Backlight Device

Abstract

To provide a backlight device that can improve performance including display quality of a display device and / or thinning.SOLUTION: A backlight device comprises a light source for emitting blue light, a light guide layer, a quantum dot phosphor layer, a reflecting layer, and a yellow phosphor layer. The light guide layer comprises a first principal surface, a second principal surface on the side opposite to the first principal surface, at least one light receiving side surface that receives the blue light emitted from the light source, and at least one non-light receiving side surface that does not receive the blue light emitted from the light source. The quantum dot phosphor layer is provided on the side of the first principal surface of the light guide layer, and includes a red quantum dot phosphor and a green quantum dot phosphor. The reflecting layer is arranged on the side of the second principal surface of the light guide layer. The yellow phosphor layer is provided between the second principal surface of the light guide layer and the reflecting layer, and in a region along the at least one non-light receiving side surface when viewed from the normal direction of the first principal surface, and includes a yellow phosphor. The quantum dot phosphor layer is in contact with the first principal surface of the light guide layer.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a backlight device. [Background technology]

[0002] Many liquid crystal display devices are equipped with a backlight device having an LED. A white LED device combining a blue LED and a phosphor is used as a backlight device equipped in a liquid crystal display device. For example, a remote phosphor type white LED device combining a blue LED that emits blue light with a green phosphor and a red phosphor is used. Specifically, the blue light emitted from the blue LED toward the light guide plate and incident on the light guide plate propagates inside the light guide plate, and the blue light emitted from the light exit surface of the light guide plate enters a wavelength conversion layer containing a green phosphor and a red phosphor. Such white LED devices are classified into an edge-light type in which blue light is emitted from the blue LED toward the side surface of the light guide plate, and a direct type in which blue light is emitted from the blue LED toward the main surface opposite to the light exit surface of the light guide plate. Patent documents 1 to 3 disclose remote phosphor type backlight devices using an edge-light type blue LED, a green quantum dot phosphor, and a red quantum dot phosphor.

[0003] As described in Patent Documents 1 to 3, in a display device using an edge-light type remote phosphor backlight device using a blue LED and green and red phosphors, color unevenness may occur in which the peripheral part of the display area appears bluer than other parts. In order to suppress the occurrence of such color unevenness, the backlight device described in Patent Document 1 has a coloring layer that exhibits yellow (i.e., the complementary color of the color of the light emitted from the blue LED) on the outer edge of the wavelength conversion layer (light conversion layer) or the reflective sheet. The coloring layer contains a yellow pigment or dye. The backlight device described in Patent Document 2 has a coloring member that exhibits yellow, which is provided on the outer peripheral part of the wavelength conversion layer (wavelength conversion member) so as to cover the side surface of the wavelength conversion layer. The coloring member contains a yellow pigment or dye. The backlight device described in Patent Document 3 has a phosphor layer (end surface wavelength conversion sheet) that contains a phosphor (e.g., a yellow phosphor) that receives blue light emitted from the blue LED and emits fluorescence, on the side surface (non-light-entering end surface) of the side surface of the light guide plate that does not receive light emitted from the light source (blue LED). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-26705 A [Patent Document 2] International Publication No. 2016 / 158370 [Patent Document 3] International Publication No. 2016 / 143765 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the inventor's investigation, when the backlight devices of Patent Documents 1 to 3 are used, there may be a problem that the degradation of the display quality of the display device cannot be sufficiently suppressed and / or the display device cannot be sufficiently thinned. The details will be described later.

[0006] The present invention has been made to solve the above problems, and aims to provide a backlight device that can improve the performance, including the display quality and / or thinness, of a display device. [Means for solving the problem]

[0007] According to an embodiment of the present invention, there are provided solutions as described in the following items.

[0008] [Item 1] A light source that emits blue light; a light guide layer having a first main surface, a second main surface opposite to the first main surface, at least one light-receiving side surface intersecting the first and second main surfaces and receiving the blue light emitted from the light source, and at least one non-light-receiving side surface intersecting the first and second main surfaces and not receiving the blue light; a quantum dot phosphor layer provided on the first main surface side of the light guide layer, the quantum dot phosphor layer including a red quantum dot phosphor that receives the blue light and emits red light and a green quantum dot phosphor that receives the blue light and emits green light; a reflective layer disposed on the second main surface side of the light guide layer; a yellow phosphor layer including a yellow phosphor that receives the blue light and emits yellow light, the yellow phosphor layer being provided between the second main surface of the light guide layer and the reflective layer and in a region along the at least one non-light-receiving side surface when viewed from a normal direction of the first main surface; having The quantum dot phosphor layer is in contact with the first main surface of the light guide layer.

[0009] [Item 2] 2. The backlight device according to item 1, wherein when the yellow phosphor layer is viewed from a normal direction of the first main surface, a width of the region is 5 mm or less.

[0010] [Item 3] 3. The backlight device according to item 1 or 2, wherein the yellow phosphor layer is in contact with a main surface of the reflective layer facing the light guide layer.

