Display device

Abstract

To provide a display device with high accuracy and high contrast by accurate local dimming.SOLUTION: The display device has a display panel and a backlight. The backlight has a light source and an optical sheet group. The light source has a light source substrate and an LED arranged in the light source substrate. The light source is divided in segments in planer view. The segment has at least one LED. The light source substrate and the LED are covered with a transparent resin. On the transparent resin, a sheet having a honeycomb division 60 is arranged.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a display device having a backlight, and more particularly to a display device that uses local dimming to enable a high contrast screen. [Background technology]

[0002] A liquid crystal display device has a TFT substrate on which pixel electrodes and thin film transistors (TFTs) are formed in a matrix, an opposing substrate facing the TFT substrate, and a liquid crystal layer sandwiched between the TFT substrate and the opposing substrate. Images are formed by controlling the light transmittance of the liquid crystal molecules for each pixel.

[0003] On the other hand, in an organic EL display device, pixels each having a light-emitting element made of an organic EL layer, a driving TFT, a switching TFT, etc. are formed in a matrix, and an image is formed by controlling the light-emitting intensity of the organic EL layer for each pixel. Because organic EL display devices are self-emitting elements, they have excellent image contrast.

[0004] However, because the pixel size can be made smaller in LCD devices, LCD devices have superior definition. Therefore, local dimming has been developed as a method for improving the contrast of LCD devices. Prior art related to local dimming is available in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2017-116683 Summary of the Invention [Problem to be solved by the invention]

[0006] Display devices for VR (Virtual Reality) and medical use require images with higher resolution and contrast. When using local dimming in such display devices, more precise control of the local dimming is also required.

[0007] In order to perform local dimming more effectively and improve contrast in such a display device, it is necessary, for example, to reduce the area of ​​the segment that serves as the unit of local dimming and to prevent the light from each segment from reaching adjacent segments.

[0008] Furthermore, if the area of ​​a segment is reduced, it becomes difficult to place multiple LEDs in the segment. On the other hand, if only one LED is placed in each segment, it becomes difficult to uniformly distribute brightness, and the LED can be seen from the screen. If a diffusion sheet is placed to address this issue, for example, the diffusion sheet will cause the light from each segment to leak into adjacent segments, which can be a problem.

[0009] An object of the present invention is to solve such problems, to effectively perform local dimming, and to realize a high-definition, high-contrast screen in a display device having a backlight. [Means for solving the problem]

[0010] The present invention is intended to solve the above problems, and the main specific means are as follows.

[0011] (1) A display device having a display panel and a backlight, wherein the backlight has a light source and a group of optical sheets, the light source has a light source substrate and LEDs arranged on the light source substrate, the light source is divided into segments when viewed in a plane, each segment has at least one LED, the light source substrate and the LEDs are covered with a transparent resin, and a sheet having honeycomb partitions is arranged on top of the transparent resin.

[0012] (2) A display device having a display panel and a backlight, wherein the backlight has a light source and an optical sheet group, the light source has a light source substrate and an LED arranged on the light source substrate, the light source is divided into segments in a plan view, and each segment has at least one of the LEDs, A display device characterized in that the light source substrate and the LED are covered with a transparent resin, and a honeycomb partition is formed within the transparent resin above the light-emitting surface of the LED. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a plan view of a liquid crystal display device. [Figure 2] FIG. 1 is a cross-sectional view of a liquid crystal display device. [Figure 3] FIG. 10 is a plan view showing an example of segments in a liquid crystal display device in a local dimming operation. [Figure 4] FIG. 1 is a plan view of Comparative Example 1. [Figure 5] FIG. 1 is a cross-sectional view of Comparative Example 1. [Figure 6] FIG. 10 is a plan view illustrating the problem of Comparative Example 1. [Figure 7] FIG. 10 is a cross-sectional view showing the problem of Comparative Example 1. [Figure 8] FIG. 1 is a cross-sectional view of Example 1. [Figure 9] FIG. 1 is a perspective view of a honeycomb partition. [Figure 10] FIG. 1 is a plan view of a honeycomb partition. [Figure 11] FIG. 2 is a cross-sectional view illustrating the operation principle of the first embodiment. [Figure 12] FIG. 10 is a plan view showing the relationship between the honeycomb partitions and the LEDs. [Figure 13] FIG. 10 is another plan view showing the relationship between the honeycomb partitions and the LEDs. [Figure 14] FIG. 10 is a cross-sectional view of Example 2. [Figure 15] FIG. 10 is a cross-sectional view illustrating the operating principle of the second embodiment. [Figure 16]10 is a graph and a table showing the effects of Example 1 and Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below using examples. [Example]

