Patent Description:
The Moire amplification technology based on microlens and micrographic arrays has been widely concerned in anti-counterfeiting field. Drinkwater et al. , put forward the use of a security device that combines a microlens array having a pore size of <NUM>-<NUM> and a micrographic array in <CIT>.

In <CIT>et al. , expand the scope of the security device based on the microlens array, i.e. reducing the pore size of the microlens to be less than <NUM>, by means of more precise processing techniques and more transformations.

The foresaid micro-optical device using the microlens structure is for unidirectional imaging, and one can only see the stereoscopic sloshing image from one side, so it has limitations no matter whether being used for packaging materials or for anti-counterfeiting of bills.

Document <CIT> discloses a security element, a security system and production methods thereof.

The object of the present invention is to disclose a micro-optical device for double-sided imaging, a preparation method therefor and an application thereof, in order to overcome the defects existing in the prior art.

The micro-optical device for double-sided imaging is according to claim <NUM>.

The beneficial effect of the present invention is that the produced micro-optical device can image on two faces; after the products prepared by adopting the device are used for packaging and anti-counterfeiting of bills, stereoscopic images can be represented on front sides and back sides; and the representation forms of the two stereoscopic images are different, thereby greatly enhancing attraction and anti-copying capability of the products.

Referring to <FIG>, the micro-optical device for double-sided imaging comprises a first microlens layer <NUM>, a functional layer <NUM>, a second microlens layer <NUM> and a miniature graphic layer <NUM> which are mutually compounded in sequence;.

Preferably, the first microlens layer <NUM> is a first microlens array formed by arranging the first microlens <NUM> in a periodic arrangement or a random arrangement, and the second microlens layer <NUM> is a second microlens array formed by arranging the plurality of second microlens <NUM> in a periodic arrangement or a random arrangement.

The substrate of the first microlens layer <NUM> has a refractive index of <NUM>~<NUM>.

The substrate of the first microlens layer <NUM> is selected from hot-compressible materials such as polyvinyl acetate, cellulose triacetate, polymethyl methacrylate, polystyrene, a mixture of alkyd resin and toluene diisocyanate, polyurethane, polypropylene, polyethylene-<NUM>,<NUM>-cyclohexane dimethylene terephthalate, and may be also selected from UV-curable materials such as epoxy acrylates, fatty acid-modified epoxy acrylates, and a mixture of styrene and epoxy acrylates.

The substrate of the second microlens layer <NUM> has a refractive index of <NUM>~<NUM>.

The substrate of the second microlens layer <NUM> is selected from hot-compressible materials such as polyvinyl acetate, cellulose triacetate, polymethyl methacrylate, polystyrene, a mixture of alkyd resin and toluene diisocyanate, polyurethane, polypropylene, polyethylene-<NUM>,<NUM>-cyclohexane dimethylene terephthalate, and may be also selected from UV-curable materials such as epoxy acrylates, fatty acid-modified epoxy acrylates, and a mixture of styrene and epoxy acrylates.

The first microlens <NUM> or the second microlens <NUM> is a spherical lens or an aspherical lens.

The geometry of the base of the first microlens or the second microlens is one of circle, triangular, rectangular or regular hexagon, or a combination thereof. Regular hexagon is preferable, because the microlens having a regular hexagonal base has the highest filling rate under the same lens pore size and the same lens spacing; the higher the filling rate of the microlens, the clearer and brighter the obtained macroscopically magnified graphic information. Referring to <FIG> illustrates a schematic diagram of the circular base microlens of the first microlens <NUM> and the second microlens <NUM> in a rectangular arrangement, and <FIG> illustrates a schematic diagram of the regular hexagonal base microlens of the first microlens <NUM> and the second microlens <NUM> in a honeycomb arrangement.

The filling rate refers to the ratio of the area occupied by the microlens to the total area. The ratio of the total area of the first microlens <NUM> to the total area of the first microlens layer <NUM> is in a range of from <NUM> % to <NUM> %, and the ratio of the total area of the second microlens <NUM> to the total area of the second microlens layer <NUM> is in a range of from <NUM> % to <NUM> %.

The material for the functional layer has a great transmittance to visible light and has a refractive index different from that of the surrounding material, which corresponds to a layer of refractive index difference array with a micro-arc shaped structure formed within the material. The functional layer <NUM> has a thickness of <NUM>~<NUM>, preferably <NUM>~<NUM>.

Preferably, as shown in <FIG>, the layer number of the functional layer <NUM> is <NUM> or more, preferably <NUM> to <NUM>; the multilayered functional layer has a stronger ability to fully reflect light than the monolayer film structure.

