Light guide member for illumination device, and illumination device

Abstract

A light guide member according to the present invention comprises a light guide layer that has a light reception part and first and second main surfaces, and a direction conversion layer that is disposed on the first or second main surface side and that directs a part of light propagating through the light guide layer toward an emission surface, wherein: the light guide layer includes a first substrate layer, an adhesive layer, and a second substrate layer in this order from the emission surface side; the direction conversion layer and first and second substrate layers are each formed from a resin; the direction conversion layer and first substrate layer each have a thickness of not more than 100 μm; the second substrate layer has a thickness of not more than 180 μm; the adhesive layer has a thickness of not less than 80 μm; the adhesive layer has a storage modulus of not more than 300 KPa; the color difference that occurs while light propagates 250 mm through each of the first and second substrate layers is Δxy≤0.03; the color difference that occurs while light propagates 250 mm through the adhesive layer is Δxy≤0.006, and the color difference that occurs while light propagates 250 mm through the light guide layer is Δxy≤0.2.

Description

Light Guide Member for Lighting Device and Lighting Device

[0001] The present invention relates to a light guide member for a lighting device and a lighting device, and particularly to a sheet-shaped light guide member for a lighting device including a light guide layer, and a sheet-shaped lighting device including a light source and a light guide layer. Here, the term "sheet-shaped" is used to include plate-shaped or film-shaped, regardless of the rigidity (flexibility) and thickness of the sheet. Note that the sheet-shaped lighting device can be used in various forms such as a roll form.

[0002] A sheet-shaped lighting device including a light source and a light guide layer is used, for example, as a backlight or a front light for a display device. In recent years, flexible lighting devices have been proposed as backlights or front lights for flexible display devices.

[0003] For example, Patent Documents 1 and 2 disclose backlights for flexible display devices. Patent Document 3 discloses a front light for a flexible display device. Patent Document 4 discloses a front light in which, although the display device is not flexible, an end portion receiving light from a light source is bent to the rear side of the display.

[0004] Japanese Patent Application Laid-Open No. 2008-140698, Japanese Patent Application Laid-Open No. 2013-137927, Japanese Patent Application Laid-Open No. 2013-88501, US Patent Application Publication No. 2018 / 0052274

[0005] When a lighting device is used as a front light for a flexible display device, the lighting device is required to have not only flexibility but also transparency. An object of the present invention is to provide a novel light guide member for a lighting device and a novel lighting device having transparency and flexibility.

[0006] According to an embodiment of the present invention, the solution described in the following items is provided.

[0007] [Item 1] A light guide member for a lighting device having an emission surface, comprising: a light receiving portion that receives light emitted from a light source; a light guide layer having a first main surface on the emission surface side and a second main surface on the opposite side of the emission surface; and a direction changing layer disposed on the first main surface side or the second main surface side of the light guide layer, which directs a portion of the light propagating through the light guide layer toward the emission surface, wherein the light guide layer comprises a first base material layer, an adhesive layer, and a second base material layer laminated in order from the emission surface side, the first main surface being the surface of the first base material layer opposite to the adhesive layer, the direction changing layer, the first base material layer, and the second base material layer being formed from resin, the thickness of the direction changing layer being 100 μm or less, and the thickness of the first base material layer being 100 μm or less. A light guide member for a lighting device, wherein when the loss coefficient (loss modulus / storage modulus) of the second substrate layer is less than 0.06, the thickness of the second substrate layer is 180 μm or less; when the loss coefficient of the second substrate layer is 0.06 or more, the thickness of the second substrate layer is 100 μm or less; the thickness of the adhesive layer is 80 μm or more; the storage modulus of the adhesive layer is 300 kPa or less; the color difference that occurs when light propagates 250 mm through the first substrate layer is Δxy ≤ 0.03; the color difference that occurs when light propagates 250 mm through the second substrate layer is Δxy ≤ 0.03; the color difference that occurs when light propagates 250 mm through the adhesive layer is Δxy ≤ 0.006; and the color difference that occurs when light propagates 250 mm through the light guide layer is Δxy ≤ 0.2.

[0008] [Item 2] The light guide member for a lighting device according to Item 1, wherein the thickness of the direction conversion layer is 60 μm or less, the thickness of the first substrate layer is 60 μm or less, the thickness of the second substrate layer is 130 μm or less if the loss coefficient (loss modulus of elasticity / storage modulus) of the second substrate layer is less than 0.06, and the thickness of the second substrate layer is 50 μm or less if the loss coefficient of the second substrate layer is 0.06 or more.

