A high-saturation all-dielectric thin film with small-angle effect

Abstract

The present invention discloses a high-saturation all-dielectric thin film with a small-angle effect, belonging to the technical field of thin films. It comprises a glass substrate layer and a refractive film layer. The refractive film layer is composed of multiple layers of high-refractive-index film layers and multiple layers of low-refractive-index film layers stacked alternately. The reflectivity of the all-dielectric thin film is greater than 85%. The slope of the transition band of the reflection spectrum of the all-dielectric thin film from the cut-off region to the high-reflection region is between 1.1 and 1.4, and the wavelength below 600 nm is the cut-off interval. The reflection of the all-dielectric thin film has a small offset chromatic aberration between 0° and 45° on the 600-800 nm red color mapping, and the Lab*a*b color mapping is between 30° and 45°. The color offset effect of the thin film structure of the present invention is not obvious, which can effectively meet the need of angle insensitivity. Moreover, the structural color of the thin film does not fade, and has the characteristics of environmental protection, metallic scintillation effect and angle-dependent color, etc., and can be widely applied in various fields.

Description

Technical Field

[0001] The present invention relates to the technical field of thin films, and particularly to a high-saturation all-dielectric thin film with a small-angle effect. Background Art

[0002] The light interference effect based on the one-dimensional photonic crystal multi-layer thin film structure is the main technical method for realizing structural color display in physical color, and is also the preferred solution for realizing structural color in the industrial field at present. Structural color display is different from the dye chemical coloring method (the color caused by the absorption of light by pigments), and mainly forms colors through the reflection, scattering, interference or diffraction of light generated in the micro-structure of organisms. Due to the advantages of non-fading, environmental protection, metallic scintillation effect and angle-dependent color change of structural color, it has application value in the fields of color paints, printing inks, liquid inks, plastics, glass, ceramic products and decorative cosmetic preparations. Among them, angle-dependent color change is an inherent characteristic of thin film structural color, which makes them be used for anti-counterfeiting of securities, documents and commodities, such as banknotes, checks, bank cards, credit cards, entry cards and tickets.

[0003] However, the existing thin film structural color still has several deficiencies as a special effect pigment, and the most significant feature is the angle effect characteristic of the thin film. The optical thin film structural color is based on working at a specific incident angle. When the incident angle changes, the hue of the thin film structural color will change, and the resonant wavelength will shift to the blue. This hinders the possibility of thin film structural color as a substitute for traditional pigments. Especially for the beauty makeup and car paint fields, structural colors with small hue change effects are more valuable. Therefore, exploring the reflective thin film structural color with small color drift using all-dielectric structures with better mechanical properties and human safety performance has positive significance for the fields of reflective display, beauty makeup, car paint and green printing. For this reason, the present invention proposes a high-saturation all-dielectric thin film with a small-angle effect to solve the deficiencies and disadvantages existing in the prior art. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a high-saturation all-dielectric thin film with a small-angle effect.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A high-saturation all-dielectric thin film with a small-angle effect, comprising a glass base layer and a refractive film layer, wherein the refractive film layer is composed of multiple layers of high refractive index film layers and multiple layers of low refractive index film layers alternately stacked;

[0007] The reflectivity of the all-dielectric thin film is greater than 85%;

[0008] The slope of the transition band of the reflection spectrum of the all-dielectric thin film from the cut-off region to the high-reflection region is between 1.1 and 1.4, and the wavelength below 600 nm is the cut-off range;

[0009] The reflection of the all-dielectric thin film has a small offset color difference between 0 and 45° on the 600-800 nm red color map, and the Lab*a*b color map is between 30 and 45°.

[0010] Preferably, the refractive index of the low-refractive-index film layer is 1.3-2.0, and the refractive index of the high-refractive-index film layer is 2.0-2.8.

[0011] Preferably, the high-refractive-index film layer is composed of one or more mixtures of titanium dioxide, hafnium dioxide, tantalum pentoxide, niobium pentoxide, zirconium dioxide, silicon nitride, zinc sulfide, etc.

[0012] Preferably, the low-refractive-index film layer is composed of one or more mixtures of silicon dioxide, aluminum oxide, magnesium fluoride, etc.

[0013] Preferably, the material of the high-refractive-index film layer is titanium dioxide; the material of the low-refractive-index film layer is silicon dioxide.

