TW202426974A - Diffusion plate for use in backlight module with low optical path distance - Google Patents

Abstract

The invention discloses a diffusion plate for us in a backlight module with a low optical path (OD) distance, which can be assembled on a backlight module with a plurality of light emitting diodes (LEDs) as the light source below. Different diffusion particle additives are added to the surface layers and the main layer of the diffusion plate, and then extrude it with foaming extrusion technology. By making different combinations of the refractive index and the amount of the original resin materials, microbubbles, and diffusion particle additives of the surface layers and the main layer, the light refractive index of the upper and lower surface layers can be substantially greater than which of the main layer. Such that, the light emitted by the light source below can be diffused more effectively, and thereby achieving a better shading effect of MURA, so as to produce a uniform surface light source.

Description

Diffuser panels for low optical distance backlight modules

The present invention relates to a diffuser plate used in a low optical path distance backlight module, in particular, a diffuser plate that can be assembled on a backlight module and can still provide good light diffusion function at a low optical path distance, thereby shielding MURA (bright and dark band) to produce a uniform surface light source.

With the development of the backlight display environment, as the design of modern backlight displays tends to be thinner, the backlight module is bound to face the demand for ultra-thinness. When the optical distance (OD) of the backlight module is reduced, the light intensity is higher and the MURA is worse. Therefore, if the traditional diffuser is continued to be used on the low optical distance backlight module, its light diffusion effect can no longer meet the requirements.

In addition, there are two main types of light-emitting diode (LED) light sources used in traditional backlight displays. One is that blue LED excites yellow fluorescent powder, and the two colors are mixed to form white light; the other is that three primary color LEDs are mixed to form white light. However, the color gamut values of backlight displays using these two light sources are relatively low, and the color expression is insufficient.

At present, the light source of backlight display is blue LED, which excites green and red quantum dots. The three lights are mixed into white light, which can increase the color gamut value to NTSC120%. However, this backlight display still has the following disadvantages. First, quantum dots are easily affected by moisture and oxygen, which reduce or even lose their activity. After long-term use, quantum dots fail, resulting in abnormal color problems of the display. Secondly, blue LED excites green and red quantum dots, and blue, green and red light are mixed into white light. There must be consistent light intensity to avoid insufficient red/green light conversion. However, because the surrounding light intensity of the display is lower than the central light intensity, it causes the surrounding blue light phenomenon and the color is inconsistent. Furthermore, most existing quantum dot films block water vapor and oxygen by attaching a water- and gas-blocking film to the surface. However, this method can only block water vapor and oxygen from entering the quantum dot film from the upper surface, and cannot prevent water vapor and oxygen from entering from the side ends of the quantum dot film. Therefore, after a period of use, the four side edges of the quantum dot film of the backlight display will still be invaded by water vapor and oxygen, causing the quantum dots to fail, resulting in color abnormalities in the surrounding areas of the backlight display. Although some companies have tried to apply a protective coating on the four side ends of the quantum dot film of the backlight display, this method requires multiple processing processes, which are complicated, costly, and have a low yield.

Therefore, the present invention provides a diffusion plate for low optical path distance backlight module, which can be assembled in a backlight module and can still provide good light diffusion function at low optical path distance, thereby shielding MURA (bright and dark band) to produce a uniform surface light source.

The main purpose of the present invention is to provide a diffusion plate for use in low optical path distance backlight modules. Different diffusion particle additives are added to the surface layer and main board layer of the diffusion plate, and then extruded using foaming technology. By making different combinations of the original resin material, microbubbles, and the refractive index and added amount of the diffusion particle additives in the surface layer and main board layer of the diffusion plate, the refractive index of the upper and lower surface layers for light is substantially greater than that of the main board layer, which can more effectively diffuse the light emitted by the light source below, thereby achieving a better shielding MURA effect to produce a uniform surface light source.

Another purpose of the present invention is to provide a diffusion plate that can be assembled on a backlight module with a blue light emitting diode (LED) as a light source. A plurality of microstructures with a plurality of concave and convex parts are formed on the surface of the diffusion plate, and a quantum dot layer containing a plurality of green quantum dots and a plurality of red quantum dots is coated in the plurality of concave parts of the plurality of microstructures, and then a water- and gas-blocking layer is provided on the upper surface of the quantum dot layer. The plurality of convex parts of the plurality of microstructures are used to separate the quantum dot layers in the plurality of concave parts so that they are independent of each other, so that the external water vapor and oxygen cannot penetrate the four sides of the quantum dot layer and invade the entire quantum dot layer, which has the advantages of simple process, low cost and high production yield.

To achieve the above-mentioned purpose, the present invention discloses a diffusion plate applied to a low optical distance backlight module, which can be assembled to a backlight module. The backlight module includes: a substrate and a plurality of light-emitting elements arranged in an array on the substrate; the diffusion plate is located above the substrate and includes:

A plate body having an upper surface and a lower surface, the lower surface facing the substrate; the plate body is a multi-layer structure formed by coextrusion, comprising a main board layer, an upper surface layer, and a lower surface layer; the upper surface layer is stacked on the side of the main board layer facing the upper surface, and the lower surface layer is stacked on the side of the main board layer facing the lower surface;

A first diffusion particle additive is added to the main board layer; the first diffusion particle additive contains a plurality of first diffusion particles; the weight percentage of the added first diffusion particle additive in the main board layer is a first weight percentage; each of the first diffusion particles has a first material refractive index; and

A second diffusion particle additive is added to the upper surface layer and the lower surface layer; the second diffusion particle additive contains a plurality of second diffusion particles; the weight percentage of the added second diffusion particle additive in the upper surface layer and the lower surface layer is a second weight percentage; each of the second diffusion particles has a second material refractive index;

The diffusion plate meets at least one of the following two conditions:

Condition 1: The refractive index of the first material of the first diffusion particle is less than the refractive index of the second material of the second diffusion particle;

Condition 2: The first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive.

In one embodiment, the material of the plate includes one of the following: polycarbonate (PC), polystyrene (PS), polymethyl methacrylate (PMMA, commonly known as acrylic), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET).

In one embodiment, the plurality of first diffusion particles contained in the first diffusion particle additive include one of the following: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads); wherein the particle size of the first diffusion particles is between 1 and 4 μm, the refractive index of the first material is between 1.42 and 1.5, and the first weight percentage of the first diffusion particle additive added to the main board layer is between 1 and 4%.

In one embodiment, the plurality of second diffuse particles contained in the second diffuse particle additive include one of the following inorganic particles: calcium carbonate, barium sulfate, titanium oxide, talc, mica, boron nitride; wherein the particle size of the second diffuse particle is between 0.05 and 8 μm, the refractive index of the second material is between 1.5 and 2.6, and the second weight percentage of the second diffuse particle additive added to the upper surface layer and the lower surface layer is between 0.1 and 1.5%.