[0009] [Item 3] The light guide member for a lighting device according to Item 1 or 2, wherein the color difference that occurs when light propagates 250 mm through the first substrate layer is Δxy ≤ 0.01, the color difference that occurs when light propagates 250 mm through the second substrate layer is Δxy ≤ 0.01, and the color difference that occurs when light propagates 250 mm through the adhesive layer is Δxy ≤ 0.001.

[0010] [Item 4] The light guide member for a lighting device according to any one of items 1 to 3, wherein the color difference that occurs while light propagates through the light guide layer for 250 mm is Δxy ≤ 0.1.

[0011] [Item 5] The light guide member for a lighting device according to any one of items 1 to 4, wherein the thickness of the adhesive layer is 100 μm or more, and the storage modulus of the adhesive layer is 200 kPa or less.

[0012] [Item 6] The light guide member for a lighting device according to any one of items 1 to 5, wherein the first base layer is formed from an acrylic resin or a cycloolefin resin, and the second base layer is formed from an acrylic resin or a cycloolefin resin.

[0013] [Item 7] The adhesive layer is formed from an optically transparent adhesive, and is a light guide member for a lighting device according to any one of items 1 to 6.

[0014] [Item 8] The light guide member for a lighting device according to any one of items 1 to 7, wherein the direction conversion layer has a plurality of internal spaces that totally reflect a portion of the light propagating through the light guide layer and direct it toward the emission surface.

[0015] [Item 9] A light guide member for a lighting device described in any one of items 1 to 8, which does not break when bent with a radius of curvature of 5 mm.

[0016] [Item 10] A light guide member for a lighting device according to any one of items 1 to 9, wherein when light is incident from the first main surface side and viewed from the second main surface side, the visible light transmittance is 60% or more and the haze value is less than 30%.

[0017] [Item 11] The light guide member for a lighting device according to any one of items 1 to 10, wherein the total thickness of the light guide layer and the direction changing layer is 600 μm or less.

[0018] [Item 12] A lighting device comprising: a light guide member for a lighting device as described in any one of items 1 to 11; and a light source that emits the light toward the light receiving section.

[0019] According to embodiments of the present invention, a novel light guide member for a lighting device and a lighting device having transparency and flexibility are provided.

[0020] This is a schematic cross-sectional view of the lighting device 100A_L according to an embodiment of the present invention in an unfolded state. This is a schematic cross-sectional view of the lighting device 100A_L according to an embodiment of the present invention in a folded state. This is a schematic cross-sectional view of the lighting device 100B_L according to embodiment 2 of the present invention in an unfolded state. This is a schematic plan view of the lighting device 100A_L. This is a schematic cross-sectional view of the internal space 64 that the lighting device 100A_L may have. This is a schematic plan view of the internal space 64. This is a schematic plan view showing variations of the internal space 64. This is a diagram illustrating a method for measuring the color difference that occurs when light propagates 250 mm through the base material layer 30A, 30B or the direction conversion layer 60A. This is a diagram illustrating a method for measuring the color difference that occurs when light propagates 250 mm through the adhesive layer 52. This is a diagram illustrating a method for measuring the color difference that occurs when light propagates 250 mm through the light guide layer 10.

[0021] Hereinafter, with reference to the drawings, a light guide member for a lighting device and a lighting device according to embodiments of the present invention will be described. The light guide member for a lighting device and a lighting device according to embodiments of the present invention are not limited to those exemplified below.

[0022] (Embodiment 1) First, an example of the configuration of a lighting device according to Embodiment 1 of the present invention, which has transparency and flexibility, will be described with reference to Figures 1A and 1B. Figure 1A shows a schematic cross-sectional view of the lighting device 100A_L according to Embodiment 1 of the present invention in an unfolded state. Figure 1B shows a schematic cross-sectional view of the lighting device 100A_L according to Embodiment 1 of the present invention in a folded state. To emphasize the folded state, Figure 1B shows a longer lighting device 100A_L compared to Figure 1A.

[0023] A transparent and flexible lighting device 100A_L can be placed in front of a flexible object 70 as a front light. The object 70 may be, for example, a display element such as a reflective display or electronic paper, or a poster. The front surface of the object 70 contains information such as text and diagrams. The object 70 may have an adhesive layer placed in front of it, which adheres to the lighting device 100A_L. The configuration comprising the lighting device 100A_L and the object 70 is also referred to as a "display device".

