Backlight module and display device

Abstract

A backlight module includes a circuit substrate, a plurality of light emitting elements, a first cholesteric liquid crystal layer, and a second cholesteric liquid crystal layer. The light emitting elements are disposed on the circuit substrate and electrically connected to the circuit substrate. The first cholesteric liquid crystal layer is disposed on the light emitting elements and overlaps a light emitting surface of each of the light emitting elements. The second cholesteric liquid crystal layer is disposed on the first cholesteric liquid crystal layer and overlaps the first cholesteric liquid crystal layer. The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a first helical direction and a second helical direction, respectively. The backlight module provided by the present application has better light emitting uniformity but lower production cost. A display device using the backlight module is also provided. The backlight module and the display device provided by the present application have better light emitting uniformity and better display quality.

Description

Technical Field

[0001] The present invention relates to a light source module and a display device, and more particularly to a backlight module and a display device. Background Art

[0002] With the increasing application of non-self-luminous displays such as liquid crystal displays, the design of backlight modules also needs to be adjusted for different applications. In order to meet the display requirements of large size, high dynamic range (HDR) and high contrast, the backlight module needs to have the function of local dimming. Therefore, direct-type backlight modules with light-emitting diodes as the main light source have gradually become the mainstream of the market. Since the overall thickness of this type of backlight module is relatively thin (for example, the optical distance is less than 10 mm), and the light-emitting diodes are point light sources, the backlight module is prone to form brighter light above the light-emitting diodes, that is, the hot spot phenomenon, resulting in a decrease in the overall brightness uniformity of the light-emitting surface. In order to solve this problem, a technical solution of covering the light-emitting diodes with a shading film having shading dots has been proposed. However, this technology requires very high assembly precision of the backlight module. Summary of the Invention

[0003] The present invention provides a backlight module which has better light emission uniformity and lower production cost.

[0004] The present invention provides a display device with better display quality.

[0005] Other purposes and advantages of the present invention can be further understood from the technical features disclosed in the present invention.

[0006] To achieve one, some, or all of the above-mentioned objectives, or other objectives, one embodiment of the present invention provides a backlight module. The backlight module includes a circuit substrate, a plurality of light-emitting elements, a first cholesteric liquid crystal layer, and a second cholesteric liquid crystal layer. The light-emitting elements are disposed on the circuit substrate and electrically connected to the circuit substrate. The first cholesteric liquid crystal layer is disposed on the light-emitting elements and overlaps the light-emitting surfaces of each light-emitting element. The second cholesteric liquid crystal layer is disposed on the first cholesteric liquid crystal layer and overlaps the first cholesteric liquid crystal layer. The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a first helical direction and a second helical direction, respectively.

[0007] To achieve one, part, or all of the above-mentioned objectives or other objectives, one embodiment of the present invention provides a display device. The display device includes a backlight module, a display panel, and a quarter-wave plate. The backlight module includes a circuit substrate, a plurality of light-emitting elements, a first cholesteric liquid crystal layer, and a second cholesteric liquid crystal layer. The light-emitting elements are disposed on the circuit substrate and electrically connected to the circuit substrate. The first cholesteric liquid crystal layer is disposed on the light-emitting elements and overlaps the light-emitting surfaces of each light-emitting element. The second cholesteric liquid crystal layer is disposed on the first cholesteric liquid crystal layer and overlaps the first cholesteric liquid crystal layer. The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a first spiral direction and a second spiral direction, respectively. The display panel is disposed overlappingly on the backlight module and includes a liquid crystal cell and a polarizer located between the liquid crystal cell and the backlight module. The quarter-wave plate is disposed between the backlight module and the display panel. The angle between the slow axis of the quarter-wave plate and the absorption axis of the polarizer is 45 degrees.

[0008] Based on the above, in a backlight module and display device according to one embodiment of the present invention, by disposing two cholesteric liquid crystal layers with identical or opposite spiral directions on the light-emitting side of the light-emitting element, a portion of the forward light emitted by the light-emitting element can be directed to an area that does not overlap with the light-emitting element, effectively improving the overall light uniformity of the backlight module. Furthermore, compared to conventional light-shielding film technology with light-shielding dots, the cholesteric liquid crystal layer and light-emitting element of the present invention do not present assembly precision issues. Consequently, the backlight module has greater process flexibility and lower production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic cross-sectional view of a backlight module according to a first embodiment of the present invention.

[0010] Figure 2 FIG. 1 is a schematic cross-sectional view of a backlight module according to a second embodiment of the present invention.

[0011] Figure 3 is a schematic cross-sectional view of a backlight module according to a third embodiment of the present invention.

