Backlight module and liquid crystal display device

Abstract

The utility model relates to the technical field of display, in particular to a backlight module and a liquid crystal display device. The light guide plate is provided with a light incident surface for receiving light rays of the LED light source and a light emergent surface for emitting the light rays from the light source at an angle phi 1; a first prism structure on the first prism sheet has a second base angle epsilon 2 away from the light source; a second prism structure on the second prism sheet has a fourth base angle theta 2 away from the light source, an included angle delta is formed between the first prism structure and the extension direction of the first prism structure, and the angular bisector of the included angle delta is perpendicular to the arrangement direction of the prism structures; # imgabs0 # imgabs1 # imgabs2 # n1 is the refractive index of the first prismatic lens, and n2 is the refractive index of the second prismatic lens.

Description

Technical Field

[0001] The present application relates to the field of display technology, and in particular to a backlight module and a liquid crystal display device. Background Art

[0002] LCD (Liquid Crystal Display) screens are widely used in various fields, such as mobile phones, tablets, laptops, LCD TVs, car displays, aerospace displays, and navigation displays. For different application fields and environments, users have different requirements for the viewing angle of the display screen. For example, for a display screen with high anti-peeping requirements, the full field angle half-peak width of the light emitted by the display screen is generally required to be around 20° to achieve a relatively narrow field of view display and achieve an anti-peeping effect; if applied to a tablet or laptop, the full field angle half-peak width of the light emitted by the backlight module is generally required to be around 40°, taking into account the light intensity and having a relatively wide field of view display; if applied to a home LCD TV, it will require a larger viewing angle to meet the viewing needs of an average family.

[0003] For example, tablets, laptops, desktop monitors, industrial control monitors and display screens for special applications require that the field of view of the emitted light should not be as narrow as that of a privacy screen, nor as wide as that of a home LCD screen. In the backlight module of this type of display screen, one of the existing practices is to use a combination of a light guide plate and two prism films to meet the relevant requirements. In this type of backlight module, the core components are two prism sheets. The characteristics of the prism sheets directly determine the light emission characteristics of the backlight module, such as the peak light emission angle and the central field of view brightness. The light emission characteristics of the backlight module are very sensitive to the structure of the prism sheet. In actual production, the refractive index of the prism sheet used has a slight change, such as a change from 1.51 to 1.53, which will cause the light emission peak to deviate by about 4°. Therefore, how to quickly determine other optimal parameters based on the differences in raw material batches and the angle tolerance of the mold, and make the product have both ideal optical properties and reduce the cost of trial and error, has become an important research topic for each backlight module manufacturer. In addition, how to quickly determine the structural parameters of each component in the backlight module so that the backlight module can emit light at a desired peak angle is also a topic that has been studied in the field. Summary of the invention

[0004] The purpose of the present application is to solve at least one of the above technical problems and to provide a backlight module and a liquid crystal display device.

[0005] In a first aspect, the present application provides a backlight module, comprising:

[0006] A light guide plate having a light incident surface and a light emitting surface;

[0007] An LED light source is arranged on the light incident surface side of the light guide plate and emits light toward the light incident surface, and the light emitting surface is configured to emit the light from the LED light source at an emission angle Φ1;

[0008] A first prism sheet, comprising a first light-transmitting surface facing the light-emitting surface, a second light-transmitting surface opposite to the first light-transmitting surface, and a plurality of first prism structures arranged along a first direction and extending along a second direction on the second light-transmitting surface, wherein a cross section of the first prism structure perpendicular to the second direction is a first triangle, and the first triangle has a first base angle ε1 close to the LED light source and a second base angle ε2 away from the LED light source in the first direction, wherein the first direction is parallel to a virtual plane defined by the emission angle Φ1;

[0009] A second prism sheet, comprising a third light-transmitting surface facing the second light-transmitting surface, a fourth light-transmitting surface opposite to the third light-transmitting surface, and a plurality of second prism structures arranged along the first direction and extending along a third direction on the fourth light-transmitting surface, wherein a cross section of the second prism structure perpendicular to the third direction is a second triangle, and the second triangle has a third base angle θ1 close to the LED light source and a fourth base angle θ2 far from the LED light source in the first direction, wherein the second direction and the third direction have an included angle δ, 0°≤δ≤24°, and an angle bisector of the included angle δ is perpendicular to the first direction;

[0010] The backlight module is configured to satisfy:

[0011]

[0012] in, n1 is the refractive index of the first prism sheet, and n2 is the refractive index of the second prism sheet.

[0013] In some possible implementations,

[0014] In some possible implementations, the first triangle and the second triangle are both isosceles triangles.

[0015] In some possible implementations, the backlight module is configured to satisfy one of the following:

[0016] n1=n2=1.61, 87°≤ε2+θ2≤89°, 45°≤ε2≤56°;

[0017] n1=n2=1.59, 89°≤ε2+θ2≤92°, 46°≤ε2≤56°;

[0018] n1=n2=1.57, 93°≤ε2+θ2≤95°, 47°≤ε2≤56°;

[0019] n1=n2=1.55, 96°≤ε2+θ2≤98°, 48°≤ε2≤56°;

[0020] n1=n2=1.53, 99°≤ε2+θ2≤100°, 50°≤ε2≤56°;

[0021] n1=n2=1.51, 102°≤ε2+θ2≤104°, 52°≤ε2≤56°;

[0022] n1=n2=1.49, 106°≤ε2+θ2≤107°, 53°≤ε2≤56°.