<FIG> illustrates the monolayer film structure of the functional layer. The material for the functional layer <NUM> has a refractive index greater than that of the surrounding material. This structure can only create a full reflection between the functional layer <NUM> and the surrounding material.

<FIG> illustrates the double-layer film structure of the functional layer. The first functional film layer <NUM> is compounded on the surface of the second microlens layer <NUM>, and the second functional film layer <NUM> is compounded on the surface of the first functional film layer <NUM>.

The refractive index of the first functional film layer <NUM> is greater than that of the second functional film layer <NUM>. The difference between the refractive index of the first functional film layer <NUM> and the refractive index of the second functional film layer <NUM> is preferably <NUM>~<NUM>. The second functional film layer <NUM> has a refractive index greater than that of the surrounding material. Such a structure may create two full reflections between the first functional film layer <NUM> and the second functional film layer <NUM> and between the second functional film layer <NUM> and the surrounding material, and thereby has a stronger ability to fully reflect light than the monolayer film structure. In theory, the more the layer number of said film, the stronger its ability to fully reflect light.

The micro-optical device has a high transmittance to the light incident from the first microlens layer, but for the light incident from the miniature graphic layer, only a part of the light can pass through and a part of the light will be reflected back by the effect of full reflection, due to the presence of the arc-shaped refractive index difference.

The material for the functional layer <NUM> preferably has a refractive index of <NUM>-<NUM>. The difference between the refractive index of the material for the functional layer <NUM> and the refractive index of the surrounding material is <NUM>~<NUM>, preferably <NUM>~<NUM>. The functional layer <NUM> is located on the surface of the second microlens and has a filling rate same as that of the second microlens layer.

The material for the functional layer <NUM> is selected from the group consisting of an oxide, a nitride, a carbide, an inorganic metal salt, a metal or a metal alloy.

The oxide is selected from the group consisting of silicon monoxide SiO, silica SiO<NUM>, titania TiO<NUM>, zirconium dioxide ZrO<NUM>, hafnium oxide HfO<NUM>, titanium monoxide TiO, trititanium pentoxide Ti<NUM>O<NUM>, niobium pentoxide Nb<NUM>O<NUM>, tantalum pentoxide Ta<NUM>O<NUM>, yttrium oxide Y<NUM>O<NUM> or zinc oxide ZnO.

The nitride is selected from the group consisting of titanium nitride TiN, silicon nitride Si<NUM>N<NUM> or boron nitride BN.

The carbide is selected from the group consisting of silicon carbide SiC or boron carbide B<NUM>C.

The inorganic metal salt is selected from the group consisting of neodymium fluoride NdF<NUM>, barium fluoride BaF<NUM>, cerium fluoride CeF<NUM>, magnesium fluoride MgF<NUM>, lanthanum fluoride LaF<NUM>, yttrium fluoride YF<NUM>, ytterbium fluoride YbF<NUM>, erbium fluoride ErF<NUM>, zinc selenide ZnSe, zinc sulfide ZnS, lanthanum titanate LaTiO<NUM>, barium titanate BaTiO<NUM>, strontium titanate SrTiO<NUM>, praseodymium titanate PrTiO<NUM> or cadmium sulfide CdS.

The metal is selected from the group consisting of Al, Cu, Ti, Si, Au, Ag, In, Mg, Zn, Pt, Ge and Ni.

The metal alloy is selected from the group consisting of gold germanium alloy AuGe, gold nickel alloy AuNi, nickel chromium alloy NiCr, titanium aluminum alloy TiAl, copper indium gallium alloy CuInGa, copper indium gallium selenium alloy CuInGaSe, zinc aluminum alloy ZnAl or aluminum silicon alloy AlSi.

The miniature graphic layer <NUM> is a miniature graphic array arranged in a periodic arrangement or a random arrangement. The material for the miniature graphic layer <NUM> is selected from hot-compressible materials such as polyvinyl acetate, cellulose triacetate, polymethyl methacrylate, polystyrene, a mixture of alkyd resin and toluene diisocyanate, polyurethane, polypropylene, polyethylene-<NUM>,<NUM>-cyclohexane dimethylene terephthalate, and may be also selected from UV-curable materials such as epoxy acrylates, fatty acid-modified epoxy acrylates, and a mixture of styrene and epoxy acrylates, having a thickness of <NUM>~<NUM> microns.

The miniature graphic is a pattern or a character of micron magnitude in size. The miniature graphic has one or more of transparency, color, reflection, interference, dispersion or polarization characteristics, as long as the graphic part and the other parts can produce a contrast. Since the miniature graphic has a small size and the general printing equipment cannot print such a fine graphic structure, the method of printing a miniature graphic as disclosed in the applicant's <CIT> may be used for the preparation.

