RU2703795C1 - Protective element based on luminescent material - Google Patents

Abstract

FIELD: protection of printed products.

SUBSTANCE: invention relates to the field of equipment associated with counterfeit protection of paper and plastic printing products. Protective luminescent element comprises two luminescent components located in different sections of the element luminescing in narrow spectral ranges with width (30–50) nm, the first one – with the central luminescence frequency in the red wavelength range from 630 nm to 660 nm and the second one – in the near infrared region of the spectrum in range from 670 nm to 900 nm. Protective element can be formed by paints containing nanocrystalline luminescent materials based on quantum dots. Proposed protective element can be visualized and identified by observing its luminescence through a band-pass light filter which absorbs radiation of the visible range, either visually or using communication devices such as smartphones or tablets.

EFFECT: disclosed luminescent element for counterfeit protection is intended for use in rapid inspection of protected printed products.

3 cl, 6 dwg

Description

The invention relates to the field of protective labeling of printed products, such as securities, banknotes, identification documents.

Various security elements are known for marking, identifying and counterfeiting printing products. These are printed elements with color-changing and / or other special properties based on interference, moire, holographic, diffraction, and other optical-physical effects. Such elements are formed on surfaces or in the volume of protected products. Checking the presence and identification of protective elements is carried out either visually or using special devices - visualizers.

(Curency News, 2013, №1 стр. 9) и защитный элемент MAGnite^® фирмы Giesecke & Devrient (Curency News, 2013, №1 стр. 8).Recently, there have been reports of the development of special applications that allow the verification of the presence of protective markings and their identification using mobile communication devices. This, for example, is the Orel StarPerf ^® security element

(Curency News, 2013, No. 1, p. 9) and the MAGnite ^® security element of Giesecke & Devrient (Curency News, 2013, No. 1, p. 8).

One of the most common protective elements for printing products is protective printed visually observable and / or latent (latent) images made with inks that, when exposed to external exciting radiation, luminesce in the visible or infrared ranges of radiation (1. "Use of chemical means for identification tags ", http://daily.sec.ru/publication.cfm?rid=45&pid=26718, 03/31/2011; 2." Ways to protect documents "www.bnti.ru 05/03/2011)

The presence and identification of labels that luminesce in the visible range of radiation is checked by lighting under investigation of the authenticity of the object by exciting radiation, most often UV radiation with a wavelength of 365 nm. It is also possible to excite luminescence with longer-wavelength radiation, for example, in the violet and even blue regions of the visible spectral range with wavelengths from 400 to 470 nm. However, for most rare earth and organic phosphors, a rather strong decrease in the luminescence level can be observed. For the currently widely used nanocrystalline materials based on quantum dots, the luminescence intensity decreases much weaker. The observation of luminescent in the visible range of protective elements is carried out without any imaging devices. In this case, the location, configuration and color of the observed luminescent images are recorded, and they are compared with similar images in the reference samples. Protective marking, performed by paints, luminescent in the visible range, is widespread, and is currently used, as a rule, for operational visual control. The disadvantage of this marking is the low level of protection against fakes associated with the wide distribution and availability of luminescent in the visible range of materials, as well as the simplicity of their visualization (authentication is carried out using only one source of UV radiation).

A significantly higher level of protection is achieved when inks (materials) are used in printed protective elements that are luminescent in the infrared range. However, marking made with such paints can only be controlled using special equipment. Known technical solutions in which to visualize IR luminescent marking, either electron-optical converters or special monochrome video cameras with matrix recording elements sensitive in the IR range are used ("Hardware Documents Authentication Based on Optical Non-Destructive Testing", Special Technique, No. 2 , 2003).

Registration and identification of IR marking can be performed according to the spectral characteristics of IR radiation (RU 2375751, 12/10/2009; RU 2015103180, 08/20/2016; RU 2355033, 05/10/2009). Authentication can be carried out in automatic modes of high-speed counting and sorting equipment.

The disadvantage of protective IR fluorescent elements is the need to use for their registration and identification of complex optical-electronic equipment. This virtually eliminates the possibility of operational control of the authenticity of the products protected by them during their manufacture, sale and use.

Another well-known solution (RU 2639807, 12/22/2017), which is the closest to the claimed one, is based on one of the physiological features of human vision associated with its color perception of electromagnetic radiation. The color recorded by the eye of the radiation is ambiguously determined by its spectral composition. For example, the yellow color of luminescent radiation with a wavelength of 580 nm may be practically the same as the color of luminescent radiation, the spectrum of which contains narrow-band emission bands at wavelengths of 620 nm and 520 nm. With separate exposure to the eye by radiation at these wavelengths, a sensation of exposure to red radiation with a wavelength of 620 nm, and accordingly green with a wavelength of 520 nm, would form. In this solution, it is proposed to use printing inks and varnishes containing phosphors based on quantum dots with narrow single radiation lines when forming protective elements. The sizes of quantum dots are in the range of 10–40 nm, and their layered nanostructure requires the use of high-precision technologies. The parameters of the narrow-band emission curves of quantum dots are extremely sensitive to the size and structure of the layers of quantum dots. In industrial production it is extremely difficult to withstand them, which, on the one hand, provides a high degree of security of the proposed protective elements, but, on the other hand, leads to high levels of marriage in the manufacture of protective elements and, accordingly, their high cost. Such a solution of the protective element in practice is difficult to implement due to the need for precision selection of single-component and multi-component phosphors.

The claimed technical solution solved the problem of developing a protective element devoid of the above disadvantages and based on a different feature of human vision, namely that the human eye perceives the color of all electromagnetic radiation with wavelengths in the range from 600 nm to 750 nm as red.

