Optical film, optical laminate, and reflective display device used in optical laminates for front lights

Abstract

The present invention provides an optical film, an optical laminate, and a reflective display device for use in optical laminates for front lights, which have a high contrast ratio and suppress the deterioration of appearance. [Solution] The optical laminate for the front light has a first emission surface positioned opposite the front of the reflective display panel, a second emission surface that emits light emitted from the first emission surface and reflected by the reflective display panel, a light-receiving surface that receives light emitted from a light source, a light guide layer having a first main surface on the side of the first emission surface and a second main surface on the side of the second emission surface, and a direction-changing layer positioned on the first main surface side of the light guide layer and having a plurality of optical cavities, each of which has a first inclined surface that directs a portion of the light propagating within the light guide layer toward the first emission surface by internal total internal reflection, and a second inclined surface opposite to the first inclined surface.

Description

[Technical Field]

[0001] The present invention relates to an optical film used in an optical laminate for a front light of a reflective display device, an optical laminate, and a reflective display device. In particular, it relates to an optical film used in an optical laminate for a front light disposed on the front surface of a reflective display panel, an optical laminate, and a reflective display device comprising such an optical laminate. The optical laminate is disposed on the front surface of the reflective display panel, for example, via an adhesive layer (including a tack layer). [Background technology]

[0002] An optical laminate for front lighting, which can be placed on the front surface of a reflective display device via an adhesive layer (including a tack layer), is disclosed, for example, in Patent Document 1. By placing the optical laminate on the front surface of the reflective display panel via an adhesive layer (including a tack layer), the reflective display device can be made more compact and easier for users to handle.

[0003] Furthermore, Patent Document 2 discloses a sheet-shaped lighting device having a light distribution structure that utilizes total internal reflection at the interface of an air cavity (optical cavity). For reference, all of the disclosures in Patent Document 2 are incorporated into this specification by reference. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2023 / 0205039 Specification [Patent Document 2] International Publication No. 2022 / 260080 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The inventors found that even when using a sheet-shaped lighting device having a light distribution structure that utilizes total internal reflection at the interface of an air cavity (optical cavity) as described in Patent Document 2, etc., a sufficient contrast ratio could not be obtained. In addition, the air cavity was sometimes visible, resulting in a reduced appearance.

[0006] Therefore, the object of the present invention is to provide an optical film, an optical laminate, a reflective display device, and a reflective display device that have a high contrast ratio and suppress the deterioration of appearance, and are used in an optical laminate for front lights. [Means for solving the problem]

[0007] According to embodiments of the present invention, the following solutions are provided.

[0008] [Item 1] An optical film included in an optical laminate for front lighting, which is positioned on the front of a reflective display panel, The optical laminate has a direction-changing layer disposed on either the main surface of the light guide layer, which directs a portion of the light propagating within the light guide layer toward the reflective display panel. The direction conversion layer has a plurality of optical cavities, Each of the plurality of optical cavities has a first inclined surface that directs a portion of the light propagating within the light guide layer toward the reflective display panel by total internal reflection, and a second inclined surface opposite to the first inclined surface. The inclination angle θa of the first inclined surface is 4° or more and 34° or less. The aforementioned plurality of optical cavities are discretely arranged along the light-guiding direction at a pitch of less than 350 μm. The projection area of ​​the first inclined surface is 2600 μm². 2 An optical film that is less than [a certain value].

[0009] [Item 2] An optical laminate for front lighting, positioned on the front of a reflective display panel, The reflective display panel has a first emission surface positioned opposite to the front surface, and a second emission surface that emits light emitted from the first emission surface and reflected by the reflective display panel. A light guide layer having a light-receiving surface that receives light emitted from a light source, a first main surface on the first emission surface side, and a second main surface on the second emission surface side, The light guide layer comprises a direction changing layer disposed on the first main surface side or the second main surface side, The direction conversion layer has a plurality of optical cavities, Each of the plurality of optical cavities has a first inclined surface that directs a portion of the light propagating within the light guide layer toward the first emission surface by internal total internal reflection, and a second inclined surface opposite to the first inclined surface. The inclination angle θa of the first inclined surface with respect to the first main surface of the light guide layer is 4° or more and 34° or less. The aforementioned plurality of optical cavities are discretely arranged along the light-guiding direction at a pitch of less than 350 μm. The projection area of ​​the first and second inclined surfaces onto the first main surface is 2600 μm². 2 An optical laminate that is less than [a certain value]. The inclination angle θa of the first inclined surface may be 4° or more and less than 10°.

