CN112505965A

CN112505965A - Backlight module and display device

Info

Publication number: CN112505965A
Application number: CN202011391245.3A
Authority: CN
Inventors: 王园英; 楚艳坤
Original assignee: Xiamen Tianma Microelectronics Co Ltd
Current assignee: Xiamen Tianma Microelectronics Co Ltd
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2021-03-16

Abstract

The invention relates to a backlight module and a display device, wherein the backlight module comprises: the optical element comprises a first membrane, a second membrane and a third membrane, wherein the first membrane, the second membrane and the third membrane are oppositely arranged, the third membrane is positioned between the first membrane and the second membrane, and the first membrane is positioned on the light-emitting side of the backlight module; a plurality of first convex parts distributed at intervals are arranged on one side of the first diaphragm, which is far away from the third diaphragm, the first convex parts comprise first inclined surfaces, and a first included angle is formed between the first inclined surfaces and a plane where the third diaphragm is located; a plurality of second convex parts which are continuously distributed are arranged on one side, away from the third membrane, of the second membrane, each second convex part comprises a second inclined surface, and a second included angle is formed between each second inclined surface and the plane where the third membrane is located; the refractive indexes of the first membrane and the second membrane are larger than that of the third membrane; the backlight source is arranged corresponding to the first membrane, and at least part of light emitted by the backlight source can enter the first membrane. The backlight module can improve the dynamic contrast of the displayed image.

Description

Backlight module and display device

Technical Field

The invention relates to the technical field of display, in particular to a backlight module and a display device.

Background

With the development of Liquid Crystal Display technology, Liquid Crystal Display panels (LCDs) have been widely used in Display devices such as mobile phones and tablet computers. The liquid crystal display panel does not emit light, and the backlight provided by the backlight module is needed to be used for image display.

Because the light emitted by the backlight source of the backlight module is relatively divergent, the light between the partitions corresponding to the display image of the LCD panel is easily interfered, and in order to improve the dynamic contrast of the display image of the LCD panel, the backlight module needs to be designed for Local dimming (Local dimming), so that the backlight source can adjust the brightness of different degrees in the corresponding areas according to different brightness degrees of the display image of the LCD panel.

Disclosure of Invention

The invention aims to provide a backlight module and a display device, wherein the backlight module can convert stray light emitted by a backlight source into near-collimated light for emitting, and reduce crosstalk among light sources.

In one aspect, the present invention provides a backlight module, including: the optical element comprises a first membrane, a second membrane and a third membrane, wherein the first membrane, the second membrane and the third membrane are oppositely arranged, the third membrane is positioned between the first membrane and the second membrane, and the first membrane is positioned on the light-emitting side of the backlight module; a plurality of first convex parts distributed at intervals are arranged on one side, away from the third diaphragm, of the first diaphragm, each first convex part comprises a first inclined surface, and a first included angle theta 1 is formed between each first inclined surface and a plane where the third diaphragm is located; a plurality of second convex parts which are continuously distributed are arranged on one side, away from the third diaphragm, of the second diaphragm, each second convex part comprises a second inclined surface, and a second included angle theta 2 is formed between each second inclined surface and the plane where the third diaphragm is located; the refractive indexes of the first membrane and the second membrane are larger than that of the third membrane; the backlight source is arranged corresponding to the first membrane, and at least part of light emitted by the backlight source can enter the first membrane.

In another aspect, the present invention provides a display device, including the backlight module as described above.

The invention provides a backlight module and a display device, wherein the backlight module comprises a first membrane, a third membrane and a second membrane which are sequentially stacked, the first membrane is positioned on the light-emitting side of the backlight module, and the refractive indexes of the first membrane and the second membrane are larger than that of the third membrane; one side of the first membrane far away from the third membrane is provided with a plurality of first convex parts which are distributed at intervals, each first convex part comprises a first inclined plane, one side of the second membrane far away from the third membrane is provided with a plurality of second convex parts which are continuously distributed, each second convex part comprises a second inclined plane, the backlight source is arranged corresponding to the first membrane, at least part of light emitted by the backlight source can enter the first membrane, so that stray light emitted by the backlight source of the backlight module can be converted into near-collimated light to be emitted to the display panel, crosstalk between the backlight sources is reduced, and the dynamic contrast of a display image is improved.