[0011] [Item 4] 4. The backlight device according to any one of items 1 to 3, wherein a gap is formed between the yellow phosphor layer and the second main surface of the light guide layer.

[0012] [Item 5] A light source that emits blue light; a light guide layer having a first main surface, a second main surface opposite to the first main surface, at least one light-receiving side surface intersecting the first and second main surfaces and receiving the blue light emitted from the light source, and at least one non-light-receiving side surface intersecting the first and second main surfaces and not receiving the blue light; a quantum dot phosphor layer provided on the first main surface side of the light guide layer, the quantum dot phosphor layer having a third main surface facing the first main surface, a fourth main surface opposite the third main surface, at least one first side surface substantially parallel to the at least one light-receiving side surface, and at least one second side surface substantially parallel to the at least one non-light-receiving side surface, the quantum dot phosphor layer including a red quantum dot phosphor that receives the blue light and emits red light, and a green quantum dot phosphor that receives the blue light and emits green light; a reflective layer disposed on the second main surface side of the light guide layer; a yellow phosphor layer provided opposite the at least one second side surface of the quantum dot phosphor layer and including a yellow phosphor that receives the blue light and emits yellow light; A backlight device comprising:

[0013] [Item 6] Item 6. The backlight apparatus of item 5, wherein the yellow phosphor layer is in contact with the at least one second side of the quantum dot phosphor layer.

[0014] [Item 7] The light-guiding layer may further include an optical sheet provided on the quantum dot phosphor layer opposite the light-guiding layer, The optical sheet has a fifth main surface on the quantum dot phosphor layer side, a sixth main surface opposite to the fifth main surface, at least one third side surface substantially parallel to the at least one light-receiving side surface, and at least one fourth side surface substantially parallel to the at least one non-light-receiving side surface; 7. The backlight device of claim 5, wherein the yellow phosphor layer is arranged to face the at least one second side surface of the quantum dot phosphor layer and the at least one fourth side surface of the optical sheet.

[0015] [Item 8] Item 8. The backlight apparatus of item 7, wherein the yellow phosphor layer is in contact with the at least one second side of the quantum dot phosphor layer and the at least one fourth side of the optical sheet.

[0016] [Item 9] Further, another optical sheet is provided on the opposite side of the optical sheet from the quantum dot phosphor layer, the other optical sheet has a seventh main surface on the optical sheet side, an eighth main surface opposite to the seventh main surface, at least one fifth side surface substantially parallel to the at least one light-receiving side surface, and at least one sixth side surface substantially parallel to the at least one non-light-receiving side surface; 9. The backlight device of claim 7 or 8, wherein the yellow phosphor layer is arranged to face the at least one second side surface of the quantum dot phosphor layer, the at least one fourth side surface of the optical sheet, and the at least one sixth side surface of the other optical sheet.

[0017] [Item 10] 10. The backlight device of item 9, wherein the yellow phosphor layer is in contact with the at least one second side of the quantum dot phosphor layer, the at least one fourth side of the optical sheet, and the at least one sixth side of the other optical sheet.

[0018] [Item 11] Item 11. The backlight device according to item 9 or 10, wherein the optical sheet and the other optical sheet are prism sheets arranged such that their ridges are perpendicular to each other.

[0019] [Item 12] Item 12. The backlight device according to any one of items 5 to 11, wherein the third main surface of the quantum dot phosphor layer is in contact with the first main surface of the light guide layer.

[0020] [Item 13] A light source that emits blue light; a light guide layer having a first main surface, a second main surface opposite to the first main surface, at least one light-receiving side surface intersecting the first and second main surfaces and receiving the blue light emitted from the light source, and at least one non-light-receiving side surface intersecting the first and second main surfaces and not receiving the blue light; a quantum dot phosphor layer provided on the first main surface side of the light guide layer, the quantum dot phosphor layer having a third main surface facing the first main surface, a fourth main surface opposite the third main surface, and a side surface intersecting with the third and fourth main surfaces, the quantum dot phosphor layer including a red quantum dot phosphor that receives the blue light and emits red light, and a green quantum dot phosphor that receives the blue light and emits green light; a reflective layer disposed on the second main surface side of the light guide layer; a yellow phosphor layer including a yellow phosphor that receives the blue light and emits yellow light, the yellow phosphor layer being provided so as to face the at least one non-light-receiving side surface of the light guide layer; having the third main surface of the quantum dot phosphor layer is in contact with the first main surface of the light guide layer.

[0021] [Item 14] The light guiding layer further includes a plastic frame disposed to surround the light guiding layer, the plastic frame has a first facing portion facing the at least one non-light-receiving side surface of the light guide layer; Item 14. The backlight device according to item 13, wherein the yellow phosphor layer is provided on the first opposing portion.

