Multilayer structure exhibiting multi-mode wrinkles and multi-structural colors, method for manufacturing same, and anti-counterfeiting device using same

Abstract

The present invention provides a multi-layer structure based on multi-mode wrinkles and multi-structural color development formed by photolithography using a gray dimming mask, a manufacturing method thereof, and a forgery prevention device using the same. A method for manufacturing a multilayer structure according to one embodiment of the present invention comprises the steps of: providing a base material; a step for forming, on the base material, an ultraviolet-curable layer containing an ultraviolet-curable chitosan; a step of arranging a gray dimming mask on the ultraviolet curing layer; irradiating ultraviolet rays onto the ultraviolet curing layer through the gray dimming mask so as to cure the ultraviolet curing layer to different degrees; developing the cured ultraviolet curing layer, and forming a high-hardness layer having different thicknesses according to different degrees of curing of the ultraviolet curing layer; and a step of forming a medium-hardness layer on the high-hardness layer.

Description

Technical Field

[0001] The present invention relates to a multilayer structure, and in particular to a multilayer structure showing multi-mode wrinkles and multi-structural colors, a method for manufacturing the multilayer structure, and an anti-counterfeiting device using the multilayer structure. Background Art

[0002] In modern society, with the development of technology, new products have been developed in a variety of ways, and the developed products can be actively traded online. Unfortunately, copying technology has also been greatly developed, making it increasingly difficult to distinguish between genuine products and copies. Various anti-counterfeiting technologies can be used for high-priced products, but it is difficult to use anti-counterfeiting technologies for slightly lower-priced products that are inevitably circulated in large quantities. For example, products such as food, medicine, and cosmetics are directly related to people's health and even life, so they need more attention from society.

[0003] Recently, the research on anti-counterfeiting of optical holograms that realize structural coloration by using photonic crystals has become a focus of attention. However, since it is difficult to make a technical difference with passive structures, a new anti-counterfeiting technology that converts active structures such as micro / nano grating structures using various external stimuli (multimodal type) is needed. Specifically, anti-counterfeiting technologies at home and abroad use anti-counterfeiting stickers with photonic crystal characteristics that have passive hologram characteristics. Since this sticker can usually show color, it is difficult to set a difference from existing products. Therefore, in order to prevent copying, a new anti-counterfeiting device that is active and has a fast response under multiple conditions (stretching, compression, bending, torsion, etc.) is needed.

[0004] Wrinkles are formed on ductile multilayer surfaces such as human skin and can exhibit inherent structural properties such as high surface-to-volume ratio, orientation, and periodicity. Due to these advantages, research on wrinkles has attracted much attention in the fields of chemical sensors, optical devices, and electronic devices. However, fine-tuning the periodicity of wrinkles is currently difficult to solve because it is difficult to control during the manufacturing process.

[0005] [Prior technical literature]

[0006] [Patent Document] (Patent Document 1) Korean Patent Registration No. 10-1672392. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a multilayer structure having multi-mode wrinkles and multi-structural color appearance formed by photolithography using a gray-tone photomask, a method for manufacturing the same, and an anti-counterfeiting device using the same.

[0008] However, these issues are merely examples, and the technical concept of the present invention is not limited thereto.

[0009] In order to solve the technical problem, the manufacturing method of the multilayer structure according to the technical idea of ​​the present invention preferably includes: a step of providing a base material; a step of forming a UV-curable layer containing UV-curable chitosan on the base material; a step of arranging a gray-tone photomask on the UV-curable layer; a step of irradiating UV rays onto the UV-curable layer through the gray-tone photomask so that the UV-curable layer is cured to different degrees; a step of developing the cured UV-curable layer to form a high-hardness layer with different thicknesses according to the different degrees of curing of the UV-curable layer; and a step of forming a medium-hardness layer on the high-hardness layer.

[0010] According to one embodiment of the present invention, preferably, the step of providing the base material includes: the step of mixing a main material of polydimethylsiloxane and a curing agent to form a mixture; the step of placing the mixture in a vacuum to remove bubbles; and the step of thermally curing the mixture to form the base material.

[0011] According to an embodiment of the present invention, preferably, the step of providing the base material further comprises: performing oxygen plasma treatment to modify the surface properties of the base material.

[0012] According to one embodiment of the present invention, preferably, the step of forming the UV-curable layer includes: a step of providing the UV-curable chitosan solution formed by dissolving a UV-curable chitosan material in an ethanol aqueous solution solvent; a step of pouring the UV-curable chitosan solution onto the base material and spin-coating it; and a step of heating the base material on which the UV-curable chitosan solution is spin-coated to evaporate the ethanol aqueous solution solvent to form the UV-curable layer.

[0013] According to an embodiment of the present invention, preferably, in the step of forming the UV-curable layer, the UV-curable chitosan material comprises azidobenzoyl-chitosan.

[0014] According to one embodiment of the present invention, preferably, in the step of forming the UV-curable layer, the UV-curable chitosan material comprises azidobenzoyl chitosan formed by a chemical reaction between carboxymethyl chitosan and N-(4-azidobenzoyloxy)succinimide.

[0015] According to an embodiment of the present invention, preferably, in the step of arranging the gray tone photomask, the gray tone photomask is formed into patterns with different ultraviolet transmittances according to a target thickness of the high hardness layer.

[0016] According to one embodiment of the present invention, preferably, in the step of arranging the gray tone photomask, the gray tone photomask has a pattern which can, through the change of gray tone, increase the curing of the ultraviolet curing layer due to the high ultraviolet transmittance in the area where the target thickness of the high hardness layer is large, and reduce the curing of the ultraviolet curing layer due to the low ultraviolet transmittance in the area where the target thickness of the high hardness layer is small.

[0017] According to one embodiment of the present invention, preferably, in the step of forming the high hardness layer, in the area of ​​the gray tone photomask with high ultraviolet transmittance, as the degree of curing of the ultraviolet curing layer increases, the thickness of the high hardness layer increases, and in the area of ​​the gray tone photomask with low ultraviolet transmittance, as the degree of curing of the ultraviolet curing layer decreases, the thickness of the high hardness layer decreases.

[0018] According to one embodiment of the present invention, preferably, in the step of forming the high hardness layer, the high hardness layer has a pattern of more than one separated discontinuous area, and the patterns of the separated discontinuous area each independently have a single thickness, or have multiple thicknesses with a step difference.

[0019] According to an embodiment of the present invention, preferably, the step of forming the medium hard layer is performed by coating a styrene-ethylene-butylene-styrene solution on the high hard layer by spin coating.

[0020] In order to solve the technical problem, the multilayer body according to the technical concept of the present invention may preferably include: a base material; a high hardness layer, which is located on the base material and has a Young's modulus larger than that of the base material, and has multiple thickness dimensions according to regions as the ultraviolet curing material is cured to different degrees according to regions; a medium hardness layer, which covers the high hardness layer and is located on the base material, and has a Young's modulus larger than that of the base material but smaller than that of the high hardness layer.

[0021] According to an embodiment of the present invention, preferably, when the multilayer structure is deformed by an applied external force, a plurality of wrinkles with different wavelengths are formed according to the thickness of the high hardness layer, thereby showing different structural colors.

