Touchpad and backlight module thereof

A touchpad and a backlight module are provided. The backlight module includes a circuit board, a first light emitting element and a second light emitting element respectively located on two surfaces of the circuit board, a bottom layer, and a second light guide plate having a second microstructure, a middle layer having a light transmitting region and a first light guide plate having a first microstructure sequentially disposed on the bottom layer. A position of the second microstructure corresponds to the light transmitting region. An area of the light transmitting region of the middle layer is smaller than or equal to an area of the first microstructure. The first light emitting element corresponds to a side surface of the first light guide plate. The second light emitting element corresponds to a side surface of the second light guide plate.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) to Patent Application No. 112116881 filed in Taiwan, R.O.C. on May 5, 2023, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Technical Field

The disclosure relates to a touchpad and a backlight module thereof, in particular to a touchpad having three light emitting modes and a backlight module thereof.

Related Art

In a backlight module, after the light source emits light into the light guide plate, light is uniformly emitted from the light exit surface of the light guide plate after being reflected and refracted by the light guide plate. Typically, the backlight module only has one light emitting mode in which the whole surface of the light guide plate emits light or the whole surface of the light guide plate does not emit light, and hardly has other light emitting modes. Therefore, the backlight module needs to be improved.

SUMMARY

According to some embodiments of the disclosure, provided is a backlight module, including a first light guide plate, a middle layer, a second light guide plate, a bottom layer, a circuit board, a first light emitting element and a second light emitting element. The first light guide plate has a first microstructure. The middle layer is attached to a bottom portion of the first light guide plate. The middle layer has a light transmitting region. The second light guide plate is attached to a bottom portion of the middle layer and has a second microstructure. A position of the second microstructure corresponds to the light transmitting region of the middle layer. An area of the light transmitting region of the middle layer is smaller than or equal to an area of the first microstructure. The bottom layer is attached to a bottom portion of the second light guide plate. The first light emitting element is located on a surface of the circuit board and corresponds to a side surface of the first light guide plate. The second light emitting element is located on an other surface of the circuit board and corresponds to a side surface of the second light guide plate.

Thereby, when only the first light emitting element emits light, the light emitted by the first light emitting element passes through the first light guide plate and interacts with the first microstructure to provide a first light emitting mode. When only the second light emitting element emits light, the light emitted by the second light emitting element passes through the second light guide plate and interacts with the second microstructure to provide a second light emitting mode. When the first light emitting element and the second light emitting element emit light at the same time, the light emitted by the first light emitting element and the second light emitting element at the same time respectively passes through the first light guide plate and the second light guide plate and respectively interacts with the first microstructure and the second microstructure to jointly provide a third light emitting mode. According to some embodiments, the area of the first microstructure is greater than the area of the second microstructure, so the first light emitting mode with a larger light emitting range, the second light emitting mode with a smaller light emitting range, and the third light emitting mode with overlapped light emission can be presented.

According to some embodiments, the first light guide plate has a first length in a first direction, and the second light guide plate has a second length in the first direction. The first length is the same as the second length.

According to some embodiments, the first light guide plate has a third length in a second direction perpendicular to the first direction, and the second light guide plate has a fourth length in the second direction. The third length is the same as the fourth length.

According to some embodiments, the first light guide plate has a third length in a second direction perpendicular to the first direction, and the second light guide plate has a fourth length in the second direction. The third length is smaller than the fourth length, or the third length is greater than the fourth length.

According to some embodiments, in a direction perpendicular to the two surfaces of the circuit board, the first light emitting element and the second light emitting element do not overlap.

According to some embodiments, the backlight module further includes a second light shielding adhesive. The second light guide plate has a second extending portion close to the second light emitting element, and the second light shielding adhesive is attached between the second extending portion and the circuit board.

According to some embodiments, a length of the middle layer in the second direction is the same as the third length of the first light guide plate or the fourth length of the second light guide plate.

According to some embodiments, one side end of the middle layer is adjacent to one side end of the circuit board or the side end of the middle layer is laminated on one surface of the circuit board.