[0023] In some possible implementations, ε2-5°≤ε1≤80°, θ2-5°≤θ1≤90°.

[0024] In some possible implementations, the backlight module is configured to satisfy at least one of the following:

[0025] 8°≤δ≤16°;

[0026] ε2≥θ2, and ε2≥45°;

[0027] 1.49≤n1≤1.61, and 1.49≤n2≤1.61.

[0028] In some possible implementations, ε2-θ2≥2°, and ε2≥45°.

[0029] In some possible implementations, 65°≤Φ1≤80°;

[0030] Preferably, 67°≤Φ1≤74°.

[0031] In some possible implementations, δ=12°, Φ1=70°.

[0032] In a second aspect, the present application proposes a liquid crystal display device, comprising a liquid crystal panel and a backlight module as described in the first aspect.

[0033] According to the backlight module provided in the present application, by optimizing the light output angle of the light guide plate, the crossing angle between the prism sheets, the refractive index of the prism sheets and the value of the corresponding bottom angle in the prism structure, light output at a specific angle between -20° and 20° (including a 0° straight viewing angle) can be achieved with sufficient light output intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present application, rather than limiting the present application.

[0035] Figure 1 1 is a side view schematic diagram of a backlight module provided in an embodiment of the present application, which schematically shows a part of the light path.

[0036] Figure 2 yes Figure 1 A schematic top view of the backlight module is shown.

[0037] Figure 3 yes Figure 1 Schematic diagram of the structure of the first prism sheet.

[0038] Figure 4 yes Figure 1 Schematic diagram of the structure of the second prism sheet.

[0039] Figure 5 yes Figure 1 Schematic diagram of the coordination between the first prism sheet and the second prism sheet.

[0040] Figure 6 yes Figure 1 A schematic structural diagram of the first prism sheet when being observed along the second direction.

[0041] Figure 7 yes Figure 1 A schematic diagram of the structure of the second prism sheet when being observed along a third direction.

[0042] Figure 8 The figure shows the light intensity distribution curve of the backlight module at the vertical viewing angle when ε2 and θ2 take different data pairs.

[0043] Fig. 9 It is a flow chart of a design method of a backlight module in one embodiment of the present application.

[0044] Description of reference numerals:

[0045] DR1-first direction, DR2-second direction, DR3-third direction;

[0046] AX-angle bisector;

[0047] 1-first prism sheet, 11-first prism structure, 1A-first light-transmitting surface, 1B-second light-transmitting surface;

[0048] 2-second prism sheet, 21-second prism structure, 2A-third light-transmitting surface, 2B-fourth light-transmitting surface

[0049] 3-light guide plate, 3A-light incident surface, 3B-bottom surface, 3C-light exit surface;

[0050] 4-Reflective sheet;

[0051] 5- Light source. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the embodiment of the present application will be clearly and completely described below in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, rather than all the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of this application. It can be understood that, in the absence of conflict, some technical means of the various embodiments described herein can be replaced or combined with each other.

[0053] In the description of this application, if there are terms such as "first", "second", etc., they are only used to distinguish the objects described and do not have any order or technical meaning. Therefore, an object defined as "first", "second", etc. may explicitly or implicitly include one or more of the objects, and, for example, the term "first element" itself does not mean the existence of the "second element", and the term "second element" itself does not mean the existence of the "first element". In addition, "one" or "a" and similar words do not indicate a quantity limitation, but rather indicate the existence of at least one, and "multiple" means not less than two.

[0054] In the description of the present application, the terms “including”, “having” indicate the existence of the described features, numbers, operations, elements and / or their combinations, but do not exclude the existence or addition of one or more other features, numbers, operations, elements and / or their combinations.

[0055] In the description of the present application, reference to "one embodiment" or "some embodiments" etc. means that one or more embodiments of the present application include a particular feature, structure or characteristic described in conjunction with the embodiment. Thus, the phrases "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. appearing in different places in the present specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways.

[0056] Figures 1 to 7 The backlight module provided in an embodiment of the present application is shown, and the backlight module includes a light source 5, a light guide plate 3, a reflective sheet 4, a first prism sheet 1 and a second prism sheet 2.

[0057] The light source 5 may be an LED (light-emitting diode), which can generate light directed toward the light incident surface 3A of the light guide plate 3 under the drive of electricity. In this embodiment, the light source 5 is an edge-entry light source 5, which is disposed on the light incident surface 3A side of the light guide plate 3.

[0058] The light guide plate 3 has a light incident surface 3A, a light emitting surface 3C and a bottom surface 3B. The light emitting surface 3C and the bottom surface 3B are arranged opposite to each other in the thickness direction of the light guide plate 3, and a plurality of light guiding microstructures not shown in the figure are formed on the bottom surface 3B. The light incident surface 3A connects the light emitting surface 3C and the bottom surface 3B on one side thereof and is formed into a long rectangle. As a well-known technology, based on the corresponding design of the structure of the light guide plate 3 (for example, the shape of the light guiding microstructure on its bottom surface 3B), the light emitting surface 3C of the light guide plate 3 can emit the light from the light source 5 (that is, the light received from the light incident surface 3A) at a desired emission angle Φ1 (that is, the peak light emission angle of the light guide plate 3, which is the angle formed by the normal of the light emitting surface 3C and the direction with the maximum light intensity in the light intensity distribution, and the angle between the direction with the maximum light intensity in the light intensity distribution and the first direction DR1 described later is 90°-Φ1).