[0022] [Item 15] Item 15. The backlight apparatus of item 13 or 14, wherein an air gap is formed between the yellow phosphor layer and the at least one non-light-receiving side of the light guiding layer. Effect of the Invention

[0023] According to an embodiment of the present invention, a backlight device is provided that can improve the performance, including the display quality and / or the thinness, of a display device. [Brief description of the drawings]

[0024] [Figure 1A] FIG. 1 is a schematic cross-sectional view of a liquid crystal display device 200A equipped with a backlight device 100A according to a first embodiment of the present invention. [Figure 1B] FIG. 1 is a schematic plan view of a liquid crystal display device 200A. [Figure 2A] 1 is a schematic perspective view of a light guide layer 112 included in a backlight device 100A. [Figure 2B] 1 is a schematic plan view showing a quantum dot phosphor layer 122 included in a backlight device 100A. [Figure 2C] 1 is a schematic plan view showing a reflective layer 132 and a yellow phosphor layer 142 of a backlight device 100A. [Diagram 3] 1 shows a schematic cross-sectional view of a liquid crystal display device 990A equipped with a backlight device 900A of Comparative Example 1. [Figure 4] 13 is a schematic diagram for explaining a problem that occurs in a liquid crystal display device 990A of Comparative Example 1. FIG. [Diagram 5] 13 shows a schematic cross-sectional view of a liquid crystal display device 990B including a backlight device 900B of Comparative Example 2. [Figure 6] FIG. 11 is a schematic cross-sectional view of a liquid crystal display device 200C including a backlight device 100B according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a schematic cross-sectional view of a liquid crystal display device 200C1 including a backlight device 100B1 according to a modified example of the second embodiment of the present invention. [Figure 8] FIG. 11 is a schematic cross-sectional view of a liquid crystal display device 200B including a backlight device 100C according to a third embodiment of the present invention. [Figure 9]FIG. 13 is a diagram showing the emission spectrum of a yellow phosphor used in a sample panel for evaluating color unevenness. [Figure 10] FIG. 13 is a diagram showing the results of the color unevenness evaluation of sample panel A. [Figure 11A] FIG. 11 is a schematic diagram for explaining a method for evaluating color unevenness. [Figure 11B] FIG. 11 is a schematic diagram for explaining a method for evaluating color unevenness. [Figure 12] 1 is a graph showing the results of color unevenness evaluation of sample panel A. [Figure 13] 1 is a graph showing the results of color unevenness evaluation of sample panel B, sample panel B1, and sample panel C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiment. In the following drawings, components having substantially the same functions are indicated by common reference symbols, and their description may be omitted.

[0026] (Embodiment 1) FIG. 1A is a schematic cross-sectional view of a liquid crystal display device 200A including a backlight device 100A according to an embodiment of the present invention, and FIG. 1B is a schematic plan view of the liquid crystal display device 200A. FIG. 1A shows a cross section taken along line 1A-1A' in FIG. 1B. FIG. 2A is a schematic perspective view of a light guide layer 112 included in the backlight device 100A, and FIG. 2B is a schematic plan view showing a quantum dot phosphor layer 122 included in the backlight device 100A. FIG. 2C is a schematic plan view showing a reflective layer 132 and a yellow phosphor layer 142 included in the backlight device 100A. A light source LS is also shown in FIG. 2A, FIG. 2B, and FIG. 2C.

[0027] 1A, the liquid crystal display device 200A includes a liquid crystal display panel 50 and a backlight device 100A that emits white light toward a rear surface 50r of the liquid crystal display panel 50. The rear surface 50r of the liquid crystal display panel 50 is the surface opposite to the front surface 50f of the liquid crystal display panel 50 on the viewer side.

[0028] The liquid crystal display panel 50 has a liquid crystal cell 10 and polarizing plates 32 and 34 provided on both sides of the liquid crystal cell 10. The liquid crystal cell 10 has a TFT substrate 12, a counter substrate 14 facing the TFT substrate 12, and a liquid crystal layer disposed between the TFT substrate 12 and the counter substrate 14. The liquid crystal display panel 50 has a display region Rd (region surrounded by a dashed line in FIG. 1B) where display is performed, and a peripheral region Rf surrounding the display region Rd. The display region Rd is defined by a plurality of pixels that the liquid crystal display panel 50 has. Each of the plurality of pixels is provided with a TFT (thin film transistor) and a pixel electrode. The TFT substrate 12 has a TFT and a pixel electrode that each of the plurality of pixels has, and a substrate (e.g., a glass substrate) that supports them. The counter substrate 14 has a substrate (e.g., a glass substrate) and a color filter layer supported by the substrate, and the color filter layer has a black matrix (light-shielding layer) in the peripheral region Rf. Although a detailed structure of the liquid crystal display panel 50 will not be described here, the liquid crystal display panel 50 may be a known liquid crystal display panel. The areas corresponding to the display area Rd and the peripheral area Rf of the liquid crystal display panel 50 may also be referred to as the display area Rd and the peripheral area Rf, respectively, of the entire liquid crystal display device 200A.

[0029] The backlight device 100A includes a light source LS that emits blue light, a light guide layer 112, a quantum dot phosphor layer 122, a reflective layer 132, and a yellow phosphor layer 142.

