CN110341344B - Method for anti-counterfeiting by using structural color - Google Patents
Method for anti-counterfeiting by using structural color Download PDFInfo
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- CN110341344B CN110341344B CN201910594783.3A CN201910594783A CN110341344B CN 110341344 B CN110341344 B CN 110341344B CN 201910594783 A CN201910594783 A CN 201910594783A CN 110341344 B CN110341344 B CN 110341344B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
- B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
- B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
- B42D25/30—Identification or security features, e.g. for preventing forgery
- B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
- B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
- B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
- B42D25/30—Identification or security features, e.g. for preventing forgery
- B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
- B42D25/373—Metallic materials
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
- B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
- B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
- B42D25/40—Manufacture
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Abstract
The invention belongs to the technical field of optical materials and application, and particularly relates to an anti-counterfeiting method by using structural colors. The method comprises the steps of utilizing a structure color to form a structure and a using method thereof, wherein the structure utilizing the structure color comprises a metal substrate and a dielectric film from bottom to top; or, from bottom to top, the non-metal substrate, the metal film and the dielectric film, the using method comprises: illuminating a sample of the structure, and observing the color change of the sample through an interference and scattering mode; if in the interference and scattering modes, completely different color changes are present, it can be determined that structural color is present in the structural sample based on this utilization of structural color. Based on the method provided by the invention, different changes of the structural color under the interference and scattering conditions can be observed by naked eyes, so that a good anti-counterfeiting effect is realized.
Description
Technical Field
The invention belongs to the technical field of optical materials and application, and particularly relates to an anti-counterfeiting method by using structural colors.
Background
The pure physical source structural color is an important means for supplementing the inherent color of materials in nature. One typical structural color is the blue wing of the large flashing butterfly, the color production being a physical phenomenon, not the result of a blue pigment. The vivid colors are often not available from dyes or pigments, which are generated due to physical effects and are precisely dependent on the material arrangement on a nanoscale, microscopic scale, and thus they are well suited for use in display and anti-counterfeiting functions of bank notes, sensitive documents, high-value coupons and tickets, etc.
Structural color is a physical phenomenon in which light diffracts and interferes in a regular structure, and structural irregularities are the source of light scattering. Materials that selectively absorb light exhibit observable color, sometimes in combination with phenomena that lead to structural color. However, the absorption of light does not belong to the structural color.
Many existing anti-counterfeiting technologies are mostly implemented by using phenomena such as diffraction, refraction or interference, and sometimes incorporate "lossy" absorbing materials. Counterfeiting is often made more difficult by the combination of the above phenomena, thereby increasing the anti-counterfeiting effect. The so-called joint use in the prior art is to combine small areas with different effects to form a color pattern, or to add these phenomena together to change the color effect produced by this area. The above-mentioned technology is used in US20100230615a1 by the american nano technology safety company (usa), but they use luminescent materials and cannot be simply attributed to the use of structural colors.
Disclosure of Invention
In this patent, we propose for the first time a method for generating color based on scattering and interference. That is, the interference and scattering phenomena are utilized cooperatively to generate observable structural color, and when the interference and scattering phenomena are not used, the color is hidden, so that the method is an ideal method for realizing the anti-counterfeiting function.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for preventing counterfeiting by using a structural color comprises a structure based on the structural color and a using method thereof, wherein the structure based on the structural color comprises a metal substrate and a dielectric film from bottom to top; or, from bottom to top, the non-metal substrate, the metal film and the dielectric film, the using method comprises: illuminating a sample of the structure, and observing the color change of the sample through an interference and scattering mode; if in the interference and scattering modes, a completely different color change is exhibited, the sample can be marked as the presence of a structural color (genuine).
The present invention provides a novel way of generating structural colors, i.e. by using interference and scattering phenomena. The structural color we have designed can only be observed if the properties of interference and scattering match.
And taking the difference between the maximum value and the minimum value in the spectrum under the interference condition as A, and the difference between the maximum value and the minimum value in the spectrum under the scattering condition as B, wherein the structural color structure satisfies that A is obviously larger than B, or A is obviously smaller than B.
I.e. the change in colour of the image can be observed so as to be clearly recognizable to the naked eye.