[0059] In the description of this application, the term "exit angle" and similar terms refer to the angle between the incident light and the normal of the corresponding exit surface. Figure 1 and Figure 2 , the vertical direction is the direction perpendicular to the light incident surface 3A, which is consistent with the first direction DR1 described later, and the horizontal direction is the direction parallel to the light incident surface 3A and extending along the length of the light incident surface 3A. Furthermore, the "vertical direction of incidence angle" and similar phrases refer to the incidence angle perpendicular to the direction of the light incident surface 3A - the virtual plane defined by the incidence angle (for example Figure 1 The virtual plane defined by Φ1 or τ2 (the paper plane) is perpendicular to the light incident surface 3A and perpendicular to the light exit surface 3C. The "horizontal emission angle" and similar phrases refer to the emission angle parallel to the light incident surface 3A - the virtual plane defined by the emission angle is parallel to the light incident surface 3A.

[0060] The first prism sheet 1 and the reflective sheet 4 are respectively arranged on opposite sides of the light guide plate 3 in the thickness direction, and the second prism sheet 2 is arranged on the side of the first prism sheet 1 away from the light guide plate 3. Specifically, the first prism sheet 1 is arranged on the light emitting surface 3C side of the light guide plate 3, and the reflective sheet 4 is arranged on the bottom surface 3B side of the light guide plate 3. In this way, the light emitted by the light source 5 and directed to the light incident surface 3A is guided by the light guide plate 3 and most of it is directly emitted from the light emitting surface 3C, and a small part is inevitably transmitted from the bottom surface 3B of the light guide plate 3. After being reflected by the reflective sheet 4, this part of the light transmitted from the bottom surface 3B of the light guide plate 3 returns to the light guide plate 3 from the bottom surface 3B again and is emitted from the light emitting surface 3C and directed to the first prism sheet 1. In this way, the amount of light directed to the first prism sheet 1 can be increased, and thereby the amount of light directed from the first prism sheet 1 to the second prism sheet 2 is increased, thereby improving the light output efficiency of the backlight module.

[0061] In other embodiments, the light transmitted from the bottom surface 3B of the light guide plate 3 accounts for a very small proportion, or the reflective sheet 4 can be omitted in order to save manufacturing costs and reduce the overall thickness of the module.

[0062] The first prism sheet 1 includes a first light-transmitting surface 1A and a second light-transmitting surface 1B arranged opposite to each other in the thickness direction, and a plurality of first prism structures 11 arranged on the second light-transmitting surface 1B, wherein the first light-transmitting surface 1A faces the light-emitting surface 3C of the light guide plate 3, and therefore, the second light-transmitting surface 1B is away from the light-emitting surface 3C of the light guide plate 3. The plurality of first prism structures 11 on the second light-transmitting surface 1B are arranged along the first direction DR1 (also the vertical direction), and each first prism structure 11 extends into a long strip along the second direction DR2. Moreover, the cross section of the first prism structure 11 perpendicular to the second direction DR2 is a triangle, that is, the first prism structure 11 is a long strip of triangular prism structure. For the convenience of explanation, the triangle corresponding to the cross section of the first prism structure 11 is called a first triangle, and the first triangle has a first base angle ε1 close to the light source 5 and a second base angle ε2 away from the light source 5 in the first direction DR1, and a vertex angle away from the first light-transmitting surface 1A in the thickness direction and the reference numeral is omitted. The aforementioned first direction DR1 is a direction perpendicular to the light incident surface 3A of the light guide plate 3 , and therefore, the first direction DR1 may also be referred to as a vertical direction, and correspondingly, the direction parallel to the light incident surface 3A may be referred to as a horizontal direction.

[0063] The second prism sheet 2 is stacked with the first prism sheet 1. In some embodiments, the second prism sheet 2 and the first prism sheet 1 are stacked close to each other, and the two are glued to each other as an inseparable whole. In other embodiments, the second prism sheet 2 and the first prism sheet 1 are two independent elements that can be detached from each other, and the second prism sheet 2 and the first prism sheet 1 are stacked separately from each other, and the space between the two is filled with air or other gas.

[0064] Similar to the first prism sheet 1, the second prism sheet 2 includes a third light-transmitting surface 2A and a fourth light-transmitting surface 2B that are arranged opposite to each other in the thickness direction, and a plurality of second prism structures 21 arranged on the fourth light-transmitting surface 2B, wherein the third light-transmitting surface 2A faces the second light-transmitting surface 1B of the first prism sheet 1, and therefore, the fourth light-transmitting surface 2B is away from the second light-transmitting surface 1B of the first prism sheet 1. The plurality of second prism structures 21 on the fourth light-transmitting surface 2B are arranged along the first direction DR1, and each second prism structure 21 extends along the third direction DR3 into a long strip, wherein the second direction DR2 and the third direction DR3 have an angle δ, and the angle bisector AX of the angle δ is perpendicular to the first direction DR1. Moreover, the cross section of the second prism structure 21 perpendicular to the third direction DR3 is a triangle, that is, the second prism structure 21 is also a long strip of triangular prism structure. For the convenience of explanation, the triangle corresponding to the cross section of the second prism structure 21 is called a second triangle. The second triangle has a third base angle θ1 close to the light source 5 and a fourth base angle θ2 away from the light source 5 in the first direction DR1, and a vertex angle that is away from the third light-transmitting surface 2A in the thickness direction and the figure mark is omitted.

[0065] It can be understood that the first direction DR1 is parallel to the virtual plane defined by the angle Φ1 and is parallel to the light emitting surface 3C.