[0024] As shown in Figure 1A, the lighting device 100A_L has a first emission surface (bottom of Figure 1A) that emits illumination light LRa for illuminating the object 70, and a second emission surface (top of Figure 1A) that emits reflected light LRb, which is generated by illuminating the object 70 with the illumination light LRa and passes through the lighting device 100A_L. The second emission surface is located on the opposite side of the first emission surface. The illumination light LRa is emitted in the direction of -Z in Figure 1, and the reflected light LRb is emitted in the direction of Z. Since the reflected light LRb enters the eye of an observer on the side of the second emission surface, the observer can see the object 70. In this specification, the first emission surface is also simply referred to as the "emission surface".

[0025] The lighting device 100A_L can be bent as shown in Figure 1B. In the example shown in Figure 1B, the lighting device 100A_L is bent so that the front of the object 70 faces inward, but it is not limited to this example. The lighting device 100A_L may also be bent so that the front of the object 70 faces outward.

[0026] The configuration of the lighting device 100A_L is described in detail below.

[0027] As shown in Figure 1A, the lighting device 100A_L includes a light source LS and a light guide member 100A that receives light emitted from the light source LS, propagates the light in the Y direction, and emits it in the -Z direction. The light guide member 100A includes a light-receiving section that receives light emitted from the light source LS, a light guide layer 10 having a first main surface 12a on the first emission surface side and a second main surface 12b on the second emission surface side, and a direction-changing layer 60A arranged on the first main surface 12a side that directs a portion of the light propagating through the light guide layer 10 toward the first emission surface.

[0028] The light-receiving portion of the light guide layer 10 may be, for example, the side surface of the light guide layer 10 on the light source LS side. Alternatively, if an incoupling element is placed on the first main surface 12a or the second main surface 12b of a protruding portion of the light guide layer 10 that protrudes from the direction conversion layer 60A in the -Y direction, the light-receiving portion of the light guide layer 10 may be the first main surface 12a or the second main surface 12b of the protruding portion of the light guide layer 10. As the incoupling element, for example, those disclosed in International Publication No. 2022 / 030543 or International Publication No. 2022 / 030544 can be used. The contents of these international publications are incorporated herein by reference.

[0029] The light guide layer 10 has a first base material layer 30A, an adhesive layer 52, and a second base material layer 30B, which are laminated in order from the first emission surface side. The adhesive layer 52 adheres the first base material layer 30A and the second base material layer 30B. The first main surface 12a is the surface of the first base material layer 30A opposite to the adhesive layer 52. The second main surface 12b is the surface of the second base material layer 30B opposite to the adhesive layer 52.

[0030] The direction conversion layer 60A has a light distribution control structure that includes a plurality of internal spaces 64. The plurality of internal spaces 64 direct a portion of the light propagating through the light guide layer 10 towards the first output surface side as irradiation light LRa by internal total internal reflection (TIR). The direction conversion layer 60A is composed of a shaping film 62 having a recess 64 (indicated by the same reference numeral as the internal spaces 64) on the surface facing the first main surface 12a, and an adhesive layer 54 disposed on this surface side of the shaping film 62 and bonding the shaping film 62 to the first base material layer 30A. Each of the plurality of internal spaces 64 has a first inclined surface ISa that directs a portion of the light propagating through the light guide layer 10 towards the first output surface side by internal total internal reflection (TIR), and a second inclined surface ISb on the opposite side of the first inclined surface ISa.

[0031] The internal space 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.).

[0032] The light distribution control structure is configured such that more than 80% of the light propagating through the light guide layer 10 is directed toward the first emission surface. The proportion of light propagating through the light guide layer 10 that is directed toward the first emission surface can be controlled, for example, by adjusting the cross-sectional shape, planar shape, size, arrangement density, and distribution of the internal space 64. The cross-sectional shape of the internal space 64 is triangular, as exemplified here, but is not limited to this, and may be trapezoidal, etc.

[0033] The light guide member 100A is designed such that the refractive indices of the base layers 30A and 30B, the adhesive layers 52 and 54, and the shaping film 62 are approximately equal. Therefore, Fresnel reflection of the irradiated light LRa and the reflected light LRb at the interfaces of these components can be suppressed.

