Display apparatus

Abstract

A display apparatus. The display apparatus comprises a display panel and a peep-proof film (100), wherein the peep-proof film (100) comprises a plurality of gate lines (121) arranged at intervals; gaps between the plurality of gate lines (121) form a plurality of slits (130), and light-transmitting mediums (122) fill the plurality of slits (130); and the refractive index of the gate lines (121) is different from that of the light-transmitting mediums (122).

Description

Display device

[0001] This application claims priority to Chinese patent application No. 202311113688.X filed on August 29, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the field of display technology, and in particular to a display device. Background Art

[0003] Current display products have been widely used in personal display devices. For the sake of user privacy, the demand for anti-peeping functions will become more and more common.

[0004] Although the current anti-peeping film has an anti-peeping effect, it is mainly made based on the principle of a shutter structure. Although this anti-peeping film can achieve anti-peeping, it will reduce the transmittance of light, causing a significant attenuation of the surface brightness of the display device, resulting in the screen being too dark when observed by the human eye, which can easily cause visual fatigue and urgently needs to be improved. SUMMARY OF THE INVENTION

[0005] The purpose of this application is to provide a display device that uses multiple wire grids to form multiple slits, and fills the multiple slits with a transparent medium. The electric field affects the reflection phase of the transparent medium to complete the modulation of polarized light, thereby achieving a visual anti-peeping effect while improving the transmittance of the screen and avoiding visual fatigue to the user.

[0006] An embodiment of the present application provides a display device, including a display panel and an anti-peep film arranged on the light-emitting side of the display panel, the anti-peep film including a plurality of wire grids arranged at intervals, the gaps between the plurality of wire grids forming a plurality of slits, and the plurality of slits being filled with a light-transmitting medium; the wire grid and the light-transmitting medium have different refractive indices. Beneficial effects

[0007] Beneficial effects of the embodiments of the present application:

[0008] In an embodiment of the present application, a display device is provided, including a display panel and an anti-peep film. The anti-peep film uses multiple wire grids to form multiple slits, and fills the multiple slits with a light-transmitting medium. By applying voltage to the multiple wire grids, the reflection phase of the light-transmitting medium is changed, and the modulation of polarized light is completed, replacing the traditional shutter structure. While achieving a visual anti-peep effect, the transmittance of the screen is improved to avoid visual fatigue to the user.

[0009] Furthermore, the privacy film can be directly attached to existing display devices without modifying their structure, making it more practical and convenient to use. Furthermore, when the wire grid is de-energized, the metastructured surface layer functions as a metallic polarizer, maintaining a high transmittance. The light-transmitting medium introduces a refractive index difference, leveraging its scattering function to further widen the viewing angle of the display device. Therefore, the privacy film's privacy function not only achieves a privacy-preventing effect, but also allows for selective activation, providing greater flexibility and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0011] FIG1 is a schematic structural diagram of a display device provided in some embodiments of the present application;

[0012] FIG2 is a cross-sectional schematic diagram of a privacy film provided in some embodiments of the present application;

[0013] FIG3 is a first top view of a privacy film provided in some embodiments of the present application;

[0014] FIG4 is a second top view of the privacy film provided in some embodiments of the present application;

[0015] FIG5 is a partial cross-sectional schematic diagram of a privacy film provided in some embodiments of the present application, mainly used to embody transparent microspheres;

[0016] FIG6 is a schematic structural diagram of an intermediate dielectric layer provided in some embodiments of the present application.

[0017] Explanation of the accompanying reference numerals: 100, anti-peep film; 110, intermediate dielectric layer; 111, substrate; 112, surface film layer; 120, metasurface layer; 121, wire grid; 122, light-transmitting medium; 1221, transparent microspheres; 130, slit; 200, backlight source; 300, polarizer; 400, array substrate; 500, color film substrate; 600, liquid crystal; 700, reflective layer. Modes for Carrying Out the Invention

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise specified, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; and "inside" and "outside" refer to the outline of the device.

