RU2533209C1 - Security element for identification of articles - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: security element for identification of articles relates to counterfeit protection and authentication of securities, which can be used for concealed marking of various objects in order to prevent unauthorised production of said objects and simplify authentication thereof. The security element comprises a stack of polymer layers glued to each other, each having a certain type of semiconductor quantum rods which luminesce in different spectral regions and are oriented in directions orthogonal to each other.

EFFECT: high reliability of the security element and longer service life thereof.

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Description

The present invention relates to the field of protection against falsification and authentication of valuable documents, in particular to hidden security tags with polarizing contrast and color coding that change color depending on the viewing conditions, which can be used for hidden marking of various objects in order to prevent unauthorized production of these objects and simplifying the process of verifying their authenticity.

Known luminescent protective elements based on semiconductor quantum dots (CT) "Method of protecting devices using quantum dots" (US Patent No. US 6,692,031 B2, IPC G07D 7/12, C09D 11/00, B41M 3/14, G07D7 / 00, application 09 / 955,808, publication date 02/17/2004, priority date 02/21/2002) [1]. Protective elements are labels based on a combination of nanoparticles of various sizes and / or chemical compositions embedded in various materials: ink, paper, plastic and explosives. Due to the properties of QDs (Efros, A. L., D. J. Lockwood, et al. Semiconductor Nanocrystals: From Basic Principles to Applications, Springer, 2003, 1-19) [2], such labels will have a unique luminescence spectrum. The common disadvantages of these labels include the fact that the identification of the security element requires analysis of the spectral characteristics of the label, which in turn significantly increases the cost and complexity of the verification process.

Known polarizing protective elements, which are two-layer structures of anisotropic cholesteric liquid crystal polymers, "Environment for object recognition and the method of its use" (US Patent No. US 7,391,546 B2, IPC G02F 1/1335, G06K 7/10, G06K 9/74, B42D15 / 10 application 10 / 557,001, publication date 06/24/2008, priority date 05/16/2003) [3]. Such material, depending on the thickness of the layer, can selectively reflect light with left- or right-handed circular polarization in a certain spectral range. This allows you to create images that are indistinguishable in daylight, but easily noticeable when viewed with the help of special filters that transmit circularly polarized light. The use of additional color and polarization coding allows increasing the degree of protection. However, this security element has a number of significant disadvantages. Such disadvantages, in particular, include the complex manufacturing process of such an element: first, two anisotropic layers that reflect light with right-handed and left-handed polarization are polymerized on auxiliary isotropic substrates. Then, using a photolithographic technique, a unique image is formed on each of these layers. Then these layers are sequentially transferred by stamping to the marked object.

Closest to the claimed invention and adopted as a prototype "Security element, method for its manufacture, containing its security label and method for identifying the authenticity of products marked with a security label" (Patent of the Eurasian Patent Office No. 011116 B1, IPC B42D 15/00, application No. 200701967 , publication date 12/30/2008, priority date 10/12/2007) [4]. According to the description of the patent, the protective element is a polymer layer containing a luminescent dye, while in the polymer layer a latent image is visualized in polarized light in the form of separate sections of the layer with induced anisotropy, and the luminescent dye is oriented in these anisotropic sections of the layer so that when ultraviolet irradiation shows polarized luminescence of anisotropic regions along with depolarized luminescence of isotropic regions of the layer .

The prototype has the following disadvantages:

1. Lack of reliability, which is due to the fact that the latent polarized luminescent image is used as the main and only protective feature.

2. The limited life of the protective element, which is associated with low resistance to photodegradation of organic dyes used as luminescent additives.

The problem of increasing the reliability of the protective element and increasing its life is solved.

The essence of the invention is as follows. The protective element is a set of polymer layers glued to each other, each of which contains one type of semiconductor quantum rods (CS) with polarized luminescence in a certain spectral range. CS located in different polymer layers luminesce in different spectral regions. In the protective element, the polymer layers with CS are arranged in such a way that the luminescence of each subsequent layer is polarized in the direction orthogonal to the direction of polarization of the CS in the previous layer. In natural light, the protective element looks like a transparent polymer film. When illuminated with depolarized light, which is absorbed by the CS, it is a uniformly luminescent field, the color of which will change when observing luminescence through the analyzer depending on the angle of rotation of the analyzer.

