Multilayer structured reflective sheet

Abstract

A multilayer structured reflective sheet, comprising the following structure layers in sequence from top to bottom: a transparent protective layer (1), a transparent resin layer (2), a retro-reflective structure layer (3), a focus forming layer (4), and a metal reflective layer (5), wherein the retro-reflective structure layer (3) is a lens array layer formed of light-transmissive micro-beads or prisms; the lens array layer is at least partially embedded into the focus forming layer (4); moreover, the thickness of the metal reflective layer (5) is 0.5-100 μm, the metal reflective layer (5) comprises a metal material and a resin, and the metal material comprises one or more of zero-dimensional metal particles and two-dimensional metal particles. By adjusting the thickness of the metal reflective layer (5) and the shape and content of the metal particles thereof, the metal reflective layer (5) does not shield signals, thereby expanding the range of application.

Description

Multi-layer structure reflecting sheet TECHNICAL FIELD

[0001] The present application relates to a multi-layer structure reflecting sheet, belonging to the technical field of reflective film. BACKGROUND

[0002] It is a long-standing practice in many countries to identify motor vehicles and part of non-motor vehicles with license plates for various regulatory management.

[0003] Some countries and regions, such as non-motor vehicle license plates (electric bicycles), temporary license plates for motor vehicles, have a trend of setting RFID chips inside the license plate or have already set chips. The illegal and irregular behavior of vehicles caused by electric bicycles and temporary license plates is increasingly serious, which significantly affects the safety of the public, and the main reason is that temporary license plates are just paper stickers on the front and rear windshields of vehicles, and some owners even do not stick them.

[0004] And the electric bicycle currently has a plastic license plate with an RFID chip, but the plastic license plate does not have a reflective function, and when the road camera captures at night, it cannot be identified because the number and background color contrast is not obvious. Without photos and other effective evidence, further processing or regulation of illegal personnel cannot be carried out.

[0005] Reference Document 1 discloses a reflective film that can penetrate electronic signals; it includes a surface layer, a glue layer, a titanium white powder layer, and a pressure-sensitive adhesive layer arranged from top to bottom, the glue layer is embedded with a glass microsphere layer, the glass microsphere layer includes a plurality of glass microspheres arranged flat, the bottom surface of the glue has a spherical convex surface corresponding in number and position to the glass microspheres, and the top surface of the titanium white powder layer is provided with a spherical concave surface connected with each spherical convex surface. Its main function is to form an interface between the titanium white powder layer and the glass microspheres, and the light is reflected at the interface, so that the reflective film has the property of reflecting light without using an aluminum plating layer, and the titanium white powder layer does not shield the signal, expanding the application range.

[0006] Reference Document 2 discloses a reflective film for vehicle license plates and a vehicle license plate. The reflective film for vehicle license plates includes a surface layer, a beaded glue layer, a glass microsphere layer, a focusing layer, and a reflective layer arranged in layers. The reflective layer is a non-signal shielding layer or a low-signal shielding layer. The reflective film for vehicle license plates of the above technical solution has good reflective effect of the reflective layer, which can realize good identification of the vehicle license plate in insufficient light; at the same time, the reflective layer in the reflective film for vehicle license plates of the above technical solution is a non-signal shielding layer or a low-signal shielding layer, which can avoid signal shielding to the chip in the vehicle license plate, and is conducive to wide application.

[0007] Although the above prior art has made some degree of research on the reflective license plate with signal transmitting function, there is still a need to improve the current license plate for motor vehicle or non-motor vehicle identification in terms of signal transmitting, reflective characteristics and manufacturing simplicity.

[0008] CITATIONS:

[0009] CITATION 1: CN218446057U

[0010] CITATION 2: CN219162416U SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] Although the prior art has made some degree of research on the reflective license plate with signal transmitting function as described above, there is still a deficiency in providing better signal penetration while also providing improved reflection clarity and contrast.

[0013] In addition, the application of intelligent driving systems in current passenger cars is becoming more and more widespread, and millimeter wave radar is widely used as a key component, and metal can significantly affect the performance of millimeter wave radar.

[0014] The technical problem to be solved by the present application is how to make the license plate background color and number contrast clear and easy to identify after shooting without affecting the penetration of RFID signals and millimeter wave radar signals, such as road snapping, and also not affecting car navigation and intelligent driving when used as a car decoration.

