterized in that, The substrate is a plastic film; the thickness of the plastic film is 50-100 μm.

8. The method for preparing the magnetic anti-counterfeiting label according to claim 1, characterized in that, Step (4) includes: using 3D printing technology to coat the surface of the magnetic functional layer with a photocurable resin that has transparent and flexible properties, and irradiating it with an ultraviolet lamp for 1-10 minutes to form a protective layer.

9. The method for preparing the magnetic anti-counterfeiting label according to claim 1 or 8, characterized in that, The thickness of the protective layer is 5-50 μm.

10. A magnetic anti-counterfeiting label, characterized in that, It comprises a substrate and a magnetic functional layer and a protective layer sequentially attached to the surface of the substrate, and is prepared by the preparation method described in any one of claims 1-9.

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