According to some embodiments of the disclosure, provided is a touchpad, including a touch circuit board, a backlight module and a cover plate. The backlight module is arranged on a top portion of the touch circuit board. The cover plate is located on a top portion of the backlight module. The backlight module includes a first light guide plate, a middle layer, a second light guide plate, a bottom layer, a circuit board, a first light emitting element and a second light emitting element. The first light guide plate has a first microstructure. The middle layer is attached to a bottom portion of the first light guide plate. The middle layer has a light transmitting region. The second light guide plate is attached to a bottom portion of the middle layer. The second light guide plate has a second microstructure. A position of the second microstructure corresponds to the light transmitting region of the middle layer, and an area of the light transmitting region of the middle layer is smaller than or equal to an area of the first microstructure. The bottom layer is attached to a bottom portion of the first light guide plate. The first light emitting element is located on a surface of the circuit board and corresponds to a side surface of the first light guide plate. The second light emitting element is located on an other surface of the circuit board and corresponds to a side surface of the second light guide plate.

According to some embodiments, the light transmitting region of the middle layer is smaller than the touch circuit board. An area of the first light guide plate is greater than an area of the cover plate, and an area of the second light guide plate is greater than the area of the cover plate.

DETAILED DESCRIPTION

Various embodiments of the disclosure will be disclosed in the accompanying drawings. For the sake of clarity, many practical details will be explained in the following description. However, it should be understood that these practical details should not be used to limit the disclosure. In addition, in order to simplify the drawings, some conventional structures and elements will be shown in the drawings in a simple and schematic way. It is to be particularly noted that the drawings are for illustrative purposes only and do not represent the actual dimensions, quantities and scales of the elements. Some of the details may not be fully drawn in order to facilitate the simplicity of the drawings.

Referring toFIG.1toFIG.4,FIG.1is a schematic view of an embodiment of a touchpad A applied to an electronic device E.FIG.2is a schematic view of a touchpad A providing a first light emitting mode through a backlight module B.FIG.3is a schematic view of the touchpad A providing a second light emitting mode through the backlight module B.FIG.4is a schematic view of the touchpad A providing a third light emitting mode through the backlight module B.

Referring toFIG.1toFIG.4, in some embodiments, the touchpad A includes the backlight module B and can be applied to the electronic device E. The backlight module B can provide a first light emitting mode (as shown inFIG.2), a second light emitting mode (as shown inFIG.3) and a third light emitting mode (as shown inFIG.4) with different light emitting effects. The first light emitting mode has the whole surface light emitting range including the touchpad A and surroundings thereof, as shown by the light gray area (which actually may have single-color or multi-color light emitting effect) inFIG.2. The second light emitting mode has the light emitting range including the touchpad A, as shown by the dark gray area (which actually may have single-color or multi-color light emitting effect) inFIG.3. The third light emitting mode has the light emitting range including the touchpad A and surroundings thereof, as shown by both the light gray area and the dark gray area inFIG.4. In this way, when in use, the backlight module is adapted to illuminate the partial or whole range of the touchpad A, which is convenient for users to see and operate and can provide a dazzling effect. The backlight module B may be applied to, but not limited to, a display of a television, a monitor, a laptop, a tablet or a mobile phone.

Referring toFIG.5,FIG.5is a schematic cross-sectional view of a first embodiment of the touchpad inFIG.4taken along line5-5. The backlight module B includes a first light guide plate10, a middle layer20, a second light guide plate30, a bottom layer40, a circuit board51, a first light emitting element52and a second light emitting element53. The first light guide plate10, the middle layer20, the second light guide plate30and the bottom layer40are sequentially laminated and arranged on one side of the circuit board51, and the first light emitting element52and the second light emitting element53emit light toward the first light guide plate10and the second light guide plate30to provide the light emitting effect. It should be noted that in some embodiments shown inFIG.5, the first light guide plate10of the backlight module B is on the top side relative to the bottom layer40, and the bottom layer40is on the bottom side relative to the first light guide plate10.

Referring toFIG.1in conjunction withFIG.5, in some embodiments, the touchpad A includes a touch circuit board A1, the backlight module B and a cover plate A2. The backlight module B is arranged between the touch circuit board A1and the cover plate A2. The cover plate A2is arranged on a top side of the backlight module B, and the touch circuit board A1is arranged on a bottom side of the backlight module B. When the touchpad A is applied to the electronic device E, the electronic device E includes a shell E1. When the backlight module B is not emitting light, the electronic device E presents the exterior color of the shell E1itself. The touchpad A is arranged in the shell E1, and the cover plate A2of the touchpad A is exposed out of the shell E1for the user to operate. In the embodiment shown inFIG.1, the electronic device E is a notebook computer. The shell E1is a case of the notebook computer, and the touchpad A is a touchpad of a host of the notebook computer, but the disclosure is not limited thereto.