[0015] SOLUTIONS FOR SOLVING THE PROBLEMS

[0016] After in-depth research, it has been found that the above technical problems can be solved by implementing the following technical solutions:

[0017] [1]. The present application first provides a multi-layer structure reflector, wherein the reflector comprises the following structure layers from top to bottom:

[0018] a transparent protective layer, a transparent resin layer, a retroreflective structure layer, a focal point forming layer and a metal reflective layer,

[0019] The retroreflective structure layer is a lens array layer formed by transparent microbeads or prisms, and the lens array layer is at least partially embedded in the focal point forming layer;

[0020] And the thickness of the metal reflective layer is 0.5-100 μm, the metal reflective layer comprises a metal material and a resin, and the metal material comprises one or more of zero-dimensional metal particles and two-dimensional metal particles.

[0021] [2]. The reflector according to [1], wherein the zero-dimensional metal particles are substantially spherical metal particles; and the two-dimensional metal particles are selected from the group consisting of flaky metal particles, disc-like metal particles, and irregular flaky metal particles.

[0022] [3]. The reflector according to [1] or [2], wherein the metal material is selected from the group consisting of aluminum, copper, silver, gold, and indium, or an alloy thereof.

[0023] [4]. The reflector according to any one of [1] to [3], wherein the content of the metal material in the metal reflective layer is 2 wt% to 90 wt%.

[0024] [5]. The reflector according to any one of [1] to [4], wherein the metal reflective layer further comprises an additive selected from the group consisting of an antioxidant, a leveling agent, a curing agent, an ultraviolet inhibitor, a dispersant, a stabilizer, and a catalyst.

[0025] [6]. The reflector according to any one of [1] to [5], wherein 20 to 90 vol% of the retroreflective structure layer is embedded in the focal point forming layer.

[0026] [7]. The reflector according to any one of [1] to [6], wherein the metal reflective layer further comprises an adhesive layer on a side distal from the focal point forming layer.

[0027] [8]. The reflector according to any one of [1] to [7], wherein,

[0028] a retroreflective coefficient of the reflector is 15 cd / (lx·m2) or more at an observation angle of 0.2° and an incident angle of 5°. 2

[0029] [9]. The reflector according to any one of [1] to [8], wherein,

[0030] an RFID signal sensitivity of the reflector is -17 dBm or less at a frequency of 920 MHz to 925 MHz.

[0031]

[0010] . The reflector according to any one of [1] to [9], wherein,

[0032] a millimeter wave radar bidirectional transmission loss of the reflector is 5 dB or less at a frequency of 76 to 81 GHz.

[0033] Effects of the Invention

[0034] By implementing the above-described embodiments, the present invention can achieve the following technical effects:

[0035] ​1) By adjusting the thickness of the metal reflective layer and the shape and content of its metal particles, this invention enables the reflective sheet to have reflective properties without using an aluminum plating layer. Furthermore, the metal reflective layer does not block the signal (signal frequency can be from 30MHz to 300GHz). This invention can obtain a reflective sheet that balances the transmittance of RFID signals and millimeter-wave radar signals as well as retroreflection performance. It also achieves high RFID signal sensitivity and retroreflection coefficient maintenance rate, and low bidirectional transmission loss of millimeter-wave radar.

[0036] 2) The reflector of the present invention has a simple structure and is easy to manufacture, which is conducive to large-scale and rapid production. Attached Figure Description

[0037] Figure 1 is a schematic diagram of the structure of a reflective sheet according to one embodiment of the present invention.

[0038] 1. Transparent protective layer

[0039] 2. Transparent resin layer

[0040] 3. Retroreflective structural layer

[0041] 4. Focal point forming layer

[0042] 5. Metal reflective layer Detailed Implementation

[0043] The present invention will now be described in detail. The descriptions of the technical features described below are based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0044] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0045] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0046] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0047] In this instruction manual, "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2℃".

[0048] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage content.

[0049] In this specification, the terms "substantially" and "essentially" are used to indicate that the standard deviation from the theoretical model, theoretical data, or target data is within a range of 2%, preferably 1%, and more preferably 0.8%.