[0022] According to one embodiment of the present invention, preferably, the high hardness layer includes at least one or more regions from first to fifth regions having first to fifth thicknesses whose thicknesses increase successively; in the first region, a structural color with a wavelength in the range of 400nm to 450nm is displayed, in the second region, a structural color with a wavelength in the range of 450nm to 500nm is displayed, in the third region, a structural color with a wavelength in the range of 500nm to 570nm is displayed, in the fourth region, a structural color with a wavelength in the range of 570nm to 600nm is displayed, and in the fifth region, a structural color with a wavelength in the range of 600nm to 750nm is displayed.

[0023] According to an embodiment of the present invention, preferably, the base material has a Young's modulus ranging from 1 MPa to 3 MPa, the high hardness layer has a Young's modulus ranging from 1000 MPa to 1300 MPa, and the medium hardness layer has a Young's modulus ranging from 800 MPa to 1000 MPa.

[0024] According to one embodiment of the present invention, preferably, the base material includes one of polydimethylsiloxane (PDMS), polyurethane (Polyurethane), copolyester (Ecoflex) (full name Ecological Flexibility, a thermoplastic elastomer material with environmentally friendly properties) and rubber series polymer substances.

[0025] According to an embodiment of the present invention, preferably, the high hardness layer comprises ultraviolet curing chitosan.

[0026] According to an embodiment of the present invention, preferably, the medium hard layer comprises styrene-ethylene-butylene-styrene.

[0027] In order to solve the technical problem, the anti-counterfeiting device according to the technical concept of the present invention may preferably include the above-mentioned multi-layer structure.

[0028] According to an embodiment of the present invention, preferably, the multilayer structure is in the form of a film.

[0029] The multilayer structure according to the technical concept of the present invention has the beneficial effect of controlling the thickness of the ultraviolet-cured chitosan layer that forms the high-hardness layer. When the multilayer structure is deformed due to the applied external force, multiple wrinkles with different wavelengths are formed according to the thickness of the high-hardness layer, thereby showing different structural colors.

[0030] According to the present invention, a transparent and flexible three-layer flexible film is proposed, which can actively show iridescent (pigment color) structural color when compressive stress or bending stress is applied. A wrinkle forming method based on photolithography using a gray tone photomask is also proposed, so that the wrinkle periodicity can be controlled in the size of tens of nanometers.

[0031] In addition, when the film is compressed or bent, it can form periodic wrinkles that can be precisely controlled in tens of nanometers in a multi-mode manner. The three-layer film structure is transparent when there is no pressure, but changes color when compressed inside, so it can be used in the field of anti-counterfeiting based on structural color called mechanochromic.

[0032] The present invention can provide a novel anti-counterfeiting system that can encrypt information in multiple colors and can be decoded using a specific color filter. The material patterning technology proposed by the present invention is a powerful method for controlling wrinkles in various applications such as anti-counterfeiting systems, soft robots, and optoelectronic devices, which can be used in the future.

[0033] The above description of the advantageous effects of the present invention is merely exemplary, and the scope of the present invention is not limited to these advantageous effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1a is a cross-sectional view of a multilayer structure according to an embodiment of the present invention;

[0035] Figure 1b This is a schematic diagram of a multilayer structure as an embodiment of the present invention, which is a simplified diagram showing a state where the structure has a single thickness (upper part), has a step difference and has multiple thicknesses (middle part), or has both forms (lower part) by region.

[0036] Figure 2 is a schematic diagram illustrating the structural color appearance and hiding mechanism of a multilayer structure according to an embodiment of the present invention;

[0037] Figure 3 is a schematic diagram illustrating the wrinkle development operation principle of a multilayer structure according to an embodiment of the present invention;

[0038] Figure 4 is a schematic diagram showing structural color displayed by wrinkles of a multilayer structure according to an embodiment of the present invention;

[0039] Figure 5 is a flow chart showing a method for manufacturing a multilayer structure according to an embodiment of the present invention;

[0040] Figure 6 is a schematic diagram showing a method for manufacturing a multilayer structure according to an embodiment of the present invention;

[0041] Figure 7 is a schematic diagram showing the synthesis of an ultraviolet curable chitosan material for a multilayer structure according to an embodiment of the present invention;

[0042] Figure 8 The results of observing wrinkles formed by the high hard layer thickness of the multilayer structure according to one embodiment of the present invention;

[0043] Fig. 9 is a graph showing the amplitude and periodicity of the high hard layer thickness formation of a multilayer structure according to an embodiment of the present invention;

[0044] Fig.10 This is a UV-visible molecular absorption spectroscopic chart for measuring various structural colors exhibited by a multilayer structure according to an embodiment of the present invention;

[0045] Fig.11 A plurality of schematic diagrams and a plurality of photographs showing the structural color phenomenon of the anti-counterfeiting altered film using the multilayer structure of one embodiment of the present invention compared with a comparative example;

[0046] Fig.12 This figure shows various applications to which the multilayer structure according to one embodiment of the present invention can be applied.

[0047] Explanation of symbols

[0048] 100: multilayer structure; 110: base material; 120: high hardness layer; 130: medium hardness layer. DETAILED DESCRIPTION

[0049] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. The multiple embodiments of the present invention are provided for those of ordinary skill in the art to further fully describe the technical solutions of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Those of ordinary skill in the art may modify the technical solutions described in the aforementioned embodiments, and these modifications do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions described in the embodiments of the present invention. On the contrary, these embodiments are provided to make the present disclosure more comprehensive and complete, and to fully convey the technical ideas of the present invention to those of ordinary skill in the art. In this specification, the same symbols always represent the same elements. Furthermore, the various elements and regions on the drawings are drawn relatively simply. Therefore, the technical ideas of the present invention are not limited by the relative sizes or spacings depicted in the drawings.

[0050] The technical idea of ​​the present invention relates to a multilayer structure that utilizes the diffraction phenomenon of light based on the unstable behavior of wrinkles generated in the multilayer structure, and can show various structural colors when external mechanical forces such as bending are applied, a manufacturing method thereof, and an anti-counterfeiting device using the multilayer structure.

[0051] Hereinafter, a thin film will be described as an example of the multilayer structure, but the technical concept of the present invention is not limited thereto.

[0052] Fine wrinkles and nanowrinkles naturally formed on the surface of ductile materials by analogy with natural materials have attracted widespread attention because they can be formed at nanometers and even micrometers at the same time. This unique instability shows the inherent advantages of high surface-to-volume ratio, periodicity, and compatibility. With these advantages, research on wrinkles has received great attention in various research fields such as stretchable device technology, optical technology, and anti-counterfeiting technology. Its main strategy is to imitate the skin structure based on the heterogeneity of double-layer thin films caused by external stimuli such as mechanical factors, chemical factors, and temperature factors. When the stress inducing heterogeneity of the hard layer and the soft substrate is applied to this double-layer system exceeding the threshold, the thin hard layer will show surface changes during the deformation of the soft substrate. Recently, considerable progress has been made in the formation of wrinkles by combining polydimethylsiloxane (PDMS) and metals, polymers, etc. as hard layer materials. However, it is still difficult to control the implementation of periodic wrinkles at the desired position in a device.

[0053] According to the technical concept of the present invention, a film is provided by utilizing the unstable behavior of a multilayer structure, that is, wrinkle development and diffraction by interference of light. The unstable behavior of wrinkles developed in a multilayer structure may occur when various stimuli are applied to two layers with different physical properties.