[0066] Figure 1 is a side view schematic diagram of the backlight module, and is also a schematic diagram of the backlight module when viewed along the extending direction of the angle bisector AX of the included angle δ. Figure 1 The direction of the light is shown schematically. Figure 6 yes Figure 1 A schematic diagram of the first prism sheet 1 when being observed along the second direction DR2, Figure 7 yes Figure 1 Schematic diagram of the first prism sheet 1 in FIG. 1 being observed along the third direction DR3. It can be understood that Figure 1 The angle ε3 in corresponds to Figure 6 The second base angle ε2 in the figure corresponds to the angle θ3 Figure 7 The fourth base angle θ2 in the prism structure 11 is θ2, and because there is an angle δ between the extension direction of the first prism structure 11 (i.e., the second direction DR2) and the extension direction of the second prism structure 21 (i.e., the third direction DR3), and the angle bisector AX of the angle δ is perpendicular to the first direction DR1, it satisfies:

[0067] Please review Figure 1The light emitted by the light source 5 and directed toward the light incident surface 3A is guided by the light guide plate 3 (and the reflective sheet) and then directed toward the light exit surface 3C at an incident angle Φ1 (i.e., the peak incident angle), and then directed toward the first light transmission surface 1A of the first prism sheet 1 at an incident angle Φ1, and then sequentially enters the first prism sheet 1 at a refraction angle γ1, and is directed toward the side surface corresponding to the second bottom angle ε2 of the first prism structure 11 at an incident angle ρ1, and then is directed out from the side surface corresponding to the second bottom angle ε2 of the first prism structure 11 at an incident angle ω1. The light is emitted from the first prism sheet 1 at an exit angle τ1, and then emitted to the third light-transmitting surface 2A of the second prism sheet 2 at an incident angle Φ2 (obviously, Φ2=τ1), and then enters the second prism sheet 2 at a refraction angle γ2 in turn, and is emitted to the side surface corresponding to the fourth bottom angle θ2 of the second prism structure 21 at an incident angle ρ2, and is emitted from the side surface corresponding to the fourth bottom angle θ2 of the second prism structure 21 at an exit angle ω2 (that is, it is emitted from the second prism sheet 2 and the backlight module at an exit angle τ2).

[0068] Assuming that the refractive index of the first prism sheet 1 is n1 and the refractive index of the second prism sheet 2 is n2, the following relationship can be obtained based on the geometric relationship and relevant optical laws:

[0069] n1*sin(γ1)=sin(Φ1);

[0070] ρ1=ε3-r1;

[0071] n1*sin(ρ1)=sin(ω1);

[0072] Φ2=τ1=ε3-ω1;

[0073] n2*sin(γ2)=sin(Φ2);

[0074] ρ2=θ3-γ2;

[0075] n2*sin(ρ2)=sin(ω2);

[0076] τ2=θ3-ω2;

[0077] Based on the above relations, we can get the following two relations:

[0078]

[0079]

[0080] According to the above relationship, the light output angle τ2 (i.e., the peak light output angle, which is also the peak light output angle in the vertical direction) of the backlight module is related to ε2, θ2, Φ1, n1, n2 and δ. Figure 1 The backlight module in the 0° normal field of view emits light, so it must meet The value of is close to 0°. More specifically, when In this case, the backlight module can be regarded as emitting light in the vertical direction with a 0° normal field of view.

[0081] In the description of this application, the positive and negative angles have the following meanings: Figure 1 At the viewing angle shown, the positive sign “+” (usually omitted) represents that the emission direction is in the clockwise direction of the light-emitting normal line, and the negative sign “-” represents that the emission direction is in the counterclockwise direction of the light-emitting normal line.

[0082] For the convenience of explanation, the above relationship It is called formula (1).

[0083] Please refer to Table 1, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.59, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles (that is, ε1=ε2, θ1=θ2) based on the above formula (1).

[0084] Table 1:

[0085]

[0086]

[0087] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 1, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0088] In the above Table 1 and the data tables described later, the so-called double peaks, or double peak phenomenon, refers to the fact that the incident light has two peaks in the vertical field of view. It is understandable that if the double peak phenomenon occurs, the energy of the light emitted by the backlight module cannot be well concentrated, resulting in a decrease in the brightness gain of the central field of view, and a double visual effect of the display screen will appear. Therefore, the occurrence of the double peak phenomenon should be avoided.

[0089] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, some data in Table 1 were selected, that is, ε2 was 54°, 52°, 50°, 48°, 46°, and θ2 was 37.5°, 38.5°, 39.5°, 41.5°, 43.5°, respectively, and ray tracing simulation was performed to obtain the following results: Figure 8 The vertical light intensity distribution curve of the backlight module is shown.

[0090] Depend on Figure 8 Summarizing the data, we can get the following Table 2:

[0091] ε2(°) θ2(°) ε2-θ2(°) Normalized relative brightness τ2(°) FWHM(°) 46 43.5 2.5 0.90 0.7 21.5 48 41.5 7.5 0.90 1 22.1 50 39.5 10.5 0.93 1.1 22.9 52 38.5 13.5 0.96 0.9 22.9 54 37.5 16.5 1 1 23.7

[0092] According to Table 2 above, although matching the appropriate θ2 value for ε2 can make the light emitted in the vertical direction with a 0° field angle, the light intensity of the backlight module will be different when the values ​​of ε2 and θ2 are different. Figure 8 From the ray tracing results and the summary in Table 2, it can be seen that the larger the ε2 value, the larger the difference between ε2-θ2, the stronger the light output intensity of the backlight module, and the full field angle half-peak width FWHM remains basically unchanged. In addition, when ε2-θ2≥2°, the light output intensity of the backlight module is ideal, and the values ​​of ε2 and θ2 can be further optimized according to the needs of the use environment to meet the display needs of different occasions.