[0015] Fig. 1 is a plan view showing an example of a liquid crystal display device. In Fig. 1, a TFT substrate 100 and a counter substrate 200 are bonded with a sealant 16, with liquid crystal sandwiched between them. A display area 14 is formed in the area where the TFT substrate 100 and the counter substrate 200 overlap. In the display area 14, scanning lines 11 extend in the horizontal direction (x direction) and are arranged in the vertical direction (y direction). Video signal lines 12 extend in the vertical direction and are arranged in the horizontal direction. Pixels 13 are formed in the area surrounded by the scanning lines 11 and the video signal lines 12.

[0016] In Fig. 1, the portion where the TFT substrate 100 does not overlap with the counter substrate 200 is a terminal region 15. A flexible wiring substrate 17 is connected to the terminal region 15 to supply power and signals to the liquid crystal display panel. A driver IC that drives the liquid crystal display panel is mounted on the flexible wiring substrate 17. A backlight is arranged on the back of the TFT as shown in Fig. 2.

[0017] Fig. 2 is a cross-sectional view of a liquid crystal display device. In Fig. 2, a backlight 20 is disposed on the back surface of a liquid crystal display panel 10. The liquid crystal display panel 10 has the following configuration: a counter substrate 200, on which a black matrix and color filters are formed, is disposed opposite a TFT substrate 100, on which pixel electrodes, common electrodes, TFTs, scanning lines, video signal lines, etc. are formed. The TFT substrate 100 and the counter substrate 200 are bonded together at their peripheries with a sealant 16, and liquid crystal 300 is sealed inside.

[0018] The liquid crystal molecules are initially aligned by alignment films formed on the TFT substrate 100 and the counter substrate 200. When a voltage is applied between the pixel electrode and the common electrode, the liquid crystal molecules rotate, and an image is formed by controlling the light from the backlight 20 for each pixel. Since the liquid crystal 300 can only control polarized light, a lower polarizer 101 is placed below the TFT substrate 100, and only polarized light is incident on the liquid crystal 300. The light modulated by the liquid crystal 300 is analyzed by the upper polarizer 201, and an image is visible.

[0019] 2, a backlight 20 is disposed on the back of the liquid crystal display panel. The backlight 20 is configured such that a diffusion sheet group 40 consisting of multiple diffusion sheets is disposed on a light source 30, and a prism sheet 50 is disposed on top of that. There are two types of backlights 20 for display devices: a side light type in which a light source such as an LED is disposed on the side of a light guide plate, and a direct type in which a light source such as an LED is disposed on the underside of a light guide plate. In the present invention, a direct type backlight is used.

[0020] In Figure 2, white LEDs are used, but if blue LEDs are used, a color conversion sheet in which phosphors are dispersed in a resin sheet may be used in addition to a diffusion sheet. Also, a polarized reflection sheet may be used to improve the efficiency of use of light from the backlight 20. The type of optical sheet to be used and the number of such optical sheets to be used are determined depending on the display device.

[0021] When displaying an image on an LCD, the bright areas transmit the backlight and the dark areas block the backlight. The contrast of the image is defined by the ratio of the bright and dark areas. In LCDs, the dark areas are created by blocking the light from the backlight with the liquid crystal. However, the liquid crystal does not completely block the backlight, and some light leaks through. This reduces the contrast.