Referring toFIG.5, in some embodiments where the backlight module B is applied to the touchpad A, areas of the first light guide plate10and the second light guide plate30are respectively greater than an area of the cover plate A2, thereby ensuring the whole surface of the cover plate A2to emit light.

Referring toFIG.2,FIG.5andFIG.6,FIG.6is a schematic view of an embodiment of a first light guide plate10of the backlight module B. The first light guide plate10has a first microstructure11(shaded area shown inFIG.6). The first microstructure11of the first light guide plate10is configured to change the direction of reflection of light and guide the light entering the first light guide plate10to the required light exit direction to provide a light emitting area with a predetermined shape or size. In some embodiments, the shape and size of the first microstructure11distributed on the first light guide plate10are associated with the light emitting shape and size of the first light emitting mode.

In some embodiments, the first microstructure11is realized by mesh dots or mesh lines printed with ink on a bottom surface of the first light guide plate10. In some embodiments, the first microstructure11may also be formed by a plurality of dots (or mesh dots or light dots), which may be, but not limited to, convex dots or concave dots, and may be of any shape, e.g., an irregular shape, a cone, a square, a triangle, a trapezoid, etc. In these embodiments, the shape and size of the dots, the spacing between the adjacent convex dots, and/or the spacing between the concave dots may be adjusted according to the type of light emitted by the first light emitting mode of the backlight module B or a material of the first light guide plate10. Thereby, the first light guide plate10receives the light emitted from the first light emitting element52, so that the light of the first light emitting element52enters the first light guide plate10from the side for total reflection, and is scattered by the first microstructure11to provide the predetermined light emitting effect.

Referring toFIG.2,FIG.3,FIG.5andFIG.7.FIG.7is a schematic view of an embodiment of a middle layer20of the backlight module B. The middle layer20is attached to a bottom portion of the first light guide plate10and has a light transmitting region21. The light transmitting region21of the middle layer20is configured to limit a light exit range of light, such that the light passing through the middle layer20can exit only through the light transmitting region21so as to provide a light emitting area with a predetermined shape or size. In some embodiments, the shape and size of the light transmitting region21of the middle layer20are associated with the light emitting shape and size of the second light emitting mode. In these embodiments, an area of the light transmitting region21of the middle layer20is smaller than or equal to an area of the first microstructure11. That is, in the second light emitting mode, light passing through the middle layer20is limited to exit only from the light transmitting region21, so that the light emitting range of the second light emitting mode (as shown inFIG.3) is smaller than the light emitting range of the first light emitting mode (as shown inFIG.2). In some embodiments, the first microstructure11has an outer contour, the area of the first microstructure11is calculated according to the outer contour of the first microstructure11.

Referring toFIG.5, in some embodiments where the backlight module B is applied to the touchpad A, a position of the light transmitting region21of the middle layer20corresponds to a top side of the touch circuit board A1. In this case, in the second light emitting mode, the light emitting range corresponding to the light transmitting region21is the touchable range of the touch circuit board A1. Thereby, the touch range of the touchpad A can be visually distinguished by the user through the light emitting range. In some embodiments, an area of the light transmitting region21of the middle layer20is smaller than an area of the touch circuit board A1, thereby ensuring that the whole light emitting range corresponding to the light transmitting region21in the second light emitting mode has the touch effect.

Referring toFIG.5andFIG.7, in some embodiments, the part of the middle layer20other than the light transmitting region21is a light shielding area22(shaded area shown inFIG.7). Specifically, the whole middle layer20is made of a light transmitting material, and a non-light transmitting material is arranged at the part other than the light transmitting region21to form the light shielding area22. In some embodiments, the light shielding area22may be formed by arranging a black colloid or a coating material of other colors by means of printing or coating.