[0093] It is necessary to explain that the τ2 value calculated by the theoretical model of formula (1) is based on a single light ray at the peak angle, and the simulation result is based on the statistical results of hundreds of thousands or even millions of light ray tracings, and the data is usually filtered and smoothed. Therefore, there will be a certain deviation between the simulation result and the theoretical value, and generally the difference of about ±2° between the simulation value and the theoretical value is recorded as a normal error, and this phenomenon exists in the following embodiments.

[0094] Next, please refer to Table 3, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.61, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on the above formula (1).

[0095] Table 3:

[0096]

[0097] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 3, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0098] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 3 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width at the full field of view angle remains basically unchanged.

[0099] Next, please refer to Table 4, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.57, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on the above formula (1).

[0100] Table 4:

[0101]

[0102]

[0103] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 4, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0104] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 4 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width at the full field of view angle remains basically unchanged.

[0105] Next, please refer to Table 5, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.55, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on formula (1).

[0106] Table 5:

[0107]

[0108] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 5, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0109] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 5 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width of the full field of view angle remains basically unchanged.

[0110] Next, please refer to Table 6, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.53, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on formula (1).

[0111] Table 6:

[0112]

[0113] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 6, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0114] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 6 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width at the full field of view angle remains basically unchanged.

[0115] Next, please refer to Table 7, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.51, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on formula (1).

[0116] Table 7:

[0117]

[0118] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 7, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0119] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 7 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width at the full field of view angle remains basically unchanged.

[0120] Next, please refer to Table 8, which shows the angle value distribution of the corresponding backlight module light output angle τ2 obtained by changing the values ​​of ε2 and θ2 when n1=n2=1.49, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles, based on formula (1).

[0121] Table 8:

[0122]

[0123] It can be seen that when the values ​​of ε2 and θ2 fall within the range of the gray background in Table 8, the vertical peak light output angle τ2 of the backlight module is around 0° (between -2° and 2°), which can be regarded as the backlight module emitting light in the vertical direction with a 0° normal field of view.

[0124] In order to understand the influence of the values ​​of ε2 and θ2 on the peak light intensity of the backlight module, the inventors selected each pair of data corresponding to the gray background area in Table 8 and performed a ray tracing simulation. Based on the results of the ray tracing, it was found that the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light intensity of the backlight module, and the half-peak width of the full field of view angle remains basically unchanged.

[0125] According to Table 1, Table 3 to Table 8 and the results of ray tracing simulation, it can be seen that when ε2<θ2, although the peak light output angle τ2 of the backlight module can be adjusted to 0° (between -2° and 2°) by selecting appropriate values ​​of ε2 and θ2, when ε2<θ2 or ε2<45°, a double peak phenomenon is likely to occur, and the light output intensity of the backlight module is significantly attenuated. Therefore, in order to avoid the aforementioned problems as much as possible, in the design process of the backlight module, when selecting the values ​​of ε2 and θ2, it is advisable to satisfy the relationship: ε2≥θ2, and ε2≥45°. It is necessary to point out that although the conclusion is drawn under the condition of δ=12° and Φ1=70°, the inventor found through calculation based on formula (1) and ray tracing simulation that the conclusion is also applicable to the case where δ and Φ1 are other angle values ​​(for example, δ is 8°, 9°, 10°, 11°, 13°, 14°, 15° or 16°, and Φ1 is 67°, 68°, 69°, 71°, 72°, 73° or 74°), which will not be elaborated here; on the other hand, the inventor found that even if the refractive indices of the first prism sheet 1 and the second prism sheet 2 are not equal, the aforementioned rule of "the larger the ε2 value, the larger the difference of ε2-θ2, the stronger the light output intensity of the backlight module, and the half-peak width of the full field of view angle remains basically unchanged" also exists. In actual production, the refractive index of the prism can be flexibly set according to demand, and its combination methods are inexhaustible. The following Table 9 shows the values ​​of the parameters related to the backlight module emitting light at a 0° normal field of view in the vertical direction when n1≠n2, δ=12°, Φ1=70°, and the first triangle and the second triangle are both isosceles triangles.

[0126] Table 9:

[0127] n1 n2 ε2 θ2 τ2 1.61 1.55 49° 42° 0.53° 1.61 1.49 49° 46.5° 0.13° 1.59 1.61 50° 40° -0.27° 1.59 1.55 50° 43° 0.22° 1.59 1.49 50° 47° 0.28° 1.57 1.61 51° 40.5° -0.12° 1.57 1.55 51° 44° -0.06° 1.57 1.49 51° 48° 0.03° 1.55 1.61 52° 41° 0.07° 1.55 1.59 52° 42° 0.21° 1.55 1.49 52° 49° -0.19° 1.53 1.61 53° 42° -0.16° 1.53 1.59 53° 43° -0.01° 1.53 1.49 53° 49.5° 0.12° 1.51 1.61 54° 42.5° 0.13° 1.51 1.55 54° 46° 0.29° 1.51 1.49 54° 50.5° -0.01° 1.49 1.61 55° 43.5° -0.01° 1.49 1.55 55° 47° 0.19°

[0128] Furthermore, the data of ε2 and θ2 when the angle value of τ2 is closest to 0° in each of Tables 1, 3 to 8 above are sorted out to obtain the values ​​of ε2 and ε2+θ2 when the refractive indices n1 and n2 (denoted as N, N=n1=n2) are different values, and the following Table 10 is obtained.