In one embodiment, the plurality of second diffusion particles contained in the second diffusion particle additive include one of the following: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads); wherein the particle size of the second diffusion particles is between 15 and 25 μm, the refractive index of the second material is between 1.42 and 1.5, and the second weight percentage of the second diffusion particle additive added to the upper surface layer and the lower surface layer is between 5 and 10%; wherein the second weight percentage is greater than the first weight percentage, and the particle size of the second diffusion particles is greater than the particle size of the first diffusion particles.

In one embodiment, the diffusion plate further includes:

A plurality of micro-structures are arranged in an array on at least the upper surface of the plate; and

An upper optical film is attached to the upper surface of the plate by an optical adhesive; wherein the thickness of the optical film is between 5 and 20 μm.

In one embodiment, the diffusion plate further includes:

A plurality of micro-structures are arranged in an array on at least the lower surface of the plate;

A lower optical film is attached to the lower surface of the plate by an optical adhesive; and

A reflective film is attached to the lower optical film; wherein the reflective film has a reflectivity of <20% for light with a wavelength below 500nm, and a reflectivity of >90% for light with a wavelength above 500nm.

In one embodiment, the diffusion plate further includes:

A plurality of micro-structures are arranged in an array on at least the upper surface of the plate; the plurality of micro-structures form a plurality of convex portions and a plurality of concave portions on the upper surface of the plate, and the plurality of concave portions are separated by the plurality of convex portions, so the plurality of concave portions are independent of each other and are not interconnected;

A quantum dot layer is disposed at the plurality of recesses on the upper surface of the plate; wherein the thickness of the quantum dot layer is t1, the distance between a top of the plurality of protrusions and a bottom of the plurality of recesses is t2, and t1<t2; and

A water- and gas-blocking layer is disposed on the upper surface of the plate and covers the plurality of protrusions and the quantum dot layer.

In one embodiment, a plurality of the microstructures, the quantum dot layer and the water- and gas-blocking layer are also disposed on the lower surface of the plate; the plurality of the microstructures form a plurality of the convex portions and a plurality of the concave portions on the lower surface of the plate, and the plurality of the concave portions are separated by the plurality of the convex portions, so the plurality of the concave portions on the lower surface of the plate are independent of each other and are not interconnected; and the quantum dot layer located on the lower surface of the plate is disposed at the plurality of the concave portions on the lower surface of the plate; in addition, the water- and gas-blocking layer on the lower surface of the plate covers the plurality of the convex portions and the quantum dot layer on the lower surface of the plate.

In one embodiment, the quantum dot layer includes a plurality of quantum dots (QDs); the plurality of quantum dots are a nanocrystal semiconductor material composed of II-VI, III-V or IV-VI group elements, and the grain diameter of each quantum dot is between 2 and 10 nm; wherein the plurality of quantum dots include a plurality of green quantum dots with a light emission wavelength of 520 to 530 nm and a plurality of red quantum dots with a light emission wavelength of 620 to 630 nm.

In one embodiment, the plurality of microstructures include a plurality of N-polygonal pyramids, wherein N is a positive integer greater than or equal to three; t2 is between 6 and 200 μm; the thickness of the water- and air-barrier layer is t3, and t3 is between 5 and 100 μm.

In one embodiment, t2 is between 25 and 50 μm, t1 is between 10 and 40 μm, and t3 is between 10 and 30 μm.

In one embodiment, the maximum width of the protrusion is between 50 and 500 μm, and the distance between two adjacent protrusions is between 50 and 1000 μm.

In one embodiment, the main board layer of the board body is formed by foam extrusion, and contains a plurality of micro bubbles in the main board layer; the weight reduction rate of the plurality of micro bubbles for the main board layer is between 15 and 25%, and the average size of the plurality of micro bubbles is between 60 and 800 μm;

Among them, the calculation formula of the weight loss rate is:

Weight loss rate (%) = (W1-W2)/W2*100%

W1=H*(L1*L2*D)

in:

H is the average thickness of the main board layer (mm);

L1 is the length of the main board layer (mm);

L2 is the width of the main board layer (mm);

D is the specific gravity of the raw material of the main board layer (g/mm3);

W1 is the theoretical weight of the main board layer (g), that is, the weight without the multiple microbubbles;

W2 is the actual weight of the main board layer (g), which is the actual weight of the main board layer containing multiple microbubbles measured by a scale.

In one embodiment, the plurality of microbubbles are generated by adding a foaming agent and a nucleating agent during the foaming extrusion molding process of the main board layer; the nucleating agent comprises at least one of the following: calcium carbonate, silicon dioxide, calcium oxide; the weight percentage of the added nucleating agent is 0.1%-0.5%.

10: Board

101: Mainboard layer

1011, 1021, 1031: diffuse particles

1012: Microbubbles

102, 103: Surface layer

11, 1022, 1032: Microstructure

111: convex part

112: Concave part

12: Quantum dot layer

120: Quantum dots

13: Water and air barrier layer

15: Optical film

151: Optical glue

152:Reflective film

211: Blue light

212: White light

91: Substrate

911: Top

92: Light-emitting element

93: LCD panel

Figure 1 is a cross-sectional schematic diagram of the first embodiment of the present invention in which a diffusion plate used in a low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display.

Figure 2A, Figure 2B and Figure 2C are schematic diagrams of three different embodiments of the microstructures provided on the upper and lower surfaces of the diffusion plate of the present invention.

Figure 3 is a cross-sectional schematic diagram of the second embodiment of the present invention, in which the diffusion plate used in the low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display.

Figure 4 is a cross-sectional schematic diagram of the third embodiment of the present invention, in which a diffusion plate applied to a low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display.

Figure 5 is a graph showing the different reflectivities of the reflective film of the present invention for light of different wavelengths.

Figures 6 and 7 are respectively a cross-sectional schematic diagram and a three-dimensional partially exploded schematic diagram of the fourth embodiment of the present invention in which a diffusion plate applied to a low optical path distance backlight module is installed in a backlight module.

FIG8 is a cross-sectional schematic diagram of the fifth embodiment of the present invention in which a diffusion plate for a low optical path distance backlight module is installed in a backlight module.

The present invention relates to a diffusion plate used in a low optical path distance backlight module. Different diffusion particle additives are added to the upper and lower surface layers and the main board layer of the diffusion plate, respectively, and then co-extruded into an integrated multi-layer diffusion plate by foaming technology. By making different combinations of the original resin material, microbubbles, and the refractive index and added amount of the diffusion particle additive in the two surface layers of the diffusion plate and the main board layer, the refractive index of the upper and lower surface layers to light is substantially greater than the refractive index of the main board layer. In this way, after the light from the light source below enters the diffuser, part of it will be refracted or reflected back and forth between the two surface layers and the main layer, which can diffuse the light more effectively, thereby shielding the MURA and producing a uniform surface light source.

In order to more clearly describe the diffusion plate and its manufacturing method for low optical path distance backlight module proposed by the present invention, the following will be described in detail with the help of diagrams.

