CN113376900A

CN113376900A - Straight following formula Mini-LED backlight unit that light-emitting is even

Info

Publication number: CN113376900A
Application number: CN202110459605.7A
Authority: CN
Inventors: 张小齐; 庄世强; 彭益
Original assignee: Shenzhen Longli Technology Co Ltd
Current assignee: Shenzhen Longli Technology Co Ltd
Priority date: 2021-01-25
Filing date: 2021-04-27
Publication date: 2021-09-10

Abstract

The invention provides a direct type Mini-LED backlight module with uniform light emission, which comprises a PCB substrate, a plurality of Mini-LED light sources, a reflecting cover and an optical diaphragm group, wherein the PCB substrate, the plurality of Mini-LED light sources, the reflecting cover and the optical diaphragm group are arranged from bottom to top; the optical diaphragm group comprises at least one diffusion diaphragm, the diffusion diaphragm is attached to the reflecting cover, and a plurality of micro-lens structures are arranged on the diffusion diaphragm, wherein the micro-lens structures are periodically distributed corresponding to each reflecting cup structure; and taking the distance between the lower surface of the diffusion film and the upper surface of the PCB substrate as H, and taking the minimum distance value of the adjacent Mini-LED light sources as P, wherein H: P is 1: 1-1: 7. The reflector and the diffusion film can act synergistically, so that not only can light spots be avoided, uniform distribution of light be realized, but also the brightness of an observation angle can be improved.

Description

Straight following formula Mini-LED backlight unit that light-emitting is even

Technical Field

The invention belongs to the field of semiconductor devices and optical systems, and particularly relates to a direct type Mini-LED backlight module with uniform light emission.

Background

The liquid crystal panel of the liquid crystal display device does not emit light by itself. Therefore, the liquid crystal display device is provided with a backlight device as a surface light source device as a light source for illuminating the liquid crystal panel on the back side of the liquid crystal panel. Mini light emitting diodes (Mini-LEDs) that can be used for surface light source backlight have drawn attention because of their advantages such as high brightness, high resolution, and long life. The Mini-LED chip size is below 200 microns, can compare favourably with OLED products in the real effect, and has competitive advantages in material cost compared with OLED. With the wider application of Mini-LED products, the designs of Mini-LED based products, such as high brightness backlight, Local dimming (HDR) type backlight, etc., are increasing. The main components of the direct type Mini-LED backlight device include an optical film set, a Mini-LED light source, and a reflective sheet, and how to effectively improve the uniformity of the emitted light without increasing the cost and the brightness of the emitted light becomes an important issue in the composition structure.

Meanwhile, in order to improve color reproducibility of the Mini-LED display, it is effective to narrow the half-value widths of the respective emission spectra of blue, green, and red of the backlight unit and improve the color purities of the respective colors of blue, green, and red. As a means for solving this problem, chinese patent CN110308587A proposes a technique in which quantum dots formed of inorganic semiconductor fine particles are used as a component of a color conversion film. The technique using quantum dots can actually narrow the half-value widths of the green and red emission spectra, improve color reproducibility, and improve the color gamut. By combining the quantum dot film having the color conversion function with the blue light source, three primary colors of blue, green, and red, that is, white light can be obtained by the blue light source. A full-color display can be manufactured by using a white light source obtained by combining the blue light source and the quantum dot film having a color conversion function as a backlight unit, and combining the backlight unit with a liquid crystal driving section and a color filter. In addition, the liquid crystal display device can be used as a white light source without a liquid crystal driving portion, and can be used as a white light source such as LED lighting. On the other hand, the fluorescent emission of the quantum dots is random and has no orientation, and therefore, a certain proportion of green and red light is emitted back to the LED backlight source and absorbed by the substrate on which the LED backlight source is mounted, thereby causing a large loss in display brightness.

As shown in fig. 1, chinese patent CN110061116A discloses a direct type backlight module using an array LED surface light source, which includes an LED substrate 100, a Mini-LED light source 101, a quantum dot film 303, a diffusion sheet 304 and a brightness enhancement film 400, wherein the Mini-LED light is distributed in a lambert shape, so that the central brightness is high, the peripheral brightness is low, and the uneven brightness is easily generated during the light emitting process of the direct type backlight module. At present, diffusion sheet light mixing is mostly adopted or scattering haze particles are added into a fluorescent film for light mixing, but the penetration rate of the whole surface light source can be reduced due to the addition of a film layer, the whole brightness of the surface light source is influenced, and the haze particles or a diffusion structure in the fluorescent film cannot achieve a good light mixing effect. Chinese patent CN110703497A discloses a backlight device with a reflector. The backlight device comprises a plurality of LED light sources, and the reflecting cover comprises a reflecting cup structure for accommodating the LED light sources and a quantum dot film above the reflecting cup structure. An opening is formed in the bottom of the reflecting cup structure, and the LED light source is arranged in the opening. The arrangement of the reflecting cup structure increases the light-emitting rate of light rays in the backlight device, and improves the utilization efficiency of light. However, light is difficult to penetrate at the connection position of the reflecting cup structure, thereby forming a light spot (mura), which affects the display effect.

Disclosure of Invention

The invention aims to provide a direct type Mini-LED backlight module with uniform light emission, which can uniformly emit light by improving the brightness angle of a Mini-LED light source.