It is well known that the common phenomenon of interference is observed in thin films, for example, the formation of colorful streaks on soap bubbles and oil films in daily life. From a technical point of view, there is an undamaged thin film coating on dielectric materials (e.g. thermal oxidation Si/SiO)2The film, with an extinction coefficient k = 0 in the visible spectral range, exhibits color due to film interference. In the reflection spectrum, there are maxima and minima. The position of minima in the spectrum is related to destructive interference, occurring at δ = (2m-1) π, where the integer m ≧ 1 refers to the number of interference orders. δ =2 π nd/λ cos (θ), where n denotes the refractive index of the insulating medium, d is the film thickness of the insulating medium, θ is the incident light angle, and λ is the wavelength of the incident light. When the difference between the maximum value and the minimum value in the visible light range is large, a distinct interference color can be generated.
However, when the thin film has a very smooth reflective surface, an ideal conductor such as Au, Ag, Cu or Al has a large reflectance, but there is little difference between the minimum and maximum values of the reflection intensity. Therefore, the surface thereof has a metallic luster as with the metal without the coating layer, and the surface coloring thereof is very insignificant. FIG. 1a is a schematic diagram of a method of depositing a 100nm Al film on a polished silicon wafer and then depositing Si thereon in different thicknesses3N4Film and deposition of Si of different thickness on polished silicon wafer not evaporated with Al3N4The film, with its corresponding reflection spectrum as shown in fig. 2a, shows that the visual effect of creating a metallic luster is caused by its high reflectivity.
Interference colors are clearly observable when the substrate is no longer a conductive metal, but rather a dielectric having a different index of refraction than the coated film. This can also be seen in fig. 1 a. The corresponding reflection spectrum is shown in fig. 2c, which shows that the selective reflection has a close relationship with the thickness of the dielectric material film, and can be tuned in the visible light range.
Preferably, the dielectric film has an extinction coefficient k = 0 in the visible spectral range.
Preferably, the metal substrate or the metal film is made of aluminum, silver, gold or copper, and the roughness of the metal is 0.5-10 nm RMS.
Preferably, the material of the dielectric film is Si3N4、TiO2、ZnO、SiO2PS, PET or PMMA; the thickness of the dielectric film is 10nm to 5 μm; the roughness of the dielectric film is 0.5 to 10nm RMS.
Preferably, the deposition is by electron beam evaporation, thermal evaporation, radio frequency and direct current sputtering, pulsed laser deposition, chemical vapor deposition, spin coating, dipping, doctor blading or offset printing.
Preferably, the structure is patterned. Patterning is more advantageous for viewing and determining objects.
Preferably, the illumination is with visible light.
The anti-counterfeiting method by using the structural color provided by the invention mainly generates interference and scattering on the metal and the dielectric film respectively through visible light, and the metal color and the scattering color are different through the phenomenon based on different substances, so that anti-counterfeiting verification is carried out.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for controlling structural color by interference and scattering so as to realize anti-counterfeiting effect.
Drawings
FIG. 1 a) deposition of Si with different thicknesses on Al and silicon substrates, respectively3N4A photograph of the reflected light color of the film; b) is a photograph of the scattered light color of the same sample. While both Al evaporated and polished silicon wafers can exhibit nearly perfect specular reflection, Si is deposited at different thicknesses3N4Samples of the coated Al substrate may exhibit different colors of scattered light. However, the uncoated Al samples and all silicon substrate samples only appeared black in this case due to their lack of scattered light; c) is a photograph in which kangaroo patterns of different colors were observed under reflected light and (d) scattered light. The dimensions of the sample were approximately 15mm x 15 mm.
FIG. 2 a) reflectance spectra of samples of Si3N4 thin films deposited on aluminum substrates, b) deposition of Si on aluminum substrates3N4Scattering spectra of coated aluminum thin film samples, c) deposition of Si on silicon substrates3N4Reflection spectra of thin film samples, d) deposition of Si on a silicon substrate3N4Scattering spectra of coated aluminum thin film samples.
FIG. 3 is a flow chart for fabricating a hidden structural color.
FIG. 4 is a flow chart of hidden structure color image production.
Fig. 5 uses a schematic of a hidden structure color image.
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, and the scope of protection is still within the scope of the invention.