[0012] Figure 4 FIG. 1 is a schematic cross-sectional view of a display device according to an embodiment of the present invention.

[0013] Figure 5 yes Figure 4 Schematic diagram of the top view of the polarizer and quarter-wave plate.

[0014] Figure 6 FIG. 4 is a schematic cross-sectional view of a backlight module according to a fourth embodiment of the present invention.

[0015] Figure 7 is a schematic cross-sectional view of a backlight module according to a fifth embodiment of the present invention.

[0016] Figure 8 is a schematic cross-sectional view of a backlight module according to a sixth embodiment of the present invention.

[0017] Figure 9A yes Figure 8 A graph showing the reflectivity of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer versus the incident angle.

[0018] Figure 9B and Figure 9C is in accordance with Figure 8 Graphs showing the reflectivity of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer versus the incident angle in some other variant embodiments of the backlight module. DETAILED DESCRIPTION

[0019] The aforementioned technical contents, features, and functions of the present invention will be more clearly understood in the following detailed description of a preferred embodiment with reference to the accompanying drawings. Directional terms such as up, down, left, right, front, and back mentioned in the following embodiments are merely references to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0020] Figure 1 is a cross-sectional view of a backlight module according to a first embodiment of the present invention. Figure 1 The backlight module 10 includes a circuit substrate 110, a plurality of light-emitting elements 120, a first cholesteric liquid crystal layer 131, and a second cholesteric liquid crystal layer 132. These light-emitting elements 120 are disposed on the circuit substrate 110 and are electrically connected to the circuit substrate 110. For example, these light-emitting elements 120 may be arranged in an array on the circuit substrate 110, and the circuit substrate 110 is used to individually control the light emission of these light-emitting elements 120. That is, the backlight module 10 of this embodiment may have a local dimming function, but is not limited to this. In this embodiment, the light-emitting element 120 is, for example, a sub-millimeter light-emitting diode (mini-LED), but is not limited to this. In other embodiments, the light-emitting element 120 may also be a micro-LED.

[0021] The light-emitting element 120 has a light-emitting surface 120es facing away from the circuit substrate 110. A first cholesteric liquid crystal layer 131 and a second cholesteric liquid crystal layer 132 are disposed on one side of the light-emitting surface 120es of the light-emitting element 120. More specifically, the first cholesteric liquid crystal layer 131 is disposed on the plurality of light-emitting elements 120 and overlaps the light-emitting surfaces 120es of these light-emitting elements 120. The second cholesteric liquid crystal layer 132 is disposed on the first cholesteric liquid crystal layer 131 and overlaps the first cholesteric liquid crystal layer 131. In this embodiment, the first and second cholesteric liquid crystal layers 131 and 132 each have substantially the same thickness T and substantially the same helical pitch P. The thickness T of each of the first and second cholesteric liquid crystal layers 131 and 132 can be greater than 10 times the helical pitch P to achieve a reflectivity of approximately 50% for light of a specific polarization state, but this is not limiting. In other embodiments, the thickness T of each of the two cholesteric liquid crystal layers can satisfy the following relationship: 3×P≤T≤20×P. In other words, the thickness of the cholesteric liquid crystal layer can be adjusted according to actual reflectivity or transmittance requirements.

[0022] On the other hand, in this embodiment, the first and second cholesteric liquid crystal layers 131 and 132 can be made of the same material and have the same average refractive index. Accordingly, the first and second cholesteric liquid crystal layers 131 and 132 can each reflect light of substantially the same wavelength. However, the present invention is not limited to this. In other embodiments, the two cholesteric liquid crystal layers can be made of different materials, for example, two cholesteric liquid crystal materials with different average refractive indices and different helical pitches, as long as the product of the average refractive index and the helical pitch of the two cholesteric liquid crystal layers is substantially the same.

[0023] It is particularly noted that in this embodiment, the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 have a first helical direction CD1 and a second helical direction CD2, respectively. The first helical direction CD1 and the second helical direction CD2 may be selectively different, but are not limited thereto. Because the cholesteric liquid crystal layer can reflect light having a polarization handedness identical to its own helical direction, light LB1 emitted from the light-emitting element 120 in a relatively forward direction (at a smaller angle with the normal to the light-emitting surface 120es) is generated into two sub-lights having different polarization handednesses upon entering the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132.