[0010] [Item 3] The optical laminate described in item 2, wherein the inclination angle θb of the second inclined surface is 50° or more and 100° or less. Note that if the light sources are arranged on both sides of the light guide layer, the angle θb of the second inclined surface may be set in the same way as the inclination angle θa of the first inclined surface.

[0011] [Item 4] The optical laminate according to item 2 or 3, wherein the plurality of optical cavities are arranged at a pitch of less than 350 μm along a direction perpendicular to the light guide direction. Furthermore, the pitch along the light guide direction and the pitch along the direction perpendicular to the light guide direction are preferably arranged at a pitch of 300 μm or less, and more preferably at 150 μm or less.

[0012] [Item 5] The optical laminate according to any one of items 2 to 4, wherein the plurality of optical cavities are voids. The plurality of optical cavities may be filled with a material having a refractive index of 1.20 or less.

[0013] [Item 6] A reflective display panel, A light source, The frontlight optical laminate according to any one of items 2 to 5, disposed on the front surface of the reflective display panel via an adhesive layer A reflective display device comprising:

[0014] [Item 7] The reflective display device according to item 6, wherein the pixel pitch of the reflective display panel is 200 μm or less. The reflective display panel may be, for example, an electrophoretic display panel or a liquid crystal display panel. [Advantages of the Invention]

[0015] According to an embodiment of the present invention, there are provided an optical film, an optical laminate, and a reflective display device used for a frontlight optical laminate having a high contrast ratio and suppressing a deterioration in appearance. [Brief Description of the Drawings]

[0016] [Figure 1] It is a schematic cross-sectional view of a reflective display device 1000 according to an embodiment of the present invention. [Figure 2] It is a schematic plan view of an optical laminate 100. [Figure 3] It is a schematic cross-sectional view of an optical cavity 64 that the optical laminate 100 may have. [Figure 4] It is a schematic plan view of the optical cavity 64. <000�118> [Figure 5] It is a schematic plan view showing variations of the optical cavity 64. [[ID=4в]] [Figure 6] It is a schematic cross-sectional view of another reflective display device 1000A according to an embodiment of the present invention. [Figure 7]This is a schematic cross-sectional view of yet another reflective display device 1000B according to an embodiment of the present invention. [Modes for carrying out the invention]

[0017] The optical film, optical laminate, and reflective display device used in an optical laminate for a front light according to an embodiment of the present invention will be described below with reference to the drawings. The optical film, optical laminate, and reflective display device used in an optical laminate for a front light according to an embodiment of the present invention are not limited to those exemplified below.

[0018] Figure 1 shows a schematic cross-sectional view of a reflective display device 1000 according to an embodiment of the present invention. The reflective display device 1000 comprises a reflective display panel 200, a light source LS, and an optical laminate 100 for front lighting disposed on the front surface of the reflective display panel 200 via an adhesive layer 56. The adhesive layer 56 includes adhesives, tacks, molecular adhesives, etc. Here, an example is shown in which the optical laminate 100 and the reflective display panel 200 are laminated without an air layer in between, but the optical laminate 100 may be disposed on the front surface of the reflective display panel 200 via an air layer or a liquid layer.