[0129] Table 10:

[0130]

[0131]

[0132] From Table 10 and Table 1, Table 3 to Table 8, we can see that:

[0133] When n1=n2=1.61, 87°≤ε2+θ2≤89°, 45°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0134] When n1=n2=1.59, 89°≤ε2+θ2≤92°, 46°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0135] When n1=n2=1.57, 93°≤ε2+θ2≤95°, 47°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0136] When n1=n2=1.55, 96°≤ε2+θ2≤98°, 48°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0137] When n1=n2=1.53, 99°≤ε2+θ2≤100°, 50°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0138] When n1=n2=1.51, 102°≤ε2+θ2≤104°, 52°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0139] When n1=n2=1.49, 106°≤ε2+θ2≤107°, 53°≤ε2≤56°, the backlight module emits light at a normal viewing angle of 0°.

[0140] The range defined by the above data is the range of values ​​when τ2 is closest to 0°. It should be noted that the range defined by the above data is somewhat different from the data in Table 10. The reason is that although the upper and / or lower limits of some of the ranges of values ​​when τ2 is closest to 0° shown in Table 10 have decimals, when actually making products, the design value will be set to an integer through tolerance control. For example, the theoretical value is 60.5°, and 60° or 61° can be used in design, with a tolerance of + / -1°. Therefore, the angle values ​​of ε2 and θ2 are generally rounded, and the accuracy of the corresponding angle values ​​is generally accurate to the single digit. Therefore, the corresponding fluctuation of the numerical range of plus or minus 0.5° in the above conclusion is considered to be able to better achieve τ2 emitting light at a 0° normal field angle, and therefore, when we count the range of values ​​of the sum of ε2+θ2 above, the upper and lower limits of the sum are recorded as reasonably expected integer values. As can be seen from Tables 1, 3 to 8, the areas circled in gray can make τ2 emit light around 0°, and the maximum deviation is within 2°. Therefore, the above summary based on Table 10 only shows the optimal value range of ε2 and θ2. Secondly, the selection of the above optimal values ​​is based on the calculation of the formula, and it is assumed that all parameters of the backlight module are ideal values. When the product is actually made, due to the existence of tolerance, the difference between ε2 and θ2 in the actual production of the product and the above theoretical value within 2° is considered to be a normal deviation.

[0141] Next, please refer to Table 11, which gives the light output angle τ2, normalized relative light output luminance and full field angle half-peak width of the backlight module measured by ray tracing simulation after changing the value of ε1 when n1=n2=1.59, δ=12°, Φ1=70°, ε2=50°, θ1=θ2=40.5°.

[0142] Table 11:

[0143]

[0144]

[0145] Table 12 gives the data of the peak light output angle τ2 in the vertical direction, the normalized relative light output luminance and the full field angle half-width of the backlight module measured by ray tracing simulation after changing the value of θ1 when n1=n2=1.59, δ=12°, Φ1=70°, ε1=ε2=50° and θ2=40.5°.

[0146] Table 12:

[0147]

[0148] Table 13 gives the peak light output angle τ2 in the vertical direction, the normalized relative light output luminance and the full field angle half-width of the backlight module measured by ray tracing simulation when n1=n2=1.59, δ=12°, Φ1=70°, ε2=50° and θ2=40.5° and the values ​​of ε1 and θ1 are changed at the same time.

[0149] Table 13:

[0150]

[0151] It is not difficult to see from Tables 11, 12 and 13 above that, under the premise that other parameters remain unchanged, when the proximal base angle ε1 of the first prism structure 11 changes between 44°-80°, the offset of the peak light output angle τ2 of the backlight module is within 1.5°; when the proximal base angle θ1 of the second prism structure 21 changes from 28°-90°, the offset of the peak light output angle τ2 of the backlight module is also within 1.5°; when other parameters remain unchanged and the values ​​of the proximal base angles ε1 and θ1 of the first prism structure 11 and the second prism structure 21 are increased at the same time, the offset of the peak light output angle τ2 is also within 1.5°.

[0152] In addition, based on optical path analysis and a large number of ray tracing simulations, the inventors found that when the sizes of the far-side bottom angles ε2 and θ2 are fixed, the peak light output angle τ2 of the backlight module is basically not affected by changing the sizes of the near-side bottom angles ε1 and θ1. Therefore, in each embodiment corresponding to Table 1, Table 3 to Table 9, if the cross-section of the first prism structure 11 and the second prism structure 21 is a non-isosceles structure, the obtained τ2 is basically consistent under the corresponding values ​​of ε2 and θ2.

[0153] Based on Table 11, it can be seen that when the near-side base angle ε1 of the first prism structure 11 gradually increases between 44°-62°, the vertical full-viewing-angle half-peak width of the backlight module remains basically unchanged, while the peak light output luminance gradually increases. After 62°, the peak light output luminance decreases significantly, and at 80°, its normalized relative light output luminance is only 0.7. From the perspective of actual industrial production, the peak light output luminance at this time is relatively weak, but it can be made into a product with relatively low quality requirements. Therefore, according to the data in Table 10, when the cross-section of the first prism structure 11 is a non-isosceles triangle, the preferred value range of its near-side base angle ε1 is ε2-5°≤ε1<80°, where ε2 is the preferred value of the far-side base angle of the first prism structure 11 obtained after simulation based on formula (1) and ray tracing.