[0019] Display products are now widely used in personal display devices. To protect user privacy, the demand for display devices with privacy protection will inevitably become increasingly common. Currently, privacy films 100 are primarily manufactured based on the principle of a Venetian blind structure. While this type of privacy film 100 can achieve privacy protection, it significantly reduces the surface brightness of the display device, presenting significant drawbacks.

[0020] In recent years, with the rapid development of micro-nano processing technology and metal surface plasmons, local phase modulation can be performed based on metasurfaces. The characteristic that the plasma propagation constant of the metal slit 130 changes with the width of the slit 130 can be utilized to achieve flexible local phase adjustment, and based on this, the law of refraction and reflection of the metasurface can be established.

[0021] The width and period of each wire grid are much smaller than the wavelength. When polarized parallel to the grid, this wire grid stimulates an induced current, resulting in strong absorption of light. When the grid is perpendicular, no resonance is achieved because the scale of the wire grid is much smaller than the wavelength, allowing light to be transmitted. Its period is very small, and at normal incidence, the diffraction grid has a very large angle. According to scattering theory, as the angle of the diffraction grid increases, the energy occupied by the grid decreases. At some wavelengths, the grid even exceeds the diffraction limit, meaning there is no diffraction grid.

[0022] Based on the above theory, the present application provides a display device, which is described in detail below. It should be noted that the description order of the following embodiments does not limit the preferred order of the embodiments.

[0023] An embodiment of the present application provides a display device, which includes a display panel and an anti-peep film arranged on the light-emitting side of the display panel, the anti-peep film includes a plurality of wire grids arranged at intervals, the gaps between the plurality of wire grids form a plurality of slits, and the plurality of slits are filled with a light-transmitting medium; the wire grid and the light-transmitting medium have different refractive indices.

[0024] In some embodiments of the present application, the plurality of wire grids are parallel to each other and are arranged at equal intervals;

[0025] Alternatively, the plurality of wire grids are parallel to each other, and the spacing between the wire grids decreases from the middle of the privacy film to both sides.

[0026] In some embodiments of the present application, when the plurality of wire grids are parallel to each other and arranged at equal intervals, the refractive index of the light-transmitting medium is gradually increased from the middle of the privacy film to both sides.

[0027] In some embodiments of the present application, when the multiple wire grids are parallel to each other and the spacing between them is decreasing from the middle of the anti-peep film to both sides, the width of the wire grid is increasing from the middle of the anti-peep film to both sides, and the refractive index of the light-transmitting medium in each of the slits is equal.

[0028] In some embodiments of the present application, the light-transmitting medium is made of acrylic resin or epoxy resin.

[0029] In some embodiments of the present application, a plurality of evenly distributed transparent microspheres are disposed inside the light-transmitting medium.

[0030] In some embodiments of the present application, the transparent microspheres are made of polycarbonate, acrylic resin, or polysiloxane resin, and have a refractive index of 1.6-1.7.

[0031] In some embodiments of the present application, the privacy film further includes:

[0032] The intermediate dielectric layer is disposed on a side of the privacy film close to the display panel and is used to support the plurality of wire grids and the light-transmitting intermediate dielectric layer.

[0033] In some embodiments of the present application, the display panel includes:

[0034] Color film substrate; and

[0035] A reflective layer is provided on one side of the color filter substrate;

[0036] Wherein, the reflective layer is located between the color film substrate and the anti-peep film, and the reflective layer is a reflective polarizer.

[0037] In some embodiments of the present application, the reflective layer constitutes an upper polarizer of the display panel.

[0038] Specifically, referring to Figure 1, some embodiments of the present application provide a display device that can adopt different display modes such as OLED (Organic Light-Emitting Diode), LCD (Liquid-Crystal Display), Micro LED (Micro Light-Emitting Diode Display), Mini LED (Mini Light-Emitting Diode Display) or VA (Vertical Alignment), which includes a display panel and an anti-peeping film 100 arranged on the light-emitting side of the display panel; the anti-peeping film 100 can increase the anti-peeping effect for the display panel, so that the display device as a whole can achieve the anti-peeping function.

