LT7164B - SECURE DATA MEDIA AND METHOD FOR MANUFACTURING SECURE DATA MEDIA - Google Patents

Abstract

The subject of the invention is a secure data carrier and a method of manufacturing the same. A secure data carrier consisting of a plurality of sheets formed by pressure thermoforming, on the surface of which there is a Fourier hologram, characterized in that the hologram on the surface (2) of the data carrier (1) is a wavy structure (3), the location, height and area of the individual protrusions of the structure (3) correspond to the dot-matrix of the Fourier hologram, created by transforming a hidden image stored in the form of a dot-matrix into a gray scale. A method of manufacturing a secure data carrier by pressure thermoforming, when at least two sheets (5) placed one on top of the other are heated, and then the stack of sheets (5) is pressed with a matrix plate, characterized in that the stack of sheets (5) is pressed directly with a matrix plate, on the surface of which there is a negative of the structure (3).

Description

The subject of the invention is a secure data carrier and a method for manufacturing a secure data carrier. The described solution is applied in the protection of valuable documents, in particular personal identity documents, the carrier of which is manufactured by pressure thermoforming from a plurality of sheets.

There are a number of solutions for security elements of valuable documents that use a Fourier hologram. In the solutions known so far, a Fourier hologram representing a matrix of complex numbers describing transparency, thickness, and angular phase parameters has been used in several ways. Patent EP2724331B1 discloses a method for reducing the transparency parameter through the interferogram phase angle, and patent PL177897B1 describes the reduction of this parameter through the thickness of the material. There are also solutions known in which the obtained Fourier hologram is used to transform the complex phases of the obtained matrix back into a transparency parameter.

Polish patent application PL438968A1 describes a data carrier, primarily used as a valuable document with security elements, having a permeable diffractive element, which can contain personal data and/or marks that individualize the data carrier, and a method for producing the data carrier. The data carrier consists of a base on which a layer sensitive to laser marking is provided, and the permeable diffractive element is located in the transparent area of the data carrier. The permeable diffractive element, which is a binary hologram of a permeable image, is illuminated by collimated light and creates a projection of the image - personal data and/or individualizing mark, observed on the projection surface of the light beam.

From patent application PL440380A1, a method of encoding hidden information in images intended for laser engraving, a security element, a data carrier, a method of manufacturing a security element, a method of verifying the authenticity of a data carrier, where all protected objects arise from the method of encoding hidden information in images intended for laser engraving. The method is characterized in that for a hidden image loaded from a file, transformed into a gray-scale bitmap (hereinafter referred to as the input image), the Fourier hologram of the input image is calculated by the iterative Fourier transform algorithm IFTA, by loading the gray-scale values of the hidden image as the amplitudes of the input matrix IFTA, the Fourier hologram is transformed into a gray-scale bitmap as a hidden image, recording the phases of the Fourier hologram as proportionally assigned shades of gray. The gray-scale bitmap can be integrated into the visible image, so the recording of the phases of the hologram becomes invisible to the naked eye. The method of encoding hidden information is used to protect data carriers in the transparent base area.

The subject of the patent is also a method of verifying the authenticity of a data carrier, according to which visual verification of the recording occurs by illuminating the security element with a point light source, e.g. a mobile phone bulb, when visual accommodation occurs at the light source.

Valuable documents are particularly vulnerable to counterfeiting attempts. Due to this problem, multiple security elements are often used on a single valuable document to increase the level of protection, and the need to develop new document security technologies is very urgent.

The purpose of this invention is to provide a new type of protected data carrier that would allow the integration of many of the known state-of-the-art document protection methods with an existing security element.

The object was achieved due to the features of the invention presented in the independent claims describing the product and its method of production. The dependent claims set out recommended and/or particularly useful aspects of the invention.

According to the invention, a secure data carrier, consisting of a plurality of sheets processed by pressure thermoforming, has a Fourier hologram on its surface. The secure carrier is characterized in that the hologram on the surface of the carrier has a wavy shape, the location, height and area of the individual bumps of the structure of which correspond to the shape of the Fourier hologram bitmap created by transforming a hidden image stored as a grayscale bitmap using the IFTA method of the iterative Fourier transform algorithm, the grayscale values of the hidden image are loaded as the amplitudes of the IFTA input matrix, and then the resulting Fourier hologram is transformed into a grayscale bitmap, recording the phases of the Fourier hologram as proportionally assigned grayscale shades, where the grayscale shades proportionally assigned to the structure are the height of the convexity. The created secure medium reproduces the bitmap image of the Fourier hologram known from patent application PL440380A1. According to this solution, the obtained Fourier hologram is used to transform the phases of the complex numbers of the obtained matrix back into the transparency parameter. Although the bitmap image works with the transparency parameter, it has been proven that when it is directly transferred to the thickness of the medium, the correct hologram of the original hidden image is obtained. In addition, it has been found that another optical phenomenon is integrated in the hologram created in this way - the splitting of light transmitted through the data carrier - without violating the corresponding field spectrum. The hidden image obtained in this way is clear and multi-colored. There is a large group of holograms called rainbow holograms, which also allow obtaining a multi-colored projection of the hidden image, but so far known solutions have been limited to the splitting of light reflected from the hologram surface. The different optical effects of the previously used methods and the proposed security measure are particularly useful because they allow a quick assessment of the method by which the hologram was created. There is no risk of counterfeiting a valuable document using another hologram technique. In addition, known solutions for engraving hologram dot graphics result in a visually noticeable darkening of the surface, while the proposed wavy structure remains organoleptically imperceptible and is very difficult to feel with fingers.