Referring toFIG.5,FIG.7andFIG.8,FIG.8is a schematic view of an embodiment of a second light guide plate30of the backlight module B. The second light guide plate30is attached to a bottom portion of the middle layer20and has a second microstructure31(shaded area shown inFIG.8). A position of the second microstructure31corresponds to the light transmitting region21(dashed box area shown inFIG.8) of the middle layer20. An area of the second microstructure31is smaller than an area of the first microstructure11. The second microstructure31of the second light guide plate30is configured to change the direction of reflection of light and guide the light entering the second light guide plate30toward the light transmitting region21of the middle layer20such that the light exits from the light transmitting region21. In some embodiments, the shape and size of the second microstructure31distributed on the second light guide plate30are associated with the shape and size of the light transmitting region21of the middle layer20. In some embodiments, an area of the second microstructure31of the second light guide plate30is greater than or at least equal to an area of the light transmitting region21, thereby ensuring that light from the second light emitting element53can emit light completely corresponding to the light transmitting region21. In some embodiments, the second microstructure31has an outer contour, the area of the second microstructure31is calculated according to the outer contour of the second microstructure31.

Referring toFIG.5andFIG.8, in some embodiments, the second microstructure31is realized by mesh dots or mesh lines printed with ink on a bottom surface of the second light guide plate30. In some embodiments, the second microstructure31may also be formed by a plurality of dots (or mesh dots or light dots), which may be, but not limited to, convex dots or concave dots, and may be of any shape, e.g., an irregular shape, a cone, a square, a triangle, a trapezoid, etc. In these embodiments, the shape and size of the dots, the spacing between the adjacent convex dots, and/or the spacing between the concave dots may be adjusted according to the type of light emitted by the second light emitting mode of the backlight module B or a material of the second light guide plate30. Thereby, the second light guide plate30receives the light emitted from the second light emitting element53, so that the light of the second light emitting element53enters the second light guide plate30from the side for total reflection, and is scattered by the second microstructure31to provide the predetermined light emitting effect.

Referring toFIG.5, the bottom layer40is attached to a bottom portion of the second light guide plate30, so as to prevent light entering the first light guide plate10, the middle layer20and the second light guide plate30from exiting from the bottom portion of the second light guide plate30. In some embodiments, the bottom layer40is made of a material with light absorbing properties.

In some embodiments, the bottom layer40and the light shielding area22of the middle layer20have the same properties after interacting with the light, so that the backlight module B in the first light emitting mode will not generate light and shadow at the junction of the light transmitting region21and the light shielding area22. In some embodiments, the bottom layer40and the light shielding area22of the middle layer20may have exactly the same color. When the bottom layer40and the light shielding area22of the middle layer20have exactly the same color, the bottom layer40and the light shielding area22of the middle layer20have the same reaction with the light. In this way, in the first light emitting mode, the bottom layer40makes up for the difference between the light transmitting region21and the light shielding area22of the middle layer20, thereby avoiding generating light and shadow at the junction of the light transmitting region21and the light shielding area22, and maintaining the best state of the first light emitting mode.

Referring toFIG.5, the first light emitting element52and the second light emitting element53are respectively located on two surfaces of the circuit board51. The first light emitting element52corresponds to a side surface of the first light guide plate10. The second light emitting element53corresponds to a side surface of the second light guide plate30. In some embodiments, the first light emitting element52contacts the side surface of the first light guide plate10, or the first light emitting element52and the side surface of the first light guide plate10have a slit therebetween due to the tolerance generated after assembly. The second light emitting element53contacts the side surface of the second light guide plate30, or the second light emitting element53and the side surface of the second light guide plate30have a slit therebetween due to the tolerance generated after assembly. It should be noted that the number of the first light emitting elements52and the second light emitting elements53may be, but not limited to, one or more respectively.

In some embodiments, the circuit board51may be, but not limited to, a flexible printed circuit (FPC) or a printed circuit board (PCB). The first light emitting elements52and the second light emitting elements53may be, but not limited to, light emitting diodes (LEDs). The first light emitting element52emits light toward the first light guide plate10, and the second light emitting element53emits light toward the second light guide plate30.

Referring toFIG.5, in these embodiments, the first light emitting element52and the second light emitting element53are arranged on two opposite surfaces of the circuit board51, and between the two opposite surfaces of the circuit board51that are provided with the first light emitting element52and the second light emitting element53is the side surface of the circuit board51. Thereby, the side surface of the circuit board51abuts against the side surface of the first light guide plate10, the middle layer20or the second light guide plate30, and the circuit board51is parallel to the first light guide plate10, the middle layer20, the second light guide plate30or the bottom layer40.