[0030] The light guide layer 112 has a first main surface 112a, a second main surface 112b opposite to the first main surface 112a, and side surfaces 112c1 to 112c4 intersecting with the first main surface 112a and the second main surface 112b. The side surfaces 112c1 to 112c4 are located between the first main surface 112a and the second main surface 112b which are substantially parallel to each other. In this example, the first main surface 112a and the second main surface 112b are rectangular, and the side surface 112c includes four side surfaces 112c1, 112c2, 112c3, and 112c4 (sometimes collectively referred to as side surfaces 112c). Of the four side surfaces 112c1 to 112c4 of the light guide layer 112, the side surface 112c1 that receives the blue light emitted from the light source LS is referred to as the light receiving side surface 112c1, and the side surfaces 112c2 to 112c4 that do not receive the blue light from the light source LS are referred to as the non-light receiving side surfaces 112c2 to 112c4. The blue light emitted from the light source LS is not substantially incident on the non-light receiving side surfaces 112c2 to 112c4. The non-light receiving side surfaces 112c2 to 112c4 do not directly receive the blue light emitted from the light source LS, but may indirectly receive the blue light emitted from the light source LS (for example, after it is incident on the light guide layer 112). The reference symbol of the light receiving side surface may be marked with R1 in parentheses, and the reference symbol of the non-light receiving side surface may be marked with R2 in parentheses (see FIGS. 1A, 1B, and 2A). The light source LS emits blue light toward the light receiving side surface 112c1 including one of the long sides (sides extending in the x direction) of the rectangle. The light source LS is disposed, for example, facing the light receiving side surface 112c1. Here, the first main surface 112a and the second main surface 112b are parallel to the xy plane, the side surfaces 112c1 and 112c3 are parallel to the xz plane, and the side surfaces 112c2 and 112c4 are parallel to the yz plane. The light source LS is, for example, a blue LED device and may have multiple blue LED chips.

[0031] The quantum dot phosphor layer 122 is provided on the first main surface 112a side of the light guide layer 112. The first main surface 112a of the light guide layer 112 is, for example, the light emission surface of the light guide layer 112. The quantum dot phosphor layer 122 includes a red quantum dot phosphor 124r that receives blue light emitted from the light source LS and emits red light, and a green quantum dot phosphor 124g that receives blue light emitted from the light source LS and emits green light. In this specification, the term "phosphor" includes fluorescent material and phosphorescent material in the narrow sense. The light emitted by a phosphor may be referred to as "fluorescence". The term "fluorescence" includes fluorescent material and phosphorescent material in the narrow sense. The quantum dot phosphor layer 122 has a third main surface 122a, a fourth main surface 122b opposite to the third main surface 122a, and four side surfaces 122c1, 122c2, 122c3, and 122c4 intersecting with the third main surface 122a and the fourth main surface 122b. The third main surface 122a of the quantum dot phosphor layer 122 is in contact with the first main surface 112a of the light guide layer 112. That is, no gap is formed between the third main surface 122a of the quantum dot phosphor layer 122 and the first main surface 112a of the light guide layer 112. The quantum dot phosphor layer 122 may be attached to the first main surface 112a of the light guide layer 112 via an adhesive layer, for example, or may be placed on the first main surface 112a of the light guide layer 112. The third major surface 122a and the fourth major surface 122b of the quantum dot phosphor layer 122 have, for example, the same shape as the first major surface 112a and the second major surface 112b of the light guide layer 112 (rectangular in this example).

[0032] The reflective layer 132 is disposed on the second main surface 112b side of the light guide layer 112. The reflective layer 132 has light reflectivity. The reflective layer 132 exhibits white color. In this example, as shown in FIG. 2C , the main surface of the reflective layer 132 has the same shape (rectangular in this example) as the first main surface 112a and the second main surface 112b of the light guide layer 112.

[0033] The yellow phosphor layer 142 includes a yellow phosphor that receives blue light emitted from the light source LS and emits yellow light. 12 :Ce 3+ (Commonly known as YAG:Ce 3+ ), α-SiAlON:Eu 2+, (Ca,Sr,Ba)3SiO4:Eu 2+ or the like can be used. The yellow phosphor layer 142 is provided between the second main surface 112b of the light guide layer 112 and the reflective layer 132, and in a region along the non-light receiving side surfaces 112c2, 112c3, and 112c4 when viewed from the normal direction of the first main surface 112a or the second main surface 112b. In the example shown in FIG. 2C, the yellow phosphor layer 142 is provided on the main surface of the reflective layer 132 on the light guide layer 112 side in a region of width W1 along three sides of the periphery of the main surface (i.e., four sides of a rectangle) except for the long side on which the light source LS is arranged. The width W1 indicates a width in a direction on the xy plane perpendicular to the direction along each of the three sides except for the long side on which the light source LS is arranged. In the example shown in the figure, a gap is formed between the yellow phosphor layer 142 and the second main surface 112b of the light guide layer 112, but the yellow phosphor layer 142 may be in contact with the second main surface 112b of the light guide layer 112. The yellow phosphor layer 142 may be provided on the second major surface 112 b of the light guide layer 112 .