[0019] The optical laminate 100 has a first emission surface positioned opposite the front surface of the reflective display panel 200, and a second emission surface that emits light Ld that is emitted from the first emission surface and reflected by the reflective display panel 200. The optical laminate 100 has a light receiving surface that receives light emitted from the light source LS, a light guide layer 10 having a first main surface on the first emission surface side and a second main surface on the second emission surface side, and a direction conversion layer 60 positioned on the first main surface side of the light guide layer 10 and having a plurality of optical cavities 64. The direction conversion layer 60 is composed of a shaping film 62 having recesses 64 (indicated by the same reference numeral as the optical cavities 64) on its surface and an adhesive layer 54. A base layer 20 is placed between the light guide layer 10 and the adhesive layer 54. The base layer 20 is made of an optically transparent resin (e.g., PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), COP (cycloolefin polymer)), and is bonded to the light guide layer 10 by the adhesive layer 52, and to the shaping film 62 by the adhesive layer 54. The base layer 20 and the adhesive layer 52 may be omitted. Here, an example is shown where the side surface of the light guide layer 10 is the light-receiving surface, but in addition to the side surface of the light guide layer 10, the side surface of the adhesive layer 52 or the side surface of the adhesive layer 52 and the base layer 20 may also be included. Alternatively, the end of the light guide layer 10 may protrude from the optical laminate 100, and an incoupling element may be placed on the first or second main surface of the protruding portion, so that the end of the first or second main surface of the light guide layer 10 is the light-receiving surface. As incoupling elements, for example, those disclosed in International Publication No. 2022 / 030543 or International Publication No. 2022 / 030544 can be used. The disclosures of these international publications are incorporated herein by reference.

[0020] The shaping film 62 is positioned on the front surface of the reflective display panel 200 via a base layer 30 and an adhesive layer 56. The base layer 30 is also made of an optically transparent resin (e.g., PMMA, PET, COP). The base layer 30 may be omitted. The base layer 30 can be used, for example, as a base when producing the shaping film 62 with an ultraviolet-curing resin. The shaping film 62 can be formed on the base layer 30 by curing the ultraviolet-curing resin while a predetermined mold is pressed against the ultraviolet-curing resin applied to the base layer 30. Preferably, the refractive index of the adhesive layer 56 is 0.008 or more smaller than the refractive index of the base layer 30 or the shaping film 62.

[0021] Each of the multiple optical cavities 64 has a first inclined surface ISa that directs a portion of the light propagating within the light guide layer 10 toward the first emission surface side (reflective display panel 200 side) by internal total internal reflection, and a second inclined surface ISb opposite to the first inclined surface ISa. The inclination angle θa of the first inclined surface ISa with respect to the first main surface of the light guide layer 10 is between 4° and 34°. The multiple optical cavities 64 are discretely arranged along the light guide direction (y direction) at a pitch of less than 350 μm, and the projection area of ​​the first inclined surface ISa onto the first main surface is 2600 μm². 2 It is less than.

[0022] As will be explained later with reference to the examples, by using a direction conversion layer 60 having a plurality of optical cavities 64 that satisfy the above conditions, the contrast ratio of the reflective display device 1000 can be improved and the deterioration of appearance can be suppressed.

[0023] The direction-changing layer 60 may be provided as an optical film to manufacturers of optical laminates or reflective display panels. For example, the direction-changing layer 60 may be composed of a shaping film 62 having recesses 64 on its surface and an adhesive layer 54, and the film may be provided as a laminate having a base layer 30, an adhesive layer 56, a base layer 20, and an adhesive layer 52, with separators placed on both sides.

[0024] By using a direction-changing layer 60 having multiple optical cavities 64 that satisfy the above conditions, light incident on the light-receiving surface of the light guide layer 10 is efficiently directed towards the reflective display panel 200, and the amount of light reflected at interfaces other than the first inclined surface ISa and emitted from the second emission surface without reaching the reflective display panel 200 can be reduced. The light emitted from the second emission surface without reaching the reflective display panel 200 increases the black luminance, thus reducing the contrast ratio (white luminance / black luminance).

[0025] The optical cavity 64 is preferably filled with air, but it may also be filled with a material whose refractive index is smaller than that of the shaping film 62 and the adhesive layer 54, for example, a resin with a refractive index of 1.40 or less, 1.30 or less, or 1.20 or less (for example, an adhesive (especially a tack), a porous resin, etc.).

[0026] Next, with reference to Figure 2, an example of the planar shape and arrangement of the optical cavity 64 will be described. Figure 2 shows a schematic plan view of the lighting device 100A.