According to one aspect of the invention, the direct type Mini-LED backlight module with uniform light emission comprises a PCB substrate, a plurality of Mini-LED light sources, a reflecting cover and an optical diaphragm group, wherein the PCB substrate, the plurality of Mini-LED light sources, the reflecting cover and the optical diaphragm group are arranged from bottom to top; the Mini-LED light source is arranged on the surface of the PCB substrate, the reflector comprises a plurality of reflecting cup structures with upper and lower openings, the Mini-LED light source is periodically arranged in the openings of the reflecting cup structures, so that the reflector reflects part of light distribution of the Mini-LED light source to one side of the display surface of the direct type Mini-LED backlight module, and the period arrangement of the Mini-LED light source refers to that: the Mini-LED light sources are arranged on the PCB substrate in a matrix form and are arranged in one-to-one correspondence with the reflecting cup structures, and the Mini-LED light sources penetrate through the lower openings of the corresponding reflecting cup structures so as to be arranged in the reflecting cup structures; the optical diaphragm group includes an at least diffusion diaphragm, and diffusion diaphragm laminating bowl sets up to make the diffusion diaphragm seal the upper shed of reflection cup structure, be equipped with a plurality of microlens structure on the diffusion diaphragm, wherein, a plurality of microlens structure correspond every reflection cup structure and form periodic distribution, and the periodic distribution of a plurality of microlens structure indicates: a plurality of micro-lens structures included in the diffusion membrane area corresponding to the position right above each reflection cup structure form a micro-lens structure group, the micro-lens structure group is used as a repeating unit which is periodically distributed, and each micro-lens structure group corresponds to each Mini-LED light source and is arranged in a matrix form; and taking the distance between the lower surface of the diffusion film and the upper surface of the PCB substrate as H, and taking the minimum distance value of the adjacent Mini-LED light sources as P, wherein H: P is 1: 1-1: 7.

The Mini-LED pitch P is associated with the backlight optical mixing distance (OD) value. Generally, in order to ensure a good optical quality effect, when a design value of a light source pitch P is fixed, the larger the backlight optical mixing distance OD is, the farther the lateral propagation distance along the light-emitting surface is, so that the larger the diffusion range of the emitted light is, the larger the physical expression of the emitted light is in the diffusion area, and the light-emitting ranges of the Mini-LED light sources are mutually covered, so that the radiation intensity is uniformly distributed in space to ensure that the Mini-LED light sources have uniform brightness transition.

Based on snell's law, the micro-lens structure on the diffusion diaphragm can make the light that comes from the light source take place to reflect, utilize the bowl and the cooperation of diffusion diaphragm to play the synergism, can make light take place the multiple reflection between bowl and diffusion diaphragm, increase optics distance of mixing light (OD, optical distance), thereby improved along the planar light-emitting degree of consistency in diffusion diaphragm place, the setting of bowl can produce the convergence effect to the light simultaneously, therefore, can improve the luminance of light at the observation visual angle on the one hand, on the other hand also can avoid the production of facula. In the direct type backlight module provided by the invention, the ratio of H to P is limited to improve the brightness angle of the Mini-LED light source and the light-emitting uniformity of the Mini-LED backlight module, when the ratio of H to P is 1: 1-1: 7, the brightness angle of the Mini-LED light source is at least increased to 2arctan (P/2H), and the light-emitting uniformity of the direct type Mini-LED backlight module is at least increased by 10%. The diffusion film and the reflecting cover are arranged in an assembly mode of being vertically attached, so that the reflecting cover directly supports the diffusion film, the structural stability of the direct type Mini-LED backlight module is improved, and meanwhile, the reflecting cover and the diffusion film enclose a plurality of optical cavities to be beneficial to improving the light energy utilization rate.

Preferably, the maximum distance between adjacent Mini-LED light sources is PF, H: PF is 1: 2. Therefore, the light emitting uniformity of the direct type Mini-LED backlight module is increased by 15%.

Preferably, the side of the diffusion film facing the PCB substrate is a light incident side of the diffusion film, the side of the diffusion film facing away from the light incident side is a light emitting side of the diffusion film, the microlens structure is disposed on the light emitting side, and the light incident side has no microlens structure. The light incident side of the diffusion membrane adopted by the invention is not provided with a micro-lens structure, and the diffusion membrane is a flat surface, thereby being beneficial to the close fit of the diffusion membrane and the reflecting cover. On the other hand, in the diffusion film, the micro-lens structure is arranged on the light-emitting side, and if a light-emitting element (such as a quantum dot film) is arranged on the light-emitting side of the diffusion film in practical application, light from the light-emitting element can be reflected when entering the diffusion film from the light-emitting side of the diffusion film, so that the loss of fluorescence of the light-emitting element can be reduced, the brightness of the backlight module can be increased, and the unbalance of the RGB ratio of the surface light source caused by the fact that the PCB substrate partially absorbs the fluorescence from the light-emitting element can be avoided.

Preferably, the ratio of the height of the micro-lens structure to the thickness of the diffusion membrane is 1:6 to 5: 6. The micro-lens structure layer is too thin, which easily causes a local light-gathering phenomenon, and further aggravates the lamp eye Mura caused by local dimming (Localdim). However, if the ratio of the microlens structure layer is greater than 5:1, the backlight module may be too thick.

Preferably, the ratio of the height of the microlens structure to the thickness of the diffusion membrane is 1: 3.

Preferably, the diameter ratio of the upper opening of the micro lens structure to the reflective cup structure is less than 1/2.

Preferably, micro-lens structures arranged on the diffusion film are correspondingly distributed right above each reflection cup structure; the micro lens structures are periodically distributed along the optical axis of the Mini-LED light source arranged in the corresponding reflecting cup, and the distribution density of the micro lens structures is reduced in a radiation mode by taking the optical axis as the center.