[0034] The backlight device 100A further includes a plastic frame 184 that holds the light guide layer 112, the quantum dot phosphor layer 122, and the reflective layer 132, and a holder 182 that holds the plastic frame 184 from the rear side. The plastic frame 184 is provided to surround the side surfaces 112c1 to 112c4 of the light guide layer 112 and to surround the side surfaces 122c1 to 122c4 of the quantum dot phosphor layer 122. In this example, the plastic frame 184 includes a first surrounding portion 191 that surrounds the side surfaces 112c1 to 112c4 of the light guide layer 112, and a second surrounding portion 193 that surrounds the side surfaces 122c1 to 122c4 of the quantum dot phosphor layer 122. The first surrounding portion 191 includes a first facing portion 192 that faces the non-light-receiving side surfaces 112c2 to 112c4 of the light guide layer 112. The second surrounding portion 193 has a second facing portion 194 facing the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122. A gap is formed between the plastic frame 184 and the non-light-receiving side surfaces 112c2 to 112c4 of the light guide layer 112. FIG. 1A shows a gap G2 between the first facing portion 192 of the plastic frame 184 and the non-light-receiving side surface 112c4 of the light guide layer 112. A gap (for example, about 0.6 mm) is formed between the plastic frame 184 and the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122. FIG. 1A shows a gap G3 between the second facing portion 194 of the plastic frame 184 and the side surface 122c4 of the quantum dot phosphor layer 122. In the illustrated example, the liquid crystal display panel 50 is attached to the plastic frame 184 via a tape (adhesive layer) TPa. The plastic frame 184 is attached to the holder 182 via a tape (adhesive layer) TPb. A tape (adhesive layer) TPc for fixing the second main surface 112b of the light guide layer 112 to the holder 182, and a tape (adhesive layer) TPd for fixing the reflective layer 132 to the holder 182 may further be provided.

[0035] The backlight device 100A further includes an optical sheet laminate 150 provided on the opposite side of the quantum dot phosphor layer 122 to the light guide layer 112. The optical sheet laminate 150 includes optical sheets 152 and 154. The optical sheet laminate 150 includes, for example, prism sheets 152 and 154 arranged such that their ridges are perpendicular to each other. For example, BEF manufactured by 3M can be used as the prism sheets 152 and 154. In this example, a gap G1 (for example, about 0.07 mm) is formed between the optical sheet laminate 150 and the liquid crystal display panel 50, that is, between the optical sheet (prism sheet) 154 and the polarizing plate 32 on the rear surface 50r side of the liquid crystal display panel 50.

[0036] The liquid crystal display device 200A including the backlight device 100A prevents degradation of display quality and achieves a slim design.

[0037] The effects obtained by the backlight device of this embodiment will be described while comparing it with a backlight device of a comparative example.

[0038] Fig. 3 shows a schematic cross-sectional view of a liquid crystal display device 990A including a backlight device 900A of Comparative Example 1. Fig. 4 is a schematic diagram for explaining a problem that occurs in the liquid crystal display device 990A.

[0039] The backlight device 900A of Comparative Example 1 differs from the backlight device 100A of the first embodiment in that it does not have the yellow phosphor layer 142. In a liquid crystal display device 990A including the backlight device 900A of Comparative Example 1, a display unevenness may occur in which a region (hatched region Rb in FIG. 4) along three sides of the display region Rd (rectangular region surrounded by a dashed line in FIG. 4) except for the long side on which the light source LS is arranged is bluer and darker than other regions of the display region Rd. The region Rb is a region of the display region Rd along the non-light-receiving side surfaces 112c2, 112c3, and 112c4 of the light guide layer 112. The region Rb may be referred to as a blue unevenness region Rb.

[0040] The luminance of the blue light emitted from the first main surface 112a (light emitting surface) of the light guide layer 112 decreases with increasing distance from the light source LS. Furthermore, the blue light may be absorbed by the plastic frame 184 facing the non-light-receiving side surfaces 112c2-112c4 of the light guide layer 112. Therefore, in the blue unevenness region Rb, the luminance of the green light emitted by the green quantum dot phosphor 124g and the red light emitted by the red quantum dot phosphor 124r in response to the blue light is lower than in other regions, resulting in display unevenness in which the blue unevenness region Rb appears bluer and darker than other regions in the display region Rd.

[0041] Furthermore, when the green light emitted by the green quantum dot phosphor 124g and the red light emitted by the red quantum dot phosphor 124r are absorbed by the plastic frame 184 facing the side surface of the quantum dot phosphor layer 122, the degree to which the blue unevenness region Rb appears blue and dark may increase. Note that, even when a gap G3 is formed between the quantum dot phosphor layer 122 and the plastic frame 184 as in the illustrated example, the green light emitted by the green quantum dot phosphor 124g and the red light emitted by the red quantum dot phosphor 124r may be absorbed by the plastic frame 184 facing the side surface of the quantum dot phosphor layer 122.