[0050] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0051] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0052] Referring to Figure 1, it illustrates the multilayer structure of a reflective sheet in a specific embodiment of the present invention. Specifically, the reflective sheet comprises, from top to bottom, the following structural layers: a transparent protective layer, a transparent resin layer, a retroreflective structural layer, a focal point forming layer, and a metal reflective layer.

[0053] (Transparent protective layer)

[0054] In this invention, there are no particular restrictions on the type and thickness of the transparent protective layer, which can be set with reference to the type and thickness of the protective layer on the surface of the reflective sheet conventionally in the art.

[0055] In some specific implementations, the material that can serve as the transparent protective layer can be selected from at least one of acrylic resin, alkyd resin, fluororesin, polyolefin resin, polyester resin, polyurethane resin, and polycarbonate. Considering weather resistance and processability, at least one of acrylic resin, polyolefin resin, and polyester resin is preferred.

[0056] For acrylate resins, they can be polymers of one or more (meth)acrylates.

[0057] For polyolefin resins, they can be homopolymers of olefins, copolymers of multiple olefins, or copolymers of olefins with other polymerizable monomers, such as ethylene-vinyl acetate copolymers.

[0058] For polyester resins, they can be condensates of aliphatic, aromatic or alicyclic diols and diacids, preferably selected from polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

[0059] In some other specific embodiments, colored pigments or dyes may be added to the resin in the transparent protective layer, preferably transparent pigments. The pigments or dyes can be as follows:

[0060] Yellow: Coloring agents of isoindoline, isoindoline, quinoline, anthraquinone, pyrazolone, flavanone, benzimidazolone, nickel azo, etc.

[0061] Red: Coloring agents of anthraquinone, dinaphthalene, quinacrine, indigo, etc.

[0062] Blue: Coloring agents such as phthalocyanine, styrax, anthraquinone, and cobalt.

[0063] Green: Colorants such as phthalocyanine, emerald green, chromium oxide, and cadmium.

[0064] Brown: Iron oxide series coloring agent, or a combination of isoindole ketone series yellow coloring agent, dinaphthalene-based red coloring agent and phthalocyanine series blue coloring agent;

[0065] Orange: Single color can be anthraquinone, pyrazolone, violet ketone, naphthalene-benzene, quinacrine, or isoindoleone yellow colorant and naphthalene-benzene red colorant can be used together;

[0066] White: Colorants based on phthaloyl, zinc, lead, etc.

[0067] Black: Colorants such as carbon black, aniline black, dinaphthalene-impregnated benzene black, and titanium black.

[0068] Furthermore, in some specific embodiments, the thickness of the transparent protective layer can be 10μm to 150μm, preferably 30μm to 120μm, more preferably 50μm to 100μm, and even more preferably 30μm to 60μm.

[0069] (Transparent resin layer)

[0070] For the transparent resin layer of the present invention, there are no particular limitations on the material and thickness in principle, and it can be set with reference to the types and thicknesses of transparent resin layers conventional in the art.

[0071] The resin in the transparent resin layer can be selected from at least one of acrylic resin, alkyd resin, fluororesin, vinyl chloride resin, polyester resin, polyurethane resin, and polycarbonate. Considering weather resistance and processability, at least one of acrylic resin, polyester resin, and vinyl chloride resin is preferred. Considering suitability during coloring or dispersibility of coloring agents, acrylic resin is preferred.

[0072] Similarly, it can have the same colored pigments or dyes as the transparent protective layer.

[0073] (Retroreflective structure layer)

[0074] The retroreflective structure layer of the present invention can be a lens array layer formed by light-transmitting microspheres or prisms, wherein the lens array layer is at least partially embedded in the focal point forming layer.

[0075] Furthermore, the lens array layer of the present invention utilizes the principle of retroreflection, which can significantly improve the brightness of the target object observed from the light source perspective compared to diffuse reflection and specular reflection.

[0076] Furthermore, the retroreflective structure layer is a lens array, and the transparent element is any shape with refractive properties, such as a light-transmitting microsphere or a prism. In some specific embodiments, the light-transmitting microspheres can be spherical, rod-shaped, ellipsoidal, or any combination thereof; in other specific embodiments, the prism is a sawtooth (triangular) prism.