[0039] Referring to FIG. 2 , in some embodiments, the privacy film 100 includes an intermediate dielectric layer 110 and a metasurface layer 120 disposed on one side of the intermediate dielectric layer 110 .

[0040] Among them, the meta-surface layer 120 is a nanostructure layer, which can modulate polarized light and narrow the outgoing light to reduce the side angle light, thereby achieving a visual anti-peeping effect while ensuring light filtering.

[0041] In this embodiment, the metasurface layer 120 includes a plurality of wire grids 121 spaced apart and arranged parallel to each other on the intermediate dielectric layer 110. The gaps between the wire grids 121 form a plurality of slits 130, each of which is filled with a light-transmitting medium 122.

[0042] The wire grids 121 may be understood as multiple metal strips spaced parallel to each other on the surface of the intermediate dielectric layer 110. The material of the wire grids 121 may be flexibly selected as needed, for example, nickel, aluminum, or other conductive materials, which are not specifically limited.

[0043] When actually manufacturing the wire grids 121 , nanoimprinting can be used to imprint multiple wire grids 121 on the intermediate dielectric layer 110 to form them into one. Other methods can also be used to form the multiple wire grids 121 , which are not specifically limited.

[0044] Similarly, the material of the light-transmitting medium 122 can be flexibly selected. For example, the light-transmitting medium 122 can be made of acrylic resin, epoxy resin, or other similar resin materials, and this is not specifically limited. However, when determining the material of the light-transmitting medium 122 and actually filling the light-transmitting medium 122, the refractive index of the light-transmitting medium 122 should be adjustable and controlled within the range of 1.2-1.8.

[0045] When filling the plurality of slits 130 with the light-transmitting medium 122 , the operation may be performed by a single-layer filling method or by a multi-layer filling method twice or more, which is not specifically limited.

[0046] It should be noted that when multiple wire grids 121 and transparent media 122 are actually set up, the spacing between the wire grids 121 and the refractive index of the transparent medium 122 will affect the final anti-peeping effect of the anti-peeping film 100; at the same time, the refractive index of the above-mentioned wire grids 121 and the transparent medium 122 should be different, that is, the refractive index of the wire grid 121 is greater than the refractive index of the transparent medium 122, or the refractive index of the transparent medium 122 is greater than the refractive index of the wire grid 121; the specific refractive index values ​​of the wire grid 121 and the transparent medium 122 are not limited here.

[0047] As shown in FIG3 , in some embodiments, to ensure the privacy protection effect of the privacy film 100, the plurality of wire grids 121 can be arranged at equal intervals on the intermediate dielectric layer 110. In this case, the refractive index of the light-transmitting medium 122 filled between the plurality of wire grids 121 can be arranged to increase gradually from the center of the privacy film 100 toward both sides.

[0048] As shown in Figure 4, in some embodiments, to ensure the privacy protection effect of the privacy film 100, the spacing between the plurality of wire grids 121 decreases from the center of the privacy film 100 toward the sides, while the width of the wire grids 121 increases from the center toward the sides. In this case, the refractive index of the light-transmitting medium 122 filling each slit 130 can be the same. Specifically, the width of the wire grid 121 can be controlled to be 30-90μm, and its height above the intermediate dielectric layer 110 can be 100-180μm; the width of the slit 130 can also be controlled to be 30-90μm.

[0049] For example, in some embodiments, the plurality of wire grids 121 may be arranged at equal intervals on the intermediate dielectric layer 110. In this case, the widths of the wire grids 121 and the slits 130 may both be 60 μm, and the refractive index of the light-transmitting medium 122 filling each slit 130 may increase gradually from the center of the privacy film 100 toward both sides, but may not exceed 1.8 at most.

[0050] For example, in some embodiments, the spacing between the plurality of wire grids 121 decreases from the center of the privacy film 100 toward the sides, while the width of the wire grids 121 increases from the center toward the sides. In this case, the width of the wire grid 121 located in the center of the privacy film 100 can be 30 μm, while the widths of the wire grids 121 arranged toward the sides of the privacy film 100 can increase from this 30 μm (not exceeding 90 μm). The width of the slits 130 (or the width of the light-transmitting medium) located in the center of the privacy film 100 can be 90 μm, while the widths of the slits 130 arranged toward the sides of the privacy film 100 can decrease from this 90 μm (not less than 30 μm). In this case, the refractive index of the light-transmitting medium 122 in each slit 130 can remain consistent.