[0042] FIG. 5 shows a schematic cross-sectional view of a liquid crystal display device 990B equipped with a backlight device 900B of Comparative Example 2.

[0043] The backlight device 900B of Comparative Example 2 differs from the backlight device 100A of Embodiment 1 in that it has a yellow coloring layer 960 instead of the yellow phosphor layer 142. The yellow coloring layer 960 contains a yellow pigment or dye, but does not contain a yellow phosphor. In a liquid crystal display device 990B using the backlight device 900B of Comparative Example 2, the blue unevenness region Rb is prevented from appearing blue, but the dark (low luminance) state of the blue unevenness region Rb is not improved.

[0044] The backlight device of Patent Document 1 has a colored layer containing a yellow pigment or dye, but the colored layer does not contain a yellow phosphor. In the backlight device of Patent Document 1, as in the backlight device 900B of Comparative Example 2, the problem that the blue unevenness region Rb is darker (lower in luminance) than other regions is not improved.

[0045] When the backlight device 100A of the embodiment 1 is used, the display quality of the display device is improved compared to the backlight devices of the comparative examples 1 and 2. The backlight device 100A of the embodiment 1 has a yellow phosphor layer 142 provided in the blue uneven region Rb. The yellow phosphor contained in the yellow phosphor layer 142 receives blue light and emits yellow light, so that the blue uneven region Rb is prevented from being colored blue and from appearing dark.

[0046] In the backlight device 100A, the quantum dot phosphor layer 122 is in contact with the first main surface 112a of the light guide layer 112. In the backlight device 100A, since no gap is formed between the quantum dot phosphor layer 122 and the light guide layer 112, the backlight device 100A can reduce the thickness of the display device.

[0047] (Embodiment 2) With reference to FIG. 6, a liquid crystal display device 200B including a backlight device 100B according to this preferred embodiment will be described.

[0048] The liquid crystal display device 200B is different from the liquid crystal display device 200A of the first embodiment that includes the backlight device 100A in that the liquid crystal display device 200B includes a backlight device 100B. The backlight device 100B includes a yellow phosphor layer 146 instead of the yellow phosphor layer 142 included in the backlight device 100A. The yellow phosphor layer 146 is provided to face the side surfaces 122c2-122c4 of the quantum dot phosphor layer 122 that are substantially parallel to the non-light-receiving side surfaces 112c2-112c4 of the light guide layer 112, among the four side surfaces 122c1-122c4. The yellow phosphor layer 146 includes a yellow phosphor that receives blue light emitted from the light source LS and emits yellow light. In this example, the yellow phosphor layer 146 is provided on the side surfaces 122c2-122c4 of the quantum dot phosphor layer 122. That is, the yellow phosphor layer 146 is in contact with the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122. The yellow phosphor layer 146 is not limited to this example, and may be provided on the second opposing portion 194 of the plastic frame 184 opposing the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122. The four side surfaces 122c1 to 122c4 of the quantum dot phosphor layer 122 may or may not be aligned with the side surfaces 112c1 to 112c4 of the light guide layer 112, respectively. The side surfaces of the quantum dot phosphor layer 122 being aligned with the side surfaces of the light guide layer 112 means that they are substantially flush with each other.

[0049] Use of backlight device 100B also suppresses degradation of the display quality of the display device, similarly to backlight device 100A.

[0050] In the backlight device 100B, the quantum dot phosphor layer 122 is in contact with the first main surface 112a of the light guide layer 112, so that the backlight device 100B can reduce the thickness of the display device, similarly to the backlight device 100A. Note that a gap may be formed between the quantum dot phosphor layer 122 and the light guide layer 112, and even when a gap is formed between the quantum dot phosphor layer 122 and the light guide layer 112, the effect of suppressing the blue unevenness region Rb from being colored blue and appearing dark can be obtained.

[0051] With reference to FIG. 7, a liquid crystal display device 200B1 including a backlight device 100B1 according to a modification of this embodiment will be described.

[0052] Yellow phosphor layer 148 of backlight device 100B1 differs from yellow phosphor layer 146 of backlight device 100B in that it is arranged to face the side surfaces of quantum dot phosphor layer 122, and also to face three of the four side surfaces of optical sheet (prism sheet) 152 that are substantially parallel to non-light-receiving side surfaces 112c2-112c4 of light guide layer 112, and further to face three of the four side surfaces of optical sheet (prism sheet) 154 that are substantially parallel to non-light-receiving side surfaces 112c2-112c4 of light guide layer 112. In this example, the yellow phosphor layer 148 is provided on the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122, on three of the four side surfaces of the optical sheet 152 that are substantially parallel to the non-light-receiving side surfaces 112c2 to 112c4 of the light guide layer 112, and on three of the four side surfaces of the optical sheet 154 that are substantially parallel to the non-light-receiving side surfaces 112c2 to 112c4 of the light guide layer 112. That is, the yellow phosphor layer 148 is in contact with the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122, the above three side surfaces of the optical sheet 152, and the above three side surfaces of the optical sheet 154. The yellow phosphor layer 148 is not limited to this example, and may be provided on the second opposing portion 194 of the plastic frame 184 that faces the side surfaces 122c2 to 122c4 of the quantum dot phosphor layer 122. Yellow phosphor layer 148 is provided so as to face only the side surfaces of quantum dot phosphor layer 122 and optical sheet 152, and may not have a portion facing the side surfaces of optical sheet 154. The side surfaces of prism sheets 152 and 154 are preferably aligned with (substantially flush with) the side surfaces of quantum dot phosphor layer 122.