[0027] As shown in Figure 2, the multiple optical cavities 64 are discretely arranged, for example, in the direction of light guidance (y-direction) of the light guide layer 10 and in a direction perpendicular to the light guide direction (x-direction). Although light propagates in various directions within the light guide layer 10, the y-direction is referred to as the light guide direction, and light having a component in the y-direction (non-zero) is said to be propagating in the y-direction. The same applies to other directions. That is, light propagating in the -y-direction includes all light having a component in the -y-direction (non-zero).

[0028] The dimensions of the optical cavity 64 (length L, width W: see Figures 3 and 4) are preferably such that, for example, the length L is 10 μm or more and 350 μm or less, and the width W is 1 μm or more and 100 μm or less. Furthermore, from the viewpoint of light extraction efficiency, the height H (see Figure 3) is preferably 5 μm or more and 30 μm or less.

[0029] As shown in Fig. 2, when viewed from the normal direction to the first main surface of the light guide layer 10, the first inclined surface ISa forms a convex curved surface on the light source LS side. The light source LS is, for example, an LED device, and a plurality of LED devices are arranged in the x direction. Since the light emitted from each of the plurality of LED devices spreads in the y direction, it is better for the first inclined surface ISa to have a convex curved surface on the light source LS side so that the first inclined surface ISa acts uniformly on the light.

[0030] In the example shown in Fig. 2, a plurality of optical cavities 64 having convex curved surfaces with substantially the same shape and in the same direction are discretely and periodically arranged over the entire region in the light guide direction (y direction) and the direction orthogonal to the light guide direction (x direction) of the light guide layer 10. As will be described later, it is preferable that the pitch Px and the pitch Py are each independently less than 350 μm, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less. However, it is not necessarily required to have a constant pitch over the entire region. For example, the pitch Py (the distance between adjacent optical cavities) may become smaller as the distance from the light source increases. The lower limit of the pitch Px and the pitch Py is not particularly limited. Px may be larger than the length L of the optical cavity 64, and Py may be larger than the width W of the optical cavity 64, and may be, for example, 10 μm or more.

[0031] The projected area of the first inclined surface ISa on the first main surface is preferably less than 2600 μm 2 from the viewpoint of appearance, and the smaller the better, for example, 2500 μm 2 or less, 2000 μm 2 or less, 1500 μm 2 or less, 1000 μm 2 or less, 800 μm 2 or less, 500 μm 2 or less. The lower limit of the projected area of the first inclined surface ISa on the first main surface is not particularly limited, but from the viewpoint of the contrast ratio, for example, 100 μm 2 or more, 200 μm 2 or more.

[0032] Next, the shape of the optical cavity 64 will be described with reference to Figures 3, 4, and 5. Figure 3 is a schematic cross-sectional view of the optical cavity 64, Figure 4 is a schematic plan view of the optical cavity 64, and Figure 5 is a schematic plan view showing a variation of the optical cavity 64.

[0033] As shown in Figure 3, the cross-sectional shape of the optical cavity 64 is, for example, triangular. The inclination angle θa of the first inclined surface ISa on the light source LS side is between 4° and 34°, as will be described later. The inclination angle θb of the second inclined surface ISb is, for example, between 50° and 100°. If the inclination angle θb is less than 50°, stray light may be generated in unintended directions. On the other hand, if the inclination angle θb exceeds 100°, processing of the shaped film may become difficult, for example. The inclination angle θb is, for example, less than 90°. Furthermore, if the light sources are arranged on both sides of the light guide layer, the angle θb of the second inclined surface can be set in the same way as the inclination angle θa of the first inclined surface.

[0034] As shown in Figures 4 and 5, the length L of the optical cavity 64 is preferably 10 μm or more and 350 μm or less, and the width W is preferably 1 μm or more and 100 μm or less. The length L is, for example, twice or more the width W. The height H (see Figure 3) is preferably 1 μm or more and 100 μm or less. Depending on the processing accuracy when forming the shaped film having the recess having the planar shape shown in Figure 4, a recess having the planar shape shown in Figure 5 may be formed. Even in such cases, the planar shape of the optical cavity can be characterized by the length L and width W. Furthermore, the shape of the curved surface convex toward the light source LS on the first inclined surface ISa can be represented, for example, by an nth-degree curve such as a quartic curve (n is an integer of 2 or more), a part of a sine curve, or a circular arc.

