Light guide plate, backlight unit, and liquid crystal display device

Abstract

Disclosed are a light guide plate, a backlight unit, and a liquid crystal display device, the light guide plate including a light incident surface through which light emitted from a light source is incident; and a light exit surface having a light exit region configured to allow light to exit and a peripheral region adjacent to the light exit region. The light guide plate includes at least one protrusion in a peripheral area.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Japanese Patent Application No. 2024-174281, filed on October 3, 2024, and Japanese Patent Application No. 2025-109562, filed on June 27, 2025, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This application relates to light guide plates, backlight units, and liquid crystal display devices. Background Technology

[0004] For example, some liquid crystal display devices are equipped with a backlight unit as an illumination device, which includes a light source, a light guide plate, and optical sheets. The optical sheets modulate the properties of the light emitted from the light guide plate and entering the liquid crystal display panel. Examples of optical sheets include diffusers, prism sheets, and polarizing reflectors. A backlight unit typically includes multiple optical sheets.

[0005] Optical sheets made of materials such as polyethylene terephthalate (PET) or polycarbonate undergo thermal expansion after prolonged use of liquid crystal display (LCD) devices. When the thermally expanded optical sheet causes its ends to contact adjacent components, the optical sheet may warp or wrinkle. Such warping or wrinkling in the optical sheet can impair the display quality of the LCD device. U.S. Patent Application Publication No. 2018 / 0095319 discloses a panel chassis for holding a liquid crystal panel. This panel chassis includes ribs with inclined surfaces to ensure space for accommodating elongated optical sheets. The inclined surfaces of the ribs have a decreasing slope in the stacking direction of the optical sheets from the side adjacent to the optical sheet with a higher coefficient of thermal expansion.

[0006] The technology disclosed in U.S. Patent Application Publication No. 2018 / 0095319 involves contacting the optical sheet with the inclined surface of the panel chassis ribs and intentionally bending the outer periphery of the optical sheet along the inclined surface, which may result in load on the optical sheet. Furthermore, to meet the latest demand for thinner frames in liquid crystal display devices or backlight units, the gap between the optical sheet and the chassis (i.e., the width of the space used to accommodate the elongated optical sheet) must be further reduced.

[0007] In view of the above, the purpose of this disclosure is to provide a light guide plate, a backlight unit, and a liquid crystal display device that can achieve a reduced gap between the optical sheet and the chassis. Summary of the Invention

[0008] The light guide plate according to a first aspect of the present disclosure includes: a light incident surface through which light emitted from a light source is incident; a light emitting surface including: a light emitting region configured to allow light to emanate, and a peripheral region adjacent to the light emitting region; and at least one protrusion in the peripheral region.

[0009] The backlight unit according to a second aspect of this disclosure includes: a light source for emitting light; a light guide plate including: a light incident surface through which light emitted from the light source is incident, and a light emitting surface including: a light emitting region configured to allow light to emanate, and a peripheral region adjacent to the light emitting region; and an optical sheet mounted on the light emitting surface of the light guide plate, wherein the light guide plate includes at least one protrusion in the peripheral region, and the optical sheet is positioned above the at least one protrusion when the optical sheet thermally expands.

[0010] The liquid crystal display device according to the third aspect of this disclosure includes: the aforementioned backlight unit; and a liquid crystal display panel mounted on the backlight unit.

[0011] It should be understood that the above general description and the following detailed description are exemplary and explanatory, and do not limit this disclosure.

[0012] This disclosure enables a reduced gap between the optical element and the chassis. This reduced gap between the optical element and the chassis allows for a thinner frame for the liquid crystal display device and the backlight unit. Attached Figure Description

[0013] A more complete understanding of this application can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:

[0014] Figure 1 This is a cross-sectional view of the liquid crystal display device according to Embodiment 1;

[0015] Figure 2 This is a plan view of the light guide plate, light source, optical sheet and lower chassis of the backlight unit according to Embodiment 1;

[0016] Figure 3 This is a plan view of the light guide plate according to Embodiment 1;

[0017] Figure 4 It is along Figure 2 A cross-sectional view of the light guide plate, optical sheet, and lower chassis taken from line AA;

[0018] Figure 5 It is along Figure 2 A cross-sectional view of the light guide plate, light source, optical sheet and lower chassis taken from line BB;

[0019] Figure 6 This is a cross-sectional view of a representative optical sheet after thermal expansion according to Example 1;

[0020] Figure 7 It is a cross-sectional view of the light guide plate and the thermally expanded optical sheet based on Comparative Example 1;