[0054] As described below, a multilayer structure film of UV-cured chitosan of various thicknesses stacked between polydimethylsiloxane and styrene-ethylene-butylene-styrene forms wrinkles on the surface of styrene-ethylene-butylene-styrene when mechanical bending is applied. Considering the Young's modulus of the material of each layer for mechanical properties, it can be appropriately selected, and by optimizing the manufacturing process, the thickness of the UV-cured chitosan can be controlled to tens of nanometers to form a wrinkled structure of hundreds of nanometers. As these wrinkled structures act as diffraction gratings, structural colors of various colors can be revealed.

[0055] In addition, due to the optical property of small refractive index difference of the materials of each layer, the multilayer structure film finally has a transparent property. Therefore, if the applied bending force is removed, the multilayer structure film will be in a transparent state again.

[0056] According to the technical concept of the present invention, a transparent, flexible, and reversibly wrinkled multilayer structure can be provided by single-step photopatterning of a gray-tone photomask with high production efficiency and economic efficiency.

[0057] Multilayer structure

[0058] FIG. 1 is a cross-sectional view of a multilayer structure 100 according to an embodiment of the present invention.

[0059] According to FIG. 1 , the multilayer structure 100 includes a base material 110 , a high hardness layer 120 , and a medium hardness layer 130 .

[0060] The materials of the base material 110, the high hardness layer 120 and the medium hardness layer 130 can be selected as a finished multilayer structure 100 with flexibility and optical transparency. When a bending force is applied to the manufactured multilayer structure 100, wrinkles of hundreds of nanometers in size will be generated on the surface, through which the surrounding incident light will be diffracted, thereby showing structural colors. In this state, if the height of the chitosan pattern is all constant, only the two structural colors of the chitosan pattern part / non-pattern part will appear. The core of the present invention is to use ultraviolet-cured chitosan material and a gray-tone photomask and adjust the height of the high hardness layer by different degrees of curing, so as to achieve the generation of various wrinkles and the resulting appearance of various structural colors according to a certain area / pattern when bending is applied.

[0061] The base material 110 may be formed of a flexible low-hardness material. The base material 110 is easily changed in shape under the action of external force. The base material 110 may include, for example, any one of polydimethylsiloxane (PDMS), polyurethane (Polyurethane), copolyester Ecoflex (full name Ecological Flexibility, a thermoplastic elastomer material with environmentally friendly characteristics) and rubber series polymer substances.

[0062] The high hardness layer 120 may be located on the base material 110. The high hardness layer 120 may have a larger Young's modulus than the base material 110. For example, compared with the low hardness material, the high hardness layer 120 may be formed of a high hardness material having a larger Young's modulus. The high hardness layer 120 may have a plurality of thickness dimensions achieved by curing the ultraviolet curable material to different degrees. When the morphology of the base material 110 is deformed under an external force, the high hardness layer 120 forms multiple micron-sized wrinkles on the surface due to the difference in physical properties, and a grating structure may be formed by the arrangement of the wrinkles. The high hardness layer 120 may have a variety of different thicknesses, and may also be composed of patterns of various shapes. The high hardness layer 120 may include a polymer substance such as chitosan, and may include UV-curable chitosan.

[0063] The medium hard layer 130 may be located on the base material 110 and cover the high hard layer 120. The medium hard layer 130 is larger than the base material 110 and has a smaller Young's modulus than the high hard layer 120. For example, the medium hard layer 130 may be formed of a medium hard material having a Young's modulus larger than that of the low hard material and smaller than that of the high hard material. The medium hard layer 130 may be formed slightly softer on the high hard layer 120, so that when the morphology of the base material 110 is deformed under an external force, due to the difference in physical properties, multiple wrinkles of nanometer size are formed on the surface, thereby forming a grating structure arranged by multiple wrinkles. The medium hard layer 130 has a larger Young's modulus than the base material 110 and may have a smaller Young's modulus than the high hard layer 120. In addition, the medium hard layer 130 may have a refractive index similar to that of the high hard layer 120. The medium hard layer 130 may contain styrene-ethylene-butylene-styrene. However, this is only an example, and the medium hard layer 130 may contain at least one of polyvinylalcohol (PVA), polymethacrylate (PMMA), acrylic, and polybutadiene.

[0064] Here, the materials forming the above-mentioned base material 110, high hard layer 120 and medium hard layer 130 are not limited to the materials described above. Compared with the base material 110, the high hard layer 120 and the medium hard layer 130 have a relatively high Young's modulus. If they can have similar refractive indices, the base material 110, the high hard layer 120 and the medium hard layer 130 can be made of various materials. In this case, the difference between the Young's modulus of the base material 110 and the high hard layer 120 and the medium hard layer 130 is about 100 times or more, which is conducive to the formation of wrinkles larger than nanometer size. For example, the base material 110 can have a Young's modulus in the range of 1 MPa to 3 MPa, the high hard layer 120 can have a Young's modulus in the range of 1000 MPa to 1300 MPa, and the medium hard layer 130 can have a Young's modulus in the range of 800 MPa to 1000 MPa.

[0065] When the multilayer structure 100 is deformed by an applied external force, multiple wrinkles with different wavelengths are formed according to the thickness of the high hard layer 120, thereby showing different structural colors. As the thickness of the high hard layer 120 increases, the wavelength of the structural color shown may increase.

[0066] For example, the high hardness layer 120 may include at least one or more regions of first to fifth regions having first to fifth thicknesses, respectively, whose thicknesses increase in sequence.

[0067] For example, the high hard layer 120 may include a first region 121 having a first thickness T1 and a second region 122 having a second thickness T2 greater than the first thickness T1. When the external force is applied, the structural color displayed in the second region 122 may have a longer wavelength than the structural color displayed in the first region 121. In addition, the high hard layer 120 may further include a third region 123 having a third thickness T3 greater than the second thickness T2. When the external force is applied, the structural color displayed in the third region 123 may have a longer wavelength than the structural colors displayed in the first region 121 and the second region 122, respectively. In addition, the high hard layer 120 may further include a fourth region 124 having a fourth thickness T4 greater than the third thickness T3. When the external force is applied, the structural color displayed in the fourth region 124 may have a longer wavelength than the structural colors displayed in the first region 121, the second region 122, and the third region 123. In addition, the high hard layer 120 may further include a fifth region 125 having a fifth thickness T5 greater than the fourth thickness T4. When the external force is applied, the structural color developed in the fifth region may have a longer wavelength than the structural colors developed in the first region 121 , the second region 122 , the third region 124 , and the fourth region 124 , respectively.

[0068] For example, a purple structural color may be displayed in the first region 121, for example, a structural color with a wavelength in the range of 400 nm to 450 nm, a blue structural color may be displayed in the second region 122, and a structural color with a wavelength in the range of 450 nm to 500 nm, a green structural color may be displayed in the third region 123, and a structural color with a wavelength in the range of 500 nm to 570 nm, a yellow structural color may be displayed in the fourth region 124, and a structural color with a wavelength in the range of 570 nm to 600 nm, and a red structural color may be displayed in the fifth region 125. However, this is only an example, and the technical concept of the present invention is not limited thereto.

[0069] Figure 2 1 is a schematic diagram for explaining the mechanism of appearance and concealment of structural color of a multilayer structure 100 according to an embodiment of the present invention.