[0154] Based on Table 12, it can be seen that, when the near-side bottom angle of the second prism structure 21 gradually increases between 28° and 90°, the peak light luminance of the backlight module is also gradually enhanced, reaching a maximum value at 80°, while the maximum and minimum values ​​of the half-peak width of the full field of view in the vertical direction differ by only 5.4°, and the influence is negligible. Therefore, the preferred range of the near-side bottom angle of the second prism structure 21 is θ2-5°≤θ1≤90°, where θ2 is the preferred value of the far-side bottom angle of the second prism structure 21 obtained according to formula (1) and ray tracing simulation.

[0155] In addition, based on Table 13, it can be seen that when other parameters remain unchanged and the near-side bottom angles ε1 and θ1 of the first prism structure 11 and the second prism structure 21 are increased at the same time, the half-peak width of the full field angle in the vertical direction of the backlight module remains basically unchanged, and the peak light luminance can also be gradually enhanced.

[0156] It should be noted that although the above conclusions based on Tables 11, 12 and 13 are obtained when the refractive indexes of the first prism sheet 1 and the second prism sheet 2 are both 1.59, the inventors found, after calculation based on formula (1) and ray tracing simulation, that the conclusions are also applicable to the cases where the first prism sheet 1 and the second prism sheet 2 have other refractive indices, which will not be elaborated herein.

[0157] The above discussion discusses the case where the peak light output angle τ2 of the backlight module is near 0° so as to realize the normal field light output of the backlight module. However, based on the origin of formula (1), it can be known that by adjusting the values ​​of n1, n2, δ, Φ1, ε2 and θ2, other desired τ2 values ​​(such as 10°, -10°, -20° or 20°) can also be obtained to meet certain usage requirements. For example, when n1 = n2 = 1.61, δ = 12°, Φ1 = 70°, and the first triangle and the second triangle are both isosceles triangles, when ε2 = 30° and θ2 = 25°, the peak light output angle τ2 of the backlight module is about 20°; when ε2 = 37.5° and θ2 = 35°, the peak light output angle τ2 of the backlight module is about 10°.

[0158] In each of the above embodiments, the peak light output angle of the backlight module in the horizontal direction is a 0° normal viewing angle.

[0159] Next, see Fig. 9 The present application also proposes a backlight module design method. Figure 1 The backlight module of the configuration shown is designed, and the design method includes:

[0160] S901, determine the values ​​of n1, n2, Φ1 and δ, where 1.49≤n1≤1.61, 1.49≤n2≤1.61, 65°≤Φ1≤80°, and 0°≤δ≤24°.

[0161] In practice, once the materials used to form the first prism sheet 1 and the second prism sheet 2 are selected, the refractive indices n1 and n2 of the first prism sheet 1 and the second prism sheet 2 are determined. The refractive index of commonly used prism sheet materials is between 1.49 and 1.61, and the commonly used light guide plate 3 has an exit angle generally between 65° and 80°, and further preferably between 67° and 74°. Therefore, for ease of implementation, n1 and n2 can be determined as values ​​between 1.49 and 1.61 (this value can be known by selecting the optical material), and Φ1 can be determined as a value between 65° and 80°, especially between 67° and 74°. In addition, based on the above introduction, it can be known that when the angle δ between the first prism structure 11 and the second prism structure 21 is between 0° and 24° and further preferably between 8° and 16°, it helps to eliminate the moiré phenomenon caused by the regular arrangement of the microstructure, thereby improving the optical quality of the backlight module. Therefore, the size of the angle δ can be determined to be between 0° and 24°, especially between 8° and 16°.

[0162] S902, according to the target light output angle τ2 of the backlight module to be designed, based on the relation Determine the values ​​of the second base angle ε2 and the fourth base angle θ2; wherein, 0°≤δ≤24°, n1 is the refractive index of the first prism sheet 1 , and n2 is the refractive index of the second prism sheet 2 .

[0163] Depending on the usage requirements, the target light output angle τ2 of the backlight module to be designed is known, usually -2° to 2° to achieve the normal field angle. Of course, it may also be any angle between the aforementioned -20° and 20° to meet specific application scenarios, such as applications that require 20° observation.

[0164] After determining the design values ​​of n1, n2, Φ1 and δ, the above relationship, i.e., equation (1), becomes a binary equation with variables ε2 and θ2. Therefore, in theory, the values ​​of ε2 and θ2 can be infinite. However, based on the above description, in order to avoid the double peak phenomenon and ensure the light output intensity of the backlight module, when determining the values ​​of ε2 and θ2, it is advisable to determine ε2 to be not less than 45° and not less than θ2, and ε2 can be further determined to be at least 2° greater than θ2.