[0021] Figure 8 This is a cross-sectional view of the ribs of the upper chassis according to Embodiment 1;

[0022] Figure 9 This is a plan view of the light guide plate according to Embodiment 2;

[0023] Figure 10 This is a plan view of the light guide plate and optical sheet according to Embodiment 2;

[0024] Figure 11 This is a schematic diagram showing the light guide plate and optical sheet according to Embodiment 3;

[0025] Figure 12 This is a schematic diagram illustrating the width of the protrusion according to Embodiment 3;

[0026] Figure 13 This is another schematic diagram used to illustrate the width of the protrusion according to Embodiment 3;

[0027] Figure 14 This is a schematic diagram showing the light guide plate and optical sheet according to Embodiment 4;

[0028] Figure 15 It is based on the modified plan view of the light guide plate;

[0029] Figure 16 It is a cross-sectional view based on another modified light guide plate and optical sheet;

[0030] Figure 17 It is a cross-sectional view based on another modified protrusion;

[0031] Figure 18 It is based on a cross-sectional view of another modified protrusion; and

[0032] Figure 19 It is a cross-sectional view based on another modified protrusion. Detailed Implementation

[0033] The following description, with reference to the accompanying drawings, describes a light guide plate, a backlight unit, and a liquid crystal display device according to some embodiments.

[0034] Example 1

[0035] The following is for reference Figures 1 to 8 The light guide plate 100, backlight unit 200, and liquid crystal display device 300 according to embodiments are described. Figure 1 As shown, the liquid crystal display device 300 includes a liquid crystal display panel 310 and a backlight unit 200. The backlight unit 200 includes a light guide plate 100. This specification will... Figure 1In the liquid crystal display device 300, the longitudinal direction (i.e., the rightward direction in the plane of the attached drawing) is defined as the +X direction, the lateral direction (i.e., the direction extending into the plane of the attached drawing) is defined as the +Y direction, and the direction perpendicular to both the +X and +Y directions (i.e., the upward direction in the plane of the attached drawing, or the direction towards the user) is defined as the +Z direction. For ease of understanding, Figure 1 An optical element 230 without shadows is shown, and it will be described below. Other accompanying drawings may also show parts without shadows.

[0036] The description begins with the light guide plate 100 and the backlight unit 200. The backlight unit 200 serves as an illumination device for the liquid crystal display panel 310 of the liquid crystal display device 300. (As...) Figure 1 and Figure 2 As shown, the backlight unit 200 includes a light guide plate 100, a lower chassis 210, a light source 220, an optical sheet 230, a reflective sheet 240, and an upper chassis 250.

[0037] The light guide plate 100 is a rectangular plate component extending along the X direction in a plan view. The light guide plate 100 guides light incident from the light source 220 toward the liquid crystal display panel 310. For example... Figures 1 to 3 As shown, the light guide plate 100 includes a main surface 102 (hereinafter referred to as the "light emitting surface 102") having a light emitting region 102a and a peripheral region 102b adjacent to the light emitting region 102a; a main surface 104 opposite to the light emitting surface 102; and four side surfaces (end faces). The light emitting region 102a of the light emitting surface 102 allows light to be emitted toward the liquid crystal display panel 310. The peripheral region 102b of the light emitting surface 102 surrounds the light emitting region 102a.

[0038] In this embodiment, light emitted from the light source 220 enters the light guide plate 100 through the side 106 (hereinafter referred to as "light incident surface 106") located on the -Y side among the four sides. The light incident through the light incident surface 106 diffuses within the light guide plate 100 and is guided toward the liquid crystal display panel 310 through the light emitting region 102a of the light emitting surface 102.

[0039] like Figures 1 to 3 As shown, the light guide plate 100 has a protrusion 120 in the peripheral region 102b of the light emitting surface 102. (In plan view) Figure 3 In this embodiment, one of the protrusions 120 is disposed in a peripheral region 102b on the shorter side 108 in the +X direction, and another protrusion 120 is disposed in a peripheral region 102b on the other shorter side 108 in the -X direction. Each of the protrusions 120 extends along the end edge (short side 108) of the light guide plate 100 on the side where the protrusion 120 is disposed. Figure 4As shown, the protrusion 120 has an inclined surface 122 in the cross-sectional view that is tilted relative to the X direction toward the light emission region 102a. The inclined surface 122 is gently curved.

[0040] The light guide plate 100 is made of a light-transmitting resin (e.g., polycarbonate). For example, the light guide plate 100 includes fine prisms on its main surface 104.