In the most advantageous solution, the base of the data carrier is saturated with a pigment that has increased sensitivity to laser radiation. By creating the data carrier with materials and manufacturing methods that are commonly used in the field of production of valuable documents, the secure data carrier is characterized by the fact that it is easy to integrate existing document protection methods into it. Of particular importance is that the hologram areas can be engraved.

The data carrier is made of polycarbonate (PC) or glycol-modified polyethylene terephthalate (PET G), or polyvinyl chloride (PVC), or symmetrically coextruded polycarbonate with glycol-modified polyethylene terephthalate (PEC) or polyurethane (PU).

It is particularly desirable that the structure of the secure data carrier has at least one security imprint, the height of which is greater than the convexity of the structure. The security imprint provided in the solution is intended to protect the holographic structure from wear during use, thereby ensuring a longer service life of this security element.

According to the invention, a method for manufacturing a secure data carrier using a pressure thermoforming process, when at least two sheets stacked on top of each other are heated and pressed simultaneously, characterized in that the stack of sheets is heated and pressed by direct pressing with a matrix plate, on the surface of which there is a negative of the structure. The negative of the structure is wavy in shape, where the location, height and area of the individual protrusions of the structure correspond to the shape of the Fourier hologram bitmap created by transforming a hidden image stored as a grayscale bitmap using the IFTA method of the iterative Fourier transform algorithm, the grayscale values of the hidden image are loaded as amplitudes of the IFTA input matrix, and then the resulting Fourier hologram is transformed into a grayscale bitmap, recording the phases of the Fourier hologram as proportionally assigned grayscale shades, where the proportionally assigned grayscale shades of the structure (3) correspond to the depth of the imprint.

The proposed method of obtaining a secure data carrier is particularly useful in that the security element is created during the production process of the carrier itself and does not require any additional process stages, only the application of tools, therefore the hologram structure is formed in parallel. The most important advantage of this method of manufacturing a security device remains the light scattering properties, therefore the projection of a colored hidden image also occurs during the process of checking the data carrier, using the illumination of the security device with a point light (e.g. a mobile phone lamp).

In subsequent stages of data carrier modification, this structure can be printed or personalized, but the specific holographic effect remains. As a result, this security element can be combined with others, thereby increasing the level of document security. For example, if an identification image is placed on the holographic structure - media identification numbers or identification images, when trying to modify the document by changing the identification image, it must be removed, which also removes the structure. Recreating the structure by other means or forming another hologram that would cause an analogous optical phenomenon in that place during the authentication of the media is impossible.

The subject matter of the invention is illustrated by examples which do not limit its scope. In the drawings of the invention:

Fig. is an image of a secure data medium;

Fig. is the first example of a security document produced using a secure data carrier;

Fig. is a visualization of the hologram adaptation in the form of a bitmap on a convex data carrier structure;

Fig. 1 is a cross-sectional view of the secure data carrier shown in Fig. 1 along line A-A;

Fig. is an example of an optical phenomenon obtained by illuminating the structure of a secure data carrier.

Fig. shows an example of a secure data carrier 1 for a valuable document. The data carrier 1 is made of eight polycarbonate sheets formed by pressure thermoforming. The sheets 5, each 100 μm thick, are placed one on top of the other. Inside there are two white sheets 5b, on the outside three on each side - transparent sheets 5a. When connected together during the pressure thermoforming process, they are thinned by approximately 10% of their thickness and form a single data carrier 1. The number and color of the sheets can vary depending on the desired properties of the final product, i.e. its rigidity, thickness and color. In this production example, the white sheets 5b have one cutout in the area of the structure 3b, which is hereinafter referred to as transparent. The outer transparent sheets 5a have a pigment that has increased sensitivity to laser radiation.

In the production method of the present invention, the stack of sheets described above is placed in a pressure thermoforming device. The device is equipped with a matrix plate, in which the negatives of the structures 3 are respectively arranged in those places where the opaque structure 3a and the transparent structure 3b will be embossed on the outer transparent sheet 5a. The matrix plates, between which the stack of sheets is located, are heated to a temperature of 180-200 ° C and press the stack of sheets 5 for 2 seconds with a force of 20 bar.