Please refer to Figure 1, which is a cross-sectional schematic diagram of the first embodiment of the present invention, in which a diffuser plate applied to a low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display. The backlight module of the present invention is installed below a liquid crystal panel 93 to form a backlight display. In this first embodiment, the backlight module includes, from bottom to top, a substrate 91, a plurality of light-emitting elements 92, and a diffuser plate. A circuit layout (not shown) is provided on the substrate 91. A plurality of light-emitting elements 92 are arranged in an array on the top surface 911 of the substrate 91 and are electrically coupled to the circuit layout. In this embodiment, the light-emitting elements 92 are blue light-emitting diodes (LEDs) that can emit blue light upward toward the body 10 of the diffuser. The light-emitting elements 92 can be conventional blue LEDs, blue Mini LEDs, or even blue Micro LEDs. A reflective layer is disposed on the top surface 911 of the substrate 91. The reflective layer can be white or other colors or surfaces with better light reflection effects, and is used to reflect light upward toward the body 10 of the diffuser.

The body 10 of the diffusion plate is located above the plurality of light-emitting elements 92 of the substrate 91 and adjacent to the substrate 91, and generally no other elements are present between the body 10 of the diffusion plate and the light-emitting elements 92 disposed on the substrate 91. In the present invention, the diffusion plate includes: a body 10, a first diffusion particle additive, a second diffusion particle additive, a plurality of microbubbles 1012, and a plurality of microstructures 1022, 1032. The body 10 has an upper surface and a lower surface. The lower surface of the body 10 faces the substrate 91 and is used as a light-entering surface; the light emitted by the light-emitting element 92 enters the body 10 through the lower surface (light-entering surface). In contrast, the upper surface of the board 10 is the light-emitting surface. After the light entering the board 10 is refracted and diffused, it is emitted from the upper surface (light-emitting surface) of the board 10 and directed toward the liquid crystal panel 93 located above. The board 10 is a multi-layer board structure formed by coextrusion, and includes a main board layer 101, an upper surface layer 102, and a lower surface layer 103. The upper surface layer 102 is stacked on the side of the main board layer 101 facing the upper surface, and the lower surface layer 103 is stacked on the side of the main board layer 101 facing the lower surface. The substrate of the plate 10 can be a non-crystalline or semi-crystalline organic polymer plastic material, which includes one of the following: polycarbonate (PC), polystyrene (PS), polymethyl methacrylate (PMMA, commonly known as acrylic), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), or a copolymer of any of the above materials. In this embodiment, the thickness ratio of the main board layer 101 to the total thickness of the two surface layers 102 and 103 (the thickness of the upper and lower surface layers added together) can be implemented in the range of 9.5:0.5~1:1, and the preferred implementation range is between 9:1~7:3. The substrates of the main board layer 101 and the two surface layers 102 and 103 can be the same material or different materials.

In this embodiment, the first diffusion particle additive includes a plurality of first diffusion particles 1011, which are added to the main layer 101. The weight percentage of the added first diffusion particle additive in the main layer 101 is a first weight percentage; each of the first diffusion particles 1011 has a first material refractive index. The second diffusion particle additive includes a plurality of second diffusion particles 1021, 1031, which are added to the upper surface layer 102 and the lower surface layer 103, respectively. The weight percentage of the added second diffusion particle additive in the upper surface layer 102 and the lower surface layer 103 is a second weight percentage; each of the second diffusion particles 1021, 1031 has a second material refractive index. The technical feature of the present invention is that the diffusion plate meets at least one of the following two conditions:

Condition 1: The refractive index of the first material of the first diffusion particle 1011 is less than the refractive index of the second material of the second diffusion particles 1021 and 1031;

Condition 2: The first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive.

By satisfying the above-mentioned condition 1, condition 2, or both conditions, the refractive index of the upper and lower surface layers 102 and 103 to which the plurality of second diffusion particles 1021 and 1031 having a relatively high refractive index or/and concentration (weight percentage) are added can be substantially higher than the refractive index of the main surface layer 101 to which the plurality of first diffusion particles 1011 having a relatively low refractive index or/and concentration (weight percentage) are added, so that the upper and lower surface layers 102 and 103 provide a slight reflection effect on the side facing the main surface layer 101. Therefore, after the light emitted by the light-emitting element 92 enters the board 10, a portion of the light will be refracted or reflected several times in the main board layer 101 between the upper and lower surface layers 102 and 103 before being emitted from the upper surface (light-emitting surface), thereby increasing the number of refraction or reflection of the light, so that the light can be diffused more effectively, thereby enhancing the effect of shielding MURA to produce a uniform surface light source.

In this embodiment, the plurality of first diffusion particles 1011 included in the first diffusion particle additive include at least one of the following polymer material diffusion particles: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads). The particle size of the first diffusion particles 1011 may be between 0.5 and 10 μm, but is preferably between 1 and 4 μm. The refractive index of the first material is between 1.42 and 1.5. The first weight percentage of the first diffusion particle additive added to the main board layer 101 may be between 0.5 and 10%, but is preferably between 1 and 4%. The first and second diffusion particle additives mentioned here are both known products available on the market.

In the present invention, the plurality of second diffusion particles 1021, 1031 included in the second diffusion particle additive can have two embodiments, the first being inorganic diffusion particles and the other being polymer material diffusion particles. In the first embodiment, the plurality of second diffuse particles 1021, 1031 contained in the second diffuse particle additive may include at least one of the following inorganic particles: calcium carbonate, barium sulfate, titanium oxide, talc, mica, boron nitride; wherein the particle size of the second diffuse particles 1021, 1031 may be implemented as between 0.01 and 10 μm, but is preferably between 0.05 and 8 μm; the refractive index of the second material is between 1.5 and 2.6, and the second weight percentage of the second diffuse particle additive added to the upper surface layer 102 and the lower surface layer 103 may be implemented as between 0.1 and 3%, but is preferably between 0.1 and 1.5%. In the second embodiment, the plurality of second diffusion particles 1021, 1031 included in the second diffusion particle additive include at least one of the following polymer material diffusion particles: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads), beads); wherein the particle size of the second diffusion particles 1021, 1031 may be implemented as between 10 and 50 μm, but is preferably between 15 and 25 μm; the refractive index of the second material is between 1.42 and 1.5; the second weight percentage of the second diffusion particle additive added to the upper surface layer 102 and the lower surface layer 103 may be implemented as between 1 and 20%, but is preferably between 5 and 10%; and, in this second embodiment, the second weight percentage must be greater than the first weight percentage, and the particle size of the second diffusion particles 1021, 1031 is greater than the particle size of the first diffusion particle 1011. By using the second diffusion particle additive defined in the first and second embodiments in combination with the first diffusion particle additive defined in the above, it is possible to ensure that the refractive index of the upper and lower surface layers 102 and 103 is substantially higher than the refractive index of the main surface layer 101, thereby achieving the effect of more effective diffusion of light, enhanced shielding of MURA, and generation of a uniform surface light source.