[0022] Local dimming enables a deep black display by not illuminating dark areas with backlight. Therefore, high contrast can be achieved. Figure 3 is an example of a liquid crystal display device that illustrates a form of local dimming. Figure 3 is a plan view of the liquid crystal display device, and the configuration is the same as that described in Figure 1. In Figure 3, the display area 14 is divided by segments 141. The dotted lines in Figure 3 indicate the boundaries of the segments 141, but this is shown for convenience and the liquid crystal display panel does not actually have such boundaries. Light sources in the backlight are arranged at positions corresponding to each segment.

[0023] In Figure 3, segment (4, 2) is a bright area, and segment (5, 2) is a dark area. With local dimming, the light source for segment (4, 2), i.e., the LED, is turned on, and the light source for segment (5, 2), i.e., the LED, is not turned on. This results in a deep black display in segment (5, 2), achieving high contrast.

[0024] However, since there are no boundaries between the segments, depending on the brightness distribution of the segments, for example, the light from segment (4, 2) may reach segment (5, 2). In this case, the backlight will also illuminate segment (5, 2), which should display black, and the effect of local dimming will not be fully realized.

[0025] 4 and 5 show a comparative example 1 showing the configuration of a backlight that enables local dimming. White LEDs 31 are used as the light source. FIG. 4 is a plan view showing the arrangement of the LEDs 31, which are the light source, in each segment 141 in the backlight. In FIG. 4, each segment 141 is separated by a dotted line. However, this dotted line is for convenience and does not actually separate the segments.

[0026] The size of each segment is 4mm square or less, for example, 2mm square in the case of Figure 5. The size of the segments 141 in the following examples is similar. In Figure 4, one LED 31 is arranged in each segment 141. The size of a segment can also be defined as the distance between the centers of adjacent LEDs in both the x and y directions. If multiple LEDs 31 are arranged in each segment, the weighted average position of the LEDs 31 can be taken.

[0027] Fig. 5 is a cross-sectional view of a backlight in Comparative Example 1. In Fig. 5, LEDs 31 are arranged on a light source substrate 32, and transparent resin 33 is formed to cover the LEDs 31. White LEDs are used for the LEDs 31. For example, acrylic resin or silicone resin is used for the transparent resin 33. The transparent resin 33 is intended to protect the LEDs 31 and the electrodes and wiring formed on the light source substrate 32. The dotted lines drawn on the light source substrate 32 in Fig. 5 indicate the boundaries of segments for convenience.

[0028] A diffusion sheet group 40 consisting of three diffusion sheets 41, 42, and 43 is arranged on transparent resin 33. The diffusion sheets homogenize the light from the light source. Therefore, there may be one diffusion sheet or four or more diffusion sheets, depending on the need. Each diffusion sheet has a thickness of, for example, 0.1 mm.

[0029] A prism sheet 50 is disposed on top of the diffusion sheet 43. The prism sheet 50 of FIG. 5 has linear prisms with triangular cross sections extending in the y direction, arranged in the x direction at a pitch of, for example, 50 microns. The prism sheet 50 of FIG. 5 functions to direct light that tends to spread in the x direction toward the z axis direction. The thickness of the prism sheet 50 is, for example, 50 microns for the prism array portion (i.e., the height of the prisms) and 70 microns for the base portion, totaling approximately 120 microns. In order to direct light that tends to spread in the y direction toward the z axis direction, a prism sheet having linear prisms with triangular cross sections extending in the x direction and arranged in the y direction may be used by overlapping it on the prism sheet 50.

[0030] The problem with Comparative Example 1 is that light from the LED 31 leaks from the transparent resin 33 that covers the LED 31 and the diffusion sheet group 40 into adjacent segments. Figure 6 is a plan view illustrating this problem. The arrangement of the segment 141 and the LED 31 is the same as in Figure 4. The arrows in Figure 6 indicate the light emitted from the LED 31. Figure 6 shows that the light emitted from the LED 31 does not remain in the segment in question, as indicated by the arrows, but also leaks into adjacent segments.