[0070] according to Figure 2, the left picture shows a state where no mechanical force is applied to the multilayer structure in the shape of a thin film. In order to distinguish, the high hardness layer 120 is colored in a light color, but it is actually transparent and may not be recognizable with the naked eye. The right picture shows a state where a bending mechanical force is applied to the multilayer structure to make the multilayer structure bend more. In this state, structural colors of various colors appear in the area where the high hardness layer 120 is located according to the thickness of the high hardness layer 120. The color of the structural color can be determined according to the thickness of the high hardness layer 120 when the incident angle and viewing angle of white light are the same. After removing the bending mechanical force, the multilayer structure can be unfolded and restored to its original state, causing the structural color to disappear and become transparent.

[0071] Figure 3 This is a schematic diagram for explaining the working principle of wrinkle development of the multilayer structure 100 according to one embodiment of the present invention.

[0072] according to Figure 3 , which shows a cross-sectional view of a multilayer structure 100. Blue represents a base material 110, yellow represents a high hardness layer 120, and gray represents a medium hardness layer 130. The red dotted line indicates a neutral surface of the multilayer structure.

[0073] Figure 3 (a) indicates the state where no external force is applied. Figure 3 As shown in (b), when external force is applied in the bending direction, the stress is distributed as shown in the black part. Furthermore, compressive stress (compression) is applied on the upper side and tensile stress (tension) is applied on the lower side. Figure 3 In (c), the high hardness layer 120 shown in yellow is enlarged and displayed, and the stress distribution is also shown. Figure 3 (d) shows wrinkles caused by applied stress. After stress is applied, it can be seen that the wavelength and amplitude of wrinkles formed in the area formed by the high hard layer 120 and the medium hard layer 130 on the base material 110 are different from the wavelength and amplitude of wrinkles formed in the area formed by only the medium hard layer 130 on the base material 110. As shown in the figure, the wavelength and amplitude of wrinkles formed in the area formed by the high hard layer 120 and the medium hard layer 130 on the base material 110 are larger. Through analysis, it is believed that this is because the Young's modulus of the high hard layer 120 is larger than that of the medium hard layer 130.

[0074] When bending force is applied to the multilayer structure 100 by external force, buckling instability behavior occurs due to the discontinuity of mechanical properties between the soft base material 110, the hard ultraviolet-cured chitosan high hard layer 120 and the medium hard layer 130, thereby forming a wrinkle arrangement pattern with a periodic width.

[0075] According to the linear buckling theory, the wrinkle wavelength (d) of the soft-hard double-layer structure is expressed by the following formula 1. In addition, the height (W) of the wrinkles is expressed by mathematical formula 2. Furthermore, mathematical formulas 1 and 2 are applicable when there is no intermediate layer, i.e., a high-hardness layer.

[0076]

Mathematical formula 1

[0077]

[0078]

Mathematical formula 2

[0079]

[0080] In the above mathematical formula 1 and mathematical formula 2, λ is the wavelength of the wrinkles formed, hf is the thickness of the hard layer, is the plane deformation coefficient (Young's modulus) and is defined as is the plane deformation coefficient of the hard layer, is the plane deformation coefficient of the soft layer, E is Young's modulus, ν is Poisson's ratio, W is the height of the wrinkle, e0 is the imposed strain, e c is the critical strain of wrinkles.

[0081] When the double-layer film is deformed in one direction (x or y) due to mechanical stress, a one-dimensional periodic wrinkle pattern is formed. c ) exhibits the characteristics of soft materials, so the size of the wrinkles is almost independent of multiple intrinsic parameters such as the elastic modulus of the hard film, the elastic modulus of the soft material, and the deformation speed.

[0082] Therefore, attempts to universally form polymorphs / multi-wrinkles are limited for cases with other physical properties such as selective UV curing, local oxidation, high inclination of the hard layer, mold structure, etc. As a corresponding solution, in order to control the surface changes caused by external stress, a three-layer film is proposed by stacking two layers on the lower soft material. The reason is that the three-layer film can produce heterogeneity differences and surface deformation rate differences caused by the neutral plane only by controlling the thickness of the stack. However, these methods are limited from the perspective of the mechanical properties of the multi-pattern (e.g., Young's modulus), and it is difficult to control the patterning position independent of the desired position. Therefore, a method is needed to control the local heterogeneity of the entire system at the desired position according to the properties of the patterned material.

[0083] These mathematical formulas 1 show a model of the surface periodic phenomenon and predict the periodicity of the multilayer structure 100. Specifically, in the multilayer structure 100 in which the high hard layer 120 and the medium hard layer 130 corresponding to the hard layer are composited with the base material 110 corresponding to the soft layer, the Young's modulus of the high hard layer 120 and the medium hard layer 130 is much higher than that of the base material 110, so the high hard layer 120 and the medium hard layer 130 can be regarded as a thin film layer with rigidity, and the size (width) of each wavelength of the wrinkles can be determined according to the relative difference in Young's modulus (E) and the relative difference in thickness (h) between the high hard layer 120 and the medium hard layer 130 and the base material 110.

[0084] The wrinkles formed on the high hard layer 120 and the medium hard layer 130 may be different as follows. A wrinkle structure of micrometer units may be formed on the high hard layer 120 to form a high wrinkle area, and a wrinkle structure of nanometer units may be formed on the medium hard layer 130 to form a low wrinkle area. As a result, the chromaticity of the structural color may appear differently on the high hard layer 120 and the medium hard layer 130. And the generated wrinkles form wrinkles with a certain wavelength on the high hard layer 120 and the medium hard layer 130, so that the high hard layer 120 and the medium hard layer 130 can show different structural colors, and an image can be formed by the structural colors appearing in the high wrinkle area and the low wrinkle area formed in the high hard layer 120 and the medium hard layer 130 respectively. However, the certain wavelength refers to the wavelength size of the average wrinkles of the high hard layer 120 and the medium hard layer 130. The high hard layer 120 and the medium hard layer 130 may have wrinkles with the same wavelength, but the high hard layer 120 and the medium hard layer 130 may have wrinkles with partially different wavelengths.

[0085] The multilayer structure 100 is a grating structure in which corrugations are arranged in a one-dimensional (1D) structure passing through the x-axis or y-axis direction through the corrugations.

[0086] Here, the load applied to the multilayer structure 100 may be a single load of compression, tension or torsional load including bending load, or may be a composite load of two or more, and the compressive deformation formed on the multilayer structure 100 may be a deformation caused by such compression, tension, bending or torsional load.

[0087] When the medium hard layer 130 has a refractive index of 96% to 104% of the high hard layer 120 or the base material 110, an active hidden-visible structure of an optical holographic image in response to an input can be realized. Specifically, the high hard layer 120 and the medium hard layer 130 do not form a grating structure according to the pleat arrangement when no external stimulus is applied, and therefore exist as a (covert) 0-dimensional grid without structural color. This is because most of the incident light is transmitted due to the transmissive transparency caused by the same or similar refractive index (R / Chitosan-R / PDMS=0.04) of the base material 110 and the high hard layer 120 and the medium hard layer 130. Therefore, the high hard layer 120 and the medium hard layer 130 can be completely hidden in the base material 110 without the appearance of the structural color of the grating structure formed by the pleat arrangement.