[0165] In some embodiments, the target light output angle τ2 of the backlight module to be designed is 0°. In order to achieve this goal and ensure that the backlight module has a higher light output intensity and avoid the double peak phenomenon, n1 and n2 can be determined as 1.61, 1.59, 1.57, 1.55, 1.53, 1.51, 1.49 and are equal to each other in step S901. If n1 and n2 are determined to be 1.61, then in step S901, When determining the values ​​of ε2 and θ2 in step S902, it is preferable to ensure that 87°≤ε2+θ2≤89°, 45°≤ε2≤56°; if n1 and n2 are determined to be 1.59, then when determining the values ​​of ε2 and θ2 in step S902, it is preferable to ensure that 89°≤ε2+θ2≤92°, 46°≤ε2≤56°; if n1 and n2 are determined to be 1.57, then when determining the values ​​of ε2 and θ2 in step S902, it is preferable to ensure that Ensure that 93°≤ε2+θ2≤95°, 47°≤ε2≤56°; if n1 and n2 are determined to be 1.55, then when determining the values ​​of ε2 and θ2 in step S902, it is preferable to ensure that 96°≤ε2+θ2≤98°, 48°≤ε2≤56°; if n1 and n2 are determined to be 1.53, then when determining the values ​​of ε2 and θ2 in step S902, it is preferable to ensure that 99°≤ε2+θ2≤100° , 50°≤ε2≤56°; if n1 and n2 are determined to be 1.51, then when determining the values ​​of ε2 and θ2 in step S902, it is advisable to ensure that 102°≤ε2+θ2≤104°, 52°≤ε2≤56°; if n1 and n2 are determined to be 1.49, then when determining the values ​​of ε2 and θ2 in step S902, it is advisable to ensure that 106°≤ε2+θ2≤107°, 53°≤ε2≤56°.

[0166] S903, determine the values ​​of ε1 and θ1.

[0167] In some embodiments, ε1 may be determined to be the same value as ε2, and θ1 may be determined to be the same value as θ2, so as to facilitate the manufacture of the first prism sheet 1 and the second prism sheet 2. In other embodiments, ε1 may be determined to be a value different from ε2, and θ1 may be determined to be a value different from θ2. However, in order to avoid deterioration of the optical performance of the backlight module, based on the above description, ε2-5°≤ε1≤80°, and θ2-5°≤θ1≤90° may be set.

[0168] The present application also provides a method for manufacturing a backlight module, the method comprising:

[0169] Designing a backlight module through the method of steps S901 to S903 above;

[0170] The backlight module is manufactured according to the determined design parameters of the backlight module.

[0171] In addition, an embodiment of the present application further provides a liquid crystal display device, which includes a liquid crystal panel and a backlight module of the above structure.

Claims

1. A backlight module, characterized in that: include: A light guide plate having a light incident surface and a light emitting surface; An LED light source is arranged on the light incident surface side of the light guide plate and emits light toward the light incident surface, and the light emitting surface is configured to emit the light from the LED light source at an emission angle Φ1; A first prism sheet, comprising a first light-transmitting surface facing the light-emitting surface, a second light-transmitting surface opposite to the first light-transmitting surface, and a plurality of first prism structures arranged along a first direction and extending along a second direction on the second light-transmitting surface, wherein a cross section of the first prism structure perpendicular to the second direction is a first triangle, and the first triangle has a first base angle ε1 close to the LED light source and a second base angle ε2 away from the LED light source in the first direction, wherein the first direction is parallel to a virtual plane defined by the emission angle Φ1; A second prism sheet, comprising a third light-transmitting surface facing the second light-transmitting surface, a fourth light-transmitting surface opposite to the third light-transmitting surface, and a plurality of second prism structures arranged along the first direction and extending along a third direction on the fourth light-transmitting surface, wherein a cross section of the second prism structure perpendicular to the third direction is a second triangle, and the second triangle has a third base angle θ1 close to the LED light source and a fourth base angle θ2 far from the LED light source in the first direction, wherein the second direction and the third direction have an included angle δ, 0°≤δ≤24°, and an angle bisector of the included angle δ is perpendicular to the first direction; The backlight module is configured to meet the following requirements: in, n1 is the refractive index of the first prism sheet, and n2 is the refractive index of the second prism sheet.

2. The backlight module according to claim 1, characterized in that:

3. The backlight module according to claim 2, characterized in that: The first triangle and the second triangle are both isosceles triangles.

4. The backlight module according to claim 2 or 3, characterized in that: The backlight module is configured to satisfy one of the following: n1=n2=1.61, 87°≤ε2+θ2≤89°, 45°≤ε2≤56°; n1=n2=1.59, 89°≤ε2+θ2≤92°, 46°≤ε2≤56°; n1=n2=1.57, 93°≤ε2+θ2≤95°, 47°≤ε2≤56°; n1=n2=1.55, 96°≤ε2+θ2≤98°, 48°≤ε2≤56°; n1=n2=1.53, 99°≤ε2+θ2≤100°, 50°≤ε2≤56°; n1=n2=1.51, 102°≤ε2+θ2≤104°, 52°≤ε2≤56°; n1=n2=1.49, 106°≤ε2+θ2≤107°, 53°≤ε2≤56°.

5. The backlight module according to claim 4, characterized in that: ε2-5°≤ε1≤80°, θ2-5°≤θ1≤90°.

6. The backlight module according to any one of claims 1 to 3, characterized in that: The backlight module is configured to satisfy at least one of the following: 8°≤δ≤16°; ε2≥θ2, and ε2≥45°; 1.49≤n1≤1.61, and 1.49≤n2≤1.

61.

7. The backlight module according to claim 1, characterized in that: ε2-θ2≥2°, and ε2≥45°.

8. The backlight module according to any one of claims 1 to 3, characterized in that: 65°≤Φ1≤80°; Preferably, 67°≤Φ1≤74°.

9. The backlight module according to any one of claims 1 to 3, characterized in that: δ=12°,Φ1=70°.

10. A liquid crystal display device, comprising a liquid crystal panel, characterized in that: It also includes a backlight module as claimed in any one of claims 1 to 9.

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