The proposed security element has the following advantages:

1. The increased degree of protection. This advantage is ensured by the fact that the protective element, in addition to polarization contrast, is characterized by the ability to change the color of its luminescence when observed through the analyzer, depending on the angle of rotation of the analyzer.

2. The increased life of the protective element. This advantage is provided by the fact that semiconductor nanocrystals have a higher resistance to photodegradation compared with organic dyes used in the prototype.

The problem is solved by creating a protective element with polarizing contrast and color coding based on multilayer structures from stretched polymer films with embedded semiconductor CS. Semiconductor CSs have linearly polarized luminescence, the direction of the electric vector of which coincides with the long axis of the nanorod (Nu, J., L.-s. Li, et al. (2001). "Linearly Polarized Emission from Colloidal Semiconductor Quantum Rods" Science 292: 2060 -2064; Chen, X., A. Nazzal, et al. (2001). "Polarization spectroscopy of single CdSe quantum rods." Physical Review B 64 (24): 245304) [5], [6]. With a random arrangement of the CS in the polymer layer, its luminescence will be completely depolarized; therefore, to create a polymer layer with polarized luminescence, the CS must be ordered in one way or another to order the CS in the layer. One of the ways of ordering the KS ensemble in the polymer layer is to stretch the polymer film with the initially randomly located KS. This leads to the appearance of a distinguished direction of the preferred orientation of the CS and, as a consequence, to the appearance of luminescence polarization. Then, two polymer films containing semiconductor CSs that luminesce in different spectral regions are glued so that the axes along which the nanorods are oriented are orthogonal to each other. When illuminated with depolarized light, which is absorbed by the SC, this protective element is a uniformly luminescent field, the color of which will change when observing luminescence through the analyzer depending on the rotation of the analyzer.

The essence of the invention is illustrated in Fig.1-6, where:

in figure 1. - Schematic representation of a security element based on quantum rods. 1 - polymer film with ordered quantum nanorods of the same type, 2 - protective element obtained by applying two films with quantum rods ordered in orthogonal directions.

figure 2. - The registration scheme of the luminescent response from the protective element 2 using a spectrofluorimeter. 3 - a radiation source, 4 - a monochromator of the excitation channel, 5 - a light filter, 6 - a waveguide, 2 - a sample, 7 - an analyzer or a neutral light filter, 8 - a waveguide, 9 - a light filter, 10 - a monochromator of a recording channel, 11 - PMT. figure 3. - Luminescence spectra of the protective element 2. 12 — recording spectra using a neutral filter (transmittance in the visible spectrum 30%), 13 — recording spectra using an analyzer, the transmit axis of the analyzer coincides with the ordering direction of the CdS CS and is perpendicular to the ordering direction of CdSe / ZnS КС ; 14 - spectra recording using an analyzer, the analyzer transmission axis coincides with the ordering direction of CdSe / ZnS KS and is perpendicular to the ordering direction of CdS KS.

figure 4. - Scheme for observing the luminescent response from the protective element 2 in natural light. 2 - protective element, 15 - analyzer (orientation changes during observation), 16 - human eye, 17 - radiation source.

To demonstrate the operability of the proposed protective element 2, two types of CS were used: CdSe / ZnS CS with the position of the maximum luminescence at a wavelength of 640 nm and CdS CS with the position of the maximum of luminescence at a wavelength of 495 nm, synthesized according to the procedure described in (T. Mokari, U . Banin. (2003). "Synthesis and Properties of CdSe / ZnS Core / Shell Nanorods." Chemistry of materials 15 (20): 3955-3960) [7].