[0088] On the contrary, when the hard layer is not a single layer but a double layer, that is, when a high hard layer is inserted as an intermediate layer to form a three-layer structure, according to the Stafford model, the equivalent Young's modulus (E eff ) is shown in Mathematical Formula 3. In addition, Mathematical Formula 4 shows the coordinate (y) of the neutral plane from the bottom of the substrate.

[0089]

Mathematical formula 3

[0090]

[0091]

Mathematical formula 4

[0092]

[0093] In Mathematical Formula 3 and Mathematical Formula 4, m is the Young's modulus of the uppermost hard layer (E f ) and the Young's modulus of the hard layer in the middle layer (E i ) ratio (m=E f / E i ), n is the thickness of the uppermost hard layer (t f ) and the thickness of the intermediate hard layer (t i ) ratio (n=t f / t i ).

[0094] Therefore, the wavelengths of wrinkles of the double layer composed of the base material 110 and the medium hard layer 130 and the triple layer composed of the base material 110, the high hard layer 120 and the medium hard layer 130 may generate wrinkles of different wavelengths due to the difference in Young's modulus, and wrinkles of different wavelengths may be generated according to the thickness of the high hard layer 120 composed of ultraviolet-cured chitosan. Furthermore, the multilayer structure 100 of the present invention can realize multi-mode generation of wrinkles and multi-structural color display by patterning the surface properties of the material.

[0095] Figure 4 This is a schematic diagram showing the structural color appearance due to wrinkles of a multilayer structure 100 according to one embodiment of the present invention.

[0096] according to Figure 4 The display shows that when white light is incident on the multilayer structure that generates wrinkles, the light is diffracted and transmitted. In addition, multiple wrinkles with different amplitudes and periods formed according to the thickness of the high hard layer composed of ultraviolet-cured chitosan can show structural colors of various colors. Considering the incident angle of white light (θ I ) and viewing angle (θ D ), fold period (d), wavelength of diffracted light (λ1) and diffraction order (n), satisfying the diffraction equation "nλ1=d(sinθ I -sinθ D )”, according to the theory of light enhancement interference and mutual cancellation interference based on this, diffracted light of a specific wavelength can be obtained from a specific viewing angle.

[0097] In the multilayer structure of the present invention, the amplitude and period of the wrinkles become different depending on whether a high-hardness layer composed of ultraviolet-cured chitosan is formed on the surface and the thickness of the high-hardness layer, so diffracted light of various wavelengths can be obtained at a specific viewing angle.

[0098] Method for producing multilayer structure

[0099] Next, the method for producing the multilayer structure will be described in detail.

[0100] Figure 5 1 is a flow chart showing a method for manufacturing a multilayer structure according to an embodiment of the present invention.

[0101] Figure 6 This is a schematic diagram showing a method for producing a multilayer structure according to an embodiment of the present invention.

[0102] according to Figure 5 and Figure 6 The manufacturing method S100 of the multilayer structure includes: a step S110 of providing a base material; a step S120 of forming an ultraviolet-cured layer containing ultraviolet-cured chitosan on the base material; a step S130 of arranging a gray-tone photomask on the ultraviolet-cured layer; a step S140 of irradiating ultraviolet rays onto the ultraviolet-cured layer through the gray-tone photomask to differentially cure the ultraviolet-cured layer; a step S150 of developing the cured ultraviolet-cured layer to form a high-hardness layer with different thicknesses according to the differential curing of the ultraviolet-cured layer; and a step S160 of forming a medium-hardness layer on the high-hardness layer.

[0103] The step of providing the substrate S110 may be formed by providing a base material formed of a flexible low-hardness material. The base material may include, for example, one of polydimethylsiloxane (PDMS), polyurethane (Polyurethane), Ecoflex (full name: Ecological Flexibility, a thermoplastic elastomer material with environmentally friendly characteristics) and a rubber series of polymer substances.

[0104] The step S110 of providing the base material may include the steps of mixing a main material of polydimethylsiloxane and a curing agent to form a mixture; placing the mixture in a vacuum to remove bubbles; and thermally curing the mixture to form the base material.

[0105] Specifically, the main material of the PDMS and the curing agent are fully mixed, for example, in a ratio of 9:1 to 11:1, for example, in a ratio of 10:1 to form a mixture, and then placed in a vacuum atmosphere for, for example, 1 minute to 60 minutes, for example, 30 minutes to remove bubbles. After the bubbles in the PDMS are completely removed, it is placed in a square plate of polystyrene material and placed in an oven at a temperature of, for example, 60°C to 80°C, for example, about 70°C, for curing, for example, 1 hour to 5 hours, for example, about 3 hours, to form a base material composed of the PDMS. The height of the base material can be controlled according to the height of the PDMS.

[0106] In addition, in order to improve the surface properties of the base material, for example, to increase wettability, a step of performing an oxygen plasma treatment before the subsequent spin coating of the UV curing layer may be further included. The oxygen plasma may be performed at 10W to 100W for 1 second to 60 seconds, for example, at 50W for 30 seconds, so that the wetting angle of the PDMS base material may be, for example, 10 degrees to 20 degrees, for example, 15 degrees.

[0107] The step S120 of forming the UV-curable layer may be performed by spin coating the UV-curable chitosan solution on the base material.

[0108] Specifically, the step S120 of forming the UV-curable layer may include: providing the UV-curable chitosan solution formed by dissolving the UV-curable chitosan material in an ethanol aqueous solution solvent; pouring the UV-curable chitosan solution onto the base material for spin coating; and heating the base material on which the UV-curable chitosan solution is spin coated to evaporate the ethanol aqueous solution solvent, thereby forming the UV-curable layer.

[0109] The solidified chitosan solution can be prepared as follows. Prepare an ethanol aqueous solution in which ultrapure water and ethanol are mixed in a ratio of, for example, 7:3 to 9:1, for example, 8:2. Dissolve the ultraviolet curable chitosan material in the ethanol aqueous solution, for example, at a concentration in the range of 0.2% w / v to 0.4% w / v, for example, at a concentration of 0.3% w / v. (Here, % w / v means weight % / volume).

[0110] The ultraviolet curable chitosan material may include azidobenzoyl chitosan. In addition, the ultraviolet curable chitosan material may include azidobenzoyl chitosan formed by chemical reaction of carboxymethyl chitosan and N-(4-azidobenzoyloxy) succinimide. But this is only an example, and the technical idea of ​​the present invention is not limited to this. The ultraviolet curable chitosan material is described in detail below.

[0111] Optionally, in order to completely dissolve the ultraviolet curable chitosan material, the material may be stirred in an ultrasonic water tank, for example, for a period of 1 minute to about 1 hour, for example, 30 minutes.

[0112] The spin coating conditions are as follows: About 200 μl of the solidified chitosan solution is poured onto the base material, and the spin coating is performed using a spin coater (SPIN-1200D, Midas system, Korea) at a rotation speed ranging from 300 rpm to 700 rpm, for example, at 500 rpm.

[0113] After the spin coating, it is placed in an oven and heated at, for example, 60 to 70° C. for 1 to 60 minutes, for example, at 65° C. for 30 minutes, to evaporate the residual solvent and form the UV-curable layer.

[0114] The UV curable layer can be formed by blade coating, spray coating, dip coating, etc. in addition to the spin coating. The UV curable layer can be formed to completely cover the base material.