Preferably, the micro lens structures are recessed toward the inside of the optical film, and in a plurality of micro lens structures corresponding to the same reflector cup structure, the slope of the recessed inclined surface of the micro lens structure increases as the distance between the micro lens structure and the optical axis decreases. The micro-lens structure is arranged into a concave structure, an inwards concave cavity is formed on the light-emitting side surface of the diffusion membrane, and the medium in the cavity is air, so that the light-emitting side forms an interface with matrixes with different transmittances, and the light reflectivity of the light source is improved. On the other hand, the microlens structure having the inclined surface with a larger inclination may converge more light in a direction orthogonal to the backlight, that is, increase the propagation OD of light, as compared with the microlens structure having the inclined surface with a smaller inclination. Therefore, the arrangement of the plurality of micro-lens structures on the optical diaphragm follows the rule, so that the light rays transmitted by the optical diaphragm can meet the conditions that the light ray diffusion angle transmitted along the collinear direction with the longer side of the micro-lens structure is larger, and the light ray diffusion angle transmitted along the collinear direction with the shorter side of the micro-lens structure is smaller.

Preferably, the microlens structure is a plane-symmetrical structure.

Preferably, the PCB substrate and the reflector are fixed by the optical adhesive layer; the lower opening of each reflecting cup structure is attached with an optical adhesive layer; the optical adhesive layer is attached to the surface of the PCB substrate and covers the Mini-LED light source, so that a Fresnel lens is formed above the Mini-LED light source. The fresnel lens thus formed above the Mini-LED light source enables light near the optical axis of the Mini-LED light source to be reflected and redirected in a higher proportion.

Drawings

FIG. 1 is a diagram of a backlight module according to the prior art;

FIG. 2 is a schematic diagram of a nine-point test method;

fig. 3 is a three-dimensional structure diagram of a diffusion film of a direct type Mini-LED backlight module according to embodiment 1 of the present invention;

FIG. 4 is a top view of a diffusion film of a direct type Mini-LED backlight module according to embodiment 1 of the present invention;

fig. 5 is an exploded view of a direct type Mini-LED backlight module according to embodiments 1 and 6 of the present invention;

fig. 6 is a cross-sectional view of a direct type Mini-LED backlight module according to embodiments 1 and 6 of the present invention;

FIG. 7 is an optical schematic diagram of a diffusion membrane of embodiment 1 of the present invention;

FIG. 8 is an optical schematic diagram of a diffusion membrane of embodiment 1 of the present invention;

FIG. 9 is an optical schematic diagram of a diffusion membrane of embodiment 1 of the present invention;

FIG. 10 is a radiation distribution diagram of a Lambertian light source;

FIG. 11 is a graph of the radiation characteristics of a Mini-LED light source;

FIG. 12 is a schematic view showing the optical principle of a Mini-LED backlight module without a diffusion film and a reflection cover;

fig. 13 is a schematic view of light spots formed on a quantum dot film by a Mini-LED backlight module without a diffusion film and a reflector;

fig. 14 is a schematic view of a direct type Mini-LED backlight module according to embodiment 6 of the present invention and its optical principle;

fig. 15 is an exploded view of a direct type Mini-LED backlight module according to embodiment 7 of the present invention;

fig. 16 is a cross-sectional view of a direct type Mini-LED backlight module according to embodiment 7 of the present invention;

fig. 17 is an exploded view of a direct type Mini-LED backlight module according to embodiment 8 of the present invention;

fig. 18 is a cross-sectional view of a direct type Mini-LED backlight module according to embodiment 8 of the present invention;

fig. 19 is a schematic structural view of a diffusion film and a reflection cover of a direct type Mini-LED backlight module according to embodiment 9 of the present invention and an optical principle thereof.

Detailed Description

Referring to the drawings, wherein like reference numbers refer to like elements throughout, the principles of the present invention are illustrated in an appropriate environment. The following description is based on illustrated embodiments of the invention and should not be taken as limiting the invention with regard to other embodiments that are not detailed herein.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The word "embodiment" is used herein to mean serving as an example, instance, or illustration. In addition, the articles "a" and "an" as used in this specification and the appended claims may generally be construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Further, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may comprise direct contact of the first and second features, or may comprise direct contact of the first and second features through another feature in between. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or meaning that the first feature is at a lesser elevation than the second feature.

The brightness and brightness uniformity test method referred to in the following examples is referred to as "national people's republic of China industry Standard SJ/T11348-2006: referring to fig. 2, the brightness of different positions on the surface of a test product is measured by a nine-point measurement method, and the brightness uniformity of the test product is represented by the minimum value of the ratio of the brightness values of eight test points P1-P8 to the brightness value of a central test point P0. Refer to the industry Standard of the people's republic of China SJ/T11343-2006: in the general specification of digital tv-lcd, the front brightness of the center point of the light-emitting surface of a high-performance backlight module should be no less than 350 nit.

The distribution test mode of the brightness angles involved in the following examples is referred to the "national people's republic of China industry Standard SJ/T11343-2006: general specifications for digital television liquid crystal displays and the industry standard of the people's republic of China SJ/T11348-2006: digital television flat panel display measurement method ":

a) placing the luminance meter at the position 3 times of the Mini-LED light source 101 (lighting a single Mini-LED light source 101 or a chip in the Mini-LED backlight module, or cutting a single Mini-LED light source 101 area of the Mini-LED backlight module) or at the position 3 times of the Mini-LED backlight module;

b) the position of the brightness meter can move horizontally and vertically, the observation distance is kept unchanged, the included angle between the brightness meter and the Mini-LED light source 101 or the illumination normal of the Mini-LED backlight module is changed from-90 degrees to 90 degrees, and the brightness data of each test position is recorded. The brightness angle of the Mini-LED light source 101 or the Mini-LED backlight module is an included angle between one third of the brightness peak value.