[0024] For example, after the light LB1 enters the first cholesteric liquid crystal layer 131, the light component having the first circular polarization state CP1 (i.e., the sub-light LB1a) is reflected by the first cholesteric liquid crystal layer 131, while the light component having the second circular polarization state CP2 (i.e., the sub-light LB1b) passes through the first cholesteric liquid crystal layer 131 and enters the second cholesteric liquid crystal layer 132. Because the second helical direction CD2 of the second cholesteric liquid crystal layer 132 has the same handedness as the polarization state of the sub-light LB1b, the sub-light LB1b that passes through the first cholesteric liquid crystal layer 131 is reflected by the second cholesteric liquid crystal layer 132.

[0025] That is, light LB1 emitted from the light-emitting element 120 in a relatively forward direction is directed by the first and second cholesteric liquid crystal layers 131 and 132 to an area that does not overlap with the light-emitting element 120 (e.g., the area between two adjacent light-emitting elements 120). On the other hand, light LB2 emitted from the light-emitting element 120 at a relatively large angle to the normal of the light-emitting surface 120es is allowed to pass through these two cholesteric liquid crystal layers. In other words, the first and second cholesteric liquid crystal layers 131 and 132 do not substantially reflect light incident at large angles.

[0026] As previously mentioned, the reflectivity of the cholesteric liquid crystal layer depends on its thickness. Therefore, the light intensity of the backlight module 10 in the area overlapping the light-emitting element 120 (i.e., the area directly above the light-emitting element 120) can be controlled by adjusting the thickness T of the two cholesteric liquid crystal layers. This reduces the difference in light intensity between the two areas and the non-overlapping areas, thereby improving the overall light uniformity of the backlight module 10.

[0027] From another perspective, compared to conventional light-shielding film technology with light-shielding dots, the cholesteric liquid crystal layer of this embodiment does not have assembly precision issues with the light-emitting element 120. Furthermore, the manufacturing process of the cholesteric liquid crystal layer is simple, and the control of the reflected wavelength range is also easy. Therefore, the backlight module 10 of this embodiment can have greater manufacturing process flexibility and cost advantages.

[0028] In this embodiment, the backlight module 10 may further optionally include a transparent substrate 140 disposed between the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132. More specifically, the two cholesteric liquid crystal layers may be directly disposed on opposite sides of the transparent substrate 140, but the present invention is not limited thereto. The transparent substrate 140 may be made of glass, a polymer (e.g., polyimide, polycarbonate, TAC, COP, PMMA, etc.), or other highly transparent materials.

[0029] Furthermore, the light-emitting element 120 of this embodiment may utilize a blue light-emitting diode and, in combination with a wavelength conversion layer 180, achieve white light illumination. Specifically, the wavelength conversion layer 180 is disposed on the side of the first and second cholesteric liquid crystal layers 131, 132 facing away from the light-emitting element 120 and overlaps the light-emitting surface 120es of each of these light-emitting elements 120. For example, light LB2 having a blue wavelength that obliquely passes through the first and second cholesteric liquid crystal layers 131, 132 is absorbed upon entering the wavelength conversion layer 180 and converted into converted light LB2c having a red (or green) wavelength. In other words, the wavelength conversion layer 180 of this embodiment may include at least two wavelength conversion materials, so that after absorbing blue light, it emits converted light of at least two wavelengths.

[0030] In this embodiment, the backlight module 10 further includes a reflective layer 160 disposed on the circuit substrate 110 and not overlapping the light-emitting elements 120. More specifically, the reflective layer 160 is located between the plurality of light-emitting elements 120. The provision of the reflective layer 160 not only increases the light extraction efficiency of the light-emitting elements 120 but also increases the chances of light being transmitted laterally between the cholesteric liquid crystal layer and the reflective layer 160, thereby further improving the overall light uniformity of the backlight module 10.

[0031] The following will list some other embodiments to illustrate the present disclosure in detail, wherein the same components will be marked with the same symbols, and the description of the same technical content will be omitted. For the omitted parts, please refer to the above embodiments and will not be repeated below.

[0032] Figure 2 is a cross-sectional view of a backlight module according to a second embodiment of the present invention. Figure 2 The backlight module 11 of this embodiment and Figure 1 The difference between the backlight module 11 and the backlight module 10 is that the backlight module 11 replaces the transparent substrate 140 of the backlight module 10 with a half-wave plate 145. Therefore, in this embodiment, the helical directions of the first cholesteric liquid crystal layer 131A and the second cholesteric liquid crystal layer 132 can be selectively the same. For example, both cholesteric liquid crystal layers have the second helical direction CD2. However, the present invention is not limited to this. In other embodiments, both cholesteric liquid crystal layers can also have the first helical direction CD1.