[0115] In the step S130 of arranging the gray tone photomask, the gray tone photomask can be formed into patterns having different ultraviolet transmittances according to the target thickness of the high hardness layer 120 .

[0116] For example, in step S130 of arranging a gray tone photomask, the gray tone photomask may have a pattern with gray tone variations so that the curing of the UV-curable layer is increased due to the high UV transmittance in an area where the target thickness of the high hardness layer 120 is large, and the curing of the UV-curable layer is reduced due to the low UV transmittance in an area where the target thickness of the high hardness layer 120 is small.

[0117] Therefore, the gray tone photomask may include a pattern having an ultraviolet transmittance ranging from 1% to 99% corresponding to the target thickness of the high hardness layer 120 .

[0118] In the step S130 of curing the ultraviolet curable layer differently, ultraviolet rays are irradiated onto the ultraviolet curable layer through the gray tone photomask, so that the ultraviolet curable layer is cured differently. In the area where the ultraviolet transmittance of the gray tone photomask is high, the curing degree of the ultraviolet curable layer can be high, and in the area where the ultraviolet transmittance of the gray tone photomask is low, the curing degree of the ultraviolet curable layer can be low.

[0119] In the step S150 of forming the high hardness layer, the cured ultraviolet curing layer is developed. Then, according to the different hardening of the ultraviolet curing layer, the high hardness layer 120 with different thicknesses is formed. For example, when the ultraviolet curing layer is developed using a developing solution such as ultrapure water, the uncured substances constituting the ultraviolet curing layer can be removed, and the cured substances are retained, thereby forming the high hardness layer 120.

[0120] In the area where the ultraviolet transmittance of the gray-tone photomask is high, as the degree of curing of the ultraviolet curing layer increases, the thickness of the high hardness layer 120 increases, and in the area where the ultraviolet transmittance of the gray-tone photomask is low, as the degree of curing of the ultraviolet curing layer decreases, the thickness of the high hardness layer 120 decreases.

[0121] The high hardness layer 120 has a pattern of more than one separated discontinuous region, and the separated discontinuous region patterns can each independently have a single thickness, or can have multiple thicknesses with a step difference. The shape of the high hardness layer 120 can be realized in accordance with the design of the gray tone photomask.

[0122] Figure 1b A schematic diagram showing the layered structure of different morphological types of this high-hardness layer. Figure 1b The top part shows the morphology in which high hardness layers with different thicknesses are separated in different regions. Figure 1b The middle represents the shape in which multiple thicknesses form steps and are continuously formed in one area. Figure 1b The following means that Figure 1b The appearance of a high hard layer that includes all the upper and middle forms.

[0123] Optionally, after the high hard layer 120 is formed, the surface of the high hard layer 120 may be modified by oxygen plasma treatment.

[0124] The step 160 of forming the medium hard layer may be performed by coating the styrene-ethylene-butylene-styrene solution on the high hard layer 120 by a spin coating method.

[0125] The styrene-ethylene-butylene-styrene solution may be a solution in which styrene-ethylene-butylene-styrene is dissolved in a toluene solvent (Toluene) at a concentration of, for example, 1 w / v to 5 w / v, for example, 3 w / v. The styrene-ethylene-butylene-styrene solution may have a mixing ratio and a concentration that can be changed according to the desired Young's modulus and refractive index.

[0126] Optionally, in order to completely dissolve the styrene-ethylene-butylene-styrene, the mixture may be stirred in an ultrasonic water tank, for example, for a period of time ranging from 1 minute to about 1 hour, for example, 30 minutes.

[0127] The spin coating conditions are as follows: About 200 μl of styrene-ethylene-butylene-styrene is injected onto the high hardness layer and spin coated using a spin coater (SPIN-1200D, Midas system, Korea) at a rotation speed ranging from 300 rpm to 700 rpm, for example, 500 rpm.

[0128] After the spin coating, the substrate is placed in an oven and heated at 60° C. to 70° C. for 1 to 60 minutes, for example, at 65° C. for 30 minutes, to evaporate the residual solvent and form a medium hard layer.

[0129] The medium hard layer may be formed by blade coating, spray coating or dip coating in addition to the spin coating. The medium hard layer may be formed by completely covering the high hard layer and the base material.

[0130] The multilayer structure 100 including the base material 110 , the high hard layer 120 , and the medium hard layer 130 is thereby completed.

[0131] The multilayer structure 100 manufactured by the manufacturing method is that when the multilayer structure 100 is deformed by an applied external force, multiple wrinkles with different wavelengths are formed according to the thickness of the high hardness layer 120, thereby showing different structural colors.

[0132] The method for producing the ultraviolet curable chitosan material is described below by way of example.

[0133] Figure 7 FIG. 1 is a schematic diagram showing the synthesis of an ultraviolet curable chitosan material for a multilayer structure according to an embodiment of the present invention.

[0134] 1) Carboxymethyl chitosan is prepared as follows. The synthesis pattern of the carboxymethyl chitosan is shown in FIG. Figure 7 As shown in (a).

[0135] 1-1) To 80 mL of a solvent prepared by mixing 40 mL of ultrapure water and 40 mL of isopropanol, 5 g of chitosan and 7 g of sodium hydroxide (NaOH) are added to form a uniform solution, and the mixture is stirred at, for example, 40°C to 60°C, for example, at 50°C, for 1 minute to 24 hours to form a solution 1-1.

[0136] 1-2) Dissolve 7.5 g of chloroacetic acid in 10 mL of isopropanol to form solution 1-2.

[0137] 1-3) Slowly injecting the 1-2 solution into the 1-1 solution, and stirring at 40° C. to 60° C., for example, 50° C., for 1 hour to 24 hours to produce a chemical reaction to form a 1-3 solution.

[0138] 1-4) 100 mL of an ethanol aqueous solution in which ultrapure water and ethanol are mixed at a ratio of 3:7 is injected into the solution 1-3 to form the solution 1-4, and then the chemical reaction is stopped to obtain sodium carboxymethyl chitosan (Na Salt Carboxymethyl Chitosan) as a precipitate.

[0139] 1-5) When the solution 1-4 is filtered and washed with an ethanol aqueous solution having a purity of 70% to 90%, the sodium salt is removed from the sodium salt of carboxymethyl chitosan, and then dried in a vacuum to obtain carboxymethyl chitosan as a final substance.

[0140] 2) Prepare N-(4-azidobenzoyloxy)succinimide as follows. The synthesis pattern of N-(4-azidobenzoyloxy)succinimide is shown in the figure below. Figure 7 as shown in (b).

[0141] 2-1) 4.5 g of N,N'-dicyclohexylcarbodiimide was added to 15 mL of tetrahydrofuran and dissolved therein to prepare a solution 2-1.

[0142] 2-2) 3.265 g of 4-azidobenzoic acid and 2.5 g of N-hydroxysuccinimide were added to 20 mL of tetrahydrofuran and dissolved to form a solution 2-2.

[0143] 2-3) In the solution 2-1, the solution 2-2 is dripped drop by drop for 1 hour to 24 hours to form the solution 2-3. A chemical reaction may occur in the solution 2-3. A precipitated byproduct may be formed by the chemical reaction.

[0144] 2-4) After the precipitated by-product is filtered out, a portion of the solvent is removed from the solution 2-3 using a rotary evaporator to concentrate the solution.