Example 1
The present invention is explained more intuitively below with respect to the above problems in connection with fig. 1 and 2:
from fig. 1a, it can be seen that the color is not clear in the interference observation mode when the substrate is aluminum, and a colorful color can be observed when the substrate is silicon, which is caused by the phenomenon shown in fig. 2a and 2c, which are reflection spectrograms of the aluminum substrate and the silicon substrate, respectively, and the maximum and minimum values of the emission spectrum in 2a are small, and thus the sample is not colored significantly, while the maximum and minimum values of the reflection spectrum are large (the minimum value is about zero) when the substrate of the sample is silicon, and thus the sample is colorful, and the color is formed by interference, and is dryThere is a direct relationship with the thickness of the film, so samples with different thicknesses of silicon nitride have a large difference in color. In the scattering observation mode, we found that the sample with the aluminum substrate showed a vivid color, while the sample with the silicon substrate did not observe the previous color, as can be seen from fig. 2b and 2d, which are the diffuse reflectance spectra of different substrate materials, respectively, the diffuse reflectance spectral intensity of the aluminum substrate sample was large compared to the silicon substrate sample, and in fact, the diffuse reflectance spectral intensity of the sample with the silicon substrate was almost negligible, so no color was observed. Further, the present invention utilizes scattered light (excluding direct reflection) and a new structural color effect can be observed, see fig. 1b for a photograph of the scattered light of the same sample. Deposition of Si on Al substrates3N4The color of the sample presents a strong dependence on the film thickness of the dielectric material, the angle dependence is not obvious, the incident light angle has small influence on the color, but the color is independent of the observation angle. This is in stark contrast to the color produced in conventional thin film interference, which is somewhat dependent on the viewing angle. Compared with the prior art, the structural color which only exists at a special angle needs to be found out, the observation angle is simpler and more convenient, and the judgment is simpler and more convenient. The corresponding scattering spectrum is shown in FIG. 2b, which has a maximum scattering value of Si3N4The thickness of the film is relevant and can be tuned in the visible range. The samples of pure metal surfaces and silicon substrates show no maxima in their scattered light intensity and their scattered light images are black, as shown in the bottom of the photograph in fig. 1 b) and in fig. 2 d). By combining this new structural color with the conventional thin film interference colors, we can observe photographs of changing colors in reflection and scattering. FIGS. 1c) and 1d) are photographs of Kangaroo, in which aluminum films in the shape of Kangaroo were first evaporated on a polished silicon wafer, and Si was then deposited over the entire surface of the sample to a thickness of 160nm3N4A film. In reflection, the background of this picture appears yellow (gold) and kangaroo appears metallic. While in scattering, the background of this picture appears black and kangaroo appears blue.
The manufacturing flow chart of the new structural color is shown in fig. 3. The hidden structural color can be obtained by polishing a metal substrate of Al, Ag, Au, Cu, or the like to obtain a smooth surface and then depositing a dielectric film thereon. The hidden structural color can also be obtained by depositing smooth metal films of Al, Ag, Au, Cu and the like on the substrate and then depositing dielectric films on the metal films.
FIG. 4 is a flow chart for making a hidden structure color image. A schematic diagram of how an image with hidden structural colors can be viewed in interference and scattering is shown in fig. 5 (lossy material may not be present in fig. 5). The method has the advantages that the sample with the hidden structural color is illuminated, the color of the sample is observed through the interference mode and the scattering mode, the authenticity of the sample is verified, the authenticity checking operation is simple, and meanwhile, the anti-counterfeiting grade is high.
The invention relates to an anti-counterfeiting method based on structural color, which comprises the following specific operations:
firstly, observing structural color from an interference angle (reflection image) under visible light (fluorescent light or common sunlight can be directly utilized);
secondly, in a darkroom, performing front illumination on the structural color, and observing the structural color in a scattering mode (reflected image);
if the color presented by the structural color changes in the scattering mode, the sample can be regarded as a genuine product; if the color does not differ in the interference and scattering modes, the sample is not authentic.
The method can be realized under visible light by naked eyes without large-scale instruments and professional personnel and operation, and as shown in figure 5, the method can be realized by a household handheld light source (flashlight).
In addition, the invention judges the structural color directly through the color change of interference and scattering, compared with the prior art, the structural color which exists only when a special angle needs to be found out, the observation angle is simpler and more convenient, and the judgment is simpler and more convenient.