This is achieved by the fact that a protective element based on a luminescent material is proposed, deposited on the surface of a valuable document, containing two luminescent components according to the invention, each of two luminescent components luminescent in narrow spectral ranges with a width of 30-50 nm, is located on a separate section of the protective element moreover, for the first luminescent component, the central luminescence frequency is in the red wavelength range of 630-660 nm, and for the second luminescent component, the central I luminescence frequency is in the near infrared region of the spectrum from 670 nm to 900 nm.

In the particular case, the areas containing the first and second luminescent components overlap.

In a particular case, the luminescent components are made on the basis of luminescent materials containing quantum dots.

Visualization and identification of the protective element is carried out through a band-pass filter that transmits near-infrared radiation from 670 nm to 900 nm, and is carried out either directly by the eyes (at the luminescence wavelength of the second component in the range from 670 nm to 700 nm), or using mobile devices such as smartphones equipped with video cameras, (at a luminescence wavelength of the second component in the range from 700 to 900 nm) by controlling changes in configuration and color, visualized images of various sections beyond itnogo element.

In FIG. 1 shows a demonstration banknote with the proposed luminescent security element deposited on its surface. In FIG. 2 and FIG. 3 shows an image of a security element depending on the method of lighting and observing the images. In FIG. 4 and FIG. 5 shows the spectra of the optical transmission dependences of the interference and absorption filters, respectively; FIG. 6 shows the transmission spectrum of a standard absorption filter SS8 (GOST 9411-81).

An example implementation of the inventive security element. The element consists of two spatially separated images (Fig. 1). Image 1 is made with a transparent varnish containing a phosphor luminescent in the visible range of radiation at a wavelength of 650 nm, and image (2) is varnished with a phosphor luminescent in the near infrared range at a wavelength of 700 nm. To ensure the narrow-band luminescence, the compositions of the first and second phosphors were formed on the basis of nanocrystalline materials containing quantum dots of two different types, with a spectral luminescence peak width of 20-40 nm. The phosphor used in the varnish of image 1 contained quantum dots of the composition CdSe / CdS / ZnS. The phosphor used in the varnish of image 2 was formed on the basis of quantum dots of the composition CdS / CdTeSe / CdS / Zns. The sizes of quantum dots of both compositions were in the range of 10–13 nm.

Under normal natural daylight with white light, both images appear translucent, have a yellowish tint and are difficult to distinguish against the background of a printing ink layer of a banknote (see Fig. 1). With a sufficiently accurate selection of the color of the varnish and the color of the background printing impression, the first and second images of the luminescent protective element can be made practically invisible. The security element becomes hidden (latent).

When a banknote is illuminated with UV radiation with a long wavelength of radiation in the range (250-440) nm or with a violet-blue spectral region with a long wavelength in the range of 400-500 nm, both images of the security element appear in contrast and have the same red color (see Fig. . 2). The protective effect in such an element was detected using a near-infrared band pass filter, which has a sharp dependence of the increase in the transmittance of radiation from 0 to values approaching one hundred percent transmittance when moving from the visible region of the spectrum to the region of the near-infrared spectrum.

To identify the protective effect, we used both a specially made interference optical filter and a standard absorption filter KS19 from a set of optical colored glasses made in accordance with GOST 9411-81. The dependences of the optical transmission of the interference and absorption filters are shown respectively in FIG. 4 and FIG. 5. When viewing, illuminated by the exciting radiation, images 1 and 2, through such band-pass transmission filters, image 1, luminescent at a wavelength of 650 nm, becomes almost invisible (see Fig. 3). The filter used absorbs radiation at a wavelength of 650 nm (Fig. 4 and Fig. 5). The brightness of image 2 decreases slightly, it remains visible and can only slightly change the shade of red. By the nature of the change in the type of images depending on the lighting and observation methods of images 1 and 2, the proposed security element can be identified.

Thus, the method of visualization and identification of the proposed protective element consists in illuminating the protective element with radiation from a long wavelength in the specified range and comparing the images of the protective element observed through the IR pass band filter and in its absence. The visualization procedure is carried out using the simplest inexpensive and affordable means - a source of UV or violet-blue radiation and an IR-bandpass filter.

The proposed security element can also be visualized using modern communication devices such as smartphones or tablets equipped with built-in video cameras and pulsed LED illuminators used for photo and video image capture. To enable visualization of the proposed security element on the camera’s lens, it is necessary to install a band-pass barrier filter that absorbs visible radiation with a wavelength of 400 nm to 660 nm, and transmits infrared radiation with a wavelength of 670 nm to 900 nm, similar to the above (see Fig. 4 and Fig. 5), and on the flash-illuminator of the camera - a band-pass filter that transmits the emission of violet-blue and UV spectral ranges with a wavelength of 350 nm to 500 nm. A CC8 standard absorption filter (GOST 9411-81) whose transmission spectrum is shown in FIG. 6. Visualized images of the security element are observed on the screen of a smartphone or tablet.

Claims (3)

1. A protective element based on a luminescent material deposited on the surface of a valuable document containing two luminescent components, characterized in that each of the two luminescent components, luminescent in narrow spectral ranges with a width of 30-50 nm, is located on a separate section of the protective element, and for the first luminescent component, the central luminescence frequency is in the red wavelength range from 630 to 660 nm, and for the second luminescent component, the central luminescence frequency It is located in the near infrared region of the spectrum in the range from 670-900 nm. 2. The protective element according to claim 1, characterized in that the sections of the element containing the first and second luminescent components spatially overlap. 3. The security element according to any one of paragraphs. 1 or 2, characterized in that the luminescent components are made on the basis of luminescent materials containing quantum dots.

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