[0145] 2-5) The concentrated solution 2-3 is added to the solution 2-4 having a ratio of diethyl ether to tetrahydrofuran of 7:3 to form the solution 2-5, and a recrystallization reaction is performed to form N-(4-azidobenzoyloxy)succinimide.

[0146] 2-6) The entire 2-5 solution is filtered and dried in vacuo to obtain N-(4-azidobenzoyloxy)succinimide.

[0147] 3) Azidobenzoyl-Chitosan was prepared as follows. The synthesis pattern of the azidobenzoyl-Chitosan is shown in FIG. Figure 7 as shown in (c).

[0148] 3-1) 2.5 g of carboxymethyl chitosan was added to 100 mL of ultrapure water and dissolved to form solution 3-1. The pH of solution 3-1 was adjusted to 10.

[0149] 3-2) Add 1 g of 4-azidobenzoic acid to 15 mL of dioxane to dissolve and form solution 3-2.

[0150] 3-3) Slowly injecting the 3-2 solution into the 3-1 solution to produce a chemical reaction, for example, at 40° C. to 60° C., for example, at 50° C. for 1 hour to 48 hours, thereby forming a 3-3 solution.

[0151] 3-4) dialyzing and freeze-drying the solution 3-3 to form azidobenzoyl chitosan.

[0152] as follows Fig.11 As shown, the multilayer structure of the present invention can be used to realize an anti-counterfeiting device. The multilayer structure can be in the form of a film.

[0153] The multilayer structure not only has input-reactive or hidden-visible characteristics, but also has the characteristic of being able to switch one-dimensional or two-dimensional grating structures, and has the characteristic of building more images into a device by using layers with multiple grating structures, so that anti-counterfeiting devices and systems with higher anti-counterfeiting freedom can be realized than the existing passive optical holograms used as anti-counterfeiting means.

[0154] According to the present invention, the following effects are achieved. First, when a thin but hard high-hardness layer with a similar refractive index is formed on a thick and flexible base material, the characteristic of the high-hardness layer to form a wrinkle pattern based on the instability of the buckling type under external stimulation can be utilized to make the structural color that can form a specific picture actively hidden or visible, thereby improving the degree of freedom required for anti-counterfeiting of the existing passive optical hologram anti-counterfeiting device. Second, when the thin and hard hard layer is composed of multiple hard layers with different Young's modulus by adjusting the Young's modulus, the size of the wrinkle wavelength of the generated surface wrinkle pattern will become different. Therefore, by utilizing the characteristic of showing structural colors with different chromaticities in each hard layer, the structural color that forms a specific image is more diverse, thereby further improving the degree of freedom of the optical hologram anti-counterfeiting device that is hidden-visible due to external stimulation. Third, since various structural colors are displayed according to the changing form of the complex, the incident angle of the incident light, and the viewing angle of the user, corresponding multiple information can be provided to the user. Fourth, if the hard and high-hardness layer is arranged in a grid pattern along the length and width directions of the base material, the surface structure changes according to the single-direction load or the combined-direction load applied to the base material, thereby controlling the size and direction of the wrinkles and making each structural color appear, thereby providing a more diverse multilayer structure.

[0155] Experimental example

[0156] In order to help understand the present invention, preferred experimental examples are presented below. However, the following experimental examples are only for helping understand the present invention, and the present invention is not limited to the following experimental examples.

[0157] A multilayer structure was produced according to the above method, and the wrinkle amplitude and periodicity of the high hard layer composed of ultraviolet cured chitosan were measured using a field emission scanning electron microscope and an atomic force microscope.

[0158] Figure 8 Graphs 1 and 2 show the results of observing wrinkles formed by the high hard layer thickness of the multilayer structure according to one embodiment of the present invention.

[0159] according to Figure 8 , (a) is a field emission scanning electron microscope photo, (b) is an atomic force microscope photo. After observation, it was confirmed that nano-sized and fine-sized wrinkles were formed within 100nm. It was also confirmed that the wavelength and periodicity of the wrinkles changed with the thickness of the high hardness layer. Therefore, the amplitude and periodicity of the formed wrinkles can be measured.

[0160] Fig. 9 is a graph showing the amplitude and periodicity of wrinkles formed by high hard layer thickness of a multilayer structure according to an embodiment of the present invention.

[0161] according to Fig. 9 , showing that according to Figure 8 The results show the amplitude and periodicity of the wrinkles formed by the thickness of the high hard layer of the multilayer structure. It can be seen that as the thickness of the high hard layer increases, the amplitude and periodicity increase in a linear or quasi-linear relationship. For example, the high hard layer forms wrinkles with an amplitude of 295nm and a periodicity of 1.4μm in a state of 23nm thickness, and forms wrinkles with an amplitude of 446nm and a periodicity of 2.2μm in a state of 80nm thickness.

[0162] Fig.10 This is a graph showing the ultraviolet-visible molecular absorption spectrometry obtained by measuring the structural color exhibited by the multilayer structure according to one embodiment of the present invention.

[0163] according to Fig.10 The multilayer structure can diffract the irradiated white light and show light of multiple wavelengths. The wavelength of the light shown can be changed according to the thickness of the high hard layer composed of ultraviolet curing chitosan. For example, as an example, when the thickness of the high hard layer has five different thicknesses, it can be seen that five wavelengths of light, purple, blue, green, yellow and red, are shown.

[0164] Fig.11 The present invention is applied to a multi-layer structure of an embodiment of the present invention. The present invention is applied to an anti-counterfeiting mold of ...

[0165] Commercially available food containers or cosmetic containers are generally sealed with thicker opaque films to maintain freshness and quality. If such a film is made into an anti-counterfeiting film using the multilayer structure of the present invention, it is possible to confirm whether the product has been counterfeited by observing whether the structural color pattern appears or not. For example, when an anti-counterfeiting film having a size larger than the diameter of the entrance of a food container or a cosmetic container is bent and placed into the entrance to seal the entrance of the container, compressive stress will act on the anti-counterfeiting film. On the contrary, if the seal is released, the bending stress acting on the anti-counterfeiting film is released and the wrinkles disappear. For such an anti-counterfeiting film, it is possible to confirm whether the product has been counterfeited or not by observing whether the wrinkles are formed or not, and by observing whether the color appears or disappears.

[0166] according to Fig.11 The display of (a) is a comparative example of the conventional pigment coloration applied to the anti-counterfeiting alteration film. When the pigment coloration is applied to the anti-counterfeiting alteration film, the pigment coloration always appears regardless of whether it is bent or not. Therefore, it is impossible to confirm whether it is a counterfeit alteration under the conditions of the comparative example.

[0167] according to Fig.11 (b) is an embodiment of the structural coloration of the present invention applied to an anti-counterfeiting alteration film. The wrinkles formed by the bending stress acting on the anti-counterfeiting alteration film show the structural color. On the contrary, when the seal is released, the bending stress acting on the anti-counterfeiting alteration film is released, the wrinkles disappear, the structural color disappears, and the anti-counterfeiting alteration film becomes transparent. Therefore, in the state of the embodiment, the anti-counterfeiting alteration can be confirmed based on the appearance and removal of the structural color of whether the anti-counterfeiting alteration film is bent or not.

[0168] Fig.12 This figure shows various applications to which the multilayer structure according to one embodiment of the present invention can be applied.