Drawings

Features, advantages and technical effects of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, like parts are provided with like reference numerals. The figures are not drawn to scale.

Fig. 1 is a schematic top view illustrating a display device according to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of the display device of FIG. 1 along the A-A direction;

FIG. 3 is a schematic top view of the backlight and the optical element in the display device shown in FIG. 1;

FIG. 4 is a schematic diagram of the light path of the backlight propagating in the optical element in the display device shown in FIG. 2;

fig. 5 is a partially enlarged schematic view of a region B in fig. 4;

FIG. 6 is a schematic diagram illustrating the path of light emitted by a backlight source exiting a first film of an optical element;

fig. 7 is a schematic cross-sectional view of a display device according to an embodiment of the present invention along the direction a-a;

FIG. 8 is a schematic top view of a backlight and an optical element in the display device shown in FIG. 1;

FIG. 9 is a schematic top view of another backlight and optical elements in the display device shown in FIG. 1;

fig. 10 is a schematic diagram showing an optical path of a backlight propagating in an optical element in the display device shown in fig. 7.

Detailed Description

Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. In the drawings and the following description, at least some well-known structures and techniques have not been shown in detail in order to avoid unnecessarily obscuring the present invention; also, the dimensions of some of the structures may be exaggerated for clarity. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The following description is given with reference to the orientation words as shown in the drawings, and is not intended to limit the specific structure of the present invention. In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "mounted" and "connected" are to be interpreted broadly, e.g., as being either fixedly connected, detachably connected, or integrally connected; can be directly connected or indirectly connected. The specific meaning of the above terms in the present invention can be understood as appropriate to those of ordinary skill in the art.

The LCD generally includes an LCD panel and a backlight module, the LCD panel displays images by controlling the rotation or deflection angle of the liquid crystal, the backlight module is responsible for providing light source to the LCD panel for the LCD panel to display images, and the lighting effect of the backlight module directly affects the visual effect of the LCD.

The light emitted by the backlight source of the backlight module is generally characterized by a lambertian light source, that is, the backlight source is an isotropic light source, the brightness of the isotropic light source is uniform in all directions, and the brightness perceived by human eyes viewing the lambertian light source in any direction is the same. Therefore, crosstalk easily occurs between the backlight source corresponding to the display frame of the backlight module and the LCD panel, which causes the phenomena of reduced dynamic contrast and reduced brightness of the display frame.

In view of this, embodiments of the present invention provide a display device, which can convert stray light emitted by a backlight into near-collimated light for emission, and reduce crosstalk between light sources, so as to improve dynamic contrast of a display screen of a display panel.

Fig. 1 is a schematic top view illustrating a display device according to an embodiment of the present invention, and fig. 2 is a schematic cross-sectional view of the display device in fig. 1 along a direction a-a.

Referring to fig. 1 and fig. 2 together, an embodiment of the invention provides a display device, which includes a display panel 20, a backlight module 10 and a cover plate 30. The cover plate 30 may be made of transparent glass or Polycarbonate (PC) material, which is convenient for light to transmit through. The display panel 20 is a liquid crystal display panel, and has a display area AA and a non-display area NA, wherein the non-display area NA at least partially surrounds the display area AA. The light emitting surface of the backlight module 10 faces the display panel 20 for providing light to the display panel 20.

The display panel 20 generally includes an array substrate 21, a color filter substrate 23, and a liquid crystal layer 22 disposed between the array substrate 21 and the color filter substrate 23, wherein the liquid crystal layer 22 includes a plurality of liquid crystal molecules.