[0041] like Figure 1 and Figure 2 As shown, the lower chassis 210 has a box shape. The lower chassis 210 is made of resin or metal. The lower chassis 210 houses the light guide plate 100, the light source 220, the optical sheet 230, and the reflector 240.

[0042] like Figure 2 As shown, the structure has a gap D1 defined between the side plate 212 of the lower chassis 210 and the end face 232a of the optical sheet 230 before thermal expansion. The gap D1 prevents contact between the side plate 212 of the lower chassis 210 and the end face 232b of the optical sheet 230 after thermal expansion, thereby protecting the optical sheet 230 from warping or wrinkling. The thermal expansion of the optical sheet 230, the optical sheet 230 before thermal expansion, the end face 232b, and other details are described below.

[0043] The light source 220 is, for example, a white light-emitting diode (LED) element. Figure 2 and Figure 5 As shown, the light source 220 is arranged along the light incident surface 106 of the light guide plate 100. Light emitted from the light source 220 enters the light guide plate 100 through the light incident surface 106.

[0044] like Figure 1 and Figure 2 As shown, an optical sheet 230 is mounted on the light emitting surface 102 of the light guide plate 100. The optical sheet 230 modulates the properties of light emitted through the light emitting region 102a of the light emitting surface 102 and entering the liquid crystal display panel 310. Examples of optical sheets 230 include diffusers, prism sheets, and polarizing reflectors. A diffuser, for example, is made of polyethylene terephthalate and diffuses transmitted light. A prism sheet, for example, is made of polyethylene terephthalate and converges transmitted light. A polarizing reflector, for example, is made of polycarbonate. A polarizing reflector transmits light with a specific polarization direction and reflects light with a polarization direction other than the specific polarization direction. In this embodiment, the optical sheet 230 consists of three optical sheets 230, which include a diffuser, a prism sheet, and a polarizing reflector stacked sequentially from one side adjacent to the light emitting surface 102.

[0045] Three optical sheets 230 are stacked on top of each other and bonded to one of the peripheral regions 102b of the light emitting surface 102 of the light guide plate 100. (As shown) Figure 2 As shown, the optical sheet 230 is bonded to the center of the peripheral region 102b on the long side 109 in the +Y direction by double-sided adhesive tape 260.

[0046] The optical plate 230 has a rectangular profile that extends in the X direction, and this rectangular profile is smaller than the profile of the light emitting surface 102 of the light guide plate 100 in a plan view. For example... Figure 4 As shown, the optical sheet 230 before thermal expansion has an edge 232 positioned above the protrusion 120 of the light guide plate 100. The optical sheet 230 before thermal expansion indicates the optical sheet 230 before the liquid crystal display device 300 is put into use, for example at a temperature of 25°C.

[0047] The optical element 230 expands due to heat emitted from the light source 220 and other electronic components disposed around the backlight unit 200. The thermally expanded optical element 230 indicates the optical element 230 that has expanded due to heat.

[0048] Figure 6 This is a cross-sectional view of the representative optical element 230 after thermal expansion. Reference numeral 232a indicates the end face of the optical element 230 before thermal expansion, while reference numeral 232b indicates the end face of the optical element 230 after thermal expansion. For ease of understanding, Figure 6 Only a single optical element 230 is shown.

[0049] In this embodiment, the edge 232 of the optical sheet 230 before thermal expansion is positioned above the protrusion 120 of the light guide plate 100. For example... Figure 6 As shown, the optical element 230 elongates along the inclined surface 122 of the protrusion 120 during expansion. Since the inclined surface 122 is inclined in the X direction, the optical element 230 elongates in the direction inclined in the X direction. Therefore, at the X-direction end of the backlight unit 200, the length L2 of the optical element 230 extending in the X direction due to thermal expansion is shorter than the actual elongation L1 of the optical element 230 due to thermal expansion. This structure can reduce the gap D1 between the side plate 212 of the lower chassis 210 and the end face 232a of the optical element 230 before thermal expansion, because the gap D1 only needs to be longer than the X-direction length L2 of the optical element 230 due to thermal expansion, and can be shorter than the actual elongation L1 of the optical element 230 due to thermal expansion.