Based on the above, referring toFIG.2toFIG.5, when only the first light emitting element52emits light, the light emitted by the first light emitting element52passes through the first light guide plate10and interacts with the first microstructure11to provide the first light emitting mode. When only the second light emitting element53emits light, the light emitted by the second light emitting element53passes through the second light guide plate30and interacts with the second microstructure31to provide a second light emitting mode. When the first light emitting element52and the second light emitting element53emit light at the same time, the light emitted by the first light emitting element52and the second light emitting element53at the same time respectively passes through the first light guide plate10and the second light guide plate30and respectively interacts with the first microstructure11and the second microstructure31to jointly provide the third light emitting mode. Specifically, the area of the first microstructure11is greater than the area of the second microstructure31, so the first light emitting mode with a larger light emitting range, the second light emitting mode with a smaller light emitting range, and the third light emitting mode with overlapped light emission can be presented, thereby providing diversified light emitting modes.

Referring toFIG.5toFIG.8, in some embodiments, the first light guide plate10, the middle layer20and the second light guide plate30are all planar structures constructed along a first direction D1and a second direction D2perpendicular to each other. In these embodiments, the first light guide plate10has a first length L1in the first direction D1and a third length L3in the second direction D2. The second light guide plate30has a second length L2in the first direction D1and a fourth length L4in the second direction D2. In some embodiments, the first light guide plate10has the first length L1greater than the third length L3so as to present a rectangular exterior, and the second light guide plate30has the second length L2greater than the fourth length L4so as to present a rectangular exterior.

Referring toFIG.5, in some embodiments, in order to make the middle layer20easily attached to the first light guide plate10or the second light guide plate30, the exterior shape and size of the middle layer20may correspond to the shape and size of the first light guide plate10or the second light guide plate30. That is, in these embodiments, the first light guide plate10, the middle layer20and the second light guide plate30have the same length in the first direction D1, and the first light guide plate10, the middle layer20and the second light guide plate30also have the same length in the second direction D2. Thereby, the middle layer20can be completely attached to the first light guide plate10or the second light guide plate30.

Referring toFIG.5, in some embodiments where the first light guide plate10, the middle layer20and the second light guide plate30have exactly the same exterior shape and size, edges of the first light guide plate10, the middle layer20and the second light guide plate30are aligned. In these embodiments, the first light emitting element52and the second light emitting element53are arranged on two opposite surfaces of the circuit board51and are adjacent to the same side surface of the circuit board51. That is, in a direction perpendicular to the two surfaces of the circuit board51that are provided with the first light emitting element52and the second light emitting element53, the first light emitting element52and the second light emitting element53overlap in position. Thereby, the first light emitting element52can be as close as possible to the first light guide plate10, and the second light emitting element53can be as close as possible to the second light guide plate30, so that the light emitted by the first light emitting element52can directly enter the first light guide plate10and the light emitted by the second light emitting element53can directly enter the second light guide plate30, thereby reducing the optical loss and improving the light utilization.

Referring toFIG.9toFIG.13,FIG.9is a schematic cross-sectional view of a second embodiment of a touchpad A.FIG.10is a schematic top view of a local structure of the touchpad A, in which first light emitting elements52on an upper surface of the circuit board51are represented by solid lines and second light emitting elements53on a lower surface of the circuit board51are represented by dashed lines.FIG.11is a schematic cross-sectional view of a third embodiment of a touchpad A.FIG.12is a schematic cross-sectional view of a fourth embodiment of a touchpad A.FIG.13is a schematic cross-sectional view of a fifth embodiment of a touchpad A. In some embodiments, the upper surface of the circuit board51shown inFIG.10is provided with a plurality of first light emitting elements52, and the first light emitting elements52are represented by solid lines. The lower surface of the circuit board51is provided with a plurality of second light emitting elements53, and the second light emitting elements53are represented by dashed lines.

In order to reduce light interference between the first light emitting element52and the second light emitting element53, in the direction perpendicular to the two surfaces of the circuit board51that are provided with the first light emitting element52and the second light emitting element53, the first light emitting element52and the second light emitting element53do not overlap in position (as shown inFIG.9orFIG.12).