[0031] FIG. 7 is a cross-sectional view illustrating this problem. The configuration in FIG. 7 is the same as that described in FIG. 5. The arrows in FIG. 7 indicate the light emitted from the LED 31. The light directed in an oblique direction leaks into adjacent segments. Therefore, accurate or effective local dimming cannot be performed.

[0032] Figure 8 is a cross-sectional view of Example 1, which addresses this issue. The basic configuration of Figure 8 is the same as that of Figure 5. Figure 8 differs from Figure 5 in that honeycomb-shaped partitions 60 are formed within the first diffusion sheet. Hereinafter, the first diffusion sheet with honeycomb partitions formed therein may also be referred to as the honeycomb diffusion sheet 45. In Figure 8, these honeycomb partitions 60 prevent light from the LEDs 31 from leaking into adjacent segments.

[0033] FIG. 9 is a perspective view of a honeycomb partition 60. Specifically, a lattice with a hexagonal planar surface is formed in a matrix. The honeycomb partition 60 can be formed, for example, from black silicone resin. The honeycomb partition 60 can be made, for example, by etching a 0.1 mm thick black silicone resin to form small hexagonal holes in a matrix. The thickness of the honeycomb partition wall is, for example, 0.05 mm.

[0034] The holes in the honeycomb matrix are then filled with a resin that will form the diffusion sheet. This completes the honeycomb diffusion sheet 45. In most cases, PET (polyethylene terephthalate) is used as the material for the diffusion sheet. However, PC (polycarbonate) or silicone resin may also be used. The honeycomb diffusion sheet 45 can also be formed by forming a large mother sheet and cutting it to the size of each display.

[0035] FIG. 10 is a plan view of a honeycomb partition 60. The wall thickness of the honeycomb partition 60 is, for example, 0.05 mm. The maximum diameter d of each honeycomb is larger than the diameter of a pixel formed on an LCD panel and smaller than the diameter of a segment. Hereinafter, unless otherwise specified, the diameter of a honeycomb refers to the maximum diameter d. As will be explained later, the size of each honeycomb can be adjusted to suit the application. In FIG. 10, the dot 70 at the center of the honeycomb is, for example, a point light source 70. Light is emitted from the point light source 70 in all directions, but the honeycomb partition 60 prevents the light from entering other honeycombs. Therefore, light from the point light source does not affect adjacent segments.

[0036] Figure 11 is a cross-sectional view showing this state. In Figure 11, a honeycomb diffusion sheet 45 is placed on top of the transparent resin 33 that covers the LEDs 31. Light from the LEDs 31 forms a point light source in each honeycomb. Light that spreads in all four directions from the point light source is blocked by the honeycomb partitions 60, and only light that goes upward is emitted from the honeycomb diffusion sheet 45. Naturally, light leakage into adjacent segments is prevented.

[0037] FIG. 12 is a plan view corresponding to FIG. 11 viewed from above. In FIG. 12, dotted lines are imaginary lines indicating the boundaries of segments 141. An LED 31 is disposed at the center of each segment 141. In FIG. 12, honeycomb partitions 60 are formed to cover each segment 141. The honeycomb partitions 60 are disposed between the light source 30 including the LED 31 and the liquid crystal display panel 10. In a typical optical configuration, the assembly accuracy of the LED 31 and the liquid crystal display panel 10 is an issue, but the honeycomb partitions 60 have a close-packed structure, and the honeycombs are distributed uniformly in all directions. Therefore, by using the honeycomb partitions 60, it is possible to realize a liquid crystal display device that is not affected by assembly accuracy and always has uniform characteristics.

[0038] Although the honeycomb partition 60 has excellent features, some problems may arise when viewed microscopically. For example, in Figure 12, the influence of the honeycomb wall corresponding to one LED differs between the first, second, and third rows from the top. Because the honeycomb walls are black and do not transmit light, the amount of light emitted from the LEDs may differ for each row.

[0039] This problem can be alleviated by reducing the honeycomb pitch. Fig. 13 is a plan view of a case where the honeycomb pitch is reduced compared to Fig. 12. In Fig. 13, the honeycomb arrangements corresponding to the LEDs 31 are different in the first, second, and third rows from the top, but this non-uniformity is reduced compared to Fig. 12. In other words, the influence of the honeycomb walls is more uniform in Fig. 13 than in Fig. 12.