The method of the invention has simple treatment, and can be realized by simple deposition, and even manually polishing metal.
Meanwhile, the invention does not need to adopt chemical ink and the like for treatment, is green and environment-friendly and has low cost.
Claims (7)
1. The method for preventing the counterfeiting by using the structural color is characterized by comprising a structure based on the structural color and a using method thereof, wherein the structure based on the structural color comprises a non-metal substrate, a metal film and a dielectric film from bottom to top, and the using method comprises the following steps: illuminating a sample of the structure, and observing the color change of the sample through an interference and scattering mode; if in the interference and scattering modes, completely different color changes are exhibited, the sample can be marked as the presence of structural color;
the metal substrate or the metal film is made of aluminum, the roughness of the metal is 0.5-10 nm RMS, and the thickness of the metal is 10 nm-10 mu m; the dielectric film is made of Si3N4(ii) a The thickness of the dielectric film is 10nm to 5 μm; the roughness of the dielectric film is 0.5 to 10nm RMS.
2. The method for preventing forgery by using structural color according to claim 1, wherein an extinction coefficient k of the dielectric film in a visible spectrum is 0.
3. The method for preventing forgery using structural colors according to claim 1, characterized in that the deposition is electron beam evaporation, thermal evaporation, radio frequency and direct current sputtering, pulsed laser deposition, chemical vapor deposition, spin coating, dipping, doctor blading or offset printing.
4. The method of claim 1, wherein the structure is patterned and the pattern is attached to the structure color.
5. The method for preventing forgery using structural colors according to claim 1, wherein the illumination uses visible light.
6. The method for preventing forgery by using structural colors according to claim 1, characterized in that under normal lighting conditions, the reflected image or spectrum is observed by interference; under darkroom conditions, front side illumination was performed and the scattered reflectance image or spectrum was observed.
7. The method according to claim 1, wherein the difference between the maximum value and the minimum value in the spectrum under the interference condition is A, the difference between the maximum value and the minimum value in the spectrum under the scattering condition is B, and the structure using the structural color satisfies that A is significantly larger than B, or A is significantly smaller than B.
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| CN111622014A (en) * | 2020-05-26 | 2020-09-04 | 湖北盟科纸业有限公司 | Production method of imitation structure color laser paper |
| CN113763801A (en) * | 2021-09-08 | 2021-12-07 | 中国科学院微电子研究所 | Anti-counterfeiting structure, preparation method of anti-counterfeiting structure and chip |
| CN114351236B (en) * | 2021-12-28 | 2023-05-30 | 哈尔滨工程大学 | Full-color domain structural color encryption module and preparation method thereof |
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| CN203456016U (en) * | 2013-01-24 | 2014-02-26 | 南京天朗制药有限公司 | False-proof or temperature indicating label made of thermally induced shape memory polymer |
| CN103145095A (en) * | 2013-03-26 | 2013-06-12 | 吉林大学 | Preparation method of panchromatic structural color or color variation pattern array |
| WO2014201559A1 (en) * | 2013-06-17 | 2014-12-24 | Corporation De L'ecole Polytechnique De Montreal | Interference security image structure |
| CN103852815B (en) * | 2014-03-11 | 2016-08-17 | 深圳市科彩印务有限公司 | A kind of optical interference color-changing anti-counterfeit thin film becoming saturation and preparation method thereof |
| CN105372731B (en) * | 2014-08-15 | 2019-11-12 | 丰田自动车工程及制造北美公司 | The red omnidirectional structure colorant as made from metal and dielectric layer |
| DE102015100520A1 (en) * | 2015-01-14 | 2016-07-28 | Leonhard Kurz Stiftung & Co. Kg | Multilayer body and method for its production |
| CN106228901B (en) * | 2016-08-23 | 2020-03-17 | 深圳南科构彩科技有限公司 | Anti-counterfeiting structure, anti-counterfeiting product and manufacturing method thereof |
| DE102016013242A1 (en) * | 2016-11-07 | 2018-05-09 | Giesecke+Devrient Currency Technology Gmbh | Safety element with optically variable translucent element |
| CN108922374B (en) * | 2018-07-17 | 2020-12-18 | 中国科学院光电技术研究所 | Sub-wavelength structure for realizing structural color and holographic double anti-counterfeiting |
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