Referring to <FIG> is a schematic diagram of making the miniature graphic by scraping ink. <FIG> is a representation of the miniature graphic "<IMG>" that is embodied by forming a contrast between the grating structure in the strokes of the miniature graphic "<IMG>" and the surrounding, because the grating has different optical characteristics. <FIG> is a representation of the miniature graphic "<IMG>" that is formed by creating a contrast between the grating structure in the strokes of the miniature graphic "<IMG>" and the grating structures of another orientation in the other parts, because the grating structures of different orientations will produce a contrast.

The miniature graphic layer <NUM> is located near the transmission focal plane of the first microlens layer <NUM> and also near the reflection focal plane of the second microlens layer <NUM>.

Referring to <FIG> is a schematic diagram of the transmission focusing of the first microlens <NUM>. The distance d<NUM> between the first microlens layer <NUM> and the miniature graphic layer <NUM> and the structural parameters of the first microlens <NUM> satisfy the following relationship: <MAT> wherein:.

<FIG> is a schematic diagram of the reflection focusing of the second microlens <NUM>.

The distance d<NUM> between the second microlens layer <NUM> and the miniature graphic layer <NUM> and the structural parameters of the second microlens <NUM> satisfy the following relationship: <MAT> wherein:.

In the above structure, when an observer observes from the side of the first microlens layer, the functional layer <NUM> is transparent for the imaging of the first microlens (the effect is little and can be ignored). The first microlens layer and the miniature graphic layer satisfy the Moire amplification condition and produce a first visual effect which, for example, is stereoscopic and sloshing. When the observer observes from the side of the miniature graphic layer, the functional layer <NUM> is likewise transparent for both the first microlens layer and the miniature graphic layer. However, under such a circumstance, the locations of the miniature graphic layer and the first microlens layer <NUM> are inverted, which do not satisfy the Moire amplification condition and will not generate obvious visual effect. But, because of the presence of the micro-arc shaped refractive index difference array, the light incident from the miniature graphic layer will be partly reflected back fully, which corresponds to that the miniature graphic layer <NUM> is reflected for imaging by the second microlens layer <NUM>. Then, the miniature graphic layer and the second microlens layer satisfy the Moire amplification condition and produce a second visual effect which, for example, is stereoscopic and sloshing. The brightness of the second visual effect is affected by the ambient light intensity and the refractive index difference of the functional layer. The stronger the ambient light intensity, the more the light of full reflection, and the more obvious the second visual effect. The greater the refractive index difference of the functional layer, the stronger its ability to fully reflect the light, and the more obvious the second visual effect.

Referring to <FIG>, when the first microlens array, the second microlens array and the miniature graphic array are in a periodic arrangement, the first microlenses of the first microlens layer <NUM>, the second microlenses of the second microlens layer <NUM> and the miniature graphics of the miniature graphic layer <NUM> are all in a periodic arrangement. There are two mutually perpendicular symmetrical axes A1 and B1 in the plane. A1 is the symmetry axis of the array in the X-axis direction, while B1 is the symmetry axis of the array in the Y-axis direction. For the three-layer structure, each layer is symmetrical in the X and Y axes. The respective units in each layer have a fixed arrangement period along the direction of the symmetrical axes. The parameters of the first microlens layer <NUM> and the miniature graphic layer <NUM> satisfy the following relationship: <MAT> wherein:.

Referring to <FIG>, it is the schematic diagram of the first microlens layer <NUM>, the second microlens layer <NUM> and the miniature graphic layer <NUM> in a random arrangement, wherein the respective units are randomly distributed and there is no symmetrical axis in the plane. The superposition of two layers of random dot arrays with the same distribution but very small differences in size and angle will generate another Moire fringe, i.e. "Glass Pattern" phenomenon. The Moire fringe generated by the dot arrays in a periodic arrangement is also in the periodic arrangement and may always extend over the entire plane. However, the Glass Pattern phenomenon will only generate a single Moire fringe at a central point of the entire plane. When the microlens layer of a randomly distribution is superimposed with the miniature graphic layer of a randomly distribution, the same stereoscopic sloshing effect as the periodic arrangement can also be produced by the Glass Pattern principle and the lens imaging effect. The difference is that the periodic arrangement produces the stereoscopic sloshing effect of periodic macroscopic graphics and the random distribution arrangement produces the stereoscopic sloshing effect of a single macroscopic graphic.