[0051] It is understandable that the above-mentioned dimensions of the wire grid 121 and the slit 130 are merely preferred embodiments given in this application based on experiments, and their specific dimensions can still be flexibly optimized and designed as needed, and no specific limitation is imposed on this.

[0052] Due to the characteristic of the plasma propagation constant of the metal slit varying with the slit width, some embodiments of the present application, when actually forming the wire grid 121 and the light-transmitting medium 122, can achieve arbitrary gradient changes in the phase angle of the outgoing light within a desired range by varying the width of the slits 130 in the wire grid 121. In other words, the phase angle of the outgoing light can be flexibly adjusted by varying the width of the wire grid 121 and the slits 130 on the intermediate dielectric layer 110. Therefore, with the help of the wire grid 121 and the light-transmitting medium 122, the embodiments of the present application can meet diverse modulation requirements within a desired range, flexibly controlling the phase angle of the outgoing light and thus flexibly adjusting the viewing angle of the corresponding display screen.

[0053] In actual application, with the help of the above-mentioned multiple wire grids 121 and the transparent medium 122, when the wire grid 121 is not energized, the anti-peep film 100 can pass all incident light; at this time, affected by the refractive index of the transparent medium 122, the light will be further scattered when passing through, so that the corresponding display device can obtain a wide-viewing angle display effect; at this time, the anti-peep film 100 does not have an anti-peep effect, but can play a role similar to that of a polarizer.

[0054] When voltage is applied to the wire grid 121, for example, when any two adjacent wire grids 121 are respectively connected to the positive and negative poles of the power supply element, an electric field will be formed between the two adjacent wire grids 121, and the electromagnetic resonance of the metal micro-nano structure will be stimulated, so that the reflection phase of the transparent medium 122 is enhanced, showing a certain reflection efficiency, achieving the effect of blurred side angle imaging, and realizing the anti-peek function.

[0055] It should be understood that the display device provided by the embodiments of the present application can change the actual function of the privacy film 100 by controlling the power state of the wire grid 121, thereby changing the display effect of the display device. When de-energized, the privacy film 100 can function as a metal polarizer; when energized, the privacy film 100 can achieve a visual privacy protection effect. Therefore, the privacy protection effect of the display device provided by the embodiments of the present application can be selectively turned on or off according to user needs, providing greater flexibility.

[0056] In the embodiment of the present application, the above-mentioned anti-peep film 100 includes an intermediate dielectric layer 110 and a meta-surface layer 120 arranged on the intermediate dielectric layer 110; but in fact, the intermediate dielectric layer 110 can also be eliminated, that is, in other embodiments, the anti-peep film 100 may not include the intermediate dielectric layer 110, and it can be composed solely of the meta-surface layer 120, and the anti-peep effect can also be achieved.

[0057] Please refer to Figures 2 and 5. In some embodiments, when the light-transmitting medium 122 is filled into the slit 130, the filling height of the light-transmitting medium 122 can be higher than the height of the wire grid 121, and the specific size of the light-transmitting medium 122 higher than the wire grid 121 can be flexibly optimized as needed. For example, the light-transmitting medium 122 can be higher than the wire grid 121 by μm, 15 μm, 20 μm, 25 μm or other sizes, and there is no specific limitation on this.

[0058] In some embodiments, in order to further improve the anti-peeping effect, when actually forming the above-mentioned transparent medium 122, a plurality of transparent microspheres 1221 can be filled into the transparent medium 122; the material of the transparent microspheres 1221 can be PC (Polycarbonate), acrylic resin or polysiloxane resin; the plurality of transparent microspheres 1221 can be evenly dispersed inside the transparent medium 122 system, and the refractive index of the transparent microspheres 1221 can be controlled within 1.6-1.7, and the specific value can be determined according to design requirements.