[0033] Specifically, in this embodiment, after the light LB1 emitted from the relatively forward-emitting light element 120 enters the first cholesteric liquid crystal layer 131A, the light component having the second circular polarization state CP2 (i.e., sub-light LB1b) is reflected by the first cholesteric liquid crystal layer 131A, while the light component having the first circular polarization state CP1 (i.e., sub-light LB1a) passes through the first cholesteric liquid crystal layer 131A. It is particularly noteworthy that sub-light LB1a first passes through the half-wave plate 145 before entering the second cholesteric liquid crystal layer 132, converting its first circular polarization state CP1 into the second circular polarization state CP2 after passing through the half-wave plate 145. Because the second helical direction CD2 of the second cholesteric liquid crystal layer 132 has the same handedness as the polarization state of sub-light LB1a, the sub-light LB1a that passes through the first cholesteric liquid crystal layer 131A and the half-wave plate 145 is reflected by the second cholesteric liquid crystal layer 132.

[0034] Since the combination of the first cholesteric liquid crystal layer 131A, the half-wave plate 145 and the second cholesteric liquid crystal layer 132 of this embodiment plays a role similar to that of the backlight module 11, Figure 1 The combination of the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 plays a role in the backlight module 10. For detailed description, please refer to the relevant paragraphs of the aforementioned embodiment and will not be repeated here. In particular, the provision of the half-wave plate 145 increases the flexibility of the material selection for the two cholesteric liquid crystal layers.

[0035] Figure 3 is a cross-sectional view of a backlight module according to a third embodiment of the present invention. Figure 3 The backlight module 12 of this embodiment and Figure 1 The difference between the backlight module 10 and the backlight module 12 of this embodiment is that the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 of the backlight module 12 of this embodiment are respectively arranged on different transparent substrates. For example, the first cholesteric liquid crystal layer 131 is arranged on the first transparent substrate 141, and the second cholesteric liquid crystal layer 132 is arranged on the second transparent substrate 142, and an optical adhesive layer 170 may be provided between the two cholesteric liquid crystal layers. More specifically, the first transparent substrate 141 with the first cholesteric liquid crystal layer 131 and the second transparent substrate 142 with the second cholesteric liquid crystal layer 132 may be bonded to each other via the optical adhesive layer 170. The optical adhesive layer 170 here is, for example, an optical clear adhesive (OCA), a hardened optical clear resin (OCR), or an optical pressure sensitive adhesive (PSA).

[0036] Figure 4 FIG. 1 is a schematic cross-sectional view of a display device according to an embodiment of the present invention. Figure 5 yes Figure 4 A top view of the polarizer and quarter wave plate. Figure 4 The backlight module 10A of this embodiment is Figure 1 The difference between the backlight module 10 and the backlight module 10 is that the thickness configuration of the two cholesteric liquid crystal layers is different.

[0037] In this embodiment, the first cholesteric liquid crystal layer 131B and the second cholesteric liquid crystal layer 132 of the backlight module 10A may have different thicknesses. For example, the thickness T" of the first cholesteric liquid crystal layer 131B may be selectively smaller than the thickness T of the second cholesteric liquid crystal layer 132. Therefore, a portion of the light energy of the more forward-emitting light LB1 of the light emitted by the light-emitting element 120 can pass through the first cholesteric liquid crystal layer 131B and the second cholesteric liquid crystal layer 132 in a specific polarization state.

[0038] Specifically, because the first cholesteric liquid crystal layer 131B is thinner than the second cholesteric liquid crystal layer 132, the reflectivity of the first cholesteric liquid crystal layer 131B for the light component of the light beam LB1 having the first circular polarization state CP1 is lower than the reflectivity of the second cholesteric liquid crystal layer 132 for the light component of the light beam LB1 having the second circular polarization state CP2. When the second cholesteric liquid crystal layer 132 is sufficiently thick (e.g., greater than ten times the helical pitch), the reflectivity of the second cholesteric liquid crystal layer 132 for the light beam LB1 can be approximately 50% (i.e., the reflectivity for the light component of the second circular polarization state CP2 is approximately 100%). Conversely, when the first cholesteric liquid crystal layer 131B is thinner (e.g., less than ten times the helical pitch), the reflectivity of the first cholesteric liquid crystal layer 131B for the light beam LB1 cannot reach 50% (i.e., the reflectivity for the light component of the first circular polarization state CP1 cannot reach 100%). Therefore, a portion of the light component of the light beam LB1 having the first circular polarization state CP1 (i.e., sub-light beam LB1c) passes through both cholesteric liquid crystal layers.