The array substrate 21 may include a transparent insulating substrate (e.g., glass) and a plurality of thin film transistors, data lines, gate lines, pixel electrodes, common electrodes, etc., formed on the insulating substrate. The data line is connected to a source terminal of the thin film transistor, the gate line is connected to a gate terminal of the thin film transistor, and the pixel electrode formed of a transparent conductive material (e.g., indium tin oxide ITO) is connected to a drain terminal of the thin film transistor. The common electrode is formed of a transparent conductive material such as indium tin oxide ITO and indium zinc oxide IZO.

The color filter substrate 23 may include a transparent insulating substrate, a color filter formed on the insulating substrate, and the like. The color filter may include a color filter of a plurality of colors, for example, red, green, and blue. . The common electrode may also be positioned in the color filter substrate 23.

The liquid crystal layer 22 of the display panel 20 is held between the color film substrate 23 and the array substrate 21, and different voltages are applied to the pixel electrodes and the common electrode to generate an electric field to drive the liquid crystal molecules to rotate so as to display an image.

The backlight module 10 may be a side-in type backlight module, including: bottom frame 5, gluey frame 4, backlight 2 and optical element 1.

The bottom frame 5 has an accommodating space for accommodating the optical element 1 and the rubber frame 4, and the material of the bottom frame 5 may be a metal material, such as an iron plate, a steel plate, an aluminum alloy plate, or a galvanized steel, or a plastic material, such as Polycarbonate (PC), depending on the specific type of the display device.

The rubber frame 4 is used for supporting the flexible circuit board 2a of the backlight source 2, and a groove 41 for accommodating the backlight source 2 is arranged on the rubber frame 4. The rubber frame 4 is usually made of resin materials and has good elasticity, and in the transportation and use processes of the backlight module 10, the rubber frame 4 can provide good buffer effect for the backlight source 2, the optical element 1 and other structures, and prevent the damage of each part due to the direct impact of the bottom frame 5. Alternatively, the rubber frame 4 and the bottom frame 5 may be adhered together by a double-sided tape after being separately manufactured. Alternatively, after the bottom frame 5 is formed by punching, the bottom frame can be integrally injection-molded with the rubber frame 4 as an insert.

The backlight 2 is disposed at a side portion of the optical element 1, the backlight 2 is an isotropic light source, and stray light emitted by the backlight 2 passes through the optical element 1 and then can be emitted to the display panel 20 as near-collimated light, so that dynamic contrast of a display screen is improved, and quality of the display screen is improved.

The specific structure and operation of the optical element 1 will be described in detail below with reference to the accompanying drawings.

Fig. 3 is a schematic plan view showing a backlight and an optical element in the display device shown in fig. 1, fig. 4 is a schematic view showing an optical path of the backlight propagating through the optical element in the display device shown in fig. 2, and fig. 5 is a schematic view showing a partially enlarged structure of a region B in fig. 4.

Referring to fig. 3 and 4, the optical element 1 includes a first film 11, a second film 12 and a third film 13 between the first film 11 and the second film 12.

The first film 11 is located on the light emitting side of the backlight module, a plurality of first protrusions 111 are arranged on one side, away from the third film 13, of the first film 11, the first protrusions 111 include a first inclined surface F1, and a first included angle θ 1 is formed between the first inclined surface F1 and the plane where the third film 13 is located.

One side of the second diaphragm 12, which is far away from the third diaphragm 13, is provided with a plurality of second protrusions 121 that are continuously distributed, each second protrusion 121 includes a second inclined surface F2, and a second included angle θ 2 is formed between the second inclined surface F2 and a plane where the third diaphragm 13 is located. Wherein the refractive index of the first and

second diaphragms

11 and 12 is greater than the refractive index of the third diaphragm 13.