Referring toFIG.9toFIG.11, in some embodiments, the first light emitting element52is arranged at a first position P1of the circuit board51, and the second light emitting element53is arranged at a second position P2of the circuit board51. The first position P1is farther from a center position of the middle layer20than the second position P2in the second direction D2. That is, the first light emitting element52and the second light emitting element53are arranged at different positions on the circuit board51in the second direction D2, the first light emitting element52and the second light emitting element53are staggered on the circuit board51, a control chip on the circuit board51is arranged at a position staggered from the first light emitting element52or the second light emitting element53.

Referring toFIG.9toFIG.11, in these embodiments, the second position P2is adjacent to a side surface of the circuit board51close to the second light guide plate30, and the second light emitting element53can be as close as possible to the side surface of the second light guide plate30after being arranged at the second position P2. Since the first light emitting element52and the second light emitting element53are staggered in the second direction D2, there is a gap between the first position P1and the side surface of the circuit board51close to the second light guide plate30in the second direction D2. In order to make the first light emitting element52be as close as possible to the side surface of the first light guide plate10, the first light guide plate10further includes a first extending portion12, and the first extending portion12extends along the second direction D2, so that the third length L3of the first light guide plate10in the second direction D2is greater than the fourth length L4of the second light guide plate30in the second direction D2.

In this way, the first light guide plate10can extend over the circuit board51to be adjacent to the side surface of the second light emitting element53and extend to the first light emitting element52to fill the gap between the first position P1and the side surface of the circuit board51, so that the first light emitting element52can be as close as possible to the first light guide plate10, thereby reducing the light interference between the first light emitting element52and the second light emitting element53, avoiding the optical loss of the first light emitting element52and improving the light utilization.

In some embodiments where the third length L3of the first light guide plate10is not equal to the fourth length L4of the second light guide plate30, in order to further avoid light interference between the first light emitting element52and the second light emitting element53, referring toFIG.10, the backlight module B further includes a light shielding adhesive60. The light shielding adhesive60is attached to the gap on the circuit board51adjacent to the first light emitting element52or the second light emitting element53. In some embodiments, the light shielding adhesive60is a non-light transmitting black tape with adhesive on both sides.

Specifically, referring toFIG.9andFIG.11, in some embodiments where the third length L3of the first light guide plate10is greater than the fourth length L4of the second light guide plate30, the backlight module B includes a first light shielding adhesive60A. The first light shielding adhesive60A is attached between the first extending portion12of the first light guide plate10and the circuit board51. Thereby, while the first light shielding adhesive60A is attached between the circuit board51and the first light guide plate10, light emitted by the first light emitting element52can be prevented from going to the second light guide plate30via the gap on the circuit board51adjacent to the first light emitting element52, thereby avoiding light interference between the first light emitting element52and the second light emitting element53.

The arrangement of different positions of the first light emitting element52and the second light emitting element53on the circuit board51in the second direction D2is not limited to the foregoing embodiments. In some embodiments shown inFIG.12andFIG.13, the first light emitting element52is arranged at a third position P3of the circuit board51, and the second light emitting element53is arranged at a fourth position P4of the circuit board51. The third position P3is closer to a center position of the middle layer20than the fourth position P4in the second direction D2.

Referring toFIG.12, in these embodiments, the third position P3is adjacent to the side surface of the circuit board51close to the first light guide plate10, so that the first light emitting element52can be as close as possible to the side surface of the first light guide plate10after being arranged at the third position P3. Since the first light emitting element52and the second light emitting element53are staggered in the second direction D2, there is a gap between the fourth position P4and the side surface of the circuit board51close to the second light guide plate30in the second direction D2. In order to make the second light emitting elements53be as close as possible to the side surface of the second light guide plate30, the second light guide plate30further includes a second extending portion32, and the second extending portion32extends along the second direction D2, so that the fourth length L4of the second light guide plate30in the second direction D2is greater than the third length L3of the first light guide plate10in the second direction D2.

In this way, the second light guide plate30can extend over the circuit board51to be adjacent to the side surface of the first light emitting element52and extend to the second light emitting element53to fill the gap between the fourth position P4and the side surface of the circuit board51, so that the second light emitting element53can be as close as possible to the second light guide plate30, thereby reducing the light interference between the first light emitting element52and the second light emitting element53, avoiding the optical loss of the second light emitting element53and improving the light utilization.

