Full-color circular polarization Micro-LED display device integrated with chiral liquid crystal film and preparation method of full-color circular polarization Micro-LED display device

Abstract

The invention relates to a full-color circular polarization Micro-LED display device integrated with a chiral liquid crystal film and a preparation method, and belongs to the technical field of novel display. According to the scheme, red and green quantum dot pixel units are accurately deposited on the surface of a blue light Micro-LED array through an ink-jet printing technology, an RGB three-primary-color light-emitting system is constructed, and wide-color-gamut full-color display is achieved in combination with the high color purity characteristic of a quantum dot material. On the basis, the chiral liquid crystal thin film is integrated on the surface of the pixel array, passing red, green and blue line polarized light is converted into circularly polarized light through a spiral periodic structure of the chiral liquid crystal thin film, ambient light reflection is effectively restrained, and the display contrast ratio is improved. According to the technology, the advantages of high resolution and low power consumption of a Micro-LED, the narrow-band light-emitting characteristic of quantum dots and the polarization regulation and control capacity of chiral liquid crystals are fused, and the problems that a traditional circular polarization display device is complex in structure, high in energy consumption, low in color gamut and the like are solved.

Description

Technical Field

[0001] The present invention belongs to the fields of display technology and optoelectronic technology, and specifically relates to a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film and a preparation method thereof. Background Art

[0002] With the rapid development of information technology and smart devices, display technology has become an important medium for human-computer interaction. As a new generation of display panel technology, Micro-LED has attracted widespread attention due to its many advantages such as high brightness, high color gamut, low energy consumption, and long life. However, traditional full-color display solutions still have many shortcomings in terms of color performance, energy consumption, and optical properties. In addition, current Micro-LED display technology is mostly based on linearly polarized light output. Although it has significant advantages in brightness, color gamut, and energy efficiency, it has the following limitations: (1) Lack of circularly polarized light generation capability: Traditional circularly polarized light relies on polarizers or complex optical components, resulting in light efficiency loss (such as brightness drop >30%) and structural redundancy, making it difficult to meet miniaturization requirements; (2) Insufficient dynamic full-color compatibility: Existing chiral liquid crystal technology is mostly combined with white light sources or monochrome LEDs, and cannot achieve circularly polarized dynamic display with independent control of red, green, and blue colors. Summary of the Invention

[0003] To address the above technical issues, the present invention proposes a full-color circularly polarized Micro-LED display device and fabrication method integrated with a chiral liquid crystal film. Based on a blue Micro-LED, red and green quantum dot pixels are integrated using inkjet printing technology to achieve full-color display. Inkjet printing technology offers high-precision, contactless processing, enabling precise formation of red and green pixel arrays on the Micro-LED surface. Combined with the blue Micro-LED, this array forms a full-color pixel unit. Due to the unique quantum confinement effect of quantum dot materials, by manipulating the size of the quantum dots, ultraviolet or blue light can be converted into different light colors, ranging from visible light to near-infrared. Quantum dots exhibit high color purity and a wide color gamut, significantly improving display color performance. Furthermore, a chiral liquid crystal film is overlaid on the full-color pixels, allowing red, green, and blue light to pass through and generate circularly polarized light. The chiral liquid crystal film possesses unique optical properties, converting linearly polarized light into circularly polarized light with excellent tunability and stability. By controlling the thickness and chirality parameters of the chiral liquid crystal film, efficient generation and manipulation of circularly polarized light can be achieved. Specifically, the invention uses a blue Micro-LED chip as the excitation light source, forms a red and green quantum dot pixel array through inkjet printing technology to achieve full-color display, and integrates a chiral liquid crystal film on the pixel surface to convert linearly polarized light into full-color circularly polarized light. By integrating quantum dot color conversion, Micro-LED miniaturization, and chiral liquid crystal optical control technology, the invention combines high resolution, a wide color gamut, low energy consumption, and circularly polarized light output. It has applications in 3D displays, anti-counterfeiting labels, AR / VR devices, and biosensors.

[0004] The present invention combines quantum dots, Micro-LEDs and chiral liquid crystal films, uses inkjet printing technology to achieve full-color display, and uses chiral liquid crystal films to generate circularly polarized light, thereby achieving full-color circularly polarized luminescent display with high resolution, high contrast, high color gamut and low energy consumption.