The first film 11, the second film 12 and the third film 13 are made of transparent materials, so that light can penetrate through the films conveniently. Alternatively, the first membrane 11 and the second membrane 12 may be made of Polymethyl methacrylate (PMMA) or Polycarbonate (PC), and the third membrane 13 may be made of Polytetrafluoroethylene (PTFE) or low refractive index glue.

The backlight 2 is disposed corresponding to the first film 11, and at least a part of light emitted from the backlight 2 can enter the first film 11. The backlight module 10 may be a side-in type backlight module, and the backlight source 2 is disposed on one side of the first film 11 of the optical element 1 along a first direction X, where the first direction X intersects with the second direction Y. Optionally, the first direction X and the second direction Y are perpendicular to each other, so that the processing difficulty of the optical element 1 is reduced.

The backlight sources 2 may be point-shaped light sources, and the plurality of backlight sources 2 are arranged in a stripe shape along the second direction Y. The point-like light sources are for example Light Emitting Diodes (LEDs), which have a better color reproducibility, a longer lifetime and less power consumption. The single LED is a point light source, and a plurality of LEDs can be arranged in a straight line at preset intervals to form a linear light source.

The backlight 2 may also be a line light source, the backlight 2 extending in the second direction Y. The linear light source is, for example, a Cold Cathode Fluorescent Lamp (CCFL), and the CCFL is a linear light source, and has low power consumption and can provide bright white light.

As shown in fig. 4, the backlight 2 is a lambertian light source and has an isotropic characteristic. At least part of the light emitted by the backlight 2 enters the first film 11 of the optical element 1 along one side of the first direction X. Since the refractive index of the first diaphragm 11 is greater than that of the third diaphragm 13, when the incident light entering from the first diaphragm 11 reaches the interface between the first diaphragm 11 and the third diaphragm 13, a part of the light having an incident angle greater than the critical angle will be totally reflected at the interface. The light totally reflected reaches the first inclined surface F1 of the first protrusion 111 at the incident angle α, is totally reflected again, reaches the interface between the first film 11 and the third film 13 again at the incident angle β, is refracted, and enters the third film 13 at the refraction angle γ.

As shown in fig. 5, since the refractive index of the second film sheet 12 is larger than that of the third film sheet 13, the refracted light reaches the interface between the third film sheet 13 and the second film sheet 12 at the incident angle γ, and is refracted to enter the second film sheet 12, and the refraction angle is ∈. The refracted light then reaches the second inclined surface F2 of the second protrusion 121 at the incident angle ω, and the light totally reflected enters the third film 13 and the first film 11 in this order from the second film 12 at an angle perpendicular to the plane of the third film 13, and finally exits from the first protrusion 111 side. Since the first inclined surface F1 and the plane of the third film 13 form the first included angle θ 1, the light emitted from the first inclined surface F1 is approximately collimated.

The light emitted from the backlight 2 is transmitted in the optical element 1 in the entire optical path, assuming that the refractive index of the first film 11 and the second film 12 is n_HThe refractive index of the third film 13 is n_LFrom the law of refraction, one can obtain: n is_H×sinβ＝n_L×sinγ。

In order for a light ray to reach the interface between the first and

third membranes

11, 13 at an angle of incidence β and to refract into the third membrane 13, the angle of incidence β needs to be less than the critical angle, i.e.:

similarly, in order to avoid light loss, total reflection also occurs when light propagates through the second film 12 into the air, so

Where n0 is the refractive index of air, n0 is typically 1.

According to n_H×sinβ＝n_L×sinγ＝n_HX sin ∈, and β ═ ε ═ 2 ω.

When 90 ° - θ 2+ ω is 90 °, ω is θ 2.

Therefore, the value range of the second included angle θ 2 between the second inclined surface F2 of the second protrusion 121 of the second diaphragm 12 and the plane where the third diaphragm 13 is located is:

arcsin(n0/n_H)≤θ2<0.5×arcsin(n_L/n_H)。

alternatively, the refractive index n of the first and

second films

11 and 12_H1.3 to 2.0, refractive index n of the third film 13_L1.0 to 1.9. When n is_H＝1.49，n_LWhen the value is 1.485, θ 2 is 47.5 °.