[0040] As shown in Figure 13, the brightness non-uniformity between segments can be reduced by reducing the honeycomb pitch. However, reducing the honeycomb pitch also reduces the overall light transmittance. Therefore, the honeycomb pitch must be determined by balancing the light uniformity between segments with the light transmittance of the entire backlight.

[0041] The LED 31 in Figures 12 and 13 can also be defined as an exit window for light from the LED. The diameter of the honeycomb can also be defined in relation to the diameter of the LED's exit window. In other words, a large honeycomb diameter can be defined as a honeycomb diameter larger than the LED's exit window, and a small honeycomb diameter can be defined as a honeycomb diameter smaller than the LED's exit window. If the LED's exit window has a short diameter and a long diameter, the long diameter of the exit window can be defined as the diameter of the exit window.

[0042] Since the honeycomb dividers are black, they can cause problems with light transmittance and moire fringing. However, this moire fringing is less severe than with other dividers, such as rectangular dividers. Even if the honeycomb dividers 60 are rotated relative to the LCD panel to prevent moire fringing, the effect of this rotation is much less severe than with other dividers. [Example]

[0043] Fig. 14 is a cross-sectional view showing the configuration of Example 2. Fig. 14 differs from Fig. 5 in that honeycomb partitions 60 are formed in the transparent resin 33 that covers the LEDs 31. As explained in Example 1, forming the honeycomb partitions 60 can prevent light from the light source from entering adjacent segments. However, in Example 2, the honeycomb partitions 60 are formed directly above the LEDs 31, which can further enhance the effect.

[0044] In Fig. 14, the height h of the honeycomb partition 60 is 0.1 mm to 0.2 mm. The material of the honeycomb partition 60 can be black silicone resin, as in Example 1. The manufacturing method of the honeycomb partition 60 is the same as that described in Fig. 9 of Example 1.

[0045] Then, a honeycomb divider 60 as shown in Figure 9 is placed on the LED array, and then acrylic resin or silicone resin is filled as the transparent resin 33, and the transparent resin 33 is then cured. If the honeycomb divider 60 is mechanically unstable and difficult to place on the LED array, first fill the spaces between the LEDs 31 with the transparent resin 33, cure it, and flatten the transparent resin 33. Then, the honeycomb divider 60 is placed, and the inside of the honeycomb is filled with the transparent resin 33 and cured.

[0046] However, since the honeycomb partitions 60 are black, there is a risk that they may affect the uniformity of light. In Example 2, the light is diffused by three diffusion sheets 41, 42, and 43, so the effect of the honeycomb partitions 60 themselves on the uniformity of light can be reduced compared to Example 1.

[0047] Figure 15 is a cross-sectional view showing the operating principle of Example 2. Light incident on each honeycomb becomes a point light source within each honeycomb. Light attempting to spread in all four directions from this point light source is blocked by honeycomb partitions 60, and only light directed upward is allowed to exit from honeycomb partitions 60. Naturally, light leakage into adjacent segments can also be prevented.

[0048] FIG. 16 is a graph and table comparing light leakage to adjacent segments between Comparative Example 1 and Examples 1 and 2. The data in the upper graph and lower table of FIG. 16 are the same. In the graph of FIG. 16, the horizontal axis represents the distance from the center of the specific segment where the LED is located, in mm. In FIG. 16, the diameter of the segment is 2 mm. The vertical axis represents relative brightness.

[0049] The correspondence between the graph in Figure 16 and the table in Figure 16 is as follows: The "boundary" in the table corresponds to 1.0 or -1.0 on the horizontal axis of the graph, the "boundary 1 segment ahead" in the table corresponds to 3 or -3 on the horizontal axis of the graph, and the "boundary 2 segments ahead" in the table corresponds to 5 or -5 on the horizontal axis of the graph.