[0005] The specific implementation plan is as follows:

[0006] A full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film, the device comprising a Micro-LED substrate, an RGB pixel unit, and a chiral liquid crystal film;

[0007] The Micro-LED substrate has a plurality of RGB pixel units arranged in an array, each RGB pixel unit including a red fluorescent material pixel unit, a green fluorescent material pixel unit and a transparent unit;

[0008] The red fluorescent material pixel unit includes a first blue light Micro-LED chip and a red fluorescent material coated on the first blue light Micro-LED chip. The red fluorescent material is used to convert the blue light emitted by the first blue light Micro-LED chip into red light. The chiral liquid crystal film can further convert the red light into red circularly polarized light.

[0009] The green fluorescent material pixel unit includes a second blue light Micro-LED chip and a green fluorescent material coated on the second blue light Micro-LED chip. The green fluorescent material is used to convert the blue light emitted by the second blue light Micro-LED chip into green light. The chiral liquid crystal film can further convert the green light into green circularly polarized light.

[0010] The transparent pixel unit includes a third blue light Micro-LED chip and a colorless transparent material coated on the third blue light Micro-LED chip. The colorless transparent material is used to directly transmit the blue light emitted by the third blue light Micro-LED chip, and the chiral liquid crystal film can then convert the blue light into blue circularly polarized light.

[0011] The present invention also proposes a method for preparing a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film, the specific steps of which are as follows:

[0012] Step S1: Design a Micro-LED substrate with a Bank material. The blue Micro-LED chip is located at the bottom surrounded by the Bank material. According to the required array arrangement, the inkjet printing pattern of the red and green fluorescent materials is designed.

[0013] Step S2: transmitting the digitized pattern to the inkjet printing control system, designing the print head and the fluorescent materials in the micro-nozzles on the print head, the starting point of the micro-jet printing, the printing path, and the end point of the micro-jet printing;

[0014] Step S3: Execute the printing process according to the designed parameters to print the red and green fluorescent materials and the colorless blank printing ink into the predetermined bank dam of the blue light Micro-LED chip, located above the blue light Micro-LED chip;

[0015] Step S4: After inkjet printing is completed, clean the excess material on the device surface;

[0016] Step S5: Curing the printing ink by heat or light so that the ink stops flowing and becomes a solid light conversion layer;

[0017] Step S6: Laminating the chiral liquid crystal film on the light conversion layer obtained above, and finally encapsulating the chiral liquid crystal film and the light conversion layer together on the Micro-LED substrate with colorless transparent glass;

[0018] Step S7: Each blue LED chip corresponds to a different control circuit to control the on / off and intensity of the blue LED chip, thereby generating red, green, and blue circularly polarized lights of different intensities.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] By integrating red and green quantum dot pixels onto blue-light micro-LEDs using inkjet printing technology, full-color display is achieved, significantly enhancing the display device's color rendering capabilities and making the displayed image more realistic and vivid. Inkjet printing technology precisely forms an array of red and green pixels on the surface of the blue-light micro-LEDs. Combined with the blue-light micro-LEDs, these pixels form a high-density full-color pixel unit, achieving higher display resolution. A chiral liquid crystal film is placed over the full-color pixels, generating circularly polarized light when red, green, and blue light passes through them, imparting unique optical properties to the display device. Compared to traditional linearly polarized light, circularly polarized light effectively reduces interference from external reflected light, improving the display's visibility and readability in various environments and broadening its application scenarios. Furthermore, the emission characteristics of circularly polarized light are more similar to the human eye's perception of natural light. Compared to conventional linearly polarized or unpolarized light, it is less irritating to the eye and less prone to visual fatigue after prolonged viewing, thus protecting the user's vision. Furthermore, while micro-LEDs inherently offer the advantage of low power consumption, the present invention further optimizes light utilization efficiency by combining quantum dots with chiral liquid crystal films. Quantum dots can efficiently convert blue light into red and green light, reducing energy loss during the conversion process; at the same time, the light regulation effect of chiral liquid crystal films also helps to improve the transmission efficiency of light, allowing more light to be effectively used for display, thereby achieving high-brightness and high-contrast display while reducing overall power consumption and extending the service life of the display device. This is of great significance for products such as portable electronic devices that have high requirements for battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : A front view of the device according to an embodiment of the present invention;