As can be seen from the foregoing description, the light refracted and entering the second film 12 reaches the second inclined surface F2 of the second convex portion 121 at the incident angle ω, and is totally reflected. In order to improve the reflectivity, optionally, a side of the second membrane 12 away from the third membrane 13 is coated with a reflective material, and the value range of the second included angle θ 2 may be: theta 2<0.5×arcsin(n_L/n_H)。

Fig. 6 is a schematic diagram illustrating the light path of light emitted from the backlight source exiting the first film of the optical element.

As shown in fig. 6, when the light rays totally reflected enter the third film 13 and the first film 11 in this order from the second film 12 at an angle substantially perpendicular to the plane of the third film 13 and finally exit from the first inclined surface F1 of the first protrusion 111, it can be obtained according to the law of refraction:

n_H×sinθ1＝n₀and x sin θ t, where θ t is an exit angle of the exit light of the backlight module 10.

The collimation of the emergent ray can be represented by (θ t- θ 1), and if the collimation is to be ensured, the target emergent angle θ target of the emergent ray is greater than or equal to (θ t- θ 1), so that a first included angle θ 1 between the first inclined plane F1 and the plane where the third diaphragm 13 is located satisfies the following condition:

sinθ1/(sinθ1+θt))≥n0/nH。

through analog simulation analysis, when the value range of the first included angle theta 1 is theta 1 not more than 5 degrees, the emergent light of the optical element 1 can narrow the light shape, the light distribution is concentrated and uniform, and the collimation is good.

Therefore, in the embodiment of the present invention, light emitted from the backlight 2 of the backlight module 10 sequentially passes through the first film 11, the third film 13, and the second film 12 of the optical element 1, and then sequentially passes through the second film 12, the third film 13, and the first film 11 to be emitted to the display panel 20, and the emitted light is approximately perpendicular to the plane where the third film 13 is located. That is, stray light emitted from the backlight 2 propagates through the optical element 1 and exits to the display panel 20 as approximately collimated light.

Referring again to fig. 3 and 4, in some embodiments, the first protrusions 111 of the first diaphragm 11 are spaced apart along the first direction X, each first protrusion 111 extends along the second direction Y, the second protrusions 121 of the second diaphragm 12 are continuously distributed along the first direction X, and each second protrusion 121 extends along the second direction Y.

Further, on the first diaphragm 11, a flat portion 112 is provided between adjacent first convex portions 111, and the flat portion 112 is parallel to the plane of the third diaphragm 13.

When the light emitted from the backlight 2 reaches the second inclined surface F2 of the second protrusion 121 of the second film 12 and is totally reflected, if the light totally reflected from the second inclined surface F2 exits from the first inclined surface F1 of the first film 11, the first inclined surface F1 and the plane of the third film 13 form a first included angle θ 1, so the exiting light is approximately collimated. If the light totally reflected from the second inclined surface F2 exits from the flat portion 112 of the first film 11, the exiting light is collimated light because the flat portion 112 is parallel to the plane of the third film 13. Thereby, the collimated light and the approximately collimated light are emitted alternately in the first direction X in the whole plane of the first film 11, and the approximately collimated light is the approximately collimated light as a whole.

Therefore, when the backlight sources 2 are point-like light sources, in the plurality of backlight sources 2 extending in the second direction Y and arranged in a stripe shape, stray light emitted by each backlight source 2 is emitted as approximately collimated light after being transmitted in the optical element 1, so that crosstalk between the backlight sources 2 is eliminated, and the dynamic contrast of a display picture is improved. When the backlight source 2 is a linear light source extending along the second direction Y, stray light emitted from each segment of the backlight source 2 is emitted as approximately collimated light after propagating in the optical element 1, so that crosstalk between segments of the backlight source 2 is eliminated, and the dynamic contrast of a display screen is improved.