To obtain polymer films with a certain type of CS, a solution of polyvinyl butyral in tetrahydrofuran was mixed with solutions of quantum nanorods in tetrahydrofuran in a ratio of 1: 2.5 by volume. To the resulting mixtures, 3 vol% dibutyl phthalate was added as a plasticizer. Films were obtained by solution irrigation. After evaporation of the solvent, the films were removed from the substrate and stretched four times along one of the directions. The concentration of CS in the films was 2 × 10 ⁵ mol / L. To create a protective element 2, polymer films containing individually CdSe / ZnS and CdS KS were glued with a layer of polyvinyl butyral so that the axes along which the KS were oriented were orthogonal to each other. A schematic representation of the protective element 2 is shown in Fig.1.

The registration scheme of the luminescent response from the protective element 2 using a spectrofluorimeter is shown in Figure 2. In this case, the light from the source 3 through the monochromator 4 and the light filter 5 enters the waveguide 6, from which it is supplied to the protective element 2. The use of the waveguide provides complete depolarization of the exciting radiation. The luminescent signal from the protective element 2 passes through the analyzer 7 and is fed into the waveguide 8. After that, the light enters the filter 9, which emits the luminescent signal from the protective element 2, and then sequentially enters the monochromator of the recording channel 10 and the photoelectronic multiplier 11.

In figure 3. the luminescence spectra of the protective element 2 are shown, recorded without an analyzer with a neutral filter (12) and for two orthogonal positions of the analyzer (13 and 14).

The degree of luminescence anisotropy of quantum nanorods in the protective element 2 was estimated by the formula:

$$p=\frac{I_H-I_V}{I_H+I_V}$$

- интенсивность люминесценции образца, возбужденного деполяризованным светом, при регистрации сигнала через анализатор, ось пропускания которого расположена параллельно (H) и перпендикулярно (V) плоскости образца соответственно.Where $$I_{H,V}$$

- the luminescence intensity of a sample excited by depolarized light when a signal is recorded through an analyzer, the transmission axis of which is parallel to (H) and perpendicular to (V) the plane of the sample, respectively.

The degree of polarization of CS luminescence calculated by formula (1) for CdS quantum nanorods was 42%, for CdSe / ZnS - 46%.

Figure 4 shows a diagram of the visual registration of the luminescent response from the protective element 2, in which the color change of the protective element 2 can be observed visually by rotating the analyzer 15 and illuminating the sample with a portable radiation source 17, for example, an LED with a suitable radiation spectrum can be used . Upon visual observation, the color of the protective element changed from green-yellow to orange.

Thus, the tasks of increasing the degree of reliability and increasing the life of the protective element for identification are solved.

Information sources

1. US patent No.US 6,692,031 B2, IPC G07D 7/12, C09D 11/00, application 09 / 955,808, publication date 02/17/2004, priority date 02/21/2002.

2. Efros, A. L., D. J. Lockwood, et al. Semiconductor Nanocrystals: From Basic Principles to Applications, Springer, 2003, 1-19.

3. US patent No. US 7,391,546 B2, IPC G02F 1/1335, G06K 7/10, application 10 / 557.001, publication date 06/24/2008, priority date 05/16/2003.

4. Patent of the Eurasian Patent Office No. 011116 B1, IPC B42D 15/00, G07D 7/12, D21H 21/48, application No. 200701967, publication date 12/30/2008, priority date 12/10/2007.

5. Hu, J., L. - s. Li, et al. (2001). "Linearly Polarized Emission from Colloidal Semiconductor Quantum Rods" Science 292: 2060-2064.

6. Chen, X., A. Nazzal, et al. (2001). "Polarization spectroscopy of single CdSe quantum rods." Physical Review B 64 (24): 245304.

7. T. Mokari and U. Baninl. (2003). "Synthesis and Properties of CdSe / ZnS Core / Shell Nanorods." Chemistry of materials 15 (20): 3955-3960.

Claims (1)

A security element for identifying the authenticity of products, consisting of a polymer layer containing luminescent particles, having a polarizing contrast, characterized in that the polymer layer is a set of polymer layers glued together, each of which contains a certain type of semiconductor quantum rods, luminescent in different spectral regions and oriented in directions orthogonal to each other.

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