[0035] Next, the reflective display device of the present invention will be described by showing examples and comparative examples.

[0036] In the examples and comparative examples, the reflective display device 1000A shown in Figure 6 was actually fabricated, and its contrast ratio and appearance were evaluated by simulation (SIM). The characteristics of the optical cavity and the evaluation results are shown in Table 1. The height H of the optical cavity (see Figure 3) was set to 8 μm in all cases. The projection area of ​​the first inclined surface ISa onto the first main surface was adjusted by changing the length L of the optical cavity (see Figure 4).

[0037] The reflective display device 1000A, like the reflective display device 1000 shown in Figure 1, comprises a reflective display panel 200A, a light source LS, and an optical laminate 100A for front lighting, which is positioned on the front surface of the reflective display panel 200A via an adhesive layer 56A.

[0038] The optical laminate 100A has a first emission surface positioned opposite the front surface of the reflective display panel 200A, and a second emission surface that emits light emitted from the first emission surface and reflected by the reflective display panel. The optical laminate 100A has a light-receiving surface that receives light emitted from the light source LS, a light guide layer 10A having a first main surface on the first emission surface side and a second main surface on the second emission surface side, and a direction conversion layer 60A positioned on the first main surface side of the light guide layer 10A and having a plurality of optical cavities 64A. The direction conversion layer 60A is composed of a shaping film 62A having recesses 64A (indicated by the same reference numeral as the optical cavities 64A) on its surface and an adhesive layer 54A. A base material layer 20A is positioned between the light guide layer 10A and the adhesive layer 54A. The base layer 20A is bonded to the light guide layer 10 by the adhesive layer 52, and is bonded to the shaping film 62 by the adhesive layer 54.

[0039] A barrier layer 40A is placed between the base layer 30A on which the shaping film 62 is formed and the reflective display panel 200A. The barrier layer 40A is bonded to the base layer 30A by an adhesive layer 55A and to the front surface of the reflective display panel 200A by an adhesive layer 56A. The barrier layer 40A protects the front surface of the reflective display panel 200A from moisture and other elements.

[0040] A PET layer 70A, intended to be a touch panel layer, is positioned above the light guide layer 10A (on the observer's side). The touch panel layer 70A is bonded to the light guide layer 10A by an adhesive layer 57A and to the cover glass 80A by an adhesive layer 59A. The cover glass 80A is provided to protect the surface of the optical laminate 100A.

[0041] The reflective display device 1000A is modeled after a reflective display device with a touch panel that is actually used. The specific components are as follows: Cover glass 80A: Glass with a thickness of 0.4 mm Adhesive layer 59A: PMMA-based adhesive with a thickness of 150 μm PET layer 70A: PET film with a thickness of 150 μm Adhesive layer 57A: PMMA-based adhesive with a thickness of 180 μm. Light guide layer 10A: PMMA film with a thickness of 0.5 mm Adhesive layer 52A: PMMA-based adhesive with a thickness of 220 μm. Substrate layer 20A: PMMA film with a thickness of 40 μm Adhesive layer 54A: PMMA-based adhesive with a thickness of 15 μm Shaped layer 62A: PMMA-based UV-curing resin with a thickness of 15 μm Substrate layer 30A: PMMA film with a thickness of 40 μm Adhesive layer 55A: Silicone-based optical transparent adhesive with a thickness of 25 μm (n D :1.41) Barrier layer 40A: A 50 μm thick PET film coated with a 100 nm thick silicon dioxide film. Adhesive layer 56A: PMMA-based adhesive with a thickness of 40 μm

[0042] The difference in refractive index between two adjacent layers is preferably 0.02 or less, more preferably 0.01 or less, and most preferably 0.005 or less. The refractive index of the PMMA film used for the light guide layer 10A and the substrate layers 20A and 30A is approximately 1.49.