[0022] Figure 2 : The present invention Figure 1 sectional view of

[0023] In the figure: 210 is a red fluorescent unit; 220 is a green fluorescent unit; 230 is a transparent unit; 310 is a first blue light Micro-LED chip, 320 is a second blue light Micro-LED chip, 330 is a third blue light Micro-LED chip; 311 is a red fluorescent material; 321 is a green fluorescent material; 331 is a colorless transparent material; 340 is a chiral liquid crystal film; 350 is a packaging glass sheet; 360 is a Micro-LED substrate. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explain the present invention, but should not be construed as limiting the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0025] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0026] Please refer to Figure 1 and Figure 2The present invention provides a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film, comprising a chiral liquid crystal film 340 and a Micro-LED substrate 360. The Micro-LED substrate 360 ​​has a plurality of RGB pixel units arranged in an array, in this embodiment, an array of 6 rows and 3 columns. Each RGB pixel unit includes a red fluorescent unit 210, a green fluorescent unit 220, and a transparent unit 230. The red fluorescent unit 210 includes a first blue Micro-LED chip 310 and a red fluorescent material 311 coated on the first blue Micro-LED chip 310. The red fluorescent material 311 can convert the blue light emitted by the first blue Micro-LED chip 310 into red light. The red light can generate red circularly polarized light when passing through the chiral liquid crystal film 340. The green fluorescent unit 220 includes a second blue Micro-LED chip 320 and a green fluorescent material 321 coated on the second blue Micro-LED chip 320. The green fluorescent material 321 converts the blue light emitted by the second blue Micro-LED chip 320 into green light, which then passes through a chiral liquid crystal film 340 to produce green circularly polarized light. The transparent unit 230 includes a third blue Micro-LED chip 330 and a colorless transparent material 331 coated on the third blue Micro-LED chip 330. The colorless transparent material 331 directly transmits the blue light emitted by the third blue Micro-LED chip 330, which then passes through the chiral liquid crystal film 340 to produce blue circularly polarized light. The device is encapsulated with an encapsulating glass sheet 350 made of a colorless transparent material. In actual production, the colorless transparent material 331 can be omitted and placed directly on the upper surface of the third blue Micro-LED chip 330.

[0027] The chiral liquid crystal film 340 uses a chiral nematic liquid crystal as a template and replicates the helical structure of the chiral nematic liquid crystal with a polymer. After removing the liquid crystal, a polymer film with a helical structure is obtained. This polymer film can maintain the helical structure of the chiral nematic liquid crystal without the constraints of a rigid liquid crystal cell. This chiral liquid crystal film 340 is covered on the pixel unit of the Micro-LED substrate 360. The RGB pixel unit generates red, green and blue light, which passes through the chiral liquid crystal film 340 to produce three-color circularly polarized light. It has a high asymmetry factor and does not need to be confined within a rigid liquid crystal cell.

[0028] The preparation method of the chiral liquid crystal film is as follows:

[0029] Step S1: adding dopants of different chirality to the polymer monomer and nematic liquid crystal, then adding a cross-linking agent and a photoinitiator, mixing them evenly, and heating and stirring;

[0030] Step S2: pouring the liquid crystal mixture into a liquid crystal cell by capillary action, cooling the liquid crystal cell to room temperature, irradiating it with ultraviolet light for a few minutes, then heating it on a heating table until the unpolymerized regions become transparent, irradiating it with ultraviolet light for a few minutes again, and finally peeling the liquid crystal cell to obtain a chiral liquid crystal polymer film;

[0031] The chiral liquid crystal film comprises nematic liquid crystal, chiral dopant, polymer monomer, crosslinking agent and photoinitiator;

[0032] The nematic liquid crystal is a nematic liquid crystal commonly used in the art, including but not limited to nematic liquid crystal HTG13520, nematic liquid crystal SLC1717, nematic liquid crystal 5CB, nematic liquid crystal E7, nematic liquid crystal MBBA, etc.;

[0033] The chiral dopant may be one or more of 4-(4-hexyloxybenzoyloxy)benzoic acid-S-2-octyl ester (S811), 4-(4'-hexyloxy)benzoyloxybenzoic acid-R-2-octanol ester (R811), (13bS)-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxacyclononatetraene (S5011), and (13bR)-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxacyclononatetraene (R5011).

[0034] The polymer monomer is one or more of 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate (RM257), 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (C6M), or 4-[6-[(1-oxo-2-propenyl)oxy]hexyl]oxybenzoic acid 4-methoxyphenyl ester (RM105);

[0035] The cross-linking agent is one or more of trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate or isooctyl methacrylate;

[0036] The photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651) or 1-hydroxycyclohexylphenyl ketone (Irgacure 184);

[0037] More specifically, a method for preparing a chiral liquid crystal film 340 is provided, and the specific steps are as follows:

[0038] Step S1: dissolving the nematic liquid crystal SLC1717 and the polymer monomer C6M in an organic solvent, then adding the chiral dopant R-811 or S-811, the crosslinker TMPTA and the photoinitiator Irgacure 651, and heating and stirring at 140°C for 2 h;

[0039] Step S2: pouring the R-811 or S-811 liquid crystal mixture containing a chiral dopant into a liquid crystal cell by capillary action, cooling the liquid crystal cell to room temperature, irradiating it with 365 nm ultraviolet light for 10 minutes, then heating it on a heating table at 140°C until the unpolymerized regions become transparent, irradiating it with 365 nm ultraviolet light for another 10 minutes, and finally peeling the liquid crystal cell to obtain a chiral liquid crystal polymer film;

[0040] Furthermore, the nematic liquid crystal accounts for 100 wt %, the chiral dopant accounts for 0.5-5 wt %, the polymer monomer accounts for 30-80 wt %, the crosslinker accounts for 5-15 wt %, and the initiator accounts for 1-5 wt %.