[0050] The following describes an exemplary comparison backlight unit (hereinafter referred to as the "backlight unit in Comparative Example 1"), wherein an exemplary optical sheet 230 made of polyethylene terephthalate is bonded to the center of a peripheral region 102b on the long side 109 of a light guide plate 100A without protrusions 120 by double-sided tape 260. When this exemplary comparison backlight unit is heated from 25°C to 95°C, the long side of the optical sheet 230 increases by 0.9 mm. These exemplary optical sheets 230 have a length of 267.61 mm on their long side and a length of 159.60 mm on their short side at a temperature of 25°C. The light guide plate 100A has the same construction as the light guide plate 100, except that it lacks protrusions 120. The exemplary comparison backlight unit has the same construction as the backlight unit 200, except that it lacks protrusions 120.

[0051] Since the long side of the optical sheet 230 of the backlight unit in Comparative Example 1 is increased by 0.9 mm, the actual elongation L1 of the optical sheet 230 due to thermal expansion at one end of the exemplary comparative backlight unit in the X direction is 0.45 mm (equal to half of 0.9 mm). Therefore, as Figure 7 As shown, the width (length in the X direction) of the gap D1 in the backlight unit in Comparative Example 1 needs to be greater than 0.45 mm (length L1) to prevent the side plate 212 of the lower chassis 210 from contacting the end face 232b of the thermally expanded optical sheet 230.

[0052] Conversely, when the backlight unit 200, including the light guide plate 100 and the aforementioned exemplary optical sheet 230, is heated from 20°C to 95°C, it is found that the X-direction length L2 of the optical sheet 230 at one end of the backlight unit 200 due to thermal expansion is 0.37 mm. Therefore, the width of the gap D1 in this backlight unit 200 only needs to be greater than 0.37 mm. That is, compared with the backlight unit in Comparative Example 1, the backlight unit 200 can achieve a reduced gap D1. The inclined surface 122 of the protrusion 120 has a maximum angle θ1 of 20°, and the height H of the protrusion 120 is 2.0 mm.

[0053] like Figure 5 As shown, a reflector 240 is disposed on the main surface 104 of the light guide plate 100. The reflector 240 reflects light emitted from the main surface 104 of the light guide plate 100 toward the light guide plate 100.

[0054] The upper chassis 250 has a frame shape. For example... Figure 1As shown, the upper base 250 has inwardly extending ribs 252. The upper base 250 is made of, for example, synthetic resin. The ribs 252 partially overlap with the peripheral region 102b of the light guide plate 100 and the optical sheet 230 corresponding to the peripheral region 102b of the light guide plate 100, and define an opening 254. The opening 254 exposes the light emitting region 102a of the light guide plate 100.

[0055] like Figure 8 As shown, rib 252 and optical plate 230 preferably define a gap D2 therebetween. Gap D2 prevents contact between optical plate 230 and rib 252.

[0056] This structure, including the optical sheet 230 positioned above the protrusion 120 of the light guide plate 100 as described above, reduces the gap D1 between the side plate 212 of the lower chassis 210 and the end face 232a of the optical sheet 230 before thermal expansion, thereby making the frame of the backlight unit 200 thinner. The backlight unit 200 including the gap D1 prevents contact between the side plate 212 of the lower chassis 210 and the end face 232b of the thermally expanded optical sheet 230, thereby reducing warping or wrinkling in the optical sheet 230.

[0057] The following describes a liquid crystal display device 300. The liquid crystal display device 300 displays characters, images, and other information. For example... Figure 1 As shown, the liquid crystal display device 300 includes the aforementioned backlight unit 200, liquid crystal display panel 310, and bezel 320. This description focuses on the liquid crystal display panel 310 and the bezel 320.

[0058] The liquid crystal display panel 310 is mounted on the rib 252 of the upper chassis 250 of the backlight unit 200. For example, the liquid crystal display panel 310 is a known in-plane switching transmissive liquid crystal display panel. The liquid crystal display panel 310 is driven by an active matrix of thin-film transistors (TFTs). The liquid crystal display panel 310 displays characters, images, and other information by modulating light from the backlight unit 200. The liquid crystal display panel 310 has a display area 311 and a peripheral area 312. The display area 311 includes pixels arranged in a matrix and can display characters, images, and other information. The peripheral area 312 includes components such as wires and driving circuitry.

[0059] The 320mm border has a box shape. For example... Figure 1 As shown, the bezel 320 has an opening 324 in the top base 322. The bezel 320 is made of, for example, metal. The bezel 320 covers the upper chassis 250 of the backlight unit 200 such that the top base 322 faces the +Z side and protects the peripheral area 312 of the liquid crystal display panel 310. The opening 324 exposes the display area 311 of the liquid crystal display panel 310.