[0059] In some embodiments, in order to extend the service life of the anti-peep film 100, an anti-glare film and / or a high-hardness protective film is further provided on the side of the meta-surface layer 120 facing away from the intermediate dielectric layer 110. The protective film can be made of acrylic resin or other materials, which is not specifically limited.

[0060] 2 and 6 , the intermediate dielectric layer 110 may be a single-layer substrate 111 or a multi-layer composite laminate structure.

[0061] In some embodiments, the intermediate dielectric layer 110 is a single-layer substrate 111. In this case, the substrate 111 can be either a rigid substrate or a flexible substrate. When the intermediate dielectric layer 110 is a rigid substrate, it can be a base glass. When the intermediate dielectric layer 110 is a flexible substrate, it can be an organic polymer or an organic-inorganic doped composite. For example, the organic polymer can be PI (polyimide) or PET (polyethylene terephthalate). The organic-inorganic doped composite can be a polyimide doped with glass fiber. Because glass fiber has high toughness, it can significantly improve the flexible strength of the intermediate dielectric layer 110, making it less susceptible to breakage and delamination.

[0062] In some embodiments, the intermediate dielectric layer 110 is a multi-layer composite laminate structure, which includes a substrate 111 and a surface film layer 112 disposed on a side of the substrate 111 close to the metasurface layer 120 .

[0063] In this case, substrate 111 can be either a rigid substrate or a flexible substrate. When intermediate dielectric layer 110 uses a rigid substrate, it can be a base glass; when intermediate dielectric layer 110 uses a flexible substrate, it can be an organic polymer or an organic-inorganic doped composite. For example, the organic polymer can be PI or PET; the organic-inorganic doped composite can be a polyimide polymer doped with glass fiber. Due to the high toughness of glass fiber, the flexible strength of intermediate dielectric layer 110 can be significantly improved, making intermediate dielectric layer 110 less susceptible to breakage and delamination.

[0064] The surface film layer 112 may be any one of TAC (Triacetyl Cellulose, triacetate cellulose film) and PET, or may be a laminate of TAC and PET, which is not specifically limited.

[0065] In this embodiment, the display panel can be any of OLED, LCD, MLED, VA, and other types of display panels, without specific limitation. That is, the display device provided in the embodiments of this application can adopt different display modes such as OLED, LCD, MLED, and VA, and its privacy protection function is not dependent on the selected display mode and is applicable to all display modes. Furthermore, the display device includes any product or component with a display function, such as a mobile phone, tablet computer, television, monitor, laptop computer, digital photo frame, and navigation system.

[0066] Referring to FIG. 1 , in some embodiments, the display panel is an LCD display panel, which includes a backlight 200, a polarizer 300 disposed on one side of the backlight 200, an array substrate 400 disposed on a side of the polarizer 300 facing away from the backlight 200, a color filter substrate 500 disposed on a side of the array substrate 400 facing away from the polarizer 300, a liquid crystal 600 disposed between the array substrate 400 and the color filter substrate 500, and a reflective layer 700 disposed on a side of the color filter substrate 500 facing away from the array substrate 400. The privacy film 100 is disposed on the side of the reflective layer 700 facing away from the color filter substrate 500.

[0067] It should be noted that the above-mentioned reflective layer 700 can be a conventional polarizer or a reflective polarizer; but considering the anti-peeping effect, the reflective layer 700 is preferably a reflective polarizer, that is, in practical applications, a reflective polarizer can be used to replace the ordinary polarizer used in the upper polarizer of a traditional LCD display panel, that is, the above-mentioned reflective layer 700 can constitute the upper polarizer on the corresponding display panel; in this way, when ambient light enters the meta-structure surface layer 120, the reflective polarizer can increase the reflection and re-emission of the ambient light entering the meta-structure surface layer 120, thereby facilitating the formation of interference light to reduce the visibility of the anti-peeping angle picture.