[0043] As the reflective display panel, a commercially available electrophoretic display panel (Kobo Libra Colour from Rakuten Kobo) with a reflectivity of 80% in the white display state and 10% in the black display state was used. Except for Examples 17 and 18 of the simulation (SIM), the pixel pitch of the reflective display panel, including the comparative example, was 170 μm in both the x and y directions, while the pixel pitch of the reflective display panel in Examples 17 and 18 was 50 μm in both the x and y directions. As the light source, a substrate with side-emitting type 335 size packages mounted at 6 mm intervals was used. For the simulation, Lighttools from Synopsys was used to construct the above configuration, calculate the brightness in the white and black display states, and calculate the contrast ratio from the brightness values.

[0044] The contrast ratio (CR) is the contrast ratio in dark conditions, and is the value obtained by dividing the brightness of the white display by the brightness of the black display when the front light source is turned on. The evaluation results for the contrast ratio are as follows: A is 9 or higher, B is 7 or higher but less than 9, and C is less than 7. From the comparison between Example 2 and Example 11, it can be seen that the simulation results reproduce the measured values. Visibility was evaluated by whether or not the optical cavity was visible when the shaping layer was laminated on the light guide plate and the light source was turned on. A indicates that the optical cavity is not visible, B indicates that the optical cavity is slightly visible but not bothersome, and C indicates that the optical cavity is easily visible.

[0045] [Table 1]

[0046] In Table 1, the first inclined plane projection area has two significant digits.

[0047] From a comparison of Examples 1-3 and Comparative Example 1, it can be seen that when the array pitch Px and Py of the optical cavity are 350 μm or more (2.1 times the pixel pitch of the reflective display panel), the contrast ratio (CR) decreases to C. In relation to the pixel pitch of the reflective display panel, it can be said that it is preferable for the array pitch Px and Py of the optical cavity to be approximately twice or less the pixel pitch of the reflective display panel. Furthermore, from the results of Examples 12-16, a contrast ratio of B is obtained when either the array pitch Px or Py of the optical cavity is 300 μm or less. Also, a contrast ratio of A is obtained when the array pitch Px and Py of the optical cavity is 150 μm or less.

[0048] Focusing on the first tilt angle θa, in Example 16 where θa is 34°, the contrast ratio is B, whereas in Comparative Examples 2, 3, and 4, where θa is 36°, 42°, and 48°, the contrast ratio is low at C. From this, it can be said that a first tilt angle θa of 34° or less is preferable.

[0049] Furthermore, in the examples where the first tilt angle θa is 30° or less, the contrast ratio is A in all examples up to Examples 4 and 5 where the first tilt angle θa is 4° and 8°, respectively. Therefore, it can be said that a first tilt angle θa of 4° or more and 34° or less is preferable.

[0050] Next, focusing on the projection area of ​​the first inclined plane, the projection area of ​​the first inclined plane is 1500 μm². 2 In Examples 4, 5, and 15 described above, the appearance was lower than that of B and the others, and the first inclined surface projection area was 2600 μm². 2 In Comparative Example 5, the appearance is rated as C. Therefore, the projection area of ​​the first inclined surface is 2600 μm². 2 Preferably, the first inclined surface projection area is less than 1500 μm². 2 The following is even more preferable: The smaller the projection area of ​​the first inclined plane, the better the appearance.

[0051] From the above, it can be seen that the reflective display panel according to the embodiment of the present invention is suitably used for reflective display panels with a pixel pitch of 200 μm or less. Although an electrophoretic display panel is used as an example here, a liquid crystal display panel can of course also be used. Furthermore, the pixels of the reflective display panel may be composed of four substantially square subpixels, as in the example electrophoretic display panel, or they may be composed of three rectangular subpixels.

[0052] In the above example, as shown in Figure 1, the directional conversion layer 60 is arranged on the first main surface side (reflective display panel side) of the light guide layer 10. However, as shown in Figure 7, the directional conversion layer 60B may be arranged on the second main surface side (opposite side from the reflective display panel) of the light guide layer 10B. Figure 7 is a schematic cross-sectional view of yet another reflective display device 1000B according to an embodiment of the present invention.