Example 1

The present embodiment provides a direct type Mini-LED backlight module, as shown in fig. 5 and 6, comprising a PCB substrate 100, a reflective cover 200, and an optical film set 300.

The composite optical membrane group 300 comprises a diffusion membrane 301 and a quantum dot film 303, wherein the diffusion membrane 301 is made of Polycarbonate (PC), the transmittance of the material is 95%, as shown in fig. 3 and 4, two side surfaces perpendicular to the thickness direction of the diffusion membrane 301 are respectively used as the light-emitting side and the light-entering side of the diffusion membrane 301, the light-emitting side of the diffusion membrane 301 is provided with a plurality of micro-lens structures 3011 periodically arranged according to a certain distribution rule, the micro-lens structures 3011 are recessed towards the inside of the diffusion membrane 301 and are of a hexagonal pyramid structure with a symmetrical surface, and the light-entering side of the diffusion membrane 301 is free of the micro-lens structures 3011.

The surface of the PCB substrate 100 is mounted with a plurality of Mini-LED light sources 101, the Mini-LED light sources 101 are periodically arranged on the surface of the PCB substrate 100, and the periodic arrangement refers to a matrix arrangement. The reflective cover 200 includes a plurality of reflective cup structures 201 opened up and down. The PCB substrate 100, the reflector 200 and the optical film set 300 are sequentially stacked and assembled from bottom to top. The PCB substrate 100 and the reflector 200 are assembled such that each Mini-LED light source 101 is arranged corresponding to one reflector cup structure 201, the Mini-LED light sources 101 are arranged in the reflector cup structures 201 through the lower openings of the reflector cup structures 201, and the reflector 200 reflects part of the light distribution of the Mini-LED light sources 101 to one side of the display surface of the direct type backlight device. By utilizing the cooperation of the reflective cover 200 and the diffusion film 301, the light can be reflected between the reflective cover 200 and the diffusion film 301 for multiple times, thereby greatly increasing the transmission OD of the light and further increasing the uniformity of the light output along the plane where the diffusion film 301 is located. The optical diaphragm set 300 is compounded with the reflecting cover 200 by the diffusion diaphragm 301 included in the optical diaphragm set, the diffusion diaphragm 301 of the optical diaphragm set 300 is attached to the top of the reflecting cover, and the thickness T of the reflecting cover 200 is equal to the distance H between the light incident side of the diffusion diaphragm 301 and the upper surface of the PCB substrate 100, so that the reflecting cover 200 directly supports the diffusion diaphragm 301, and the stability of the direct type Mini-LED backlight module is improved; meanwhile, the upper opening of the reflection cup structure 201 is covered by the diffusion membrane 301, so that a plurality of optical cavities are enclosed by the diffusion membrane 301 and the plurality of reflection cup structures 201, and therefore the light energy utilization rate can be improved.

The light-emitting side of the diffuser film 301 used in this embodiment is provided with a plurality of concave microlens structures 3011, so that a plurality of concave cavities are formed on the surface of the light-emitting side, and the concave cavities are filled with air medium, and it should be understood by those skilled in the art that the refractive index of air is smaller than that of most known materials. When incident light passes through materials with different refractive indexes, Snell's Law (Snell's Law) is satisfied, namely ni × sin δ — nt × sin θ, wherein ni means the refractive index of the material on the incident light side, δ means the incident angle, nt means the refractive index of the material on the transmission light side, and θ means the emergent angle. According to the principle of Snell's Law, when a light ray meets or is incident on a medium having a small refractive index, a part of the light ray is refracted from a normal line at an exit angle θ with respect to the normal line, which is larger than an incident angle δ. However, incident light (e.g., light ray 1a in fig. 7) that enters the meeting surface (material-air boundary in this embodiment) of the medium in the normal direction of the surface is not refracted but continues to travel in a straight line in its incident direction. The light ray in fig. 7 reaches the meeting surface of the microlens structure 3011 and the air medium at an incident angle of 2 α with respect to the normal of the surface of the microlens structure 3011, and since the incident angle 2 α of the light ray is not equal to zero (0), the light ray is refracted into the air medium at an exit angle 2 β having a different angle value from the incident angle 2 α according to snell's law, the light ray is refracted, and since the refractive index of the air medium is smaller than that of the microlens structure 3011, the incident angle 2 α of the light ray is smaller than its exit angle 2 β. As further shown in fig. 7, a light ray propagating into the microlens structure 3011 reaches the meeting surface of the microlens structure 3011 and the air medium at an incident angle 3a relative to the normal of its surface, the incident angle 3 α of the light ray being greater than the critical angle δ c at the meeting surface, in which case the light ray does not exit the microlens structure 3011 and is reflected at the surface of the microlens structure 3011, which is referred to as "total internal reflection". As described above, when a light ray travels from a material having a higher reflection coefficient to a material having a lower reflection coefficient, the light ray will behave according to the snell's law formula set forth above. According to this formula, the exit angle θ will approach 90 degrees as the angle of incidence increases. However, at the critical angle δ c, and for all angles greater than the critical angle δ c, total internal reflection will occur (i.e. the light ray will not be refracted but will be reflected and propagate through the surface). As will be understood by those skilled in the art, the critical angle δ c is determined by setting the exit angle (refraction angle) to 90 degrees and solving for the incident angle according to snell's law.