[0041] In this embodiment, the red fluorescent material 311 is CdSe quantum dots, with an emission wavelength of 630 nm and a half-width of 23 nm; the green fluorescent material 321 is also CdSe quantum dots, with an emission wavelength of 525 nm and a half-width of 20 nm. The red fluorescent material 311, the green fluorescent material 321, and the colorless transparent material 331 are formed by inkjet printing. The specific steps are as follows:

[0042] Step S1: Design a Micro-LED substrate with a bank material, with all blue Micro-LED chips located at the bottom of the bank material. Use CAD software to design the inkjet printing pattern of the red and green phosphor materials according to the desired array arrangement.

[0043] Step S2: The digital pattern is transmitted to the inkjet printing control system, and the fluorescent materials in the print head and the micro-nozzles on the print head, the starting point of the micro-jet printing, the printing path and the end point of the micro-jet printing are designed. Figure 1 The array arrangement shown;

[0044] Step S3: After installing the corresponding fluorescent material printing ink and colorless transparent printing ink in the micro-nozzle, the printing process is executed according to the designed parameters to accurately print the printing ink onto the chips inside the predetermined bank dam of all blue light Micro-LED chips, with a printing thickness between 1 and 200 μm;

[0045] Step S4: After the inkjet printing is completed, the excess material on the surface is cleaned;

[0046] Step S5: photocuring the printing ink so that the ink no longer flows and becomes a solid light conversion layer;

[0047] Step S6: A chiral liquid crystal film is evenly applied to the light conversion layer obtained in step S5. Finally, a UV-curable adhesive is applied around the transparent glass, covering the chiral liquid crystal film. The glass is then irradiated with 365 nm UV light for 5 minutes. The chiral liquid crystal film and the light conversion layer are then encapsulated together on the Micro-LED substrate.

[0048] Step S7: Each blue LED chip corresponds to a different control circuit to control the on / off and intensity of the blue LED chip, thereby generating red, green, and blue circularly polarized lights of different intensities.

[0049] Furthermore, the interval between the blue light Micro-LED chips is 5~40 μm.

[0050] Furthermore, the fluorescent material printing ink includes the following components by weight: 0-20 parts of diffusion particles, 30-60 parts of resin, 10-40 parts of red quantum dot material or 10-40 parts of green quantum dot material; the particle size of the diffusion particles is 0.5-100 μm, and the material is one or more of nano metal oxide, silicone resin, styrene resin, methyl methacrylate microspheres and micron silicon dioxide.

[0051] Furthermore, the curing method is thermal curing or ultraviolet curing.

[0052] Furthermore, the monomer components of the resin glue of the fluorescence conversion material are one or more of acrylic resins, polyurethanes, epoxy resins, and silicone resins.

[0053] Furthermore, the Micro-LED blue light chip is suitable for a wavelength of 430-470 nm and a chip size between 1 and 50 μm.

[0054] Furthermore, the thickness of the light conversion layer formed on the blue Micro-LED chip is 1-10 μm.

[0055] Furthermore, the viscosity of the printing ink ranges from 10 to 10,000 cps, and the printing method can be piezoelectric or electrohydrodynamic inkjet printing.

[0056] The present invention also proposes a Micro-LED circularly polarized light-emitting display device based on multiple fluorescent materials. The light source device includes a driving circuit and the above-mentioned display device from bottom to top.