[0060] As described above, the light guide plate 100 of the backlight unit 200 includes a protrusion 120 in the peripheral region 102b of the light emitting surface 102, and the edge 232 of the optical sheet 230 is positioned above the protrusion 120. During the thermal expansion of the optical sheet 230, the edge 232 of the optical sheet 230 elongates on the inclined surface 122 of the protrusion 120 in a direction inclined from the X direction. This structure can reduce the gap D1 between the side plate 212 of the lower chassis 210 and the end face 232a of the optical sheet 230 before thermal expansion. Therefore, the backlight unit 200 can achieve a thinner frame. The liquid crystal display device 300 including the backlight unit 200 can also achieve a thinner frame.

[0061] Example 2

[0062] In Embodiment 1, the optical sheet 230 is bonded to the center of the peripheral region 102b on the long side 109 of the light guide plate 100. The optical sheet 230 may also be bonded to the peripheral region 102b on the short side 108 of the light guide plate 100.

[0063] Except for the structure of the protrusion 120 of the light guide plate 100 and the bonding position of the optical sheet 230, the backlight unit 200 in this embodiment has the same construction as the backlight unit in Embodiment 1. This description focuses on the structure of the protrusion 120 of the light guide plate 100 and the bonding position of the optical sheet 230.

[0064] like Figure 9 As shown, only the peripheral region 102b on the short side 108 in the -X direction includes the protrusion 120 of the light guide plate 100 in this embodiment. Other features of the protrusion 120 in this embodiment are the same as those of the protrusion 120 in Embodiment 1.

[0065] like Figure 10 As shown, in this embodiment, the optical sheet 230 is bonded to the peripheral region 102b on the short side 108 in the +X direction using double-sided adhesive tape 260. In this embodiment, the edge 232 of the optical sheet 230 before thermal expansion is the same as the edge 232 of the optical sheet 230 in Embodiment 1, and is positioned above the protrusion 120 of the light guide plate 100. Other features of the optical sheet 230 in this embodiment are the same as those of the optical plate 230 in Embodiment 1.

[0066] In this embodiment, the edge 232 of the optical sheet 230 is also positioned above the protrusion 120 of the light guide plate 100. Therefore, during the thermal expansion of the optical sheet 230, the edge 232 of the elongated optical sheet 230 elongates in a direction inclined from the X direction. Thus, the backlight unit 200 can achieve a reduced gap D1 between the side plate 212 of the lower chassis 210 and the end face 232a of the optical sheet 230 before thermal expansion.

[0067] The following describes an exemplary comparison backlight unit (hereinafter referred to as the "backlight unit in Comparative Example 2"), in which an exemplary optical sheet 230 is bonded with double-sided tape 260 to a peripheral region 102b on the short side 108 in the +X direction of a light guide plate 100A without protrusions 120. When this exemplary comparison backlight unit is heated from 25°C to 95°C, the edge 232 of the elongated optical sheet 230 on the -X side elongates by 1.3 mm. The exemplary optical sheet 230 has the same construction as the exemplary optical sheet 230 in Embodiment 1. Except that the light guide plate 100A does not have protrusions 120, the light guide plate 100A has the same construction as the light guide plate 100 in the embodiment. Except for the light guide plate 100A, the backlight unit in Comparative Example 2 has the same construction as the backlight unit 200.

[0068] In the backlight unit of Comparative Example 2, the edge 232 of the elongated optical sheet 230 on the -X side is extended by 1.3 mm. Therefore, in the backlight unit of Comparative Example 2, the width of the gap D1 between the side plate 212 of the lower chassis 210 on the -X side and the end face 232a of the optical sheet 230 on the -X side before thermal expansion needs to be greater than 1.30 mm (length L1) to prevent contact between the side plate 212 of the lower chassis 210 and the end face 232b of the optical sheet 230 after thermal expansion.

[0069] Conversely, when the backlight unit 200 of this embodiment, including the light guide plate 100 and the exemplary optical sheet 230 described above, is heated from 20°C to 95°C, it is found that the X-direction length L2 of the optical sheet 230 due to thermal expansion is 1.15 mm. Therefore, the width of the gap D1 on the -X side of the backlight unit 200 only needs to be greater than 1.15 mm. That is, compared with the backlight unit in Comparative Example 2, the backlight unit 200 of this embodiment can achieve a reduced gap D1. The inclined surface 122 of the protrusion 120 has a maximum angle θ1 of 20°, and the height H of the protrusion 120 is 3.2 mm.

[0070] Therefore, as described above, the backlight unit 200 in this embodiment can reduce the gap D1 between the side plate 212 of the lower chassis 210 and the end face 232a of the optical sheet 230 before thermal expansion. Therefore, the backlight unit 200 in this embodiment can achieve a thinner frame. The liquid crystal display device 300 including the backlight unit 200 in this embodiment can also achieve a thinner frame.