[0068] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0069] The above is a detailed introduction to a display device provided in an embodiment of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A display device, comprising a display panel and an anti-peep film arranged on a light-emitting side of the display panel, wherein the anti-peep film comprises a plurality of wire grids arranged at intervals, wherein the gaps between the plurality of wire grids form a plurality of slits, and the plurality of slits are filled with a light-transmitting medium; the wire grid and the light-transmitting medium have different refractive indices.

2. The display device according to claim 1, wherein: The plurality of wire grids are parallel to each other and arranged at equal intervals; Alternatively, the plurality of wire grids are parallel to each other, and the spacing between the wire grids decreases from the middle of the privacy film to both sides.

3. The display device according to claim 1, wherein: The plurality of wire grids are parallel to each other and are arranged at equal intervals, and the refractive index of the light-transmitting medium is arranged to increase gradually from the middle of the anti-peep film to both sides.

4. The display device according to claim 1, wherein: The plurality of wire grids are parallel to each other, and the spacing between them decreases from the middle of the privacy film to both sides, the width of the wire grids increases from the middle of the privacy film to both sides, and the refractive index of the light-transmitting medium in each of the slits is equal.

5. The display device according to claim 1, wherein: The material of the light-transmitting medium is acrylic resin or epoxy resin.

6. The display device according to claim 1, wherein: A plurality of evenly distributed transparent microspheres are arranged inside the light-transmitting medium.

7. The display device according to claim 6, wherein: The transparent microspheres are made of polycarbonate, acrylic resin or polysiloxane resin, and have a refractive index of 1.6-1.

7.

8. The display device according to any one of claims 1 to 7, wherein: The privacy film also includes: The intermediate medium layer is arranged on a side of the anti-peep film close to the display panel and is used for carrying the plurality of wire grids and the light-transmitting medium.

9. The display device according to any one of claims 1 to 7, wherein: The display panel comprises: Color film substrate; and A reflective layer, disposed on one side of the color film substrate; Wherein, the reflective layer is located between the color film substrate and the anti-peep film, and the reflective layer is a reflective polarizer.

10. The display device according to claim 9, wherein: The reflective layer constitutes an upper polarizer of the display panel.

11. The display device according to claim 1, wherein: The width of the wire grid is 30-90 μm, and the width of the slit is 30-90 μm.

12. The display device according to claim 1, wherein: The anti-peep film further comprises an intermediate dielectric layer, and the plurality of wire grids are a plurality of strip-shaped metals arranged in parallel and at intervals on the surface of the intermediate dielectric layer.

13. The display device according to claim 12, wherein: The wire grid is made of nickel or aluminum.

14. A display device comprising a display panel and an anti-peep film disposed on a light-emitting side of the display panel, wherein the anti-peep film comprises an intermediate dielectric layer and a metasurface layer disposed on one side of the intermediate dielectric layer; The metasurface layer includes a plurality of wire grids spaced apart on the intermediate dielectric layer, the gaps between the plurality of wire grids form a plurality of slits, and the plurality of slits are filled with a light-transmitting medium; the wire grids and the light-transmitting medium have different refractive indices.

15. The display device according to claim 14, wherein: The superstructure surface layer is a nanostructure layer.

16. The display device according to claim 14, wherein: The plurality of wire grids are parallel to each other and arranged at equal intervals; Alternatively, the plurality of wire grids are parallel to each other, and the spacing between the wire grids decreases from the middle of the privacy film to both sides.

17. The display device according to claim 14, wherein: The plurality of wire grids are parallel to each other and are arranged at equal intervals, and the refractive index of the light-transmitting medium is arranged to increase gradually from the middle of the anti-peep film to both sides.

18. The display device according to claim 14, wherein: The plurality of wire grids are parallel to each other, and the spacing between them decreases from the middle of the privacy film to both sides, the width of the wire grids increases from the middle of the privacy film to both sides, and the refractive index of the light-transmitting medium in each of the slits is equal.

19. The display device according to claim 14, wherein: A plurality of evenly distributed transparent microspheres are arranged inside the light-transmitting medium.

20. The display device according to claim 19, wherein: The transparent microspheres are made of polycarbonate, acrylic resin or polysiloxane resin, and have a refractive index of 1.6-1.7.

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