[0034] [Materials of the light guide member 100A] From the viewpoint of transparency and flexibility, the materials of the components included in the light guide member 100A are as follows.

[0035] In the light guide member 100A, the first base layer 30A, the second base layer 30B, and the shaping film 62 are formed from a resin. This resin may be, for example, an acrylic resin such as PMMA (polymethyl methacrylate), or a cycloolefin resin such as COP (cycloolefin polymer). The adhesive layers 52 and 54 are formed from an optically transparent adhesive (OCA) containing a resin. This resin may be, for example, an acrylic resin. The direction changing layer 60A, which is composed of the shaping film 62 and the adhesive layer 54, can be said to be formed from a resin.

[0036] [Material parameters of the light guide member 100A regarding transparency] The material parameters of the components included in the light guide member 100A regarding transparency are as follows.

[0037] In the CIExy chromaticity diagram, the color difference that occurs when light propagates 250 mm through the first substrate layer 30A may be, for example, Δxy ≤ 0.03. The color difference that occurs when light propagates 250 mm through the second substrate layer 30B may be, for example, Δxy ≤ 0.03. The color difference that occurs when light propagates 250 mm through the adhesive layer 52 may be, for example, Δxy ≤ 0.006. The color difference that occurs when light propagates 250 mm through the light guide layer 10, which includes the first substrate layer 30A, the second substrate layer 30B, and the adhesive layer 52, may be, for example, Δxy ≤ 0.2. The color difference that occurs when light propagates 250 mm through the direction conversion layer 60A may be, for example, Δxy ≤ 0.03. The smaller the color change of the irradiated light LRa from the light source LS, through the light guide layer 10, and into the object 70 via the direction conversion layer 60, the clearer the object 70 can be seen.

[0038] When the above conditions are met, the light guide member 100A has transparency that allows the object 70 to be clearly seen. From the viewpoint of increasing the transparency of the light guide member 100A, it is preferable that the color difference that occurs when light propagates 250 mm through the first substrate layer 30A is Δxy ≤ 0.01. It is preferable that the color difference that occurs when light propagates 250 mm through the second substrate layer 30B is Δxy ≤ 0.01. It is preferable that the color difference that occurs when light propagates 250 mm through the adhesive layer 52 is Δxy ≤ 0.001. It is preferable that the color difference that occurs when light propagates 250 mm through the light guide layer 10 is Δxy ≤ 0.1. It is preferable that the color difference that occurs when light propagates 250 mm through the direction conversion layer 60A is Δxy ≤ 0.01.

[0039] When the light guide layer 10 is viewed from the direction normal to the first main surface, the ratio of the area of ​​the multiple internal spaces 64 to the area of ​​the direction conversion layer 60A (occupancy rate) is preferably 1% to 80%, the upper limit is more preferably 50% or less, even more preferably 45% or less, and to obtain high transmittance and / or low haze value, it is preferably 30% or less, even more preferably 10% or less, and even more preferably 5% or less. For example, when the occupancy rate of the internal spaces is 50%, a haze value of 30% can be obtained. The occupancy rate of the internal spaces 64 may be uniform, or the occupancy rate may be increased with increasing distance so that the brightness does not decrease even when the distance from the light source LS increases. For mass production by the roll-to-roll method or roll-to-sheet method, it is preferable that the occupancy rate of the internal spaces 64 is uniform.

[0040] By adjusting the above-mentioned color difference for each layer and the area ratio of the multiple internal spaces 64, when light is incident from the first main surface 12a and viewed from the second main surface 12b, the light guide member 100A may have characteristics such as a visible light transmittance of 60% or more and a haze value of less than 30%. Preferably, the visible light transmittance is 70% or more, and more preferably 80% or more. Preferably, the haze value is less than 10%, and more preferably 5% or less. Since the light guide member 100A has a high visible light transmittance and a low haze value, the object 70 becomes easier to see through the light guide member 100A. Here, visible light is defined as light with a wavelength of 380 nm or more and 780 nm or less. The visible light transmittance and haze value can be measured, for example, using a haze meter (manufactured by Murakami Color Technology Laboratory: product name HM-150).

[0041] [Material parameters of the light guide member 100A regarding flexibility] The material parameters of the components included in the light guide member 100A regarding flexibility are as follows.