[0014] Due to the above technical solutions, the beneficial effects of the present invention are as follows: The small-angle high-saturation all-dielectric thin film structure of the present invention has an insignificant color shift effect, which can effectively meet the need for angle insensitivity; the structural color of the thin film of the structure of the present invention does not fade, and has the characteristics of environmental protection, metal scintillation effect and angle-dependent color; the thin film of the present invention can be effectively applied to fields such as color paints, printing inks, liquid inks, plastics, glass, ceramic products and decorative cosmetic preparations, etc., and has remarkable practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 : Schematic diagram of the structure of the all-dielectric thin film of the present invention.

[0016] Figure 2 : Spectral tristimulus values and linear reflection spectrum of the red structural color thin film in Example 1 of the present invention.

[0017] Figure 3 : Red structural color thin film with linear (left) and rectangular (right) reflection spectra in Example 1 of the present invention.

[0018] Figure 4 : Angle-dependent color spectral drift of the red structural color thin film S1 in Example 1 of the present invention.

[0019] Figure 5 : Angle-dependent color spectral drift of the red structural color thin film S2 in Example 1 of the present invention.

[0020] Figure 6 : Chromaticity diagram of the red structural color films S1 and S2 in Example 1 of the present invention at 0° - 45°.

[0021] In the figure: 001, glass base layer; 002, refractive film layer; 201, high refractive index film layer; 202, low refractive index film layer. Detailed implementation manners

[0022] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Embodiment:

[0024] The high-saturation all-dielectric film with a small-angle effect in this embodiment, as Figure 1 shown, comprises a glass base layer 001 and a refractive film layer 002, and the refractive film layer 002 is composed of multiple layers of high refractive index film layers 201 and multiple layers of low refractive index film layers 202 stacked alternately;

[0025] The reflectivity of the all-dielectric film is greater than 85%;

[0026] The all-dielectric film satisfies that the slope of the transition band from the cut-off region to the high-reflection region of the reflection spectrum is between 1.1 and 1.4, and the linear target value for wavelengths below 600 nm is the cut-off interval, and the film system structure is optimized to obtain an optical film with a small-angle effect;

[0027] The reflection of the all-dielectric film has a small offset chromatic aberration between 0° and 45° in the 600 - 800 nm red color mapping, and the Lab*a*b color mapping is between 30° and 45°.

[0028] In Example 1, the outermost layer of the refractive film layer 002 is a low-refractive-index film layer 202, which is composed of alternating stacks of the low-refractive-index film layer 202 and the high-refractive-index film layer 201. A total of 27 layers of the high-refractive-index film layer 201 and the low-refractive-index film layer 202 are provided. In the refractive film layer 002, the low-refractive-index film layer 202 is on odd layers. The physical thicknesses of all odd layers from the first layer to the subsequent layers are 110.28 nm, 30.27 nm, 158.86 nm, 19.82 nm, 156.57 nm, 145.92 nm, 39.62 nm, 197.5 nm, 32.49 nm, 322.17 nm, 139.41 nm, 146.56 nm, 165.85 nm, 88.97 nm. The physical thicknesses of all even layers from the second layer to the subsequent layers are 8.28 nm, 93.6 nm, 116.23 nm, 116.73 nm, 85.81 nm, 99.96 nm, 16.17 nm, 111.42 nm, 110.65 nm, 92.02 nm, 87.53 nm, 92.44 nm, 108.38 nm. The total physical thickness of the refractive film layer of all layers is 2893.59 nm.

[0029] This solution is further optimized as follows: As Figure 1 shown, the high-refractive-index film layer 201 is composed of one or a mixture of titanium dioxide, hafnium dioxide, tantalum pentoxide, niobium pentoxide, zirconium dioxide, silicon nitride, zinc sulfide, etc.

[0030] The low-refractive-index film layer 202 is composed of one or a mixture of silicon dioxide, aluminum oxide, magnesium fluoride, etc.

[0031] The refractive index of the low-refractive-index film layer 202 in the refractive film layer 002 is 1.3 - 2.0, and the refractive index of the high-refractive-index film layer 201 is 2.0 - 2.8. In this embodiment, the material of the high-refractive-index film layer 201 is titanium dioxide.

[0032] The material of the low-refractive-index film layer 202 is silicon dioxide. In this embodiment, the refractive index of titanium dioxide is 2.34867, and the refractive index of silicon dioxide is 1.4618.