[0039] In other words, the light emitted by the backlight module 10A of this embodiment may have a first circular polarization state CP1, but the present invention is not limited thereto. In other embodiments, the relative thicknesses of the first and second cholesteric liquid crystal layers may be adjusted to cause the light emitted by the backlight module to have a second circular polarization state CP2. For example, the thickness of the first cholesteric liquid crystal layer may be greater than ten times the helical pitch, while the thickness of the second cholesteric liquid crystal layer may be less than ten times the helical pitch.

[0040] In this embodiment, a backlight module 10A can serve as a backlight source for a display panel 200 and is arranged to overlap with the display panel 200 to form a display device 1. The display panel 200 includes a liquid crystal cell 210 and two polarizers 221 and 222 disposed on opposite sides of the liquid crystal cell 210. The polarizer 221 is located between the liquid crystal cell 210 and the backlight module 10A, and the absorption axis AX1 of the polarizer 221 can be selectively perpendicular to the absorption axis AX2 of the polarizer 222, but the present invention is not limited thereto. In other embodiments, the absorption axes AX1 and AX2 of the two polarizers 221 and 222 can be arranged to be parallel to each other depending on the operating mode of the liquid crystal cell 210 (e.g., twisted nematic mode, vertical alignment mode, horizontal electric field mode, and optically compensated birefringence mode).

[0041] It is particularly noted that, in order to increase the light energy utilization rate of the display device 1, a quarter wave plate 250 may be further provided between the polarizer 221 of the display panel 200 and the backlight module 10A, wherein the angle α between the slow axis SA of the quarter wave plate 250 and the absorption axis AX1 of the polarizer 221 is 45 degrees (e.g., Figure 5 shown).

[0042] Figure 6 is a cross-sectional view of a backlight module according to a fourth embodiment of the present invention. Figure 6 , the backlight module 20 of this embodiment is compared with Figure 1 The backlight module 10 may further include a first optical film 151 and a second optical film 152. The first optical film 151 is disposed between the light-emitting elements 120 and the first cholesteric liquid crystal layer 131. The second optical film 152 is disposed between the second cholesteric liquid crystal layer 132 and the wavelength conversion layer 180. Specifically, the first optical film 151 includes a first substrate SB1 and a plurality of first optical microstructures MS1. These first optical microstructures MS1 are disposed on a surface SB1s of the first substrate SB1 facing the plurality of light-emitting elements 120. The second optical film 152 includes a second substrate SB2 and a plurality of second optical microstructures MS2. These second optical microstructures MS2 are disposed on a surface SB2s of the second substrate SB2 facing the wavelength conversion layer 180.

[0043] Since the configuration and functions of other components of this embodiment are similar to those of Figure 1 For detailed description of the backlight module 10, please refer to the relevant paragraphs of the aforementioned embodiment, which will not be repeated here.

[0044] In the present embodiment, the first optical microstructure MS1 and the second optical microstructure MS2 are, for example, both prism structures, and have a vertex angle β1 and a vertex angle β2 away from the first substrate SB1 and the second substrate SB2, respectively. Preferably, the vertex angle β1 of the first optical microstructure MS1 and the vertex angle β2 of the second optical microstructure MS2 may be less than 120 degrees. For example, in the present embodiment, the two vertex angles of the first optical microstructure MS1 and the second optical microstructure MS2 may be selectively the same, but are not limited to this. In other embodiments, the two vertex angles of the first optical microstructure MS1 and the second optical microstructure MS2 may also be designed to be different based on the light output type or light output uniformity requirements of the backlight module.

[0045] Specifically, in this embodiment, light LB emitted by the light-emitting element 120, which is emitted in a relatively forward direction, is deflected after passing through the first optical microstructure MS1 of the first optical film 151 and enters the first and second cholesteric liquid crystal layers 131 and 132 at a larger angle. After passing through the second cholesteric liquid crystal layer 132 and entering the second optical microstructure MS2 of the second optical film 152, the light LB is deflected in a relatively forward direction and exits the second optical film 152. The forward direction herein is, for example, the normal direction to the light-emitting surface 120es (or surface SB2s).

[0046] The arrangement of these two optical films can direct the light LB emitted by the light-emitting element 120 in a more forward direction toward an area away from the area directly above the light-emitting element 120 (e.g., an area between two adjacent light-emitting elements 120 and not overlapping the light-emitting element 120). In other words, the configuration of the two optical films can further improve the overall light uniformity of the backlight module.