[0077] The material of the microspheres or prisms is composed of at least one of glass, ceramic, polymer, and ore. In some preferred embodiments, their refractive index can be 1.7 to 2.5, more preferably 2.19 to 2.21. The (long) diameter of the microspheres is 10 μm to 150 μm, preferably 50 μm to 110 μm, more preferably 60 μm to 110 μm.

[0078] In some preferred embodiments of the present invention, the lens array layer is a single-layer planar array formed by the light-transmitting microspheres; all the light-transmitting microspheres in the lens array layer have the same shape, and the geometric center of all the light-transmitting microspheres is located in a plane.

[0079] In some other preferred embodiments of the invention, 20% to 90%, preferably 60% to 80%, of the volume of the lens array layer is embedded in the focal forming layer described below. In a specific embodiment, a portion of the lens array layer fills the focal forming layer, so that when incident light enters the microspheres, it is reflected from the transparent resin layer on the microsphere side and returns along the original path using the lens array principle.

[0080] Therefore, when the reflective sheet of the present invention is photographed and light shines into it, the contrast is much more obvious than that of the characters on the license plate and other parts without lens arrays.

[0081] (Focus Forming Layer)

[0082] There are no particular restrictions on the material and structure of the focal layer of the present invention. It is mainly used for focusing reflected light to improve the clarity of the reflective surface.

[0083] The material of the focal layer can include a transparent resin, which may be selected from at least one of acrylic resin, alkyd resin, fluororesin, vinyl chloride resin, polyester resin, polyurethane resin, and polycarbonate. Considering weather resistance and processability, at least one of acrylic resin, polyester resin, and vinyl chloride resin is preferred, and acrylic resin is more preferred. In addition, the focal layer may optionally be colored.

[0084] In addition, from the perspective of imparting focusing characteristics, the junction between the focal forming layer and the metal reflective layer described below has a continuously undulating curved surface structure. Such a curved surface provides a focusing effect through the structure concave towards the metal reflective layer.

[0085] (Metallic reflective layer)

[0086] As is well known, in existing technologies, metals are the preferred material for reflective layers due to their superior reflectivity compared to other materials. While some metals, such as indium, do possess reflective properties, their cost is prohibitively high. This high cost stems from the fact that indium is significantly more expensive than aluminum, and the evaporation rate for indium is much slower. Aluminum evaporation can typically reach speeds of up to 300 m / min, while indium evaporation is only a few meters per minute. Furthermore, current research using metal vapor deposition to create metal reflective layers, even with a thickness of only 50–1000 angstroms, still results in significant signal shielding.

[0087] Therefore, the metal reflective layer of the present invention does not need to be deposited by vapor deposition. Instead, a composite layer containing metal materials and resin is used as the metal reflective layer. Since the metal material is granular and has gaps, it is beneficial to improve the signal penetration.

[0088] The metal reflective layer of this invention can assist the retroreflective structure layer to achieve good light reflection efficiency. In some specific embodiments, the metal reflective layer includes a metal material and a resin.

[0089] Unlike conventional reflective layers formed by vapor-depositing metal (on an entire surface), which would result in significant signal shielding, this invention proposes the following method:

[0090] A reflective layer is formed by a composite layer containing metallic materials and resin. The metallic material used is either zero-dimensional or two-dimensional. Using such a metallic material not only provides excellent light reflection but also allows signals to be emitted from the metallic reflective layer.

[0091] Furthermore, compared to one-dimensional metal materials, zero-dimensional metal materials have better dispersion and better reflection uniformity. Two-dimensional metal materials have good directional alignment during coating, thus exhibiting superior light reflectivity.

[0092] In this invention, there are no particular limitations on the type and thickness of the metal material. For example, the metal material can be selected from at least one of aluminum, copper, silver, gold, and indium; when the metal material is two or more of the above metals, the metal material is an alloy of the above metals. In some specific embodiments, the metal can be granular, disc-shaped, flake-shaped, or other irregularly shaped, or any combination thereof. Most preferably, the metal reflective layer of this invention can use one or more combinations of the above-mentioned two-dimensional metal materials. For these two-dimensional metallic materials, their length (the longest distance in the plane) can range from 0.1 μm to 50 μm, for example, 0.5 μm, 1 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 45 μm, etc.; their thickness can range from 0.0001 μm to 50 μm, for example, 0.001 μm, 0.01 μm, 0.1 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 45 μm, etc. Furthermore, for usable zero-dimensional metallic materials, their particle size can range from 0.1 μm to 50 μm, for example, 0.5 μm, 1 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 45 μm, etc.