In some embodiments, the backlight 2 is below the plane of the flat portion 112. Since the light emitted from the backlight 2 is isotropic stray light, the backlight 2 is lower than the plane where the flat portion 112 is located, so that the light emitted from the backlight 2 enters the optical element 1 as much as possible, and the light transmittance of the light entering the optical element 1 can be improved.

In some embodiments, as shown in fig. 2, the backlight module 10 further includes a light shielding member 6, the light shielding member 6 is disposed on a side of the flexible circuit board 2a of the backlight 2 facing away from the backlight 2, and an orthographic projection of the light shielding member 6 on the bottom frame 5 covers the orthographic projection of the flexible circuit board 2a and a portion of the optical element 1 on the bottom frame 5. A portion of the optical element 1 refers to a portion of the optical element 1 corresponding to the non-display area NA of the display panel 20. The light-shielding member 6 is provided in such a manner as to prevent light emitted from the backlight 12 from leaking out from the gap between the optical element 1 and the backlight 2 to cause light leakage.

In some embodiments, as shown in fig. 2, the backlight module 10 further includes a reflector 3, and the reflector 3 is disposed between the optical element 1 and the bottom frame 5. The reflecting member 3 is made of a highly reflective material such as polyethylene terephthalate (PET), Polycarbonate (PC), and Polystyrene (PS). The reflector 3 is disposed on a side of the optical element 1 facing away from the display panel 20. When the visible light emitted by the backlight source 2 is emitted through the optical element 1, part of the light is led out from one side of the optical element 1 departing from the display panel 20, and the light led out from the display panel 20 can be reflected to the optical element 1 again by the reflecting member 3, so that the backlight brightness of the backlight module 10 is enhanced, and the utilization rate of the backlight source 2 is improved.

It will be appreciated that the reflector 3 may replace the reflective material applied to the side of the second membrane 12 of the optical element 1 remote from the third membrane 13. In addition, the reflective material coated on the side of the second film 12 of the optical element 1 far from the third film 13 and the reflector 3 disposed between the optical element 1 and the bottom frame 5 can further improve the reflectivity of the light of the backlight module 10.

In some embodiments, as shown in fig. 2, the backlight module 10 further includes other optical films disposed on the optical element 1, and the optical films may include, for example, a lower diffusion film, a lower brightness enhancement film, an upper brightness enhancement film and an upper diffusion film which are stacked from bottom to top, and a prism structure is disposed on a light emitting surface of at least one of the lower brightness enhancement film and the upper brightness enhancement film, so that light emitted from the optical element 1 generates a condensing effect, thereby improving brightness of the backlight module 10 within a specific viewing angle range.

In some embodiments, a first polarizer 24 is further disposed between the display panel 20 and the backlight module 10, and a second polarizer 24 is further disposed between the display panel 20 and the cover 30. The first and

second polarizers

24 and 25 may polarize incident light entering the display panel 20 to allow transmission of light vibrating in only one direction.

Fig. 7 is a schematic cross-sectional view of another display device provided according to an embodiment of the invention along a-a direction, fig. 8 is a schematic top-view structure of one of the backlights and the optical element in the display device shown in fig. 1, and fig. 9 is a schematic top-view structure of the other of the backlights and the optical element in the display device shown in fig. 1.

Referring to fig. 7 to 9, an embodiment of the invention further provides a display device, which has a structure similar to that of the display device shown in fig. 2, except that the backlight module 10 is a direct-type backlight module, and the backlight source 2 and the optical element 1 have different structures and optical paths.

In particular, the backlight 2 may be a point-like light source, such as a Light Emitting Diode (LED), which has better color reproducibility, longer lifetime, and less power consumption. The backlight 2 may also be a linear light source extending in the second direction Y, such as a CCFL, which consumes less power and can provide bright white light. The number of the optical elements 1 is plural, and the plural optical elements 1 are distributed in an array along the first direction X and the second direction Y.