The periodic distribution arrays and the random distribution arrays both follow the basic principle of Moire fringes. Therefore, the relevant theoretical formulae, formula (<NUM>) and formula (<NUM>), for the Moire amplification in a periodic distribution, as mentioned above are likewise applicable to the random distribution. By reasonably selecting the size ratio and the rotational angle of two layers of random distribution arrays, a naked-eye-stereoscopic and orthogonally sloshing visual effect will be also produced.

The preparation method of the present invention comprises the steps of:.

The micro-optical device for double-sided imaging of the present invention may be used for preparing the security line of bills.

<FIG> is a schematic diagram of a bill having double-sided window security lines that utilizes the micro-optical device of the present invention. The micro-optical device of the present invention is partially exposed on both A and B sides of the bill. <FIG> is a sectional schematic diagram of a bill.

The first visual effect of the micro-optical device of the present invention can be seen by observing the security line from the A-side window <NUM>, and the second visual effect of the micro-optical device of the present invention can be seen by observing the security line from the B-side window <NUM>, which greatly enhances the anti-counterfeiting characteristic of the security line.

Preparing the micro-optical device for double-sided imaging having the structures shown in <FIG> and <FIG>.

The pore size D<NUM> of the first microlens <NUM> is <NUM> microns, the spherical cap height h<NUM> is <NUM>; the pore size D<NUM> of the second microlens <NUM> is <NUM>, the spherical cap height h<NUM> is <NUM>; α<NUM>=<NUM>°, α<NUM>=<NUM>;.

The geometry of the base of the first microlens <NUM> and the second microlens <NUM> is a regular hexagon;.

The first microlens <NUM>, the second microlens <NUM> and the miniature graphic are in a periodic arrangement;.

Both the first microlens <NUM> and the second microlens <NUM> are spherical lenses.

The filling rate of the first microlens <NUM> is <NUM>%;.

The filling rate of the second microlens layer <NUM> is <NUM>%;.

The functional layer is a <NUM> thick zinc sulfide coating with a refractive index of <NUM>;.

The miniature graphic layer <NUM> is located near the transmission focal plane of the first microlens layer <NUM>, the distance d<NUM> between the first microlens layer <NUM> and the miniature graphic layer <NUM> and the structural parameters of the first microlens <NUM> satisfy the following relationship: <MAT> wherein:
the parameters of the first microlens are substituted into the above formula to obtain the distance d<NUM> between the first microlens layer <NUM> and the miniature graphic layer, d<NUM> = <NUM>.

The miniature graphic layer <NUM> is also located near the reflection focal plane of the second microlens <NUM>. The distance d2 between the second microlens <NUM> and the miniature graphic layer <NUM> and the structural parameters of the second microlens <NUM> satisfy the following relationship: <MAT> wherein:
the parameters of the second microlens are substituted into the formula to obtain the distance d<NUM> between the second microlens layer and the miniature graphic layer, d<NUM>=<NUM>.

The parameters of the first microlens layer <NUM> and the miniature graphic layer <NUM> satisfy the following relationship: <MAT> wherein:.

The parameters of the second microlens layer <NUM> and the miniature graphic layer <NUM> satisfy the following relationship: <MAT> wherein:.

The results are calculated as follows: m<NUM>=<NUM>, m<NUM>=<NUM>.

It can be seen from formulae (<NUM>) and (<NUM>) that the ratio of period of the microlens array to the miniature graphic array and the inclined angle α have the most direct impact on the visual effect. When α=<NUM>, namely, the symmetrical axes of the microlens array layer and the miniature graphic array layer are parallel to each other, the system will generate a naked-eye-stereoscopic visual effect. If the ratio of period of the microlens array to the miniature graphic array is greater than <NUM>, the visual effect is reflected as stereoscopic subsidence; and if the ratio of period of the microlens array to the miniature graphic array is less than <NUM>, the visual effect is reflected as stereoscopic floating. When the ratio of period of the microlens to the miniature graphic is equal to <NUM>, and α≠<NUM>, the system will generate an orthogonally sloshing visual effect.

In the device of the present invention, there are three layer relationship combinations: the first microlens layer and the miniature graphic layer, the second microlens layer and the miniature graphic layer, and the first microlens layer and the second microlens layer.

In the case where the miniature graphic parameters are fixed, multiple visual effect combinations can be realized by designing different first microlens parameters and second microlens parameters.

In this Example, D1=<NUM>, D2=<NUM>, T1/T3=<NUM>, α<NUM>=<NUM>°, T2/T3=<NUM>, α<NUM>=<NUM>, the final effect is that the first visual effect is orthogonally sloshing, the second visual effect is stereoscopic subsidence, and a layer of faint Moire fringe will be seen from both the first visual effect and the second visual effect.