[0033] The optical thin film in the embodiment of the present invention includes 27 film layers, and the corresponding thickness and material of each layer are shown in Table 1 below. Among them, the material of the low-refractive-index film layer is all SiO2, and the material of the high-refractive-index film layer is TiO2. In Example 1 of the present invention, it is a high-saturation red small-angle color shift thin film structural color material, including a substrate and a multi-layer interference thin film provided on the substrate. Table 1 is the material and physical thickness table of each film layer of the optical thin film.

[0034] Table 1 Structure of the high-saturation small-angle color shift red thin film in Example 1 of the invention;

[0035]

[0036]

[0037] The chromaticity coordinates of the object color depend on both the relative spectral power distribution of the illumination light source and the reflection or transmission characteristics of the object. The International Commission on Illumination (CIE) has proposed a standard colorimetry system, which stipulates the measurement principle of color, the basic data of the stimulus function, and the calculation method of the pigment coordinates to meet the quantitative and standardized requirements for color characteristics in industrial production. The CIE1931 standard colorimetric system quantitatively represents colors with X, Y, and Z. For the color reflected by an object, there is:

[0038]

[0039]

[0040]

[0041] ρ(λ) is the reflection spectrum of the object. The tristimulus values are the representations of the stimulation degree measures of the three primary colors that cause the human retina to have a certain color sensation. The amounts of the three primary colors (X), (Y), and (Z) used to match the equal-energy spectral stimulus are called the "CIE1931 standard colorimetric observer spectral tristimulus values", denoted by The chromaticity coordinates of the equal-energy white spectral color can be drawn in the XYZ system to obtain the CIE1931 XYZ system chromaticity diagram.

[0042] To solve the technical problem of color drift, as Figure 2 shown, another technical solution adopted by the present invention is: constructing a linear reflection spectrum, and using the distribution law of the spectral tristimulus values to make the reflection spectrum and the triangular integral region in the spectral tristimulus values be close to the same proportion. Furthermore, a small hue drift and lightness change are achieved while the spectrum drifts towards the short wave. The core spectral design concept of the small-angle effect lies in: based on the linear target value that the slope of the transition band from the cut-off region to the high-reflection region of the reflection spectrum is between 1.1 and 1.4, and the wavelength below 600 nm is the cut-off interval, optimizing the film structure to obtain an optical thin film with a small-angle effect.

[0043] As Figure 3 shown, the thin film with a linear reflection spectrum having a slope of 1.1 - 1.4 in the transition band from the cut-off region to the high-reflection region effectively solves the problem of color shift with angle, resulting in the phenomenon of metamerism. The reason is that the triangular region S1 formed by the thin film reflection spectrum and the in the spectral tristimulus values and the triangular region formed by the thin film reflection spectrum and the tristimulus values The ratio of the formed triangular region S2 maintains a proportional increase during the spectral translation. Furthermore, it has the effect of slowing down the color change, i.e., changing from red to orange. The cut-off of wavelengths below 600 nm is beneficial for the generation of the color of high-saturation red-based thin films, enhancing the color purity.

[0044] Through CIE, the CIE1976 (L * a * b * ) uniform color space is established to uniformly evaluate the color difference.

[0045]

[0046] Among them, X, Y, and Z represent the tristimulus values of the color sample, and Xn, Yn, and Zn are the tristimulus values of the white stimulus when the CIE standard illuminant irradiates a perfect diffuser and then is reflected by the perfect diffuser surface and reaches the observer's eyes, where Yn = 100. The color difference between two colors can be calculated by the following formula, and the color change degree is quantitatively evaluated using the color difference formula.

[0047]

[0048] ΔL * =L2 * -L1 * ,Δa * =a2 * -a1 * ,Δb * =b2 * -b1 *

[0049] Some percentages of light in the desired range of 650 nm ± 50 nm can still satisfy a high degree of intersection with the tristimulus values under large-angle conditions, thereby enhancing the red purity. At the same time, for such obliquely frequency-reflected light, the reflection will not be attenuated due to light absorption at large angles and can provide dazzling structural colors to the human eye at different viewing angles. First, an optical thin film structure with a cut-off of wavelengths below 600 nm is obtained through film system structure simulation. The spectral optimization is carried out using linear target values to obtain the linear spectral red thin film structure S1. The observation angle is changed to evaluate the spectral drift degree of this design. The change in the observation angle is set in the range between 0° and 60°, the illumination light source is selected as D65, and in the reflection measurement mode, the reflectance curve (380 nm - 780 nm) of the optical thin film with the change of the angle is as