[0050] In the graph and table of Figure 16, the luminance should theoretically be symmetrical across the center of a specific segment, but due to errors and other factors, it is slightly asymmetrical. However, the trend can be discerned. In the graph of Figure 16, if we take the average of the luminance in the positive direction of the horizontal axis and the luminance in the negative direction of the horizontal axis, a more reasonable comparison becomes possible.

[0051] In the graph of Fig. 16, the narrower the base of the brightness distribution, the less light leaks into adjacent segments. As shown in Fig. 16, light leakage is significantly reduced in Examples 1 and 2 compared to Comparative Example 1. In the graph of Fig. 16, the effects of Examples 1 and 2 are almost the same, but Example 2 shows a slightly better effect. This is because the honeycomb partitions are positioned closer to the LEDs, which are the light sources.

[0052] The values ​​in the table of Figure 16 indicate the brightness values ​​at the boundaries between adjacent segments, assuming that the brightness at the center of a particular segment is 100. In the table, the boundaries, the one-segment boundaries, and the two-segment boundaries are as described above. The three-segment boundaries in the table correspond to 7 and -7 on the horizontal axis of the graph, but are not shown on the graph.

[0053] In the above explanation, a light guide plate is not used, but the same effect can be obtained by using a light guide plate if necessary. Also, although the LED is white, a combination of a blue LED and a color conversion sheet may also be used.

[0054] As described above, by using the present invention, accurate and effective local dimming can be performed, and an image with high contrast can be formed. Furthermore, by using local dimming, power saving can be realized. [Explanation of symbols]

[0055] 10...display panel, 11...scanning line, 12...video signal line, 13...pixel, 14...display area, 15...terminal area, 16...sealing material, 17...flexible wiring board, 20...backlight, 30...light source, 31...LED, 32...light source board, 33...transparent resin, 40...diffusion sheet group, 41...first diffusion sheet, 42...second diffusion sheet, 43...third diffusion sheet, 45...honeycomb diffusion sheet, 50...prism sheet, 60...honeycomb partition, 100...TFT substrate, 101...lower polarizer, 200...counter substrate, 201...upper polarizer, 300...liquid crystal, 141...segment

Claims

1. A display device having a display panel and a backlight, the backlight includes a light source and a group of optical sheets; the light source includes a light source substrate and an LED disposed on the light source substrate; The light source is divided into segments when viewed in a plane, At least one of the LEDs is present in the segment; the light source substrate and the LED are covered with a transparent resin; a honeycomb partition is formed in the transparent resin above the light-emitting surface of the LED; A display device, characterized in that the diameter of the honeycomb of the honeycomb partition is larger than the diameter of the pixel of the display panel and smaller than the diameter of the segment.

2. 2. The display device according to claim 1, wherein a diffusion sheet is disposed on the sheet having the honeycomb partitions.

3. 2. The display device according to claim 1, wherein a plurality of diffusion sheets are disposed on the sheet having the honeycomb partitions.

4. 3. The display device according to claim 2, wherein a prism sheet is disposed on the diffusion sheet.

5. 2. The display device according to claim 1, wherein the LED has an exit window through which light is emitted, and the diameter of the honeycomb of the honeycomb partition is larger than the diameter of the exit window and smaller than the diameter of the segments.

6. A display device having a display panel and a backlight, the backlight includes a light source and a group of optical sheets; the light source includes a light source substrate and an LED disposed on the light source substrate; The light source is divided into segments when viewed in a plane, At least one of the LEDs is present in the segment; the light source substrate and the LED are covered with a transparent resin; a honeycomb partition is formed in the transparent resin above the light-emitting surface of the LED; The display device is characterized in that the LED has an exit window for emitting light, and the diameter of the honeycomb of the honeycomb partition is larger than the diameter of the exit window and smaller than the diameter of the segments.

7. 7. The display device according to claim 6, wherein a diffusion sheet is disposed on the honeycomb partition.

8. 7. The display device according to claim 6, wherein a plurality of diffusion sheets are disposed on the honeycomb partition.

9. 8. The display device according to claim 7, wherein a prism sheet is disposed on the diffusion sheet.

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