Fig. shows an example of a valuable document formed in the secure data carrier 1 shown in Fig. 1. Using the laser engraving method, the individualizing elements of the document were applied to the data carrier 1: a photograph of the document owner 8, a hologram 6 produced according to the method described in patent application PL445971A1, and a personalized engraving 7 in the area of the transparent structure 3b. The structure 3, including the opaque structure 3a and the transparent structure 3b, is obtained in the process of joining the sheets by pressure thermoforming. The pressing matrix imprints the structure 3 on the outer surface of the sheet 5a, creating wavy protrusions. The structure 3 is a Fourier hologram, the location, height and area of the individual protrusions of the structure 3 correspond to the shape of the Fourier hologram dot graphics, in which the height of the protrusions is assigned proportionally to the shades of gray. The Fourier hologram bitmap is understood as an image created from a hidden bitmap image by applying the iterative Fourier IFTA transform algorithm method, and then transforming the Fourier hologram into a grayscale bitmap, recording the grayscale values of the hidden image as the IFTA amplitudes of the input matrix, where the Fourier hologram phases are assigned proportionally to the grayscale shades. Fig. 3 shows a visualization that reproduces the created microscopic wave structure 3 on the surface 2 of the data carrier 1, created from the Fourier hologram bitmap image in grayscale (top photo). Fig. 4 shows a cross-section of the data carrier 1 through the line A-A in the area of the opaque structure 3a, the location of the cross-section is shown in Fig. 1. In this example, around the structure 3a, which has a height of 30-60 μm, there is one circular imprint 4, as shown in the outline in Fig. 1. and Fig. 2, with a height of 60-80 μm.

Fig. shows an optical phenomenon that is visible to the observer. The “GP” image hidden in the hologram is revealed as a multi-colored inscription. When the hologram is located in the area of a transparent base, the hidden image can be directly projected onto the observer’s retina by illuminating the structure 3 with a point light source, created, for example, by a mobile phone lamp, in a similar manner to that described in patent application PL440380A1. If the structure 3 is located in an opaque area, the hidden image can also be read, but this requires the use of the method described in patent application PL445971A1. Using a smartphone with an application installed for verifying the authenticity of a valuable document, a photograph is taken, focusing on the surface of the data carrier, and the image is saved as a bitmap. The application resizes the image downloaded from the camera and cuts out the part of the photo of interest that contains the hidden signal. The image thus processed is converted to grayscale, and then entered into the two-dimensional FFT (Forward fast Fourier Transform) algorithm input matrix as the real component Re. The imaginary components (Im) are assumed to have a default value of = 0. After the FFT transformation, the hidden image calculated in the form of a spectrum matrix is converted into a bitmap. The conversion is carried out according to the amplitudes stored in the spectrum matrix, applying a noise-limiting filter in the low and high frequency regions. If necessary, in order to improve the readability of the hidden image, the above steps are iteratively repeated, based on observations of the received image, optimizing the camera image brightness and zoom settings. After performing these steps, the application generates the image shown in Fig. 5 on the smartphone screen, but the image generated in this way remains in grayscale.

In the illustrated example, both the opaque structure area 3a and the transparent structure area 3b contain an engraving that does not affect the legibility of the hologram. Thus, for example, the hologram may be marked with an engraving indicating the location of the hologram, which allows the data carrier to be checked, or hidden under an engraving to protect the engraved data, and an attempt to remove the engraving will also destroy the holographic structure.

Claims (5)

DEFINITION OF THE INVENTION 1. A secure data carrier formed from a plurality of sheets formed by pressure thermoforming, on the surface of which there is a Fourier hologram, characterized in that the hologram on the surface (2) of the data carrier (1) is a wavy structure (3), where the location, height and area of the individual protrusions of the structure (3) correspond to the shape of the Fourier hologram bitmap generated by transforming a hidden image stored as a grayscale bitmap using the iterative Fourier transform algorithm IFTA, recording the gray values of the hidden image as the amplitudes of the IFTA input matrix, and then transforming the resulting Fourier hologram into a grayscale bitmap, recording the phases of the Fourier hologram as proportionally assigned shades of gray, where the height of the protrusion is assigned to the structure (3) proportionally to the shades of gray. 2. A secure data carrier according to claim 1, characterized in that the data carrier (1) consists of a pigment base characterized by increased sensitivity to laser radiation. 3. Secure data carrier according to claim 1 or 2, characterized in that the data carrier (1) is made of polycarbonate (PC) or glycol-modified polyethylene terephthalate (PET G), or polyvinyl chloride (PVC), or symmetrically coextruded polycarbonate with glycol-modified polyethylene terephthalate (PEC) or polyurethane (PU). 4. A secure data carrier according to claim 1, 2 or 3, characterised in that it comprises at least one security imprint (4) located at the structure (3) and having a height greater than the height of the structure (3). 5. A method for manufacturing a secure data carrier according to claim 1, using pressure thermoforming, when at least two sheets (5) placed on top of each other are heated and compressed at the same time, characterized in that the stack of sheets (5) is heated and pressed with a heated matrix plate, on the surface of which is a negative of the structure (3), where the negative of the structure is a wavy surface of the structure (3), the location, height and area of the individual protrusions of which correspond to the negative shape of the Fourier hologram bitmap created by transforming a hidden image stored as a bitmap in a gray scale, using the iterative Fourier transform algorithm IFTA, recording the gray values of the hidden image as the amplitudes of the IFTA input matrix, and then transforming the resulting Fourier hologram into a grayscale bitmap, recording the phases of the Fourier hologram as proportionally assigned shades of gray, where the structure (3) is assigned depth proportional to shades of gray.