Discussion on the most flaming interference color

2022-08-01
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Light interference color changing ink is a new type of ink with dynamic color changing effect, which came out in the 1990s. The pictures and texts printed with it can change different colors from different angles. Especially when observing at about 0 ° and at about 60 °, it will show two very distinct colors. This color change effect comes from the light interference pigment in the ink. What is light interference pigment? This should start from the color of nature. It is well known that color is the photosensitive response of the eye and brain to the visible spectrum (wavelength range 400 ~ 700nm). When white light (such as natural light) shines on an object, we only feel the light with reflected wavelength ("reflected color") on the surface of the object, and the rest of the wavelength is absorbed by the object and cannot be felt. The absorption and reflection of light waves by different objects are very different, so everything in the world has its own characteristics. "Reflection color" is determined by the intrinsic characteristics of the object. No matter how the viewing angle and the direction of the light source change, the color of the object remains unchanged. "Interference color" on the contrary, it does not belong to the characteristics of the object itself, but is the color presented due to the physical effect of light interference. For example, soap bubbles do not absorb light, and they are colorless and transparent to get rid of the backward situation of low-end materials relying on price competition. However, when their thickness meets the light interference conditions, they will show rainbow colors. "Interference color" can change color with the change of light incidence angle and observation angle, which can not be achieved by "reflection color". Light interference pigment is a masterpiece of human imitating nature. Thin film ceramic particles based on the principle of parallel plate multi beam interference can easily repair optics, which is the theoretical basis of artificial "interference color". Thin film optics has realized the human desire to control and select the reflection spectrum and optical properties of the object surface. Fig. 1 is a schematic diagram of the multilayer optical film structure (the film thickness is in nanometers) (only the reflected light and related physical quantities related to us are discussed here, and the complex film calculation expressions are omitted). According to the thin film optics theory, the amplitude vectors of the reflected light on the film interface of the testing machine at different levels are R1, r2e-2i81,..., rk+1e-2i (81 +... 821.8k), where R1, R2,..., rk + 1 are the functions of the refractive indices N0 and N1, N1 and N2,..., NK + 1 and NK on both sides of the interface, which is called the reflection coefficient. δ Is the phase difference between each reflected light: α 1=2π/ λ· N1d1cos θ 1、…、 δ k=2π/ λ· Nkdkcos θ K where: λ Is the wavelength of incident light, D1 and DK are the thickness of the first film and the k film respectively θ 1、 θ K is the incident angle of light on the first layer and the k-th layer respectively (01 θ 2、…、 θ K by θ 0 and N0, N1,..., NK). The reflectivity r of the multilayer optical film is the reflection coefficient R (i.e., N1,..., NK) and phase difference δ (i.e λ、θ 0 and D1,..., DK). Based on this, we analyze as follows: ① for a certain (designed and formed as required) film structure, the material n, thickness D and incident medium N0 of the film layer are known constants, and its surface reflectance R is only the wavelength of incident light λ And incident angle θ Function for 0. Given a θ 0, so that the membrane system can be obtained in this θ Reflection spectrum curve distributed by wavelength at 0. That is, each determined film system has a specific reflection spectrum. And the reflection spectrum will change with the incident angle θ 0. This is the reason why the "interference color" produced by the artificial film system can change color with the change of light incidence angle and observation angle. Fig. 1 interface reflection diagram of multilayer optical film ② we can design the film system according to needs, reasonably calculate the selected film material and film thickness, and change the values of N and D to achieve the predetermined reflection spectrum and optical performance indicators. Realize people's desire to control and select the reflection spectrum and optical properties of the object surface. Light interference pigments are produced by grinding, grading, surface treatment and a series of pigmentation treatments of optical films with interference structure. It successfully utilizes the properties of optical thin films that can produce various dynamic interference colors. This unique flake pigment maintains all the optical properties of the optical film. As long as the observation angle and the light incidence angle are different, each piece of pigment will reflect colorful colors like the mirror. Accurate use of light interference technology can accurately control the change of color. Fig. 2 structure change of light interference pigment film system. Optical thin films are formed by alternately depositing materials with different refractive indices on the same carrier under high vacuum according to the requirements of film structure. The material is evaporated to the carrier in the form of molecules or atoms. In order to ensure the uniformity and compactness of the film, the consistency of evaporation rate must be strictly controlled; In order to control the color index of the film system, the error of the film thickness must be controlled within angstrom (1 angstrom = 10-1nm = - 10-7mm). The precision and particularity of visible optical film production. On the premise that the film system design meets the spectral requirements, the number of film layers should be as few as possible to reduce the production cost. At present, the ideal optical interference pigment film system is a 5-layer symmetrical structure as shown in Figure 2, and the film system thickness is 1 μ M, the middle is an opaque reflection spread (which can be regarded as the common base of the upper and lower interference cavities), and the two sides are symmetrical transparent colorless dielectric layer and translucent metal layer, so that the upper and lower sides of the diaphragm have the same interference color. By changing the thickness of the transparent medium layer, the color of the film system can be changed to obtain various colors of light interference pigments. As the film system is made under high vacuum, all colorless or transparent inorganic materials are used. The generated light interference pigment has stable performance, compact structure, no fading, strong weather resistance, good shear resistance, and can be arbitrarily crushed according to the requirements of ink for particle size. At present, there are interference pigments made by chemical coating with natural mica and metal aluminum as substrates; There are also interference pigments made by using the characteristics of liquid crystal chips. However, it can not be compared with light interference pigments in terms of color types and physical properties. They are mainly used in the coating industry, which is difficult to meet the stringent requirements of printing inks for sheet pigments. The dynamic color changing effect of the printing products of the photochromic ink can not be reproduced with the high-definition scanner and color copying. First, we should take the resource-saving development road machine and other equipment to copy; In addition, its design and production technology are highly professional; Complex manufacturing process; Huge investment; It is difficult to copy, so it is used by more than 70 countries in the world for currency anti-counterfeiting. Since the use of RMB 100 in the 99 edition, the anti-counterfeiting mark has not been imitated on the counterfeit currency, and has become an important publicity mark to identify the true and false RMB in the newspapers and periodicals. In addition, it can also be widely used for anti-counterfeiting of all kinds of securities, famous trademarks, certificates, bills, product packaging and other printed materials. At present, only the United States can produce thin-film light interference pigments in the world, and there are only a few companies using American pigments to produce light change inks. Huizhou Huayang Optical Technology Co., Ltd. has successfully independently developed and mass produced light interference pigments and light change inks, and its products have reached the international advanced level. At present, it has been used in many famous cigarette packaging and anti-counterfeiting printing of important certificates. □

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