Claims

1. A full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film, characterized in that: The device includes a Micro-LED substrate, an RGB pixel unit and a chiral liquid crystal film; The Micro-LED substrate has a plurality of RGB pixel units arranged in an array, each RGB pixel unit including a red fluorescent material pixel unit, a green fluorescent material pixel unit and a transparent unit; The red fluorescent material pixel unit includes a first blue light Micro-LED chip and a red fluorescent material coated on the first blue light Micro-LED chip. The red fluorescent material is used to convert the blue light emitted by the first blue light Micro-LED chip into red light. The chiral liquid crystal film then converts the red light into red circularly polarized light. The green fluorescent material pixel unit includes a second blue light Micro-LED chip and a green fluorescent material coated on the second blue light Micro-LED chip. The green fluorescent material is used to convert the blue light emitted by the second blue light Micro-LED chip into green light. The chiral liquid crystal film then converts the green light into green circularly polarized light. The transparent pixel unit includes a third blue light Micro-LED chip and a colorless transparent material coated on the third blue light Micro-LED chip. The colorless transparent material is used to directly transmit the blue light emitted by the third blue light Micro-LED chip, and the chiral liquid crystal film then converts the blue light into blue circularly polarized light.

2. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 1, characterized in that: The preparation method of the chiral liquid crystal film is as follows: Step S1: adding different chiral dopants to the polymer monomer and nematic liquid crystal, then adding a cross-linking agent and a photoinitiator, mixing them evenly, and heating and stirring; Step S2: Pour the liquid crystal mixture into the liquid crystal box through capillary action. After the liquid crystal box is cooled to room temperature, irradiate it with ultraviolet light for a few minutes, then place it on a heating table and heat it until the unpolymerized area becomes transparent. Then irradiate it with ultraviolet light for a few minutes, and finally peel off the liquid crystal box to obtain a chiral liquid crystal polymer film.

3. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 2, characterized in that: The nematic liquid crystal is a nematic liquid crystal, including but not limited to nematic liquid crystal HTG13520, nematic liquid crystal SLC1717, nematic liquid crystal 5CB, nematic liquid crystal E7, and nematic liquid crystal MBBA.

4. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 2, characterized in that: The chiral dopant is one or more of 4-(4-hexyloxybenzoyloxy)benzoic acid-S-2-octyl ester, i.e., S811, 4-(4'-hexyloxy)benzoyloxybenzoic acid-R-2-octanol ester, i.e., R811, (13bS)-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxacyclononatetraene, i.e., S5011, and (13bR)-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxacyclononatetraene, i.e., R5011.

5. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 2, characterized in that: The polymer monomer is one or more of 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate, i.e. RM257, 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, i.e. C6M, or 4-[6-[(1-oxo-2-propenyl)oxy]hexyl]oxybenzoic acid 4-methoxyphenyl ester, i.e. RM105.

6. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 2, characterized in that: The crosslinking agent is one or more of trimethylolpropane triacrylate TMPTA, 1,6-hexanediol diacrylate or isooctyl methacrylate.

7. The full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 2, characterized in that: The photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone Irgacure 651 and 1-hydroxycyclohexylphenyl ketone Irgacure 184.

8. A method for preparing a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film, characterized in that: The specific steps are as follows: Step S1: Design a Micro-LED substrate with a Bank material. The blue Micro-LED chip is located at the bottom surrounded by the Bank material. According to the required array arrangement, the inkjet printing pattern of the red and green fluorescent materials is designed. Step S2: transmitting the digitized pattern to the inkjet printing control system, designing the print head and the fluorescent materials in the micro-nozzles on the print head, the starting point of the micro-jet printing, the printing path, and the end point of the micro-jet printing; Step S3: Execute the printing process according to the designed parameters to print the red and green fluorescent materials and the colorless blank printing ink into the predetermined bank dam of the blue light Micro-LED chip, located above the blue light Micro-LED chip; Step S4: After inkjet printing is completed, clean the excess material on the device surface; Step S5: Curing the printing ink by heat or light so that the ink stops flowing and becomes a solid light conversion layer; Step S6: Laminating the chiral liquid crystal film on the light conversion layer obtained above, and finally encapsulating the chiral liquid crystal film and the light conversion layer together on the Micro-LED substrate with colorless transparent glass; Step S7: Each blue LED chip corresponds to a different control circuit to control the on / off and intensity of the blue LED chip, thereby generating red, green, and blue circularly polarized lights of different intensities.

9. The method for preparing a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 8, characterized in that: The display device is encapsulated with a colorless transparent glass sheet, and the glass sheet is glued to the Micro-LED substrate on all sides with glue.

10. The method for preparing a full-color circularly polarized Micro-LED display device integrated with a chiral liquid crystal film according to claim 8, characterized in that: The fluorescent material printing ink includes the following components by weight: 0-20 parts of diffusion particles, 30-60 parts of resin, and 10-40 parts of red quantum dot material or 10-40 parts of green quantum dot material; the particle size of the diffusion particles is 0.5-100 μm, and the material is one or more of nano-metal oxide, silicone resin, styrene resin, methyl methacrylate microspheres and micron silicon dioxide.

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