[0071] Example 3

[0072] The description in this embodiment focuses on the width (length in the X direction) W1 of the protrusion 120 of the light guide plate 100.

[0073] Similar to Embodiment 1, in this embodiment, the optical sheet 230 is bonded to the center of the peripheral region 102b on the long side 109 of the light guide plate 100 by double-sided adhesive tape 260. As shown in Embodiment 1, the edge 232 of the optical sheet 230 before thermal expansion is placed above the protrusion 120 of the light guide plate 100.

[0074] Similar to Embodiment 1, in this embodiment, one of the protrusions 120 of the light guide plate 100 is disposed in the peripheral region 102b on the short side 108 in the +X direction, and the other protrusion 120 is disposed in the peripheral region 102b on the short side 108 in the -X direction. Figure 11 ).like Figure 11 and Figure 12 As shown, the protrusion 120 of the light guide plate 100 in this embodiment has a rectangular shape in the cross-sectional view.

[0075] The protrusion 120 can have any shape, as long as it can receive the edge 232 of the optical sheet 230 placed above it, as described below. For ease of understanding, Figure 11 Optical element 230 is shown with a single thick line.

[0076] If the edge 232 of the optical sheet 230 slips off the protrusion 120 of the light guide plate 100 due to the contraction of the optical sheet 230, it may not return to its original position above the protrusion 120 of the light guide plate 100 even after the optical sheet 230 re-expands. Therefore, the edge 232 of the optical sheet 230 needs to remain positioned above the protrusion 120 of the light guide plate 100 within the operating temperature range (e.g., ambient temperature from -40°C to 95°C). The following assumes an example where the optical sheet 230 is mounted on the light guide plate 100 at a temperature of 25°C, such that the outermost tip 234 of the edge 232 of the optical sheet 230 is aligned with the outer edge 124 of each protrusion 120, as shown below. Figure 12 As shown. In this example, as Figure 13 As shown, at the lower limit temperature Tm of the operating temperature range (e.g., Tm = -40°C), it is desirable that the outermost tip 234 of the edge 232 of the shrunken optical sheet 230 is located above the upper surface 126 of the protrusion 120. Figure 13 In the figure, reference numeral 232c indicates the end face of the shrunken optical plate 230.

[0077] In order to position the outermost tip 234 of the edge 232 of the contracted optical sheet 230 above the upper surface 126 of the protrusion 120 as described above, the length Lr of the edge 232 of the optical sheet 230 overlapping with the protrusion 120 at a temperature of 25°C needs to be longer than the contracted length Ls of the optical sheet 230 above the protrusion 120 after the temperature drops from 25°C to the lower limit temperature Tm (i.e., Lr>Ls). The length Lr is represented by the following expression (1), where θ2 indicates the angle of the edge 232 of the optical sheet 230 relative to the upper surface 126 of the protrusion 120 (or the light emitting surface 102 of the light guide plate 100). The length Ls is represented by the following expression (2), where α indicates the coefficient of thermal expansion of the optical sheet 230, and La indicates the length of the optical sheet 230 mounted on the light guide plate 100 at a temperature of 25°C, since the optical sheet 230 is bonded to the center of the peripheral region 102b on the long side 109 of the light guide plate 100, and the protrusion 120 is provided on the peripheral region 102b of the light guide plate 100 in the +X direction and the peripheral region 102b in the -X direction.

[0078]

[0079]

[0080] The above expressions (1) and (2) and the condition that the length Lr is longer than the length Ls (Lr>Ls) indicate that the width W1 of the protrusion 120 in this embodiment is expected to satisfy the following expression (3):

[0081]

[0082] In an exemplary case, the optical element 230 designed for a 4.2-inch liquid crystal display panel 310 has a length La of 98.8 mm and a coefficient of thermal expansion α of 7.59 × 10⁻⁶. -5 With a temperature of 20°C, an angle θ2 of 20°C, and a lower limit temperature Tm of -40°C, expression (3) indicates that the width W1 of the protrusion 120 is expected to be greater than 0.23 mm. In another exemplary case, the length La of the optical sheet 230 designed for a 14-inch liquid crystal display panel 310 is 314.5 mm, and the coefficient of thermal expansion α, angle θ2, and lower limit temperature Tm have the same values ​​as described above (the coefficient of thermal expansion α is 7.59 × 10⁻⁶). -5 / °C, angle θ2 is 20°, lower limit temperature Tm is -40°C), expression (3) shows that the width W1 of protrusion 120 is expected to be greater than 0.73 mm.