[0050] shown in Figure 4As can be seen, the maximum reflection wavelength is around 700 nm, and the maximum reflectance is close to 90%, indicating that this optical thin film is a red optical thin film. The spectral cut-off wavelength drifts from 600 nm at 0° to 550 nm. Similarly, the 0 - 60° reflection spectrum curve of the existing known red thin film structure S2 is obtained through film stack structure simulation, as Figure 5 shown. The maximum reflection wavelength is between 600 - 700 nm, indicating that this optical thin film is a red optical thin film. The spectral cut-off wavelength drifts from 600 nm at 0° to 530 nm. It can be seen that the reflectance of the all-dielectric structure design has theoretically reached a relatively high level of over 90%. Therefore, both structures S1 and S2 have relatively high color brightness. At the same time, by optimizing the film stack of the thin film, the suppression of the secondary peak can be achieved, and both can make the thin film show relatively high saturation

[0051] The color difference changes between 0 - 45° are calculated through the CIE1931 color locus chromaticity diagram and Lab chromaticity coordinates to evaluate the optical performance and color performance of the designed S1 and S2. The observation angle change is set in the range between 0° and 45°, the illumination light source is selected as D65, and in the reflection measurement mode, the corresponding color coordinate change trajectories of S1 and S2 are listed in the CIE1931 chromaticity diagram, as Figure 6 shown. It can be seen that compared with the conventional rectangular thin film structure, although the spectrum of the linear structure has the characteristic of short-wave drift, the color shift effect is significantly weakened. At the same time, under the condition of the 0° observation angle, it has a higher color saturation.

[0052] The reflection of the S1 and S2 multi-layer stack has hue data and offset color difference ΔE CIE (L * a * b * ) between 0 - 45°, as shown in Table 2. It can be seen that when the red thin film structure S1 with a linear spectrum changes from 0° to 45°, ΔE CIE (L * a * b * ) has a smaller change amount, so it has a smaller color change effect. At the same time, at the 0° observation angle, the a / b value of the red thin film structure S1 with a linear spectrum is greater than that of the red thin film structure S2 with a rectangular spectrum, so it has a higher purity red color rendering effect.

[0053] Table 2 Chromaticity coordinates and color differences of the red thin film structures S1 and S2 at different angles;

[0054]

[0055]

[0056] In summary, the thin-film structural color of the present invention has the advantages of non-fading, environmental protection, metallic scintillation effect, and angle-dependent color change, etc. It has an extremely high reflectivity. At the same time, through the optimized design of the thin film, the structure of the optical thin film is more diverse and the color is more vivid, showing high-purity colors with a small angular drift effect.

[0057] In this embodiment, when the red thin-film structure S1 changes from 0° to 45°, ΔE CIE (L * a * b * ) has a smaller change amount, and thus has a smaller color change effect.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A high-saturation all-dielectric thin film with a small-angle effect, characterized in that: It is composed of a glass substrate layer (001) and a refractive film layer (002), and the refractive film layer (002) is composed of an alternating stack of multiple high-refractive-index film layers (201) and multiple low-refractive-index film layers (202); The reflectivity of the all-dielectric thin film is greater than 85%; The slope of the transition band of the reflection spectrum of the all-dielectric thin film from the cut-off region to the high-reflection region is between 1.1 and 1.4, and the wavelength below 600 nm is the cut-off interval; The all-dielectric thin film reflection has a small offset chromatic aberration between 0-45° on the 600-800 nm red color map, and the Lab*a*b color map is between 30-45°; 2. The high-saturation all-dielectric thin film with small-angle effect according to claim 1, characterized in that: The refractive index of the low-refractive-index film layer (202) is 1.3-2.0, and the refractive index of the high-refractive-index film layer (201) is 2.0-2.8; 3. The high-saturation all-dielectric thin film with small-angle effect according to claim 2, wherein: The high-refractive-index film layer (201) is composed of one or a mixture of multiple of titanium dioxide, hafnium dioxide, tantalum pentoxide, niobium pentoxide, zirconium dioxide, silicon nitride, zinc sulfide, etc.; 4. The high-saturation all-dielectric thin film with small-angle effect according to claim 3, characterized in that: The low-refractive-index film layer (202) is composed of one or a mixture of multiple of silicon dioxide, aluminum oxide, magnesium fluoride, etc.; 5. The high-saturation all-dielectric thin film with a small-angle effect according to claim 3, characterized in that: The material of the high-refractive-index film layer (201) is titanium dioxide; the material of the low-refractive-index film layer (202) is silicon dioxide.

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