As shown in fig. 8, the light rays 4a and 5a meet the surface at incident angles 4 α, 5 α, respectively, which are smaller than the critical angle δ c, however, the incident angle 4 α of the light rays with respect to the normal of the surface is larger than the incident angle 5 α of the light rays with respect to the normal of the surface. Therefore, according to snell's law, the exit angle 4 β of the light ray with respect to the normal of the surface is different from the exit angle 5 β of the light ray with respect to the normal of the surface. As will be appreciated by those skilled in the art, the exit angle 4 β of a light ray from the normal to the surface will be greater than the exit angle 5 β of a light ray from the normal to the surface.

In the direct type Mini-LED backlight module provided in this example, when the fluorescent light source of the quantum dot film 303 enters from the light exit side of the diffusion film 301, the microlens structure 3011 of the diffusion film 301 reflects the incident light with an incident angle outside the critical angle δ c, so that most of the incident light from the quantum dot film 303 is reflected back to the quantum dot film 303. Referring to fig. 9, a light ray 6a and a light ray 7a meet the outer surface of the microlens structure 3011 at an incident angle 6 α smaller than the critical angle δ c and an incident angle 7 α larger than the critical angle δ c, respectively, the light ray with the incident angle 6 α enters the diffusion membrane 301 at an exit angle 6 β with respect to the normal of the surface, and the light ray with the incident angle 7 α is reflected at an exit angle 7 β with respect to the normal of the surface and is totally reflected back to the quantum dot film 303. Thus, light from the quantum dot film 303 is reflected by the microlens structure 3011 of the diffusion membrane 301, reducing the loss of fluorescence of the quantum dot film 303 and increasing the luminance. Meanwhile, the phenomenon that yellow light occurs due to the fact that the proportion of RGB of the surface light source is unbalanced because the PCB substrate 100 partially absorbs red light and green light RG is avoided.

Example 2

Only the differences between this embodiment and embodiment 1 will be described below, and the descriptions of the similarities will be omitted. In this embodiment, based on the device structure of the direct type Mini-LED backlight module provided in embodiment 1, the ratio of the height of the microlens structure 3011 on the surface of the diffusion film 301 to the thickness of the diffusion film 301 is used as a variable (the height of the microlens structure 3011 is not changed, and the ratio is adjusted by changing the thickness of the diffusion film 301), and different diffusion films 301 are designed to perform an optical performance test.

The numbers of the diffusion films 301 and the ratios of the heights of the corresponding microlens structures 3011 to the thicknesses of the diffusion films 301 are respectively as follows: diffusion membranes 1A, 1: 6; diffusion membranes 1B, 1: 3; diffusion membrane 1C, 5: 6; diffusion membrane 1D, 1: 1.

Referring to embodiment 1, the direct type Mini-LED backlight module is assembled by using the diffusion film 301 of this embodiment, and the brightness uniformity of the assembled direct type Mini-LED backlight module is tested. Specific results are shown in table 1, a Local light-gathering phenomenon is easily caused by a thin microlens structure 3011 layer, and further the lamp eye Mura caused by Local dimming (Local dimming) is aggravated; however, if the ratio of the microlens structure 3011 layer is greater than 5:6, the backlight module may be too thick.

TABLE 1 Learn for diffusion films and corresponding direct type Mini-LED backlight module optical performance statistics

Diffusion membrane for participating in test	Brightness uniformity of direct type Mini-LED backlight module
		Diffusion diaphragm 1A	83.26％
Diffusion diaphragm 1B	87.39％
		Diffusion film 1C	92.06％
Diffusion diaphragm 1D	90.67％

Example 3

Only the differences between this embodiment and embodiment 1 will be described below, and the descriptions of the similarities will be omitted. In this embodiment, based on the device structure of the direct type Mini-LED backlight module provided in embodiment 1, the distribution manner of the microlens structures 3011 on the surface of the adopted diffusion film 301 is used as a variable, and different diffusion films 301 are designed to perform an optical performance test.

The numbers of the diffusion membranes 301 and the distribution of the corresponding microlens structures 3011 are as follows: the diffusion membrane 2A is formed by uniformly distributing and isolating a plurality of micro-lens structures 3011; a diffusion membrane 2B, a plurality of microlens structures 3011 are uniformly distributed and are continuously arranged adjacently; the diffusion membrane 2C takes the distribution center of the micro-lens structures 3011 as a central axis perpendicular to the distribution plane of the micro-lens structures, and the distribution density of the micro-lens structures 3011 is reduced in a radiation mode along the central axis; a diffusion membrane 2D having a distribution center of the plurality of microlens structures 3011 as a central axis perpendicular to a distribution plane thereof, wherein a slope of a concave inclined surface of the microlens structure 3011 increases as a distance between the microlens structure 3011 and the central axis decreases; the distribution is the distribution of the microlens structures 3011 in the repeating unit of the periodic distribution of the microlens structures 3011 on the diffusion film 301.

Referring to embodiment 1, the diffusion film 301 of this embodiment is used to assemble a direct type Mini-LED backlight module, so that the central axis of the corresponding distribution unit of the microlens structure 3011 coincides with the optical axis of the Mini-LED light source 101. And testing the brightness uniformity of the assembled direct type Mini-LED backlight module. As shown in table 2, compared to the backlight module using the diffusion film 2A, the backlight module using the diffusion films 2B, and 2C can improve the brightness uniformity of the backlight module to different degrees.