[0042] The thickness of the first base layer 30A may be, for example, 100 μm or less. While there is no particular lower limit, the thickness of the first base layer 30A may be, for example, 10 μm or more or 20 μm or more. If the loss coefficient (loss modulus G'' / storage modulus G') of the second base layer 30B is less than 0.06, the thickness of the second base layer 30B may be, for example, 180 μm or less. If the loss coefficient of the second base layer 30B is 0.06 or more, the thickness of the second base layer 30B may be, for example, 100 μm or less. A smaller loss coefficient indicates higher elasticity, and a larger loss coefficient indicates higher viscosity. While there is no particular lower limit, the thickness of the second base layer 30B may be, for example, 10 μm or more or 20 μm or more. The storage modulus of the adhesive layer 52 may be, for example, 300 kPa or less. While there is no particular lower limit, the storage modulus of the adhesive layer 52 may be 300 kPa or less. The performance rating is, for example, 10 kPa or more or 50 kPa or more. The thickness of the adhesive layer 52 may be, for example, 80 μm or more. There is no particular upper limit, but the thickness of the adhesive layer 52 may be, for example, 300 μm or less or 200 μm or less. The thickness of the direction changing layer 60A may be, for example, 100 μm or less. There is no particular lower limit, but the thickness of the direction changing layer 60A may be, for example, 10 μm or more or 20 μm or more. The thinner the base layers 30A, 30B and the direction changing layer 60A, the easier it is to bend the light guide member 100A. The thicker the adhesive layer 52, the more the distortion when bending the light guide member 100A can be reduced.

[0043] If the above conditions are met, the light guide member 100A has foldable flexibility. From the viewpoint of increasing the flexibility of the light guide member 100A, the thickness of the first base layer 30A is preferably 80 μm or less or 60 μm or less. If the loss coefficient of the second base layer 30B is less than 0.06, the thickness of the second base layer 30B is preferably 130 μm or less. If the loss coefficient of the second base layer 30B is 0.06 or more, the thickness of the second base layer 30B is preferably 50 μm or less. The storage modulus of the adhesive layer 52 is preferably 200 kPa or less or 150 kPa or less. The thickness of the adhesive layer 52 is preferably 100 μm or more. The thickness of the direction changing layer 60A is preferably 80 μm or less or 60 μm or less. As an example of foldable flexibility, the light guide member 100A does not break even when bent with a radius of curvature of 5 mm.

[0044] The thin light guide member 100A is advantageous in terms of size and weight reduction. By adjusting the thicknesses of the base material layers 30A, 30B, the adhesive layers 52, 54, and the shaped film 62, the total thickness of the light guide layer 10 and the direction conversion layer 60A can be set to, for example, 100 µm or more and 600 µm or less. The upper limit of this total thickness is preferably 550 µm or less or 500 µm or less, for example.

[0045] From the above, the light guide member 100A and the lighting device 100A_L according to Embodiment 1 of the present invention can have transparency that allows the object 70 to be clearly visually recognized, and foldable flexibility. Furthermore, the light guide member 100A and the lighting device 100A_L according to Embodiment 1 of the present invention can be made thin. The light guide member 100A and the lighting device 100A_L according to Embodiment 1 of the present invention can be used, for example, as a front light for flexible display devices.

[0046] (Embodiment 2) Next, with reference to FIG. 2, a configuration example of a lighting device according to Embodiment 2 of the present invention having transparency and flexibility will be described. FIG. 2 shows a schematic cross-sectional view of the lighting device 100B_L according to Embodiment 2 of the present invention in an unfolded state. A schematic cross-sectional view of the lighting device 100B_L in a folded state is omitted. The lighting device 100B_L includes a light source LS and a light guide member 100B. While the light guide member 100A shown in FIG. 1A includes the direction conversion layer 60A disposed on the first main surface 12a side, the light guide member 100B shown in FIG. 2 includes the direction conversion layer 60B disposed on the second main surface 12b side.

[0047] The direction conversion layer 60B has a light distribution control structure including a plurality of internal spaces 64. The plurality of internal spaces 64 direct part of the light propagating through the light guide layer 10 toward the first emission surface side as irradiation lightLRa by total internal reflection (TIR). The direction conversion layer 60B is constituted by a shaped film 62 having recesses 64 on the surface opposite to the second main surface 12b, a third base material layer 30C disposed on this surface side of the shaped film 62, an adhesive layer 54 that bonds the shaped film 62 and the third base material layer 30C, and an adhesive layer 56 that bonds the shaped film 62 and the second base material layer 30B.