[0083] Example 4

[0084] In embodiment 3, the optical sheet 230 is bonded to the center of the peripheral region 102b on the long side 109 of the light guide plate 100. The description in this embodiment focuses on the width W1 of the protrusion 120 of the light guide plate 100, in which the optical sheet 230 is bonded to the peripheral region 102b on the short side 108 of the light guide plate 100.

[0085] Similar to Example 2, in this example, the optical sheet 230 is bonded to the peripheral region 102b on the short side 108 in the +X direction using double-sided adhesive tape 260. Figure 14 As in Embodiment 2, the edge 232 of the optical sheet 230 before thermal expansion is positioned above the protrusion 120 of the light guide plate 100. For ease of understanding, Figure 14 Optical element 230 is shown with a single thick line.

[0086] In this embodiment, as in Embodiment 2, only the peripheral region 102b on the shorter side 108 in the -X direction includes the protrusion 120 of the light guide plate 100. Figure 14 As shown, the protrusion 120 of the light guide plate 100 in this embodiment has a rectangular shape in the cross-sectional view.

[0087] Similar to Embodiment 3, in this embodiment, the edge 232 of the optical sheet 230 is expected to remain positioned above the protrusion 120 of the light guide plate 100 within the operating temperature range (e.g., ambient temperature from -40°C to 95°C). When the optical sheet 230 is mounted on the light guide plate 100 at a temperature of 25°C, such that the outermost tip 234 of the edge 232 of the optical sheet 230 is aligned with the outer edge 124 of the protrusion 120, the length Lr of the edge 232 of the optical sheet 230 overlapping with the protrusion 120 at the temperature of 25°C needs to be longer than the contraction length Ls of the optical sheet 230 above the protrusion 120 after the temperature drops from 25°C to the lower limit temperature Tm (i.e., Lr>Ls), as in Embodiment 3.

[0088] In this embodiment, the length Lr is also represented by the above expression (1). The length Ls is represented by the following expression (4), because the optical sheet 230 is bonded to the peripheral region 102b on the short side 108 in the +X direction, and the protrusion 120 is only provided to the peripheral region 102b on the short side 108 in the -X direction.

[0089]

[0090] The above expressions (1) and (4), as well as the condition that the length Lr is longer than the length Ls (Lr>Ls), indicate that the width W1 of the protrusion 120 in this embodiment is expected to satisfy the following expression (5):

[0091]

[0092] In an exemplary case, the optical element 230 designed for a 4.2-inch liquid crystal display panel 310 has a length La of 98.8 mm and a coefficient of thermal expansion α of 7.59 × 10⁻⁶. -5 Given a temperature of 20°C, an angle θ2 of 20°C, and a lower limit temperature Tm of -40°C, expression (5) indicates that the width W1 of the protrusion 120 is expected to be greater than 0.46 mm. In another exemplary case, where the length La of the optical sheet 230 designed for a 14-inch liquid crystal display panel 310 is 314.5 mm, and the coefficient of thermal expansion α, angle θ2, and lower limit temperature Tm of the optical sheet 230 have the same values ​​as described above, expression (5) indicates that the width W1 of the protrusion 120 is expected to be greater than 1.46 mm.

[0093] Variant

[0094] Within the scope of this disclosure, the above embodiments can be modified in various ways.

[0095] For example, the backlight unit 200 only needs to include at least one optical element 230.

[0096] In the above embodiment, the backlight unit 200 is an edge-lit backlight unit, which allows light emitted from the light source 220 to enter the side surface 106 (light incident surface 106) of the light guide plate 100. The backlight unit 200 can also be a direct-lit backlight unit, which allows light emitted from the light source 220 to enter the main surface 104 of the light guide plate 100. In this variation, the main surface 104 of the light guide plate 100 corresponds to the light incident surface.

[0097] The light guide plate 100 in the above embodiments has a rectangular outline in the plan view. The light guide plate 100 may also have an outline other than a rectangular outline in the plan view.

[0098] In the above embodiment, one or more protrusions 120 of the light guide plate 100 are disposed in the peripheral region 102b on the short side 108. The protrusions 120 of the light guide plate 100 only need to be disposed in the peripheral region 102b. For example, one or more protrusions 120 of the light guide plate 100 may be disposed in the peripheral region 102b on the long side 109. Alternatively, one or more protrusions 120 of the light guide plate 100 may be disposed in both the peripheral region 102b on the short side 108 and the peripheral region 102b on the long side 109.