As shown in FIG. 1, in the first embodiment of the diffusion plate of the present invention, a plurality of micro-structures 1022 and 1032 (Micro-Structures) are arranged in an array on the upper surface and the lower surface of the plate body 10, respectively, which can further improve the light diffusion effect of the diffusion plate. In addition, the main board layer 101 of the plate body 10 is formed by foaming extrusion, and a plurality of micro-bubbles 1012 are included in the main board layer 101. The weight reduction rate of the plurality of micro-bubbles 1012 for the main board layer 101 can be implemented in a range of 5-30%, but the weight reduction rate is preferably 10-20%, and the average size of the plurality of micro-bubbles 1012 is between 60-800μm; wherein, the calculation formula of the weight reduction rate is:

Weight loss rate (%) = (W1-W2)/W2*100%;

W1=H*(L1*L2*D);

in:

H is the average thickness of the main board layer (mm);

L1 is the length of the main board layer (mm);

L2 is the width of the main board layer (mm);

D is the specific gravity of the material of the main board layer (g/mm ³ );

W1 is the theoretical weight of the main board layer (g), that is, the weight without the multiple microbubbles;

W2 is the actual weight of the main board layer (g), which is the actual weight of the main board layer containing multiple microbubbles measured by a scale.

In this embodiment, the plurality of microbubbles 1012 are generated by adding a foaming agent and a nucleating agent in appropriate amounts during the foaming extrusion molding process of the main board layer 101; the nucleating agent includes at least one of the following: calcium carbonate, silicon dioxide, and calcium oxide; the weight percentage of the added nucleating agent can be implemented in the range of 0.01%-5%, but the preferred range is 0.1%-0.5%. The weight loss rate of the microbubbles 1012 can be controlled by the amount of the foaming agent added, and the bubble diameter of the microbubbles 1012 can be controlled by adding the nucleating agent and adjusting the process temperature. The process temperature of the foaming co-extrusion process of the multi-layer plate body 10 of the diffusion plate of the present invention is adjusted according to the types of raw material resin and foaming agent. The processing temperature of the present invention is the general polycarbonate processing temperature, and the optimal temperature is 220~270℃.

Please refer to FIG. 2A, FIG. 2B and FIG. 2C, which are schematic diagrams of three different embodiments of the microstructures disposed on the upper and lower surfaces of the diffusion plate of the present invention. The diffusion plate of the present invention extrude a plurality of microstructures 1022, 1032 on the upper and lower surfaces of the plate body by an extrusion process. The microstructures 1022, 1032 have a plurality of convex portions or concave portions, and the concave-convex structures can be regularly or irregularly distributed on the upper and lower surfaces of the diffusion plate body 10. The microstructures 1022 and 1032 can be circular, deformed (as shown in Figure 2A), irregular matte (as shown in Figure 2B), pyramid (as shown in Figure 2C)...etc. in top view. The best overall brightness effect is achieved when the light incident surface of the plate 10 is a mirror surface (without microstructure and smooth surface) and the light emitting surface is provided with a pyramid-shaped microstructure.

In the other embodiments of the present invention described below, since most of the components and functions are the same as those in the first embodiment described above, the same or similar components will be given the same names and numbers, and the details will not be repeated.

Please refer to FIG. 3, which is a cross-sectional schematic diagram of a second embodiment of the present invention in which a diffusion plate applied to a low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display. In the second embodiment, the backlight module also includes, from bottom to top, a substrate 91, a plurality of light-emitting elements 92, and a diffusion plate. The diffusion plate is located above the substrate 91 and also includes: a plate body 10 (including a main board layer 101, an upper surface layer 102, and a lower surface layer 103), a first diffusion particle additive (including first diffusion particles 1011), a second diffusion particle additive (including second diffusion particles 1021, 1031), a plurality of micro bubbles 1012, and a plurality of micro structures 1022, 1032. Since most of the components, structures and functions of the diffusion plate of the second embodiment shown in FIG. 3 are the same or similar to those of the first embodiment shown in FIG. 1 , the details of these same or similar components will not be repeated. The difference from the aforementioned first embodiment is that in the second embodiment shown in FIG. 3 , the diffusion plate further includes an upper optical film 15, which is attached to the upper surface of the plate body 10 by an optical glue 151; wherein the thickness of the optical glue 151 is between 5 and 20 μm. The optical glue 151 described herein is a known product available on the market together with the upper optical film 15. The optical glue 151 is used as an adhesive medium for attaching the upper optical film 15 to the upper surface of the plate body 10. The upper optical film 15 provides a color conversion function of converting blue light into white light, and is a known product available on the market. Thus, the present invention can use a blue light emitting diode as the light emitting element 92, and the diffusion plate of the present invention and the upper optical film 15 adhered to the upper surface of the plate body 10 convert it into uniform white light, providing the function of a white light backlight module.

Please refer to FIG. 4, which is a cross-sectional schematic diagram of a third embodiment of the present invention in which a diffusion plate applied to a low optical path distance backlight module is installed in a backlight module and combined with a liquid crystal panel to form a backlight display. In the third embodiment, the backlight module also includes, from bottom to top, a substrate 91, a plurality of light-emitting elements 92, and a diffusion plate. The diffusion plate is located above the substrate 91 and also includes: a plate body 10 (including a main board layer 101, an upper surface layer 102, and a lower surface layer 103), a first diffusion particle additive (including first diffusion particles 1011), a second diffusion particle additive (including second diffusion particles 1021, 1031), a plurality of micro bubbles 1012, and a plurality of micro structures 1022, 1032. Since most of the components, structures and functions of the diffusion plate of the second embodiment shown in FIG. 3 are the same or similar to those of the second embodiment shown in FIG. 2 , the details of these same or similar components will not be repeated. The difference from the aforementioned second embodiment is that in the third embodiment shown in FIG. 4 , the diffusion plate further includes a lower optical film 15 and a reflective film 152, which are attached to the lower surface of the plate body 10 by an optical glue 151; wherein the thickness of the optical glue 151 is between 5 and 20 μm; and the reflective film 152 is attached to the lower side of the lower optical film 15. The optical glue 151, the lower optical film 15 and the reflective film 152 are all known products available on the market. The optical adhesive 151 is used as a bonding medium to bond the lower optical film 15 and the reflective film 152 to the lower surface of the board 10. The lower optical film 15 provides a color conversion function of converting blue light into white light. As shown in FIG. 5 , it is a curve diagram of the different reflectivities of the reflective film of the present invention for light of different wavelengths. As can be seen from FIG. 5 , the reflectivity of the reflective film 152 for light with a wavelength below 500 nm is <20%, and the reflectivity of the reflective film 152 for light with a wavelength above 500 nm is >90%. In other words, the blue light emitted by the lower blue LED can smoothly pass through the reflective film 152 and the lower optical film 15 and enter the inside of the board 10. In contrast, the light converted into white light by the lower optical film 15 can no longer pass downward through the reflective film 152, but will be reflected by the reflective film 152 and emit upward toward the upper surface of the board 10. In this way, the present invention can use a blue light emitting diode as a light emitting element 92, and the diffusion plate of the present invention and the lower optical film 15 and the reflective film 152 attached to the lower surface of the board 10 convert it into uniform white light and emit it upward, providing the function of a white light backlight module