Referring toFIG.12andFIG.13, in some embodiments where the third length L3of the first light guide plate10is smaller than the fourth length L4of the second light guide plate30, the backlight module B includes a second light shielding adhesive60B, and the second light shielding adhesive60B is attached between the second extending portion32of the second light guide plate30and the circuit board51. Thereby, while the second light shielding adhesive60B is attached between the circuit board51and the second light guide plate30, light emitted by the second light emitting element53can be prevented from going to the first light guide plate10via the gap on the circuit board51adjacent to the second light emitting element53, thereby avoiding light interference between the first light emitting element52and the second light emitting element53.

Referring toFIG.9toFIG.13, in some embodiments where the third length L3of the first light guide plate10is not equal to the fourth length L4of the second light guide plate30, the length of the middle layer20in the second direction D2may be equal to the third length L3(as shown inFIG.9) or equal to the fourth length L4(as shown inFIG.11toFIG.13). In these embodiments, the arrangement of the position of the middle layer20may be different, which will be described as follows.

Referring toFIG.11, in some embodiments where the length of the middle layer20in the second direction D2is equal to the smaller of the third length L3and the fourth length L4, the side surface of the middle layer20is adjacent to the side surface of the circuit board51. Referring toFIG.9,FIG.12andFIG.13, in some embodiments where the length of the middle layer20in the second direction D2is equivalent to the larger of the third length L3and the fourth length L4, a part of the middle layer20is laminated between the first light guide plate10and the second light guide plate30, and the remaining part is laminated between the circuit board51and the first light guide plate10or the second light guide plate30which has a greater length in the second direction D2.

Referring toFIG.9andFIG.11toFIG.13, in some embodiments, the backlight module B further includes a plurality of attachment members70(in the cross-sectional views ofFIG.9andFIG.11toFIG.13, in order to clearly present the structure of layers, the attachment members70are not shown). The first light guide plate10, the middle layer20, the second light guide plate30and the bottom layer40of the backlight module B are attached through the attachment members70. In these embodiments, the first light guide plate10and the middle layer20, the middle layer20and the second light guide plate30, and the second light guide plate30and the bottom layer40are respectively attached through the attachment members70. In some embodiments, the attachment members70may be an optically clear adhesive (OCA for short, or optical acrylic adhesive). The optically clear adhesive has the characteristics of high light transmittance, high bonding strength and small curing shrinkage, so that the first light guide plate10, the middle layer20, the second light guide plate30and the bottom layer40can be actually glued without affecting the optical characteristics between the layers.

Referring toFIG.11andFIG.13, in some embodiments, the backlight module B further includes a transflective layer80, located between the first light guide plate10and the middle layer20. The transflective layer80has light reflectivity and light transmittance, and is configured to reflect light from the first light emitting element52to the first light guide plate10and make light from the second light emitting element53pass through the transflective layer80. In this way, when only the first light emitting element52emits light, the transflective layer80can reflect the light from the first light emitting element52to the first light guide plate10before the light exits, thereby forming the first light emitting mode. When only the second light emitting element53emits light, the light from the second light emitting element53can pass through the second light guide plate30, the middle layer20and the transflective layer80and then exit, thereby forming the second light emitting mode. When the first light emitting element52and the second light emitting element53emit light at the same time, the transflective layer80can reflect the light from the first light emitting element52and allow the light from the second light emitting element53to pass through it, so that the light from the first light emitting element52and the second light emitting element53can overlap and then exit, thereby forming the third light emitting mode.

Referring toFIG.11, in some embodiments where the backlight module B includes the transflective layer80and the third length L3of the first light guide plate10is greater than the fourth length L4of the second light guide plate30, the length of the transflective layer80in the second direction D2is the same as the third length L3of the first light guide plate10, and the first light shielding adhesive60A is attached to a position between the circuit board51and the transflective layer80corresponding to the first extending portion12. In these embodiments, the length of the middle layer20in the second direction D2is the same as the fourth length L4of the second light guide plate30, and the side surface of the middle layer20is attached to the side surface of the circuit board51.

Referring toFIG.13, in some embodiments where the backlight module B includes the transflective layer80and the third length L3of the first light guide plate10is smaller than the fourth length L4of the second light guide plate30, the length of the transflective layer80in the second direction D2is the same as the fourth length L4of the second light guide plate30, the length of the middle layer20in the second direction D2is the same as the third length L3of the first light guide plate10, and the second light shielding adhesive60B is attached to a position between the circuit board51and the middle layer20corresponding to the second extending portion32.