TABLE 2 participating diffusion films and their corresponding direct type Mini-LED backlight module optical performance statistics

Diffusion membrane for participating in test	Brightness uniformity of direct type Mini-LED backlight module
		Diffusion diaphragm 2A	87％
Diffusion diaphragm 2B
		90％
Diffusion diaphragm 2C			93％
	Diffusion membrane 2D	94％

Example 4

Only the differences between this embodiment and embodiment 1 will be described below, and the descriptions of the similarities will be omitted. In this embodiment, based on the device structure of the direct type Mini-LED backlight module provided in embodiment 1, the ratio of the diameter of the bottom of the cone of the microlens structure 3011 to the diameter of the upper opening of the reflective cup structure 201 of the reflective cover 200 is used as a variable, and different direct type Mini-LED backlight modules are designed for performing optical performance tests.

The numbers of the direct type Mini-LED backlight modules and the ratio of the diameter of the cone bottom of the corresponding micro-lens structure 3011 to the diameter of the upper opening of the reflective cup structure 201 of the reflective cover 200 are as follows: a direct type Mini-LED backlight module 1A, 1: 10; a direct type Mini-LED backlight module 1B, 1: 2; direct type Mini-LED backlight module 1C, 1: 1. And carrying out a brightness uniformity test on the direct type Mini-LED backlight module which is tested by the embodiment. As shown in table 3, in the tested backlight module, the brightness uniformity of the direct type Mini-LED backlight module 1A is the best, and by comparing the ratio variable and the brightness uniformity set in this embodiment corresponding to the tested backlight module, the following rules can be obtained: the smaller the ratio of the diameter of the conical bottom of the micro-lens structure to the diameter of the upper opening of the reflecting cup structure of the reflecting cover is, the better the brightness uniformity of the corresponding backlight module is.

TABLE 3 direct type Mini-LED backlight module and optical performance statistics thereof

Example 5

Only the differences between this embodiment and embodiment 1 will be described below, and the descriptions of the similarities will be omitted. In the parameters according to the present embodiment, the distance between the lower surface of the diffusion film 301 and the PCB substrate 100 is defined as H, the minimum distance between the adjacent Mini-LED light sources 101 on the surface of the PCB substrate 100 is defined as P, and the maximum distance between the adjacent Mini-LED light sources 101 is defined as PF.

1.1 with H/P as a variable

In this embodiment, based on the device structure of the direct type Mini-LED backlight module provided in embodiment 1, different direct type Mini-LED backlight modules are designed with H/P as a variable, so as to perform an optical performance test. The numbers of the direct type Mini-LED backlight modules to be tested and the corresponding H/P values are respectively as follows: a direct type Mini-LED backlight module 2A, 2: 1; a direct type Mini-LED backlight module 2B, 1: 1; a direct type Mini-LED backlight module 2C, 1: 2; a direct type Mini-LED backlight module 2D, 1: 5; a direct type Mini-LED backlight module 2E, 1: 7; and the direct type Mini-LED backlight module 2F is 1: 8. The direct type Mini-LED backlight module which is tested by the embodiment is subjected to testing of the brightness angle of the Mini-LED light source 101 and the brightness uniformity of the surface light source. As shown in Table 4, the Mini-LED light source brightness angle of the backlight module increased with the decrease of the H/P value. When the H/P is in the range of 1/7-1, the brightness angle of the Mini-LED light source 101 is at least increased to 2arctan (P/2H), the light-emitting uniformity of the direct type Mini-LED backlight module is at least increased by 10%, wherein when the H/P is 1/2, the brightness uniformity of the direct type Mini-LED backlight module is increased by 15%; when H/P is 1/5, the brightness angle of the Mini-LED light source 101 increases from 120 ° to 140 °, and the brightness angle of the backlight module increases to 160 °. However, when the H/P value is as low as 1/8, the backlight module emits light with obvious bright spots and dark shadows, and the light cannot be uniformly emitted, which may be caused by too small H value.

The distance P between the Mini-LED light sources 101 is related to the VOD (vertical Mini-LED area light source) value of the longitudinal light mixing distance of the backlight module. The larger the P/VOD is, the better the backlight design is, namely the backlight module can reduce the using number of Mini-LED chips under the same longitudinal light mixing distance VOD; or at the same Mini-LED light source 101 pitch P, the longitudinal light mixing distance VOD can be reduced so that the backlight module can be made thinner. Generally, in order to ensure a good optical quality effect, when the design value of the light source pitch P is fixed, the larger the transverse light mixing distance HOD (parallel to the Mini-LED surface light source) of the backlight module is, the longer the transverse propagation distance along the light exit surface is, so that the larger the diffusion range of the light exit is, the larger the brightness angle obtained by testing the physical expression of the light exit is, and the uniform spatial distribution of the radiation intensity is obtained to ensure that the brightness transition between the Mini-LED light sources 101 is uniform.