The present invention is based on the aforementioned technical concept and manufactures several different diffusion plates for testing. Each diffusion plate is given different structural or material parameters, including: the particle size, refractive index, and amount of the diffusion particles added to the main plate layer and the two surface layers, the material of the main plate layer and the two surface layers, the thickness ratio of the two surface layers and the main plate layer relative to the plate body, the presence and type of surface microstructures, whether the main plate layer generates microbubbles by a foaming process and the diameter of the microbubbles, whether the light-emitting surface (the upper surface of the plate body) has an optical film and optical glue, and the thickness of the optical glue, whether the light-incoming surface (the lower surface of the plate body) has a reflective film, etc. Then, we tested or observed the optical effects of these diffusers with different parameters one by one (including brightness, light diffusion, Mura, taste, etc.), analyzed and compared these optical effects, and then organized the results into the following Tables 1 to 6.

In Tables 1 to 6 below, the columns "Particle size", "Refractive index", and "Amount added" refer to the particle size, refractive index, and amount added (weight percentage) of the plurality of diffusion particles contained in the diffusion particle additive added to the upper surface layer, main plate layer, or lower plate layer of the diffusion plate. The column "Thickness ratio" refers to the ratio of the thickness of the upper surface layer, main plate layer, or lower plate layer to the thickness of the entire plate body. The column "Material" refers to the substrate material of the upper surface layer, main plate layer, or lower plate layer, where PS refers to polystyrene and MS refers to methyl methacrylate. The "Surface Structure" field refers to whether a microstructure is set on the upper surface (light-emitting surface) or lower surface (light-entering surface) of the board, and the type of microstructure (in this field, "fog" means that an irregular fog microstructure is set, and "pyramid" means that a pyramid-shaped microstructure is set). The "Foaming Process" field refers to whether microbubbles are generated in the main layer through a foaming process, and the bubble diameter of the microbubbles. The "Optical Film" field refers to whether an optical film is attached to the upper surface (light-emitting surface) of the board by optical glue, and the thickness of the optical glue. The "Reflective Film" field refers to whether a reflective film is set on the lower surface (light-entering surface) of the board. "Brightness (%)", "Light Diffusion (%)", "Mura (the value is expressed on a scale of 1 to 5, where 1 means the most severe Mura and 5 means the lightest Mura, so the optical performance is the best)", "Taste (the value is expressed on a scale of 1 to 5, where 1 means the worst visual optical taste and 5 means the best taste)".

Table 1 shows the structure and material information of the tested diffusion plates of various comparative examples and embodiments. From the content of Table 1, it can be seen that the particle size, refractive index, and addition amount of the plurality of diffusion particles added to the two surface layers and the main layer of the diffusion plates of comparative examples 1 and 2 are "the same", so they belong to the comparative examples of diffusion plates made according to the known technology. In contrast, in the diffusion plates of Examples 1 to 6, the multiple diffusion particles added to the two surface layers of the plate body have at least one or more of the "particle size", "refractive index", and "addition amount" that is "greater than" the diffusion particles added to the main plate layer of the plate body, so that the refractive index of the two surface layers is higher than that of the main plate layer, so the diffusion plates are made according to the aforementioned technical concept of the present invention. That is, in Tables 1 to 6, Comparative Examples 1 and 2 are diffusion plates made according to the known technology, while Examples 1 to 6 are diffusion plates made according to the aforementioned technical concept of the present invention.

Table 1: Structure and material information of the comparative examples and embodiments of the diffusion plates tested

In Table 2 below, the main board layers of the diffusion plates of Examples 1, 2, 2-1, 3, and 3-1 all have diffusion particle additives added to them, and the main board layers of some examples also form microbubbles through a foaming process; and the upper and lower surface layers of the diffusion plates of each example have diffusion particle additives with relatively high particle size, refractive index, or addition amount added. In Example 2, the diffusion particles added to the upper and lower surface layers are inorganic additives, and the refractive index of the inorganic diffusion particles of the additives of the two surface layers is greater than the refractive index of the diffusion particles contained in the additive added to the main board layer. In Example 3, the diffusion particles added to the upper and lower surfaces are organic additives (i.e., polymer plasticizer additives), and the refractive index of the organic diffusion particles of the additives of the two surface layers is greater than the refractive index of the diffusion particles contained in the additives added to the main layer. The structures and materials of Example 2-1 and Example 3-1 generally correspond to Example 2 and Example 3, respectively, except that Example 2-1 and Example 3-1 further increase the concentration (addition amount) of the additives of the upper and lower surfaces. As can be seen from Table 2, Example 1, Example 2, Example 2-1, Example 3, and Example 3-1 are significantly higher than Comparative Example 1 and Comparative Example 2 in terms of optical performance such as brightness, light diffusion, and Mura. Moreover, the brightness of Example 2-1 is worse than that of Example 2, and the brightness of Example 3-1 is also worse than that of Example 3, which proves that when the concentration of the additives in the upper and lower surfaces increases, the brightness will decrease.

Table 2: Comparison of diffusion particles with different particle sizes, refractive indices or addition amounts added to the two surface layers and the main layer of the diffusion plate

In Table 3 below, mist-like microstructures are set on both the upper and lower surfaces of Example 3, while pyramid-like microstructures are set on both the upper and lower surfaces of Example 4. Comparative Examples 1 and 2 do not have any microstructures. From Table 3, it can be seen that Example 4 with a pyramid-like microstructure has a higher brightness than Example 3, while the MURA performance of the light diffusion of the two is the same, which proves that when the surface microstructure is pyramid-like, it can have a higher brightness than the mist-like microstructure.

Table 3: Comparison of the surface microstructures of the diffuser with different light-entry and light-exit surfaces

In the following Table 4, the diffusion plates of Examples 3, 5, and 6 have different materials or different thickness ratios of the main layer and the two surface layers. From Table 4, it can be seen that the ratio of the thickness of the main layer to the total thickness of the two surface layers of the diffusion plates of Examples 3 and 6 is 9:1, while the ratio of the thickness of the main layer to the total thickness of the two surface layers of the diffusion plate of Example 5 is 6:4; and, the performance of Examples 3 and 6 in light diffusion and MURA is better than that of Example 5; it can be roughly inferred that the preferred implementation range of the ratio of the thickness of the main layer to the total thickness of the two surface layers of the diffusion plate of the present invention should be between 9:1 and 7:3. In addition, because Example 6 uses MS as the substrate for both surface layers and PS as the substrate for the main layer, Example 6 can achieve better MURA performance than Example 3 (both surface layers and the main layer are made of PS material).