[0093] The resin in the metal reflective layer may include a transparent resin, which may be selected from at least one or a combination of acrylic resin, polyester resin, polycarbonate resin, vinyl chloride resin, polystyrene resin, polyolefin resin, fluororesin, cyclic olefin resin, silicone resin, and polyurethane resin. Considering weather resistance and transparency, at least one of acrylic resin, polycarbonate resin, vinyl chloride resin, and polyurethane resin is preferred.

[0094] In some preferred embodiments, at least one of antioxidants, leveling agents, curing agents, UV inhibitors, dispersants, stabilizers, and catalysts may be added to the metal reflective layer. Considering secondary oxidation, it is best to add any two or more additives, and different additives are selected according to the material of the resin to prevent oxidation and yellowing.

[0095] Furthermore, without affecting the technical effect of the present invention, in order to improve the whiteness of the metal reflective layer, inorganic dyes or pigments, such as titanium dioxide, can be added to the metal reflective layer.

[0096] In some preferred embodiments, the content of the metal material in the metal reflective layer is 2 wt% to 90 wt%, preferably 2 wt% to 70 wt%, more preferably 3 wt% to 50 wt%; and the content of the resin is 5 wt% to 97 wt%, preferably 10 wt% to 90 wt%, more preferably 30 wt% to 85 wt%.

[0097] Furthermore, the thickness of the metal reflective layer and the metal content have an inversely proportional effect on signal shielding; that is, when the thickness of the metal reflective layer increases, the signal shielding can remain unchanged by reducing the metal content. With a constant metal content, the thickness of the metal reflective layer and the retroreflection coefficient of the reflective sheet have a directly proportional effect; that is, when the thickness of the metal reflective layer increases, the retroreflection coefficient of the reflective sheet also increases. In some specific embodiments, the thickness of the metal reflective layer can be 0.5 μm to 100 μm, preferably 1 μm to 60 μm, and more preferably 1 μm to 40 μm.

[0098] In one specific implementation, the metallic reflective layer can be formed by processes such as blade coating, roller coating, and slot coating.

[0099] (Adhesive layer)

[0100] In this invention, an adhesive layer may be further provided on the surface of the metal reflective layer opposite to the retroreflective structure layer.

[0101] There are no particular limitations on the material of such adhesive layer. Commonly used pressure-sensitive adhesives in this field, such as acrylics, can be used. Alternatively, the adhesive layer can also be a layer formed by hot melt adhesive.

[0102] When using pressure-sensitive adhesive, a release material can also be provided on one side of the adhesive surface. The release material can be paper or films such as PET or CPP. Furthermore, the thickness of the pressure-sensitive adhesive can be 10μm to 150μm, preferably 20μm to 60μm, and more preferably 30μm to 50μm.

[0103] The hot melt adhesive can be PA hot melt adhesive, TPU hot melt adhesive, EVA hot melt adhesive, or PES hot melt adhesive. The thickness of the hot melt adhesive can be 1μm to 150μm, preferably 3μm to 40μm, and more preferably 6μm to 30μm.

[0104] In the aforementioned reflective sheets, if the adhesive layer is a pressure-sensitive adhesive film, it can be directly adhered to the material. If the adhesive layer is a hot melt adhesive, it can be used for injection molding, hot stamping, and in-film labeling.

[0105] The reflective sheet of this invention exhibits excellent transmission performance for RFID and millimeter-wave radar signals, as well as good retroreflection performance. In some specific embodiments of this invention, with an observation angle of 0.2° and an incident angle of 5°, the retroreflection coefficient of the reflective sheet is 15 cd / (lx·m). 2The above are also mentioned. In some specific embodiments of the present invention, the RFID signal sensitivity is below -17dBm, and the frequency is between 920MHz and 925MHz. In some specific embodiments of the present invention, the bidirectional transmission loss of the millimeter-wave radar is below 5dB, preferably 3dB, and the frequency is between 76 and 81GHz.