[0048] [Materials and Parameters of Light Guide Member 100B] Among the constituent elements included in the light guide member 100B, the materials and parameters of the base material layers 30A, 30B and the adhesive layer 52 are as described above.

[0049] In the direction changing layer 60B, the shaped film 62 and the third base material layer 30C are formed of resin. This resin may be, for example, an acrylic resin such as PMMA, or a cycloolefin resin such as COP. The adhesive layers 54 and 56 are formed of a resin-based optically clear adhesive (OCA). This resin may be, for example, an acrylic resin. It can be said that the direction changing layer 60B composed of the shaped film 62, the third base material layer 30C, and the adhesive layers 52 and 54 is formed of resin. The area occupancy rate of the internal space 64 is as described above.

[0050] The thickness of the direction changing layer 60B may be, for example, 100 μm or less. Although the lower limit is not particularly limited, the thickness of the direction changing layer 60B may be, for example, 10 μm or more or 20 μm or more. It is preferable that the thickness of the direction changing layer 60B is 80 μm or less or 60 μm or less. By adjusting the thicknesses of the base material layers 30A, 30B, 30C, the adhesive layers 52, 54, 56, and the shaped film 62, the total thickness of the light guide layer 10 and the direction changing layer 60B can be set to, for example, 100 μm or more and 600 μm or less. The upper limit of this total thickness is preferably, for example, 550 μm or less or 500 μm or less.

[0051] From the above, the light guide member 100B and the illumination device 100B_L according to Embodiment 2 of the present invention, similar to the light guide member 100A and the illumination device 100A_L according to Embodiment 1 of the present invention, can have transparency that allows the object 70 to be clearly visually recognized, and foldable flexibility. Further, the light guide member 100B and the illumination device 100B_L according to Embodiment 2 of the present invention can be made thin. The light guide member 100B and the illumination device 100B_L according to Embodiment 2 of the present invention can be used, for example, as a front light for a flexible display device.

[0052] (Planar shape and arrangement of the internal space 64) Next, an example of the planar shape and arrangement of the internal space 64 will be described with reference to Figure 3. Figure 3 shows schematic plan views of the lighting devices 100A_L and 100B_L.

[0053] As shown in Figure 3, the multiple internal spaces 64 are discretely arranged, for example, in the light-guiding direction (Y direction) and in a direction perpendicular to the light-guiding direction (X direction) of the light-guiding layer 10. The size of the internal spaces 64 (length L, width W: see Figures 4A and 4B) is preferably such that the length L is 10 μm or more and 500 μm or less, and the width W is preferably 1 μm or more and 100 μm or less. Furthermore, from the viewpoint of light extraction efficiency, the height H (see Figure 4A) is preferably 1 μm or more and 100 μm or less.

[0054] Here, an example is shown in which multiple internal spaces 64 are discretely arranged in the light-guiding direction (Y direction) and in a direction perpendicular to the light-guiding direction (X direction) of the light-guiding layer 10. However, the example is not limited to this, and the multiple internal spaces 64 can be discretely arranged in the light-guiding direction (Y direction) and in a direction intersecting the light-guiding direction of the light-guiding layer 10. The discrete arrangement of the internal spaces 64 can be appropriately set according to the shape of the light-guiding layer 10 and the desired light distribution. Although light propagates in various directions within the light-guiding layer 10, the Y direction is referred to as the light-guiding 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).

[0055] The multiple internal spaces 64 are, for example, discretely arranged in the light-guiding direction and in directions intersecting the light-guiding direction. The discrete arrangement of the multiple internal spaces 64 helps to reduce the area ratio of the internal spaces 64 and obtain high transmittance and / or low haze value. The discrete arrangement may or may not have periodicity (regularity) in at least one direction. However, from the viewpoint of mass production, it is preferable that the multiple internal spaces 64 are uniformly arranged. For example, in the example shown in Figure 3, multiple internal spaces 64 having substantially the same shape and a curved surface convex in the same direction are discretely and periodically arranged throughout the entire region of the light-guiding layer 10 in the light-guiding direction (Y direction) and in a direction perpendicular to the light-guiding direction (X direction). In this case, the pitch Px is preferably, for example, 10 μm or more and 500 μm or less, and the pitch Py is preferably, for example, 10 μm or more and 500 μm or less. In the example shown in Figure 3, they are arranged with a 1 / 2 pitch offset in each of the Y and X directions.