Table 4: Comparison of the material and thickness ratio changes of the main layer and two surface layers of the diffusion plate

In Table 5 below, Example 4-1 is based on the same structure and material as Example 4 and an optical film is additionally attached to the light-emitting surface of the diffuser. Comparative Example 3-1 is based on the same structure and material as Example 3 but no surface microstructure is set on the light-emitting surface of the diffuser. From Table 5, it can be seen that the thickness of the optical adhesive attached in Example 7 is greater than 20μm, resulting in low brightness. In addition, the brightness of Comparative Example 3-1 is also low because there is no surface microstructure on the light-emitting surface of the diffuser.

Table 5: Comparison of the thickness of optical film and optical glue on the light-emitting surface of the diffuser

In the following Table 6, Example 4-2 is based on the same structure and material as Example 4 and additionally attaches a reflective film to the light-entering surface of the diffuser. As can be seen from Table 6, the diffuser of Example 4-2 has a reflective film attached to the light-entering surface, so compared to Example 4, the diffuser of Example 4-2 can obtain better quality at low OD.

Table 6: Comparison of reflective film attached to the light-incident surface of the diffuser

From the above Tables 1 to 6, it can be seen that the structures and materials of Embodiments 4-1, 4-2 and 6 made according to the technical concept of the present invention are the best embodiments of the diffusion plate of the present invention applied to the backlight module with low optical path distance, and can achieve relatively optimal optical performance.

In one embodiment, the diffusion plate of the present invention can be assembled on a backlight module with a blue light emitting diode (Blue LED) as the lower light source. A plurality of microstructures having a plurality of concave portions and convex portions are formed on the upper surface of the diffusion plate, and a quantum dot layer including a plurality of green quantum dots and a plurality of red quantum dots is coated in the plurality of concave portions of the plurality of microstructures, and then a water- and gas-blocking layer is disposed on the upper surface of the quantum dot layer. The plurality of convex portions of the plurality of microstructures are used to separate the quantum dot layers located in the plurality of concave portions so that they are each independent, thereby preventing external water vapor and oxygen from penetrating the entire quantum dot layer through the four side edge faces of the quantum dot layer, which can have the advantages of simple process, low cost and high production yield. The present invention attaches a water- and gas-blocking film to the upper surface of the diffusion plate, and uses a microstructure to block water vapor from entering the quantum dot layer from the side end face, so that the distance for water vapor to enter the quantum dot layer from the end face is reduced to a minimum. Since it is extruded in one piece, the subsequent processing and production costs can be reduced, and a relatively high production yield can be achieved.

Please refer to FIG. 6 and FIG. 7, which are respectively a cross-sectional schematic diagram and a three-dimensional partially exploded schematic diagram of a fourth embodiment of the present invention, in which a diffusion plate for a low optical path distance backlight module is installed in a backlight module. In the fourth embodiment, the backlight module also includes, from bottom to top, a substrate 91, a plurality of light-emitting elements 92, and a diffusion plate. The diffusion plate is located above the substrate 91 and also includes: a plate body 10 (including a main board layer 101, an upper surface layer 102, and a lower surface layer 103), a first diffusion particle additive (including first diffusion particles 1011), a second diffusion particle additive (including second diffusion particles 1021, 1031), a plurality of micro bubbles 1012, and a plurality of micro structures 11, 1032. The diffusion plate of the fourth embodiment also needs to meet at least one of the following two conditions: Condition 1: the first material refractive index of the first diffusion particle 1011 is less than the second material refractive index of the second diffusion particles 1021, 1031; Condition 2: the first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive. Since most of the components, structures and functions of the diffusion plate of the fourth embodiment shown in Figures 6 and 7 are the same or similar to those of the first embodiment shown in Figure 2, the details of these same or similar components will not be repeated. The difference from the first embodiment is that in the fourth embodiment shown in FIG. 6 and FIG. 7 , the diffusion plate further includes: a quantum dot layer 12 and a water- and gas-blocking layer 13; and the plurality of microstructures 11 disposed on the upper surface of the plate body 10 also have a special structure different from the aforementioned embodiment.

In the fourth embodiment, the plate body 10 is a three-layer plate structure with polystyrene (PS) as the base material, and the thickness of the plate body 10 is preferably between 0.8 mm and 2.5 mm. The plate body 10 of the diffusion plate is located above and adjacent to the substrate 91, and generally there are no other components between the plate body 10 of the diffusion plate and the light-emitting element 92 disposed on the substrate 91. The quantum dot layer 12 requires consistent blue light intensity to convert red/green light and mix into uniform white light; because the peripheral light intensity of the display is lower than the central intensity, it is easy to have insufficient red/green light conversion, resulting in a blue light phenomenon around the display. The board 10 of the present invention is formed by foam extrusion, and contains a plurality of micro bubbles 1012 and diffusion particles 1011, 1021, and 1031 in the board 10, which has higher light refraction and light diffusion effects, improves the light intensity in the area around the display, and thus improves the blue light problem. A plurality of microstructures 11 are arranged in an array on the upper surface of the board 10, and a plurality of protrusions 111 and a plurality of concave portions 112 are formed on the upper surface of the board 10. The plurality of concave portions 112 are separated by the plurality of protrusions 111, so the plurality of concave portions 112 are independent of each other and not connected to each other. The quantum dot layer 12 is arranged at the plurality of concave portions 112 on the upper surface of the board 10, and no quantum dot layer 12 is arranged at the plurality of protrusions 111. The thickness of the quantum dot layer 12 is t1, the distance from a top of the plurality of protrusions 111 to a bottom of the plurality of recesses 112 is t2, and t1<t2. In other words, the height t2 of the protrusion 111 of the microstructure 11 is greater than the thickness t1 of the quantum dot layer 12, so that the quantum dot layers 12 located in different recesses 112 are not connected or in contact with each other. The water- and gas-blocking layer 13 is disposed on the entire upper surface of the plate 10 and is closely covered on the plurality of protrusions 111 and the quantum dot layer 12. The water- and gas-blocking layer 13 can isolate and prevent external water vapor and oxygen from invading the upper surface of the quantum dot layer 12. The thickness of the water- and gas-blocking layer 13 is t3, which can be selected from an existing commercially available water- and gas-blocking film, and is directly bonded to the convex portions 111 of the plurality of microstructures 11 and the quantum dot layer 12 on the upper surface of the plate 10. The distance between two adjacent convex portions 111 is P. In the fourth embodiment, the quantum dot layer 12 includes a plurality of quantum dots 120 (Quantum Dot; referred to as QD). The plurality of quantum dots 120 can be selected from existing commercially available nanocrystal semiconductor materials, composed of II-VI, III-V or IV-VI group elements, and the grain diameter of each quantum dot 120 is between 2 and 10 nm. The light emission wavelength of the plurality of quantum dots 120 in the quantum dot layer 12 may be between 490 and 650 nm; in this embodiment, the plurality of quantum dots 120 include a plurality of green quantum dots with a light emission wavelength of 520 to 530 nm and a plurality of red quantum dots with a light emission wavelength of 620 to 630 nm. The blue light 211 emitted upward by the light-emitting element 92 can be mixed into white light 212 after passing through the quantum dot layer 12, and then emitted upward from the upper surface of the plate body 10 and directed toward the liquid crystal panel 93.