As shown in fig. 8, when the backlight 2 is an LED, in each optical element 1, one edge of the first film 11 along the first direction X is provided with a mounting groove 113, and the backlight 2 is disposed in the mounting groove 113. The plurality of first protrusions 111 of the first diaphragm 11 and the plurality of second protrusions 121 of the second diaphragm 12 are symmetrically disposed at both sides of the mounting groove 113 in the second direction Y.

As shown in fig. 9, when the backlight 2 is a CCFL, the mounting groove 113 is a strip-shaped groove extending in the first direction X; the plurality of first protrusions 111 of the first diaphragm 11 are symmetrically arranged at both sides of the mounting groove 113; the plurality of second protrusions 121 of the second diaphragm 12 are symmetrically disposed at both sides of the mounting groove 113.

In addition, the first protrusions 111 of the first diaphragm 11 are spaced apart along the first direction X, each first protrusion 111 extends along the second direction Y, the second protrusions 121 of the second diaphragm 12 are continuously distributed along the first direction X, and each second protrusion 121 extends along the second direction Y. On the first diaphragm 11, a flat portion 112 is provided between adjacent first convex portions 111, and the flat portion 112 is parallel to the plane of the third diaphragm 13. Optionally, the backlight 2 is lower than the plane of the flat portion 112, so that the light emitted by the backlight 2 enters the optical element 1 as much as possible, and the light transmittance of the light entering the optical element 1 is improved.

Fig. 10 is a schematic diagram showing an optical path of a backlight propagating in an optical element in the display device shown in fig. 7. As shown in fig. 10, the entire optical path of the light emitted from the backlight 2 propagating in each optical element 1 is as follows:

at least part of the light emitted from the backlight 2 enters the first film 11 of the optical element 1 on both sides of the mounting groove 113 in the second direction Y, respectively. On each side of the mounting groove 113 in the second direction Y, since the refractive index of the first film sheet 11 is greater than that of the third film sheet 13, the light entering from the first film sheet 11 reaches the first inclined surface F1 of the first protrusion 111 at the incident angle α, and then is totally reflected, and reaches the interface between the first film sheet 11 and the third film sheet 13 at the incident angle β, a part of the light will enter the third film sheet 13 after being refracted at the interface, and the refraction angle γ is.

Since the refractive index of the second membrane 12 is greater than that of the third membrane 13, the refracted light beam will be refracted to enter the second membrane 12 at an incident angle γ when reaching the interface between the third membrane 13 and the second membrane 12, and the refraction angle is ∈. The refracted light then reaches the second inclined surface F2 of the second protrusion 121 at the incident angle ω, and the light totally reflected enters the third film 13 and the first film 11 in this order from the second film 12 at an angle perpendicular to the plane of the third film 13, and finally exits from the first protrusion 111 side.

When the light emitted from the backlight 2 reaches the second inclined surface F2 of the second protrusion 121 of the second film 12 and is totally reflected, if the light totally reflected from the second inclined surface F2 exits from the first inclined surface F1 of the first film 11, the first inclined surface F1 and the plane of the third film 13 form a first included angle θ 1, so the exiting light is approximately collimated. If the light totally reflected from the second inclined surface F2 exits from the flat portion 112 of the first film 11, the exiting light is collimated light because the flat portion 112 is parallel to the plane of the third film 13. Therefore, the stray light emitted by each backlight source 2 is emitted from the mounting groove 113 along the two sides of the second direction Y, and the collimated light and the approximately collimated light are emitted in a staggered manner along the second direction Y. The stray light emitted from the plurality of backlights 2 propagates through the plurality of optical elements 1, and exits to the display panel 20 as approximately collimated light on the whole in a plane formed by the first direction X and the second direction Y.