[0047] Figure 7 is a cross-sectional view of a backlight module according to a fifth embodiment of the present invention. Figure 7 The backlight module 20A of this embodiment is Figure 6 The backlight module 20 differs from the backlight module 20A in that the optical microstructures are configured differently. In this embodiment, a plurality of first optical microstructures MS1 are directly disposed on a surface 131s of the first cholesteric liquid crystal layer 131 facing the plurality of light-emitting elements 120, while a plurality of second optical microstructures MS2 are directly disposed on a surface 132s of the second cholesteric liquid crystal layer 132 facing the wavelength conversion layer 180.

[0048] Since the optical microstructures MS1 and MS2 of this embodiment play similar roles in the backlight module 20A, Figure 6 The role of the optical microstructure on the backlight module 20 is described in detail in the relevant paragraphs of the aforementioned embodiment, which will not be repeated here.

[0049] Figure 8 is a schematic cross-sectional view of a backlight module according to a sixth embodiment of the present invention. Figure 9A yes Figure 8 A graph showing the reflectivity of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer versus the incident angle. Figure 9B and Figure 9C is in accordance with Figure 8 Refer to the graph of the reflectivity of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer versus the incident angle in some other variant embodiments of the backlight module. Figure 8 The backlight module 30 of this embodiment is Figure 1 The difference between the backlight module 10 and the backlight module 30 is that the light emitting surface 120es of the light emitting element 120 of the backlight module 30 can also be provided with an encapsulation pattern 190, and the encapsulation pattern 190 can have different degrees of reflectivity. In this embodiment, the encapsulation pattern 190 can be made of a thinned metal layer or an encapsulation material doped with reflective particles.

[0050] When the encapsulation pattern 190 has a reflectivity greater than 0%, part of the light emitted by the light-emitting element 120 (e.g., light LB3) will be reflected by the encapsulation pattern 190 to the side of the light-emitting element 120. Therefore, in order to match the encapsulation pattern 190 with different degrees of reflectivity, the reflectivity distribution of the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 for light at different incident angles θ may be different. For example, when the reflectivity of the encapsulation pattern 190 is greater, more light is reflected to the side, and the incident angle θ at which the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 have the maximum reflectivity is also greater. Accordingly, the opportunity for light to be transmitted laterally can be increased, which helps to improve the overall light uniformity of the backlight module 30. The incident angle θ here is, for example, the angle between the optical path of the incident light and the normal direction of the surface 131s of the first cholesteric liquid crystal layer 131 facing the light-emitting element 120.

[0051] For example, when the reflectivity of the packaging pattern 190 is between 0% and 20%, since most of the light (e.g., the light LB1) will still be emitted through the light emitting surface 120es and pass through the packaging pattern 190, the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 can have a maximum reflectivity for light with an incident angle θ between 0 degrees and 30 degrees, and this maximum reflectivity is between 80% and 100% (e.g., Figure 9A As shown in FIG. 1 , a brighter light output directly above the light emitting element 120 can be avoided, thereby preventing a hot spot phenomenon from occurring. This helps to improve the uniformity of light output from the backlight module 30 .

[0052] When the reflectivity of the packaging pattern 190 is between 20% and 50%, since the proportion of light reflected to the side of the light emitting element 120 increases, the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 can have a maximum reflectivity for light with an incident angle θ between 20 degrees and 60 degrees, and this maximum reflectivity is between 60% and 100% (e.g. Figure 9B Therefore, light with an incident angle θ between 20 degrees and 60 degrees can be reflected by the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 and transmitted laterally, thereby improving the light uniformity of the backlight module 30.

[0053] When the reflectivity of the packaging pattern 190 is between 50% and 100%, since the proportion of light reflected to the side of the light emitting element 120 increases, the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 can have a maximum reflectivity for light with an incident angle θ between 40 degrees and 80 degrees, and this maximum reflectivity is between 60% and 100% (e.g. Figure 9C Therefore, light with an incident angle θ between 40 degrees and 80 degrees can be reflected by the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 and transmitted laterally, thereby improving the light uniformity of the backlight module 30.

[0054] In summary, in a backlight module and display device according to one embodiment of the present invention, by disposing two cholesteric liquid crystal layers with identical or opposite spiral directions on the light-emitting side of the light-emitting element, a portion of the forward light emitted by the light-emitting element can be directed to an area that does not overlap with the light-emitting element, effectively improving the overall light uniformity of the backlight module. Furthermore, compared to conventional light-shielding film technology with light-shielding dots, the cholesteric liquid crystal layer and light-emitting element of the present invention do not present assembly precision issues. Consequently, the backlight module exhibits greater process flexibility and lower production costs.