In this embodiment, the thickness t1 of the quantum dot layer 12 can be implemented in a range of 5 to 150 μm , but t1 is preferably implemented in a range of 10 to 40 μm . The distance t2 from the top of the plurality of protrusions 111 to the bottom of the plurality of concave portions 112 (or can be called the height of the protrusion) can be implemented in a range of 6 to 200 μm , but t2 is preferably implemented in a range of 25 to 50 μm ; and t1<t2. The thickness t3 of the water- and gas-barrier layer 13 can be implemented in a range of 5 to 100 μm , but t3 is preferably implemented in a range of 10 to 30 μm . The maximum width of the protrusion 111 is between 50 and 500 μm . The practical range of the distance P between two adjacent protrusions 111 is between 50 and 1000 μm , but the preferred practical range is between 250 and 500 μm .

Please refer to FIG8, which is a cross-sectional schematic diagram of the fifth embodiment of the present invention in which the diffusion plate of the low optical path distance backlight module is installed in a backlight module. In the fifth embodiment, the backlight module also includes: a substrate 91, a plurality of light-emitting elements 92 and a diffusion plate in order from bottom to top. The diffusion plate is located above the substrate 91 and also includes: a plate body 10 (including a main board layer 101, an upper surface layer 102, and a lower surface layer 103), a first diffusion particle additive (including first diffusion particles 1011), a second diffusion particle additive (including second diffusion particles 1021, 1031), a plurality of micro bubbles 1012, a plurality of micro structures 11, a quantum dot layer 12, and a water-blocking and air-blocking layer 13. The diffusion plate of the fifth embodiment also needs to meet at least one of the following two conditions: Condition 1: the first material refractive index of the first diffusion particle 1011 is less than the second material refractive index of the second diffusion particles 1021, 1031; Condition 2: the first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive. Since most of the components, structures and functions of the diffusion plate of the fifth embodiment shown in FIG8 are the same or similar to those of the fourth embodiment shown in FIG6 and FIG7, the details of these same or similar components will not be repeated. The difference from the fourth embodiment is that in the fifth embodiment shown in FIG8 , the diffusion plate of the present invention is provided with a plurality of microstructures 11, quantum dot layers 12, and water- and gas-blocking layers 13 on both the upper and lower surfaces of the plate body 10. In other words, in addition to the plurality of microstructures 11, quantum dot layers 12, and water- and gas-blocking layers 13 on the upper surface of the plate body 10 as in the embodiments shown in FIG6 and FIG7 , the fifth embodiment shown in FIG8 is also provided with a plurality of the microstructures 11, the quantum dot layers 12, and the water- and gas-blocking layers 13 on the lower surface of the plate body 10. The plurality of microstructures 11 form a plurality of convex portions 111 and a plurality of concave portions 112 on the lower surface of the plate body 10. The plurality of concave portions 112 are separated by the plurality of convex portions 111, so the plurality of concave portions 112 on the lower surface of the plate body 10 are independent of each other and are not connected to each other. In addition, the quantum dot layer 12 located on the lower surface of the plate body 10 is disposed at the plurality of concave portions 112 on the lower surface of the plate body 10. In addition, the water- and gas-blocking layer 13 on the lower surface of the plate body 10 covers the plurality of convex portions 111 and the quantum dot layer 12 on the lower surface of the plate body 10. In this embodiment, the structures of the plurality of microstructures 11, the quantum dot layer 12 and the water- and gas-blocking layer 13 disposed on the upper and lower surfaces of the plate 10 are substantially the same, and the thickness of the quantum dot layer 12 is also smaller than the height of the convex portion 111 of the microstructure 11.

However, the above-mentioned embodiments should not be used to limit the scope of application of the present invention. The scope of protection of the present invention should be based on the technical spirit defined by the scope of the patent application of the present invention and the scope of its equivalent changes. That is, all equivalent changes and modifications made according to the scope of the patent application of the present invention will not lose the essence of the present invention, nor will they deviate from the spirit and scope of the present invention, so they should be regarded as further implementation of the present invention.

10: Board

101: Mainboard layer

1011, 1021, 1031: diffuse particles

1012: Microbubbles

102, 103: Surface layer

1022, 1032: Microstructure

91: Substrate

911: Top

92: Light-emitting element

93: LCD panel

Claims (10)