Table 4 refers to direct type Mini-LED backlight module and optical performance statistics thereof

1.2 with H/PF as variable

In this embodiment, based on the device structure of the direct type Mini-LED backlight module provided in embodiment 1, different direct type Mini-LED backlight modules are designed with H/P as a variable, so as to perform an optical performance test. The numbers of the direct type Mini-LED backlight modules to be tested and the corresponding H/PF values are respectively as follows: a direct type Mini-LED backlight module 3A, 1: 1; a direct type Mini-LED backlight module 3B, 1: 2; and 3, a direct type Mini-LED backlight module 3C, 1: 3. And testing the brightness angle and the brightness uniformity of the backlight module of the direct type Mini-LED backlight module which is tested by the embodiment. As shown in Table 5, the backlight module brightness angle increases with decreasing H/PF value. In the above-mentioned reference products, the direct type Mini-LED backlight module 3B is preferred, and when H/PF reaches 1/2, the luminance angle of the backlight module is increased to at least 2arctan (PF/2H).

TABLE 5 direct type Mini-LED backlight module and optical performance statistics thereof

Example 6

Based on the structural composition of the direct type Mini-LED backlight module of embodiment 1 and the performance test results of the backlight modules of embodiments 2 to 5, this embodiment provides an optimized direct type Mini-LED backlight module. Based on embodiment 1, the structure of the direct type Mini-LED backlight module provided in this embodiment is shown in fig. 5 and 6, and only the differences between this embodiment and embodiment 1 will be described below, and the description of the similarities will not be repeated here. The microlens structure 3011 formed on the light exit side of the diffusion film 301 is arranged as follows: each microlens structure 3011 is adjacent to at least one other microlens structure 3011, the distribution center of the plurality of microlens structures 3011 is taken as a central axis perpendicular to the distribution plane, the distribution density of the microlens structures 3011 decreases in a radial manner along the central axis, and the slope of the concave inclined plane of the microlens structure 3011 increases as the distance between the microlens structure 3011 and the central axis decreases; the distribution mode is a mode that the microlens structures 3011 in the repeating units are periodically distributed on the diffusion membrane 301 by the microlens structures 3011; the ratio of the height of the microlens structure 3011 to the thickness of the diffusion membrane 301 is 1: 3. In addition, the ratio of the diameter of the tapered bottom of the microlens structure 3011 to the diameter of the upper opening of the reflector cup structure 201 of the reflector 200 is 1:10, and the PCB substrate 100 and the diffusion film 301 are disposed such that H/P is 1: 5. The diffusion film 301 having the above-described structure has a visible light transmittance of 64% on the light incident side and a visible light transmittance of 91% on the light outgoing side.

The Mini-LED chip is a light source close to a lambertian light source (Lambert's cosine law), the radiation intensity or luminous intensity I of which, viewed from an ideal diffuse reflecting surface, is proportional to the cosine of the angle θ between the direction of the emitted light and the surface normal, cos θ. As shown in fig. 10, each wedge in the circle represents an equal angle d Ω, and for a lambertian surface, the number of photons emitted into each wedge per second is proportional to the area a of the wedge. As shown in fig. 11, the radiation characteristic curve of the Mini-LED light source 101 on the PCB substrate 100 is M-shaped, and the angle a between two peaks of the light emitted from the "M" type peak is generally defined to illustrate the diffusion degree, the larger the angle a, the better the diffusion effect, and the range of the angle a between the "M" type peaks of the Mini-LED light source 101 is generally within 120 °. However, the Mini-LED pitch P (pitch) is typically tens of times larger than the size of the Mini-LED chip, on the order of centimeters. Since the thickness of the optical film 20 of the Mini-LED backlight module is only in the millimeter level, the Mini-LED light source 101 on the PCB substrate 100 forms the light spot 001 and the dark area 002 on the quantum dot film 303 in the backlight device without the reflection cover 200 and the diffusion film 301 as shown in fig. 12 and 13. Therefore, in order to form a surface light source with the light emitted from the plurality of Mini-LED chips to avoid dark areas and reduce the number of Mini-LED chips used (i.e. increase the Mini-LED pitch P), it is necessary to reduce the intensity of the light radiation emitted at a certain angle in the direction close to the normal line of the surface of the Mini-LED chips (e.g. θ < 30 °), and increase the intensity of the light radiation emitted at a certain angle in the direction away from the normal line of the surface of the Mini-LED chips (e.g. 30 ° < θ < 60 °).

However, in this embodiment, the diffusion film 301 and the reflection cover 200 are disposed above the PCB substrate 100 and attached to each other vertically, and the incident light is partially reflected back to the reflection cover 200 by the plurality of microlens structures 3011 and is reflected again to the diffusion film 301 by the reflection cover 200 on the surface of the PCB substrate 100. The multiple reflections of the light between the reflective cover 200 and the diffuser film 301 greatly increase the OD of the light propagation, and thus the propagation along the plane of the diffuser film 301. As shown in fig. 14, the luminance angle of the Mini-LED light source 101 extends from L1 to L2 (dashed line).

The direct type Mini-LED backlight module provided in this embodiment is subjected to a brightness test, and the test results are shown in table 6, wherein the minimum value of the ratio of the brightness values of the eight test points P1-P8 to the brightness value of the central test point P0 represents the brightness uniformity of the product to be tested. The minimum value of the brightness of the direct type Mini-LED backlight module of the embodiment appears at P7, with the value of 12167nit, and the brightness uniformity is calculated according to P7/P0, with the value of 90.21%.

Table 6 brightness test data of direct type Mini-LED backlight module provided in this embodiment

Example 7

Based on the direct type Mini-LED backlight module provided in embodiment 6, this embodiment provides a new direct type Mini-LED backlight module by further improving the optical film set forming the direct type Mini-LED backlight module.