[0053] Use of backlight device 100B1 also suppresses degradation of the display quality of the display device, similarly to backlight device 100A.

[0054] In the backlight device 100B1 as well, the quantum dot phosphor layer 122 is in contact with the first main surface 112a of the light guide layer 112, so that the backlight device 100B1 can reduce the thickness of the display device, similarly to the backlight device 100A.

[0055] (Embodiment 3) With reference to FIG. 8, a liquid crystal display device 200C including a backlight device 100C according to this preferred embodiment will be described.

[0056] The liquid crystal display device 200C differs from the liquid crystal display device 200A of the first embodiment that includes the backlight device 100A in that the liquid crystal display device 200C includes a backlight device 100C. The backlight device 100C includes a yellow phosphor layer 144 instead of the yellow phosphor layer 142 included in the backlight device 100A. The yellow phosphor layer 144 is provided to face the non-light-receiving side surfaces 112c2 to 112c4 of the light guide layer 112. The yellow phosphor layer 144 includes a yellow phosphor that receives blue light emitted from the light source LS and emits yellow light. In this example, the yellow phosphor layer 144 is provided on the first facing portion 192 of the plastic frame 184. The yellow phosphor layer 144 is not in contact with the light guide layer 112. A gap is formed between the yellow phosphor layer 144 and the non-light-receiving side surface 112c4 of the light guide layer 112.

[0057] Use of backlight device 100C also suppresses degradation of the display quality of the display device, similarly to backlight device 100A.

[0058] In backlight device 100C, quantum dot phosphor layer 122 is in contact with light guide layer 112, and no gap is formed between quantum dot phosphor layer 122 and light guide layer 112, so that backlight device 100C can make the display device thinner than the backlight device of Patent Document 3. The backlight device of Patent Document 3 cannot be made sufficiently thin because a gap is provided between the wavelength conversion layer and the light guide layer.

[0059] (Color unevenness evaluation results) The effect obtained by the backlight device according to the embodiment of the present invention was examined by evaluating the degree of color unevenness using a sample panel.

[0060] As shown in FIG. 2C, a yellow phosphor layer 142 was formed by applying (or printing) a yellow phosphor ink (fluorescence amount 3) to an area of ​​width W1 along three of the four sides of the periphery of the reflective layer 132, excluding the long side where the light source LS is arranged, to obtain a sample panel A having the same structure as the backlight device 100A. The sample panel A has a size corresponding to a 13.3-type (13.3-inch) liquid crystal display panel. The value of "fluorescence amount" was defined as follows. The total light reflectance of the reflective layer on which the yellow phosphor layer was formed on the surface was measured, and a graph was obtained as shown in FIG. 9, with the horizontal axis representing wavelength and the vertical axis representing total light reflectance. The total light reflectance was measured using a spectrophotometer (CM-3700d, manufactured by Konica Minolta, Inc.). In FIG. 9, the total light reflectance of the reference sample was shown as 100%. The same measurement was also performed on a reflective layer on which the yellow phosphor layer was not formed on the surface ("without phosphor layer" in FIG. 9). The difference between the highest total light reflectance value (%) of the reflective layer with a yellow phosphor layer formed on its surface (the value at a wavelength near 570 nm in the illustrated example) and the total light reflectance (%) of a reflective layer without a yellow phosphor layer printed thereon at that wavelength is defined as the "fluorescence amount." For example, the difference in total light reflectance at the portion indicated by the arrow in Fig. 9 (wavelength 570 nm) is 108%-97%=11%, so the fluorescence amount in this case is 11. Note that Fig. 9 also shows the emission spectrum of the light source LS (blue LED) ("Blue LED" in Fig. 9).

[0061] The width W1 and the amount of fluorescence of the yellow phosphor layer 142 of the sample panel A were changed, and the color unevenness in the blue unevenness region Rb was visually evaluated. The emission spectrum of the yellow phosphor layer 142 is shown in FIG. 9, and the result of the visual evaluation is shown in FIG. 10. As shown in FIG. 10, the degree of color unevenness was evaluated in 11 stages from -5 to 5. The smaller the value, the more blue the color appears, and the larger the value, the more yellow the color appears. The range of -2 to 2 was determined as OK (color unevenness is suppressed). In the table on the left of FIG. 10, the OK range is surrounded by a thick frame. It can be seen that the width W1 of the yellow phosphor layer 142 is preferably 5 mm or less. Note that the range in which color unevenness occurs may vary depending on the size and structure of the display panel, so the preferable range of the width W1 of the yellow phosphor layer 142 is not limited to the above and may be changed.