A diffusion plate used in a low optical distance backlight module can be assembled on a backlight module; the backlight module includes: a substrate and a plurality of light-emitting elements arranged on the substrate in an array; the diffusion plate is located above the substrate and includes: A plate body having an upper surface and a lower surface, the lower surface facing the substrate; the plate body is a multi-layer structure formed by coextrusion, comprising a main board layer, an upper surface layer, and a lower surface layer; the upper surface layer is stacked on the side of the main board layer facing the upper surface, and the lower surface layer is stacked on the side of the main board layer facing the lower surface; A first diffusion particle additive is added to the main board layer; the first diffusion particle additive contains a plurality of first diffusion particles; the weight percentage of the added first diffusion particle additive in the main board layer is a first weight percentage; each of the first diffusion particles has a first material refractive index; and A second diffusion particle additive is added to the upper surface layer and the lower surface layer; the second diffusion particle additive contains a plurality of second diffusion particles; the weight percentage of the added second diffusion particle additive in the upper surface layer and the lower surface layer is a second weight percentage; each of the second diffusion particles has a second material refractive index; The diffusion plate meets at least one of the following two conditions: Condition 1: The refractive index of the first material of the first diffusion particle is less than the refractive index of the second material of the second diffusion particle; and Condition 2: The first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive; The diffusion plate further includes: A plurality of micro-structures are arranged in an array on at least the upper surface of the plate; the plurality of micro-structures form a plurality of convex portions and a plurality of concave portions on the upper surface of the plate, and the plurality of concave portions are separated by the plurality of convex portions, so the plurality of concave portions are independent of each other and are not interconnected; A quantum dot layer is disposed at the plurality of recesses on the upper surface of the plate; wherein the thickness of the quantum dot layer is t1, the distance between a top of the plurality of protrusions and a bottom of the plurality of recesses is t2, and t1<t2; and A water- and gas-blocking layer is disposed on the upper surface of the plate and covers the plurality of protrusions and the quantum dot layer. The diffusion plate used for the low optical path distance backlight module as described in claim 1, wherein a plurality of the microstructures, the quantum dot layer and the water- and gas-blocking layer are also arranged on the lower surface of the plate body; the plurality of the microstructures form a plurality of the convex parts and a plurality of the concave parts on the lower surface of the plate body, and the plurality of the concave parts are separated by the plurality of the convex parts, so the plurality of the concave parts on the lower surface of the plate body are independent of each other and not interconnected; and the quantum dot layer located on the lower surface of the plate body is arranged at the plurality of the concave parts on the lower surface of the plate body; in addition, the water- and gas-blocking layer on the lower surface of the plate body covers the plurality of the convex parts and the quantum dot layer on the lower surface of the plate body. The diffusion plate used in the low optical path distance backlight module as described in claim 1, wherein the quantum dot layer includes a plurality of quantum dots (QUANTUM DOT, referred to as QD); the plurality of quantum dots are a nanocrystal semiconductor material composed of II-VI, III-V or IV-VI group elements, and the grain diameter of each quantum dot is between 2 and 10 nm; wherein the plurality of quantum dots include a plurality of green quantum dots with a light emission wavelength of 520 to 530 nm and a plurality of red quantum dots with a light emission wavelength of 620 to 630 nm. A diffusion plate for low optical path distance backlight module as described in claim 1, wherein the plurality of microstructures include a plurality of N-sided pyramids, wherein N is a positive integer greater than or equal to three; t2 is between 25 and 50 μm, and t1 is between 10 and 40 μm; the thickness of the water- and gas-barrier layer is t3, and t3 is between 10 and 30 μm; wherein the maximum width of the convex portion is between 50 and 500 μm, and the distance between two adjacent convex portions is between 50 and 1000 μm. The diffuser plate for use in a low optical path distance backlight module as described in claim 1, wherein the plurality of first diffuser particles contained in the first diffuser particle additive include one of the following: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads), beads); wherein the particle size of the first diffusion particle is between 1 and 4 μm, the refractive index of the first material is between 1.42 and 1.5, and the first weight percentage of the first diffusion particle additive added to the main layer is between 1 and 4%; wherein the plurality of second diffusion particles contained in the second diffusion particle additive include one of the following inorganic particles: calcium carbonate, barium sulfate, titanium oxide, talc, mica, boron nitride; wherein the particle size of the second diffusion particle is between 0.05 and 8 μm, the refractive index of the second material is between 1.5 and 2.6, and the second weight percentage of the second diffusion particle additive added to the upper surface layer and the lower surface layer is between 0.1 and 1.5%. As described in claim 1, the diffuser plate used in a low optical distance backlight module, wherein the diffuser plate further includes: An upper optical film is attached to the upper surface of the plate by an optical adhesive; wherein the thickness of the optical film is between 5 and 20 μm; A lower optical film is attached to the lower surface of the plate by an optical adhesive; and A reflective film is attached to the lower optical film; wherein the reflective film has a reflectivity of <20% for light with a wavelength below 500nm, and a reflectivity of >90% for light with a wavelength above 500nm. A diffusion plate used in a low optical distance backlight module can be assembled on a backlight module; the backlight module includes: a substrate and a plurality of light-emitting elements arranged on the substrate in an array; the diffusion plate is located above the substrate and includes: A plate body having an upper surface and a lower surface, the lower surface facing the substrate; the plate body is a multi-layer structure formed by coextrusion, comprising a main board layer, an upper surface layer, and a lower surface layer; the upper surface layer is stacked on the side of the main board layer facing the upper surface, and the lower surface layer is stacked on the side of the main board layer facing the lower surface; A first diffusion particle additive is added to the main board layer; the first diffusion particle additive contains a plurality of first diffusion particles; the weight percentage of the added first diffusion particle additive in the main board layer is a first weight percentage; each of the first diffusion particles has a first material refractive index; and A second diffusion particle additive is added to the upper surface layer and the lower surface layer; the second diffusion particle additive contains a plurality of second diffusion particles; the weight percentage of the added second diffusion particle additive in the upper surface layer and the lower surface layer is a second weight percentage; each of the second diffusion particles has a second material refractive index; The diffusion plate meets at least one of the following two conditions: Condition 1: The refractive index of the first material of the first diffusion particle is less than the refractive index of the second material of the second diffusion particle; and Condition 2: The first weight percentage of the first diffusion particle additive is less than the second weight percentage of the second diffusion particle additive; The main board layer of the board body is formed by foam extrusion, and contains a plurality of micro bubbles in the main board layer; the weight reduction rate of the plurality of micro bubbles for the main board layer is between 15 and 25%, and the average size of the plurality of micro bubbles is between 60 and 800 μm; Among them, the calculation formula of the weight loss rate is: Weight loss rate (%) = (W1-W2)/W2*100%; W1=H*(L1*L2*D); in: H is the average thickness of the main board layer (mm); L1 is the length of the main board layer (mm); L2 is the width of the main board layer (mm); D is the specific gravity of the material of the main board layer (g/mm ³ ); W1 is the theoretical weight of the main board layer (g), that is, the weight without the multiple microbubbles; W2 is the actual weight of the main board layer (g), which is the actual weight of the main board layer containing multiple microbubbles measured by a scale. As described in claim 7, the diffusion plate used for the low optical path distance backlight module, wherein the plurality of microbubbles are generated by adding a foaming agent and a nucleating agent in the foaming extrusion molding process of the main board layer; the nucleating agent comprises at least one of the following: calcium carbonate, silicon dioxide, calcium oxide; the weight percentage of the added nucleating agent is 0.1%-0.5%. The diffuser plate for use in a low optical path distance backlight module as described in claim 7, wherein the plurality of first diffuser particles contained in the first diffuser particle additive include one of the following: silicone beads, acrylic beads (PMMA beads), polystyrene beads (PS beads), acrylic-polystyrene copolymer particles (PMMA-PS beads), beads); wherein the particle size of the first diffusion particle is between 1 and 4 μm, the refractive index of the first material is between 1.42 and 1.5, and the first weight percentage of the first diffusion particle additive added to the main layer is between 1 and 4%; wherein the plurality of second diffusion particles contained in the second diffusion particle additive include one of the following inorganic particles: calcium carbonate, barium sulfate, titanium oxide, talc, mica, boron nitride; wherein the particle size of the second diffusion particle is between 0.05 and 8 μm, the refractive index of the second material is between 1.5 and 2.6, and the second weight percentage of the second diffusion particle additive added to the upper surface layer and the lower surface layer is between 0.1 and 1.5%. As described in claim 7, the diffuser plate used in a low optical path distance backlight module, wherein the diffuser plate further includes: A plurality of micro-structures are arranged in an array on the upper surface and the lower surface of the plate; An upper optical film is attached to the upper surface of the plate by an optical adhesive; wherein the thickness of the optical film is between 5 and 20 μm; A lower optical film is attached to the lower surface of the plate by an optical adhesive; and A reflective film is attached to the lower optical film; wherein the reflective film has a reflectivity of <20% for light with a wavelength below 500nm, and a reflectivity of >90% for light with a wavelength above 500nm.

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