[0055] However, what is described above is only a preferred embodiment of the present invention, and it should not be used to limit the scope of implementation of the present invention. That is, all simple equivalent changes and modifications made in accordance with the claims and the content of the invention are still within the scope of the patent of the present invention. In addition, any embodiment or claim of the present invention does not need to achieve all the purposes, advantages or features disclosed by the present invention. In addition, the abstract and title (invention name) are only used to assist in the retrieval of patent documents, and are not used to limit the scope of rights of the present invention. In addition, the terms "first", "second", etc. mentioned in this specification or claims are only used to name the name of the element or to distinguish different embodiments or scopes, and are not used to limit the upper or lower limit on the number of elements.

[0056] Description of reference numerals:

[0057] 1: Display device

[0058] 10, 10A, 11, 12, 20, 20A, 30: Backlight module

[0059] 110: Circuit board

[0060] 120: Light-emitting element

[0061] 120es: light-emitting surface

[0062] 131, 131A, 131B: first cholesteric liquid crystal layer

[0063] 131s, 132s: Surface

[0064] 132: Second cholesteric liquid crystal layer

[0065] 140, 141, 142: Transparent substrate

[0066] 145: Half wave plate

[0067] 151, 152: Optical film

[0068] 160: Reflection layer

[0069] 170: Optical adhesive layer

[0070] 180: Wavelength conversion layer

[0071] 190: Package pattern

[0072] 200: Display panel

[0073] 210: LCD box

[0074] 221, 222: Polarizer

[0075] 250: Quarter wave plate

[0076] AX1, AX2: Absorption axis

[0077] CD1, CD2: spiral direction

[0078] CP1: first circular polarization state

[0079] CP2: second circular polarization state

[0080] LB, LB1, LB2, LB3: Light

[0081] LB1a, LB1b, LB1c: sub-light beams

[0082] LB2c: Converting Light

[0083] MS1, MS2: Optical microstructures

[0084] P: pitch

[0085] SA: Slow Axis

[0086] SB1, SB2: Base board

[0087] SB1s, SB2s: Surface

[0088] T, T": film thickness

[0089] α: Angle

[0090] β1, β2: vertex angle

[0091] θ: angle of incidence.

Claims

1. A backlight module, characterized in that: The backlight module includes a circuit substrate, a plurality of light-emitting elements, a first cholesteric liquid crystal layer and a second cholesteric liquid crystal layer, wherein: The plurality of light emitting elements are disposed on the circuit substrate and electrically connected to the circuit substrate; The first cholesteric liquid crystal layer is disposed on the plurality of light-emitting elements and overlaps the light-emitting surface of each of the plurality of light-emitting elements; and The second cholesteric liquid crystal layer is disposed on the first cholesteric liquid crystal layer and overlaps the first cholesteric liquid crystal layer, wherein the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a first spiral direction and a second spiral direction, respectively. In which, at least part of the outgoing light from one of the multiple light-emitting elements and having a smaller angle with the normal direction of the corresponding light-emitting surface will be guided by the first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer to the area between one of the multiple light-emitting elements and another adjacent one of the multiple light-emitting elements.

2. The backlight module according to claim 1, wherein: The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer each have a helical pitch P, and the thickness T of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer each satisfies the following relationship: 3×P≤T≤20×P.

3. The backlight module according to claim 1, wherein: Also includes: The light-transmitting substrate is disposed between the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer.

4. The backlight module according to claim 1, wherein: Also includes: A half-wave plate is disposed between the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer, wherein the first spiral direction of the first cholesteric liquid crystal layer is the same as the second spiral direction of the second cholesteric liquid crystal layer.

5. The backlight module according to claim 1, wherein: The first cholesteric liquid crystal layer is disposed on a first light-transmitting substrate, and the second cholesteric liquid crystal layer is disposed on a second light-transmitting substrate.

6. The backlight module according to claim 5, wherein: An optical adhesive layer is further provided between the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer.

7. The backlight module according to claim 1, wherein: The film thickness of the first cholesteric liquid crystal layer is different from the film thickness of the second cholesteric liquid crystal layer.

8. The backlight module according to claim 1, wherein: Also includes: The wavelength conversion layer is disposed on a side of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer away from the plurality of light-emitting elements, and overlaps the light-emitting surface of each of the plurality of light-emitting elements.

9. The backlight module according to claim 8, wherein: Also includes: The first optical film is arranged between the plurality of light-emitting elements and the first cholesteric liquid crystal layer. The first optical film has a first substrate and a plurality of first optical microstructures. The plurality of first optical microstructures are arranged on a surface of the first substrate facing the plurality of light-emitting elements.