In some embodiments, the transflective layer80is a see through mirror (STM). The transflective layer80may be, but not limited to, an optical thin film, a dielectric material, silicone or an epoxy resin adhesive material mixed with titanium dioxide, silicon dioxide or aluminum oxide reflective particles. In some embodiments, the transflective layer80may also be a white diffuser having an 80% transmittance and a reflective effect.

Referring toFIG.9andFIG.11toFIG.13, in some embodiments, the backlight module B further includes a diffuser90, arranged on a side of the first light guide plate10away from the middle layer20, i.e., the light exit side of the first light guide plate10. Thereby, by arranging the diffuser90on the light exit side of the first light guide plate10, the backlight module B can provide uniform light emission.

In some embodiments, the diffuser90is made of a material with a high light transmittance (for example, but not limited to, polyethylene terephthalate (PET), polycarbonate (PC) or polymethyl methacrylate (PMMA)), and the diffuser90includes a plurality of scattering particles. Light passing through the diffuser90interacts with the scattering particles so as to be refracted, reflected and scattered constantly, thereby achieving the effect of uniform light.

Referring toFIG.5andFIG.9toFIG.13, in some embodiments, the backlight module B further includes a plurality of light barrier covering members M. The light barrier covering members M are located on a periphery of the whole backlight module B to cover the first light guide plate10, the middle layer20, the second light guide plate30, the circuit board51, the first light emitting elements52and the second light emitting elements53. In these embodiments, the light barrier covering member M is a non-light transmitting black polyester film (Mylar), thereby reducing the possibility of light leakage from the non-light exit direction of the backlight module B and improving the light emitting effect.

According to the foregoing description, by means of the arrangement of the area of the first microstructure11of the first light guide plate10, the design of the shape of the light transmitting region21of the middle layer20and the arrangement of the area of the second microstructure31of the second light guide plate30, the light emitting effect of the backlight module B in the first light emitting mode, the second light emitting mode and the third mode can be changed.

In some embodiments, the brightness of the backlight module B in the first light emitting mode and the second light emitting mode may also be adjusted according to needs. Parameters for adjusting the brightness presented by each light emitting mode include one or a combination of the numbers of the first light emitting elements52and the second light emitting elements53, and the thickness of the first light guide plate10or the second light guide plate30, the thickness (light intensity) of the first light emitting elements52or the second light emitting elements53and the density of the first light emitting elements52or the second light emitting elements53arranged (as shown inFIG.10, the spacing between the first light emitting elements52is greater than the spacing between the second light emitting elements53) in each light emitting mode.

For example, in some embodiments where the backlight module B includes a plurality of first light emitting elements52and a plurality of second light emitting elements53, when the first light emitting mode and the second light emitting mode are required to present the same brightness, the brightness presented by the light emitted by the first light emitting elements52after passing through the first light guide plate10is the same as the brightness presented by the light emitted by the second light emitting elements53after passing through the second light guide plate30.

In these embodiments, the first light emitting elements52and the second light emitting elements53arranged on the two opposite surfaces of the circuit board51have the same light emitting properties, the first light guide plate10and the second light guide plate30have the same thickness, and the density of the first light emitting elements52arranged on the circuit board51along the first direction D1is the same as the density of the second light emitting elements53arranged on the circuit board51along the first direction D1. Thereby, the first light emitting mode and the second light emitting mode present the same brightness.

In some embodiments, in order to make the backlight module thinner without affecting the brightness presented, the thickness of the first light emitting elements52, the thickness of the first light guide plate10and the density of the first light emitting elements52arranged on the circuit board51along the first direction D1are the same as those in the foregoing embodiments. The thickness of the second light emitting elements53is reduced (the light intensity is reduced), that is, the thickness of the second light emitting elements53is smaller than the thickness of the first light emitting elements52. The thickness of the second light guide plate30is reduced, that is, the thickness of the second light guide plate30is smaller than the thickness of the first light guide plate10. Here, while the thickness of the second light guide plate30is reduced, the flux of light entering the second light guide plate30is also reduced. Therefore, in order to maintain the brightness presented as in the foregoing embodiments, the number of the second light emitting elements53is increased, and the density of the second light emitting elements53arranged on the circuit board51along the first direction D1is also increased, thereby making the brightness the same as in the foregoing embodiments and also reducing the overall thickness of the backlight module B to make the backlight module thinner.