[0099] In the above embodiment, the peripheral region 102b on the short side 108 includes a single protrusion 120. For example... Figure 15As shown, the peripheral region 102b on the short side 108 may have a plurality of protrusions 120. The protrusions 120 are aligned along the end edge (short side 108) on the side where the protrusions 120 are provided.

[0100] In the above embodiment, the edge 232 of the optical sheet 230 before thermal expansion is placed above one or more protrusions 120 of the light guide plate 100. The optical sheet 230 only needs to be placed above the protrusions 120 of the light guide plate 100 after thermal expansion. In other words, when the optical sheet 230 thermally expands, the optical sheet 230 only needs to be in the state of being placed above the protrusions 120 of the light guide plate 100.

[0101] If the optical sheet 230 is placed above one or more protrusions 120 of the light guide plate 100 after thermal expansion, the gap D1 can be reduced by a structure in which the thermally expanded optical sheet 230 elongates in a direction inclined from the X direction, as in the embodiment described above. For example, as Figure 16 As shown, the optical sheet 230 before thermal expansion does not necessarily need to be placed above the protrusion 120; it is sufficient that the optical sheet 230 after thermal expansion is placed above the protrusion 120.

[0102] One or more protrusions 120 can have any shape, as long as the protrusion 120 can receive the optical sheet 230 placed above the protrusion 120 before thermal expansion. For example, as Figures 17 to 19 As shown, the protrusion 120 may have a triangular, trapezoidal, or rectangular shape in the cross-sectional view. Alternatively, the protrusion 120 may have a shape such that the protrusion 120 can receive the optical sheet 230 to be placed above the protrusion 120 during or after the thermal expansion of the optical sheet 230.

[0103] For illustrative purposes, some exemplary embodiments have been described above. Although specific embodiments have been given in the foregoing discussion, those skilled in the art will recognize that changes in form and detail may be made without departing from the broader spirit and scope of the invention. Therefore, the specification and drawings should be regarded as illustrative rather than restrictive. Consequently, this detailed description should not be regarded as limiting, and the scope of the invention is defined only by the included claims and the full scope of their equivalents.

Claims

1. A light guide plate, comprising: Light incident surface, through which light emitted from the light source enters; The light-emitting surface includes: A light emission region, configured to allow the light to exit, and The peripheral region, which is adjacent to the light emitting region; as well as At least one protrusion in the peripheral region.

2. The light guide plate according to claim 1, wherein, In a plan view of the light emitting surface, the at least one protrusion extends along the end edge on the side where the at least one protrusion is provided.

3. The light guide plate according to claim 1, wherein... In a plan view of the light emitting surface, the plurality of protrusions are aligned along the end edges where the plurality of protrusions are provided.

4. A backlight unit, comprising: A light source, used to emit light; Light guide plate, comprising: A light-incident surface through which light emitted from the light source enters the light-incident surface, and The light-emitting surface includes: A light emission region, configured to allow the light to exit, and The peripheral region, which is adjacent to the light emitting region; and An optical element, which is mounted on the light-emitting surface of the light guide plate, wherein... The light guide plate includes at least one protrusion in the peripheral region, and When the optical sheet thermally expands, the optical sheet is placed above the at least one protrusion.

5. The backlight unit according to claim 4, wherein, In a plan view of the light emitting surface, the at least one protrusion extends along the end edge on the side where the at least one protrusion is provided.

6. The backlight unit according to claim 4, wherein In a plan view of the light emitting surface, the plurality of protrusions are aligned along the end edges where the plurality of protrusions are provided.

7. The backlight unit according to claim 4, further comprising: A chassis configured to cover the peripheral region of the light-emitting surface and the portion of the optical sheet corresponding to the peripheral region of the light-emitting surface, wherein... The portion of the optical sheet corresponding to the peripheral region of the light-emitting surface and the chassis define a gap therebetween.

8. The backlight unit according to claim 4, wherein The light emitting surface has a rectangular shape in the plan view of the light emitting surface. The optical sheet is bonded to one of the peripheral regions on the long side of the light emitting surface, and The at least one protrusion is disposed in one of the peripheral regions on the short side of the light emitting surface.

9. The backlight unit according to claim 4, wherein, The optical element remains positioned above the at least one protrusion within the operating temperature range.

10. A liquid crystal display device, comprising: The backlight unit according to any one of claims 4 to 9; as well as A liquid crystal display panel is mounted on the backlight unit.

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