10. The backlight module according to claim 9, wherein: The plurality of first optical microstructures are a plurality of prism structures, each of the plurality of prism structures has a vertex angle away from the first substrate, and the vertex angle is less than 120 degrees.

11. The backlight module according to claim 9, wherein: Also includes: The second optical film is arranged between the second cholesteric liquid crystal layer and the wavelength conversion layer. The second optical film has a second substrate and a plurality of second optical microstructures. The plurality of second optical microstructures are arranged on a surface of the second substrate facing the wavelength conversion layer.

12. The backlight module according to claim 11, wherein: The plurality of second optical microstructures are a plurality of prism structures, each of the plurality of prism structures has a vertex angle away from the second substrate, and the vertex angle is less than 120 degrees.

13. The backlight module according to claim 8, wherein: A plurality of first prism structures are provided on a surface of the first cholesteric liquid crystal layer facing the plurality of light-emitting elements. Each of the plurality of first prism structures has a first vertex angle away from the first cholesteric liquid crystal layer, and the first vertex angle is less than 120 degrees.

14. The backlight module according to claim 13, wherein: A plurality of second prism structures are disposed on a surface of the second cholesteric liquid crystal layer facing the wavelength conversion layer. Each of the plurality of second prism structures has a second vertex angle away from the second cholesteric liquid crystal layer, and the second vertex angle is less than 120 degrees.

15. The backlight module according to claim 1, wherein: Also includes: The reflective layer is disposed on the circuit substrate and located between the plurality of light emitting elements.

16. The backlight module according to claim 15, wherein: The light-emitting surface of each of the multiple light-emitting elements is provided with an encapsulation pattern, and the reflectivity of the encapsulation pattern is between 0% and 20%. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer are used to reflect light from each of the multiple light-emitting elements. There is an incident angle between the light path of the light and the normal direction of the surface of the first cholesterol liquid crystal layer facing the multiple light-emitting elements. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer have a maximum reflectivity for the light with an incident angle between 0 degrees and 30 degrees, and the maximum reflectivity is between 80% and 100%.

17. The backlight module according to claim 15, wherein: The light-emitting surface of each of the multiple light-emitting elements is provided with an encapsulation pattern, and the reflectivity of the encapsulation pattern is between 20% and 50%. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer are used to reflect light from the reflective layer. There is an incident angle between the light path of the light and the normal direction of the surface of the first cholesterol liquid crystal layer facing the multiple light-emitting elements. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer have a maximum reflectivity for the light with an incident angle between 20 degrees and 60 degrees, and the maximum reflectivity is between 60% and 100%.

18. The backlight module according to claim 15, wherein: The light-emitting surface of each of the multiple light-emitting elements is provided with an encapsulation pattern, and the reflectivity of the encapsulation pattern is between 50% and 100%. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer are used to reflect light from the reflective layer. There is an incident angle between the light path of the light and the normal direction of the surface of the first cholesterol liquid crystal layer facing the multiple light-emitting elements. The first cholesterol liquid crystal layer and the second cholesterol liquid crystal layer have a maximum reflectivity for the light with an incident angle between 40 degrees and 80 degrees, and the maximum reflectivity is between 60% and 100%.

19. A display device, characterized in that: The display device includes a backlight module, a display panel and a quarter-wave plate, wherein: The backlight module includes a circuit substrate, a plurality of light-emitting elements, a first cholesteric liquid crystal layer and a second cholesteric liquid crystal layer, wherein: The plurality of light emitting elements are disposed on the circuit substrate and electrically connected to the circuit substrate; The first cholesteric liquid crystal layer is disposed on the plurality of light-emitting elements and overlaps the light-emitting surface of each of the plurality of light-emitting elements; and The second cholesteric liquid crystal layer is disposed on the first cholesteric liquid crystal layer and overlaps the first cholesteric liquid crystal layer, wherein the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a first spiral direction and a second spiral direction, respectively. wherein at least a portion of the light emitted from one of the plurality of light-emitting elements and forming a small angle with the normal direction of the corresponding light-emitting surface is guided by the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer to a region between the one of the plurality of light-emitting elements and another adjacent one of the plurality of light-emitting elements; The display panel is overlapped with the backlight module and comprises a liquid crystal cell and a polarizer located between the liquid crystal cell and the backlight module; and The quarter wave plate is disposed between the backlight module and the display panel, wherein an angle between a slow axis of the quarter wave plate and an absorption axis of the polarizer is 45 degrees.

20. The display device according to claim 19, wherein The backlight module further includes: The wavelength conversion layer is disposed on a side of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer away from the plurality of light emitting elements and overlaps the light emitting surface of each of the plurality of light emitting elements.

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