The values of the first included angle θ 1 between the first inclined surface F1 and the plane where the third film 13 is located, and the value of the second included angle θ 2 between the second inclined surface F2 and the plane where the third film 13 is located are similar to the values of the corresponding parameters in the optical element 1 in the lateral backlight module, and are not described again.

While the invention has been described with reference to a preferred embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. 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. A backlight module, comprising:

the optical element comprises a first membrane, a second membrane and a third membrane, wherein the first membrane, the second membrane and the third membrane are oppositely arranged, the third membrane is positioned between the first membrane and the second membrane, and the first membrane is positioned on the light-emitting side of the backlight module; a plurality of first convex parts distributed at intervals are arranged on one side, away from the third diaphragm, of the first diaphragm, each first convex part comprises a first inclined surface, and a first included angle theta 1 is formed between each first inclined surface and a plane where the third diaphragm is located; a plurality of second convex parts which are continuously distributed are arranged on one side, away from the third membrane, of the second membrane, each second convex part comprises a second inclined surface, and a second included angle theta 2 is formed between each second inclined surface and the plane where the third membrane is located; wherein the refractive index of the first and second membranes is greater than the refractive index of the third membrane;

the backlight source is arranged corresponding to the first membrane, and at least part of light emitted by the backlight source can enter the first membrane.

2. The backlight module according to claim 1, wherein a side of the second film sheet away from the third film sheet is coated with a reflective material, and the second included angle θ 2 satisfies the following condition:

θ2<0.5×arcsin(n_L/n_H)；

wherein n is_LIs the refractive index of the third film sheet, n_HIs the refractive index of the first and second diaphragms.

3. A backlight module according to claim 1, wherein the second included angle θ 2 satisfies the following condition:

arcsin(n0/n_H)≤θ2<0.5×arcsin(n_L/n_H)；

where n0 is the refractive index of air.

4. The backlight module as claimed in claim 1, wherein the first included angle θ 1 satisfies the following condition:

and θ t is the emergent angle of the emergent light of the backlight module.

5. The backlight module according to claim 4, wherein the first included angle θ 1 has a value range of: theta 1 is less than or equal to 5 degrees.

6. The backlight module as claimed in claim 1, wherein the refractive index n of the first film and the second film is_H1.3 to 2.0, the refractive index n of the third film_L＝1.0～1.9。

7. The backlight module as claimed in claim 1, wherein the first protrusions of the first film are spaced apart along a first direction, each of the first protrusions extends along a second direction, the second protrusions of the second film are continuously distributed along the first direction, each of the second protrusions extends along the second direction, and the first direction intersects the second direction.

8. The backlight module according to claim 7, wherein the backlight source is disposed on one side of the first film of the optical element along the first direction;

the backlight sources are point-shaped light sources, and the plurality of backlight sources are arranged in a strip shape along the second direction;

or, the backlight source is a linear light source, and the backlight source extends along the second direction.

9. The backlight module according to claim 7, wherein the number of the optical elements is plural, and the plural optical elements are distributed in an array along the first direction and the second direction;

the backlight source is a point-shaped light source, in each optical element, an installation groove is formed in one side edge of the first membrane along the first direction, and the backlight source is arranged in the installation groove;

or, the backlight source is a linear light source, in each optical element, the first membrane is provided with an installation groove extending along the first direction, and the backlight source is arranged in the installation groove;

the plurality of first convex parts of the first diaphragm and the plurality of second convex parts of the second diaphragm are symmetrically arranged at two sides of the mounting groove along the second direction.

10. The backlight module according to any one of claims 1 to 9, wherein a flat portion is disposed between adjacent first protrusions on the first film, and the flat portion is parallel to a plane of the third film.

11. A backlight module according to claim 10, wherein the backlight source is lower than the plane of the flat portion.

12. A display device, comprising:

a display panel;

the backlight module according to any of claims 1 to 11, wherein a light emitting surface of the backlight module faces the display panel for providing a light source to the display panel.