[0169] Fig.12 (a) shows the transparent state of the multilayer structure in the unfolded state (neutral) without external stimulation. When compressive stress is applied and the multilayer structure is bent inward, a pattern is displayed by the mechanochromic reaction caused by the wrinkles. Here, the colors of the flowers and branches are different. This can be achieved by controlling the thickness of the high hardness layer of the present invention. These characteristics show that the generation of wrinkles is entirely the result of material patterning, and there is no interaction on the surrounding surface. On the contrary, even if compressive stress is applied, the pattern cannot be displayed when the multilayer structure is bent outward.

[0170] according to Fig.12(b) and (c) show the process of decoding the new barcode system. The barcode has red target information and blue virtual information, which are clear and encrypted. It is transparent in the unfolded state (neutral). When bent inward, the red and blue barcodes appear due to the mechanochromic reaction caused by the wrinkles, and this can be achieved by controlling the thickness of the high hard layer of the present invention. And by filtering, only the required red target information can be obtained.

[0171] according to Fig.12 (d) provides a method for inserting information in color. The type of information to be inserted is illustrated according to the color. The required information is a physical property pattern that appears in a specific color (red), and the unnecessary information is a physical property pattern that appears in blue. Barcodes in which multiple colors are inserted under compression cannot be distinguished by smartphone applications, which indicates encrypted information and virtual information. These characteristics make it difficult to distinguish information. However, if a simple color filter is used, unnecessary colors can be filtered out, and only the required information can be obtained through a commercial barcode reading application. Furthermore, only specific colors can be extracted through color filters, and information formed in specific colors can be obtained through smartphone applications.

[0172] The above embodiments and drawings are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art can still modify or make equivalent substitutions for the technical solutions described in the aforementioned embodiments, and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the embodiments of the present invention.

Claims

1. A method for producing a multilayer structure, characterized in that: include: Steps to provide basic materials; forming a UV-curable layer comprising UV-curable chitosan on the base material; a step of arranging a gray tone photomask on the ultraviolet curing layer; The step of irradiating ultraviolet rays onto the ultraviolet curable layer through the gray tone photomask so that the ultraviolet curable layer is cured to different degrees; The cured ultraviolet curing layer is developed to form high hard layers with different thicknesses according to different degrees of curing of the ultraviolet curing layer; and a medium hard layer is formed on the high hard layer.

2. The method for producing a multilayer structure according to claim 1, wherein: The step of providing the base material includes: mixing a main material of polydimethylsiloxane and a curing agent to form a mixture; placing the mixture in a vacuum to remove bubbles; and thermally curing the mixture to form the base material.

3. The method for producing a multilayer structure according to claim 1, wherein: The step of providing the base material further includes the step of performing oxygen plasma treatment to modify the surface properties of the base material.

4. The method for producing a multilayer structure according to claim 1, wherein: The steps of forming the ultraviolet curing layer include: providing the ultraviolet curing chitosan solution formed by dissolving the ultraviolet curing chitosan material in an ethanol aqueous solution solvent; pouring the ultraviolet curing chitosan solution onto the base material and spin coating it; and heating the base material on which the ultraviolet curing chitosan solution is spin coated to evaporate the ethanol aqueous solution solvent to form the ultraviolet curing layer.

5. The method for producing a multilayer structure according to claim 4, characterized in that: In the step of forming the UV-curable layer, the UV-curable chitosan material comprises azidobenzoyl-chitosan.

6. The method for producing a multilayer structure according to claim 4, wherein: In the step of forming the ultraviolet curing layer, the ultraviolet curing chitosan material comprises azidobenzoyl chitosan formed by a chemical reaction between carboxymethyl chitosan and N-(4-azidobenzoyloxy)succinimide.

7. The method for producing a multilayer structure according to claim 1, wherein: In the step of arranging the gray tone photomask, the gray tone photomask is formed into a pattern having different ultraviolet transmittances according to a target thickness of the high hardness layer.

8. The method for producing a multilayer structure according to claim 7, wherein: In the step of arranging the gray tone photomask, the gray tone photomask has a pattern in which, through the change of gray tone, the curing of the ultraviolet curing layer is increased due to the high ultraviolet transmittance in the area where the target thickness of the high hardness layer is large, and the curing of the ultraviolet curing layer is reduced due to the low ultraviolet transmittance in the area where the target thickness of the high hardness layer is small.

9. The method for producing a multilayer structure according to claim 7, wherein: In the step of forming the high hardness layer, in the area of ​​the gray tone photomask with high ultraviolet transmittance as the degree of curing of the ultraviolet curing layer increases, the thickness of the high hardness layer increases, and in the area of ​​the gray tone photomask with low ultraviolet transmittance as the degree of curing of the ultraviolet curing layer decreases, the thickness of the high hardness layer decreases.

10. The method for producing a multilayer structure according to claim 1, wherein: In the step of forming the high hardness layer, the high hardness layer has a pattern of more than one separated discontinuous region, and the patterns of the separated discontinuous region each independently have a single thickness, or have multiple thicknesses with a step difference.

11. The method for producing a multilayer structure according to claim 1, wherein: The step of forming the medium hard layer is performed by coating a styrene-ethylene-butylene-styrene solution on the high hard layer by spin coating.

12. A multilayer structure, characterized in that: include: Basic materials; A high-hardness layer, which is located on the base material and has a Young's modulus larger than that of the base material, and has multiple thickness dimensions according to regions as the ultraviolet curing material is cured to different degrees according to regions; a medium-hardness layer, which covers the high-hardness layer and is located on the base material, and has a Young's modulus larger than that of the base material but smaller than that of the high-hardness layer.

13. The multilayer structure according to claim 12, characterized in that When the multilayer structure is deformed by an applied external force, a plurality of wrinkles with different wavelengths are formed according to the thickness of the high hardness layer, thereby showing different structural colors.

14. The multilayer structure according to claim 12, characterized in that The high hardness layer includes at least one or more regions from the first to fifth regions having first to fifth thicknesses whose thicknesses increase successively; in the first region, a structural color with a wavelength in the range of 400nm to 450nm is displayed, in the second region, a structural color with a wavelength in the range of 450nm to 500nm is displayed, in the third region, a structural color with a wavelength in the range of 500nm to 570nm is displayed, in the fourth region, a structural color with a wavelength in the range of 570nm to 600nm is displayed, and in the fifth region, a structural color with a wavelength in the range of 600nm to 750nm is displayed.

15. The multilayer structure according to claim 12, characterized in that The base material has a Young's modulus ranging from 1 MPa to 3 MPa, the high hard layer has a Young's modulus ranging from 1000 MPa to 1300 MPa, and the medium hard layer has a Young's modulus ranging from 800 MPa to 1000 MPa.

16. The multilayer structure according to claim 12, characterized in that The base material includes one of polydimethylsiloxane (PDMS), polyurethane, copolyester (Ecoflex) and rubber series polymer substances.

17. The multilayer structure according to claim 12, characterized in that The high hardness layer contains ultraviolet curing chitosan.

18. The multilayer structure according to claim 12, characterized in that The medium hard layer comprises styrene-ethylene-butylene-styrene.

19. An anti-counterfeiting device, characterized in that: A multilayer structure according to any one of claims 12 to 18.

20. The anti-counterfeiting device according to claim 19, characterized in that: The multilayer structure is in the form of a thin film.

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