[0062] Furthermore, a quantitative evaluation of the degree of color unevenness was investigated, which will be described with reference to Figs. 11A, 11B, and 12.

[0063] A line (dashed line in Figure 11A) parallel to the long side of sample panel A was drawn through the center of the short side, and the chromaticity on that line was measured using a two-dimensional color luminance meter (CA2500, manufactured by Konica Minolta, Inc.). The measurement results were displayed on a graph, such as that shown in Figure 11B, where the x-axis indicates the distance (mm) from the edge of the panel and the y-axis indicates chromaticity y. From the graph, the blue area and yellow area were estimated as follows: Blue area: Area where chromaticity y is lower in the negative direction compared to the center of the panel Yellow area: The area where the chromaticity y is raised by the yellow phosphor layer

[0064] FIG. 11B shows an example graph for the case where the yellow phosphor layer has a fluorescence amount of 11 and a width W1 of 2 mm. FIG. 11B also shows the regions Rb and Ry for estimating the blue and yellow areas, respectively. The degree of color unevenness is expressed as the difference between the yellow area and the blue area (yellow area - blue area). The smaller the difference between the yellow area and the blue area (yellow area - blue area), the more blue the area appears to be, and the larger the difference between the yellow area and the blue area (yellow area - blue area), the more yellow the area appears to be. It could be expressed that color unevenness is suppressed when the value of the difference between the yellow area and the blue area (yellow area - blue area) is in the range of -0.060 or more and 0.005 or less.

[0065] Sample panels B, B1, and C corresponding to backlight devices 100B, 100B1, and 100C were similarly prepared and evaluated for color unevenness. A yellow phosphor layer with a fluorescence intensity of 18 was used here. The results are shown in FIG. 13. Color unevenness was suppressed in all of sample panels B, B1, and C. As shown in FIG. 13, it was found that the value of the difference between the yellow area and the blue area (yellow area - blue area) was within the range of -0.060 or more and 0.005 or less in all of sample panels B, B1, and C. [Industrial Applicability]

[0066] The backlight device according to the embodiment of the present invention can improve the performance, including the display quality and / or the thinness, of a display device. [Explanation of symbols]

[0067] 10: Liquid crystal cell 12: TFT substrate 14: Opposing substrate 32: Polarizing plate 50: Liquid crystal display panel 50f:Front 50r: Rear 100A, 100B, 100B1, 100C: Backlight device 112: Light guiding layer 112a: 1st principal surface 112b: second main surface 112c, 112c1, 112c2, 112c3, 112c4: Side 122: Quantum dot phosphor layer 122a: 3rd principal surface 122b: 4th principal surface 122c1, 122c2, 122c3, 122c4: Side 124g: Green quantum dot phosphor 124r: Red quantum dot phosphor 132: Reflective layer 142, 144, 146, 148: Yellow phosphor layer 150: Optical sheet laminate 152, 154: Optical sheets 200A, 200B, 200B1, 200C, 200C1: Liquid crystal display device

Claims

1. A light source that emits blue light; a light guide layer having a first main surface, a second main surface opposite to the first main surface, at least one light-receiving side surface intersecting the first and second main surfaces and receiving the blue light emitted from the light source, and at least one non-light-receiving side surface intersecting the first and second main surfaces and not receiving the blue light; a quantum dot phosphor layer provided on the first main surface side of the light guide layer, the quantum dot phosphor layer having a third main surface facing the first main surface, a fourth main surface opposite the third main surface, and a side surface intersecting with the third and fourth main surfaces, the quantum dot phosphor layer including a red quantum dot phosphor that receives the blue light and emits red light, and a green quantum dot phosphor that receives the blue light and emits green light; a reflective layer disposed on the second main surface side of the light guide layer; a yellow phosphor layer including a yellow phosphor that receives the blue light and emits yellow light, the yellow phosphor layer being provided so as to face the at least one non-light-receiving side surface of the light guide layer; having the third main surface of the quantum dot phosphor layer is in contact with the first main surface of the light guide layer; The light guiding layer further includes a plastic frame disposed to surround the light guiding layer, the plastic frame has a first facing portion facing the at least one non-light-receiving side surface of the light guide layer; the yellow phosphor layer is provided in contact with the first opposing portion, a gap is formed between the yellow phosphor layer and the at least one non-light-receiving side of the light guide layer.

2. an optical sheet provided on the opposite side of the quantum dot phosphor layer from the light guide layer; Another optical sheet provided on the opposite side of the optical sheet from the quantum dot phosphor layer; and the optical sheet has a fifth main surface on the quantum dot phosphor layer side and a sixth main surface opposite to the fifth main surface, the other optical sheet has a seventh main surface on the optical sheet side and an eighth main surface opposite to the seventh main surface, the fifth main surface of the optical sheet is in contact with the fourth main surface of the quantum dot phosphor layer, The backlight device according to claim 1 , wherein the seventh main surface of the other optical sheet is in contact with the sixth main surface of the optical sheet.

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