[0053] The reflective display device 1000B comprises a reflective display panel 200B, a light source LS, and an optical laminate 100B for frontlighting, which is positioned on the front of the reflective display panel 200B via an adhesive layer 52B. The adhesive layer 52B includes adhesives, tacks, molecular adhesives, and the like.

[0054] The optical laminate 100B has a first emission surface positioned opposite the front surface of the reflective display panel 200B, and a second emission surface that emits light Ld that is emitted from the first emission surface and reflected by the reflective display panel 200B. The optical laminate 100B has a light-receiving surface that receives light emitted from the light source LS, a light guide layer 10B having a first main surface on the first emission surface side and a second main surface on the second emission surface side, and a direction-changing layer 60B positioned on the second main surface side of the light guide layer 10B and having a plurality of optical cavities 64B. The direction-changing layer 60B is composed of a shaping film 62B having recesses 64B (indicated by the same reference numeral as the optical cavities 64B) on its surface and an adhesive layer 54B. The light guide layer 10B is bonded to the substrate layer 30B on which the shaping film 62B is formed by an adhesive layer 56B, and is bonded to the front surface of the reflective display panel 200B by the adhesive layer 52B. [Industrial applicability]

[0055] According to embodiments of the present invention, it is possible to provide an optical film, an optical laminate, and a reflective display device for use in an optical laminate for front lights that have a high contrast ratio and suppress the deterioration of appearance. [Explanation of Symbols]

[0056] 10: Light guide layer 20, 30: Base material layer 52, 54, 56: Adhesive layer 60: Directional change layer 62: Shaping film 64: Optical cavity 100: Optical laminate 200: Reflective display panel LS:Light source Ld: Light used for display

Claims

1. An optical film included in an optical laminate for front lighting, which is positioned on the front of a reflective display panel, The optical laminate has a direction-changing layer disposed on either the main surface of the light guide layer, which directs a portion of the light propagating within the light guide layer toward the reflective display panel. The direction conversion layer has a plurality of optical cavities, Each of the plurality of optical cavities has a first inclined surface that directs a portion of the light propagating within the light guide layer toward the reflective display panel by internal total internal reflection, and a second inclined surface opposite to the first inclined surface. The inclination angle θa of the first inclined surface is 4° or more and 34° or less. The aforementioned plurality of optical cavities are discretely arranged along the light-guiding direction at a pitch of less than 350 μm. The projection area of ​​the first inclined surface is 2600 μm². ２ An optical film that is less than [a certain value].

2. An optical laminate for front lighting, positioned on the front of a reflective display panel, The reflective display panel has a first emission surface positioned opposite to the front surface, and a second emission surface that emits light emitted from the first emission surface and reflected by the reflective display panel. A light guide layer having a light-receiving surface that receives light emitted from a light source, a first main surface on the first emission surface side, and a second main surface on the second emission surface side, The light guide layer comprises a direction changing layer disposed on the first main surface side or the second main surface side, The direction conversion layer has a plurality of optical cavities, Each of the plurality of optical cavities has a first inclined surface that directs a portion of the light propagating within the light guide layer toward the first emission surface by internal total internal reflection, and a second inclined surface opposite to the first inclined surface. The inclination angle θa of the first inclined surface with respect to the first main surface of the light guide layer is 4° or more and 34° or less. The aforementioned plurality of optical cavities are discretely arranged along the light-guiding direction at a pitch of less than 350 μm. The projection area of ​​the first inclined surface and the second inclined surface onto the first main surface is 2600 μm². ２ An optical laminate that is less than [a certain value].

3. The optical laminate according to claim 2, wherein the inclination angle θb of the second inclined surface is 50° or more and 100° or less.

4. The optical laminate according to claim 2, wherein the plurality of optical cavities are discretely arranged at a pitch of less than 350 μm along a direction perpendicular to the light guide direction.

5. The optical laminate according to claim 2, wherein the plurality of optical cavities are voids.

6. Reflective display panel, Light source and An optical laminate for a front light according to any one of claims 2 to 5, disposed on the front surface of the reflective display panel via an adhesive layer, A reflective display device equipped with the following features.

7. The reflective display device according to claim 6, wherein the pixel pitch of the reflective display panel is 200 μm or less.

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