[0106] The reflective sheet of the present invention has a wider range of applications. It is not only suitable for use in various vehicles, such as for use in various motor vehicle or non-motor vehicle license plates, labels, and certificates that are easy to identify by electrical signals and vision; it is also suitable for use in car decorations, such as car stickers.

[0107] Example

[0108] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0109] Example 1:

[0110] As shown in Figure 1, 100 parts by weight of acrylic resin solution (trade name: RS-1200, Enshiai (Hangzhou) Film Co., Ltd.), 14 parts by weight of methylated melamine resin solution (trade name: NIKALAC MS-11, SANWA CHEMICAL CO.,LTD.), 1.5 parts by weight of ultraviolet absorber (trade name: Seesorb 103, SHIPRO KASEIKAISHA CO.,LTD.), and 16.7 parts by weight of solvent (MIBK / toluene = 8 / 2) were mixed and stirred to prepare a resin compound for forming a transparent protective layer. The resin compound was coated on an engineering substrate film and dried to form a transparent protective layer with a thickness of approximately 36 μm. A transparent polyethylene terephthalate film with a thickness of 75 μm (trade name: Tetoron Film S-75, Teijin Co., Ltd.) was used as the engineering substrate film.

[0111] 100 parts by weight of acrylic resin (trade name: RS-3000, Enshiai (Hangzhou) Film Co., Ltd.), 22 parts by weight of color-developing masterbatch (trade name: AR-6300, TOKUSHIKI Co., Ltd.), 13.6 parts by weight of isocyanate-based crosslinking agent (trade name: Sumijoule N-75, Sumika Bayer Urethane Co., Ltd.), and 20 parts by weight of toluene and 10 parts by weight of methyl isobutyl ketone (MIBK) as solvents were mixed and stirred to prepare a resin complex liquid for forming a transparent resin layer. The resin complex liquid was then coated onto a transparent protective layer and dried at 100°C for 5 minutes to form a transparent resin layer with a thickness of approximately 13 μm.

[0112] Glass microspheres (trade name: NB-23S, Enshiai (Hangzhou) Film Co., Ltd.) were attached to the above-mentioned transparent resin layer and heat-treated at 145°C for 3 minutes and 30 seconds. The glass microspheres were then immersed in the transparent resin layer in such a way that they were exposed from the transparent resin layer, and approximately 75% of the diameter of the glass microspheres were maintained in the transparent resin layer.

[0113] 100 parts by weight of acrylic resin solution (trade name: RS-5000, Enshiai (Hangzhou) Film Co., Ltd.), 5.5 parts by weight of methylated melamine resin solution (trade name: NIKALAC MS-11, SANWA CHEMICAL CO.,LTD.), and 39.3 parts by weight of solvent (MIBK / toluene = 4 / 6) were mixed and stirred to prepare a resin compound for the focal point forming layer. The resin compound was coated on a transparent resin layer and a micro glass ball and dried to form a focal point forming layer with an average thickness of approximately 23 μm.

[0114] 100 parts by weight of acrylic resin, 5 parts by weight of metal material, and 10 parts by weight of toluene and 10 parts by weight of MIBK as solvents are mixed and stirred to form a resin complex liquid for the reflective layer. The resin complex liquid is coated on the focal point forming layer and dried to form a metal reflective layer with an average thickness of about 1 μm. The metal material is aluminum silver paste (the aluminum sheet is in the shape of scales and has a length of 20 μm).

[0115] Acrylic resin 100 parts, isocyanate 3 parts and EAC 5 parts are mixed and stirred to prepare an adhesive component. The adhesive component is coated on release paper to form an adhesive layer of about 40 μm, and then bonded to the metal reflective layer using a laminating machine to form a reflective license plate reflective material.

[0116] Example 2:

[0117] Same as Example 1, except that the metal material is 50 parts by weight.

[0118] Example 3:

[0119] Same as in Example 1, except that the metal material is 100 parts by weight.

[0120] Example 4:

[0121] Same as Example 1, except that the thickness of the metal reflective layer is 40 μm.

[0122] Example 5:

[0123] Same as Example 2, except that the thickness of the metal reflective layer is 40 μm.