Only the differences between the direct type Mini-LED backlight module of the present embodiment and the direct type Mini-LED backlight module of embodiment 6 will be described below, and the details of the similarities are not repeated herein. In this embodiment, an optical film set 300 adopted in the direct type Mini-LED backlight module is formed by sequentially compounding a diffusion film 301, a transflective film 302 and a quantum dot film 303, and the specific structure is shown in fig. 15 and 16

The direct type Mini-LED backlight module provided in this embodiment is subjected to a brightness test, and the test results are shown in table 7, wherein the minimum value of the ratio of the brightness values of the eight test points P1-P8 to the brightness value of the central test point P0 represents the brightness uniformity of the product to be tested. The minimum value of the brightness of the direct type Mini-LED backlight module of the embodiment appears at P8, the value is 13487nit, and the brightness uniformity is calculated according to P8/P0, and the value is 98%.

Table 7 brightness test data of direct type Mini-LED backlight module provided in this embodiment

Example 8

The structure of the direct type Mini-LED backlight module provided in this embodiment is shown in fig. 17 and 18. Only the differences between this embodiment and embodiment 6 will be described below, and the descriptions of the similarities will be omitted.

An optical adhesive layer is arranged between the Mini-LED light source 101 and the reflection cover 200, the optical adhesive layer is attached to the surface of the PCB substrate 100 and covers the Mini-LED light source 101, so that a Fresnel lens is formed above the Mini-LED light source 101, and the lower opening of each reflection cup structure 201 is attached to the optical adhesive layer, so that the Mini-LED light source 101 and the reflection cover 200 are integrally packaged, adhered and fixed by the optical adhesive layer. The fresnel lens with the optical glue layer formed above the Mini-LED light sources 101 causes light near the optical axis of the Mini-LED light sources 101 to be reflected and redirected in a higher proportion.

Example 9

Fig. 19 is a schematic view illustrating the structure and optical principle of the diffusion film 301 and the reflective cover 200 of the direct type Mini-LED backlight module according to this embodiment. Only the differences between this embodiment and embodiment 6 will be described below, and the descriptions of the similarities will be omitted.

A plurality of microlens structures 3011 are disposed on the light-emitting side and the light-entering side of the diffusion film 301, respectively, so that the diffusion film 301 has a biconcave lens-like structure in which the light-emitting side and the light-entering side are both recessed toward the inside of the diffusion film 301. The size of the microlens structure 3011 near the optical axis of the Mini-LED light source 101 is larger than the size of the microlens structure 3011 away from the optical axis of the Mini-LED light source 101. The biconcave lens-like microlens structure 3011 has a light-gathering effect, so that a uniformly diffused surface light source is focused in a viewing angle direction, and the brightness is improved.

While the invention has been described above with reference to certain embodiments, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, the various features of the various embodiments of the present disclosure may be used in any combination, provided that there is no structural conflict, and the combination is not exhaustively described in this specification for brevity and resource conservation. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. The utility model provides a straight following formula Mini-LED backlight unit that light-emitting is even which characterized in that:

the LED backlight module comprises a PCB substrate, a plurality of Mini-LED light sources, a reflector and an optical diaphragm set, wherein the Mini-LED light sources are arranged on the surface of the PCB substrate from bottom to top;

the optical diaphragm group comprises at least one diffusion diaphragm, the diffusion diaphragm is attached to the reflection cover, and a plurality of micro-lens structures are arranged on the diffusion diaphragm and are periodically distributed corresponding to each reflection cup structure;

and taking the distance between the lower surface of the diffusion film and the upper surface of the PCB substrate as H, and taking the minimum distance value of the adjacent Mini-LED light sources as P, wherein H: P is 1: 1-1: 7.

2. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 1, wherein: and taking the maximum distance between the adjacent Mini-LED light sources as PF, and H: PF is 1: 2.

3. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 1, wherein: with the diffusion diaphragm orientation the side of PCB base plate is the income light side of diffusion diaphragm, with the side of diffusion diaphragm back to the income light side is the light-emitting side of diffusion diaphragm, the microlens structure set up in the light-emitting side, it does not have to go into the light side the microlens structure.

4. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 3, wherein: the ratio of the height of the micro-lens structure to the thickness of the diffusion membrane is 1:6 to 5: 6.

5. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 4, wherein: the ratio of the height of the micro-lens structure to the thickness of the diffusion membrane is 1: 3.

6. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 1, wherein: the diameter ratio of the micro-lens structure to the upper opening of the reflecting cup structure is less than 1/2.

7. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 3, wherein:

the micro-lens structures arranged on the diffusion film are correspondingly distributed right above each reflecting cup structure;

the micro lens structures are periodically distributed along the optical axis of the Mini-LED light source arranged in the corresponding reflecting cup, and the distribution density of the micro lens structures is reduced in a radiation mode by taking the optical axis as the center.

8. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 7, wherein:

the micro lens structure is concave towards the inner part of the optical diaphragm, and in a plurality of micro lens structures corresponding to the same reflecting cup structure, the slope of the concave inclined plane of the micro lens structure is increased along with the reduction of the distance between the micro lens structure and the optical axis.

9. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 8, wherein: the micro-lens structure is in a plane symmetrical structure.

10. The direct type Mini-LED backlight module with uniform light emission as claimed in claim 1, wherein:

the PCB substrate and the reflecting cover are fixedly bonded through an optical adhesive layer;

the lower opening of each reflecting cup structure is attached to the optical adhesive layer;

the optical adhesive layer is attached to the surface of the PCB substrate and covers the Mini-LED light source, so that a Fresnel lens is formed above the Mini-LED light source.