Preparing the micro-optical device for double-sided imaging having the structures as shown in <FIG> and <FIG>.

The pore size D<NUM> of the first microlens <NUM> is <NUM>, the spherical cap height h<NUM> is <NUM>; the pore size D<NUM> of the second microlens <NUM> is <NUM>, the spherical cap height h<NUM> is <NUM>; α<NUM>=<NUM>°, α<NUM>=<NUM>;.

The miniature graphic layer <NUM> is located near the transmission focal plane of the first microlens layer <NUM>, the distance d<NUM> between the first microlens layer <NUM> and the miniature graphic layer <NUM> and the structural parameters of the first microlens <NUM> satisfy the following relationship: <MAT> wherein:
the parameters of the first microlens are substituted into the above formula to obtain the distance d<NUM> between the first microlens layer <NUM> and the miniature graphic layer, d<NUM>=<NUM>.

The miniature graphic layer <NUM> is also located near the reflection focal plane of the second microlens <NUM>. The distance d<NUM> between the second microlens <NUM> and the miniature graphic layer <NUM> and the structural parameters of the second microlens <NUM> satisfy the following relationship: <MAT> wherein:
the parameters of the second microlens are substituted into the formula to obtain the distance d<NUM> between the second microlens layer and the miniature graphic layer, d<NUM>=<NUM>.

The results are calculated as follows: m<NUM>=<NUM>, m<NUM>=<NUM>;.

The second microlens <NUM> has a pore size of D<NUM>=<NUM>, an arrangement period of T<NUM>=<NUM> and a filling rate of <NUM> %, the functional layer <NUM> has the material of hafnium oxide, a thickness of <NUM> and a refractive index of <NUM>, and the other structural parameters are the same as those in Example <NUM>. Under the above structural parameters, the information about the second visual effect cannot be directly identified and will be identified by irradiation with an additional point light source or parallel light source.

As shown in <FIG>, this Example is a variant of Example <NUM>, and its structure is the same as that defined in Example <NUM>, except that a holographic information layer <NUM> is added between the first microlens layer and the second microlens layer. At present, the holographic technology has been very mature, and lithography holographic can produce various colorful holographic effects. Essentially, the production of theholographic effect is the interference fringe generated by incident lights of different wavelengths on the grating structures of different orientations and different parameters. The microlens array consists of many micron-scale spherical lenses, and each of the small lenses converges the light to form a highly divergent light cone. When the microlens array is directly combined with the holography, the characteristics of converging the light of the microlens will damage the propagation route of the interference fringes and make the holographic effect disappear. In the present invention, the presence of micro-arc faced functional layer is just to generate a layer of micro-arc shaped refractive index difference within the material, and the layer of refractive index difference has a very small influence on the propagation of light. The interference light generated by the holographic information layer can be observed by the human eyes through the micro-arc faced functional layer. Therefore, only the first visual effect can be seen when one observes from the side of the first microlens, and the holographic information cannot be seen, in this Example. When one observes from the side of the miniature graphic layer, both the second visual effect and the holographic information can be seen. At present, due to the popularity and popularization of the holographic technology, the simple holographic anti-counterfeiting function is more and more weak. In this Example, the holographic technology and the micro-optical technology are combined efficiently, which not only greatly improves the ornamental performance of products, but also increases the technical difficulty thereof.

<FIG> is another variant of the structure.

Claim 1:
A micro-optical device for double-sided imaging, comprising
a first microlens layer (<NUM>), a functional layer (<NUM>), a second microlens layer (<NUM>) and a miniature graphic layer (<NUM>) which are mutually compounded in sequence;
the first microlens layer (<NUM>) is a first microlens array formed by arranging a plurality of first microlenses (<NUM>);
the second microlens layer (<NUM>) is a second microlens array formed by arranging a plurality of second microlenses (<NUM>);
the functional layer (<NUM>) is arranged on the surface of the second microlens layer (<NUM>), and a material for the functional layer (<NUM>) has a refractive index different from that of a surrounding material, characterized in that
the layer number of the functional layer (<NUM>) is two, the first functional film layer (<NUM>) is compounded on the surface of the second microlens layer (<NUM>), the second functional film layer (<NUM>) is compounded on the surface of the first functional film layer (<NUM>); the refractive index of the first functional film layer (<NUM>) is greater than that of the second functional film layer (<NUM>), the refractive index of the second functional film layer (<NUM>) is greater than that of the surrounding material, and the difference between the refractive index of the first functional film layer (<NUM>) and the refractive index of the second functional film layer (<NUM>) is <NUM> to <NUM>.