[0124] Example 6:

[0125] Same as Example 3, except that the thickness of the metal reflective layer is 35 μm.

[0126] Comparative Example 1:

[0127] Similar to Example 1, except that the metal reflective layer is replaced with vacuum-plated aluminum with a thickness of 100 angstroms.

[0128] Comparative Example 2:

[0129] Same as Example 1, except that the metal reflective layer is replaced with a white reflective layer.

[0130] 100 parts by weight of acrylic resin, 100 parts by weight of white pigment (trade name: DAD 100; DIC Corporation), and 20 parts by weight of toluene and 10 parts by weight of MIBK as solvent are mixed and stirred to form a resin compound for the reflective layer. The resin compound is applied onto the focal point forming layer and dried to form a white reflective layer with an average thickness of approximately 40 μm.

[0131] Comparative Example 3:

[0132] Similar to Example 1, except that 5 parts by weight of the metal material were replaced with an equal part by weight of needle-shaped metal (20 μm in length). Due to uneven mixing, a usable sample could not be obtained.

[0133] Comparative Example 4:

[0134] Same as Example 1, except that the thickness of the metal reflective layer is 120 μm.

[0135] Result comparison:

[0136] 1) Retroreflection coefficient was tested according to GA666-2018 "Reflective Film for Motor Vehicle License Plates"; the unit is candela per lux per square meter (cd / (lx·m)). 2)); Data with an observation angle of 0.2° and an incident angle of 5°.

[0137] 2) RFID signal sensitivity is tested according to the requirements of GB / T29768-2013 "Information Technology Radio Frequency Identification 800 / 900MHz Air Interface Protocol", with data values ​​between 920 and 925MHz; the unit is dBm.

[0138] 3) Millimeter-wave radar testing equipment: QAR automotive radome tester using Rohde & Schwarz imaging technology; referring to the frequency range of automotive millimeter-wave radar, the test frequency range is 77GHz band (76~77GHz) and 79GHz band (76~81GHz) for bidirectional transmission loss of millimeter-wave radar signals; the unit is dB.

[0139] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0140] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

A multi-layered reflective sheet, characterized in that, The reflective sheet comprises the following structural layers from top to bottom: Transparent protective layer, transparent resin layer, retroreflective structure layer, focal point forming layer, and metallic reflective layer. The retroreflective structure layer is a lens array layer formed by transparent microspheres or prisms, and the lens array layer is at least partially embedded in the focal point forming layer; Furthermore, the thickness of the metal reflective layer is 0.5 to 100 μm, and the metal reflective layer comprises a metal material and a resin, wherein the metal material comprises one or more of zero-dimensional metal particles and two-dimensional metal particles. The reflective sheet according to claim 1 is characterized in that, The zero-dimensional metal particles are substantially spherical metal particles; the two-dimensional metal particles are selected from scaly metal particles, disc-shaped metal particles, or irregularly shaped sheet-like metal particles. The reflective sheet according to claim 1 or 2 is characterized in that, The metallic material is selected from one of aluminum, copper, silver, gold, indium, or alloys thereof. The reflective sheet according to any one of claims 1-3 is characterized in that, The metal reflective layer contains 2 wt% to 90 wt% of metal material. The reflective sheet according to any one of claims 1-4 is characterized in that, The metal reflective layer also includes additives, which are one or more of antioxidants, leveling agents, curing agents, UV protectants, dispersants, stabilizers, and catalysts. The reflective sheet according to any one of claims 1-5 is characterized in that, 20-90% by volume of the retroreflective structure layer is embedded in the focal point forming layer. The reflective sheet according to any one of claims 1-6 is characterized in that, The metal reflective layer also has an adhesive layer on the side away from the focal point forming layer. The reflective sheet according to any one of claims 1-7 is characterized in that, With an observation angle of 0.2° and an incident angle of 5°, the retroreflection coefficient of the reflector is 15 cd / (lx·m). 2 )above. The reflective sheet according to any one of claims 1-8 is characterized in that, The RFID signal sensitivity of the reflector is below -17dBm, and the frequency is between 920MHz and 925MHz. The reflective sheet according to any one of claims 1-9 is characterized in that, The reflector has a bidirectional transmission loss of less than 5dB for millimeter-wave radar and a frequency of 76-81GHz.

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