[0056] As shown in Figure 3, when viewed from the direction normal to the first main surface of the light guide layer 10, the first inclined surface ISa forms a curved surface that is convex toward the light source LS. The light source LS that emits light toward the light receiving section may be, for example, an LED device. Multiple LED devices are arranged in the X direction along the light receiving section of the light guide layer 10. Since the light emitted from each of the multiple LED devices spreads in the Y direction, having a curved surface that is convex toward the light source LS allows the first inclined surface ISa to act uniformly on the light.

[0057] Next, the shape of the internal space 64 will be described with reference to Figures 4A, 4B, and 4C. Figure 4A shows a schematic cross-sectional view of the internal space 64, Figure 4B shows a schematic plan view of the internal space 64, and Figure 4C shows schematic plan views illustrating variations of the internal space 64.

[0058] As shown in Figure 4A, the cross-sectional shape of the internal space 64 is, for example, triangular. The inclination angle θa of the first inclined surface ISa on the light source side (light incident side) is, for example, 10° to 70°. If the inclination angle θa is less than 10°, the light utilization efficiency may be low, and if it exceeds 70°, processing may be difficult. The inclination angle θb of the second inclined surface ISb on the opposite side of the first inclined surface ISa is, for example, 50° to 100°. If the inclination angle θb is less than 50°, the amount of light in an undesirable direction may increase, and similarly, if it exceeds 100°, the amount of light in an undesirable direction may also increase. Furthermore, in order to increase the amount of irradiated light LRa emitted from the first emission surface and decrease the amount of stray light (light other than reflected light LRb) emitted from the second emission surface, it is preferable that the inclination angle θa of the first inclined surface ISa be, for example, 20° or more and 50° or less, and the inclination angle θb of the second inclined surface ISb be, for example, 70° or more and 90° or less.

[0059] As shown in Figures 4B and 4C, in the planar shape of the internal space 64 when viewed from the direction normal to the first main surface of the light guide layer 10, the length L of the internal space 64 is preferably 10 μm or more and 500 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 4A) is preferably 1 μm or more and 100 μm or less. When forming a shaped film having a recess having the planar shape shown in Figure 4B, a recess having the planar shape shown in Figure 4C may be formed depending on the processing accuracy of the mold. Even in such cases, the planar shape of the internal space can be characterized by the length L and width W.

[0060] (Examples and Comparative Examples) Next, the lighting device 100A_L of Embodiment 1 of the present invention will be described with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0061] [Lighting devices of Examples 1 to 6] The lighting devices of Examples 1 to 6 have substantially the same structure as the lighting device 100A_L shown in Figure 1A. The lighting devices of Examples 1 to 6 are positioned in front of a flexible object 70. The object 70 is flexible and does not break even when bent with a radius of curvature of 5 mm (R5).

[0062] The lighting devices of Examples 1 to 6 are equipped with the same direction-changing layer 60A. The materials and parameters of the shaping film 62 and adhesive layer 54 included in the direction-changing layer 60A are as follows. However, "Δxy / 250mm" below represents the color difference that occurs when light propagates through the layer for 250mm. • Shaping film 62 Material: PMMA Thickness: 55μm • Adhesive layer 54 Material: Acrylic OCA Thickness: 10μm • Direction-changing layer 60A Thickness: 65μm Δxy / 250mm: 0.0063

[0063] Here, the acrylic OCA is a copolymer of 2-ethylheylacrylate, N-vinylpyrrolidone, and hydroxyethyl acrylate. The same applies below.

[0064] The shaping film 62 was manufactured by the method described in Japanese Patent Publication No. 2013-524288. Specifically, the surface of a PMMA film was coated with lacquer (FineCure RM-64 manufactured by Sanyo Chemical Industries, Ltd.), an optical pattern was embossed onto the film surface containing this lacquer, and then the lacquer was cured to produce the desired textured shaping film.

[0065] The lighting devices of Examples 1 to 6 are equipped with different light guide layers 10. The materials and parameters of the first base layer 30A, the second base layer 30B, and the adhesive layer 52 included in the light guide layer 10 are as follows.

[0066] <Example 1> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0067] <Example 2> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 60 μm Loss factor: 0.01677 Δxy / 250 mm: 0.0039 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0068] <Example 3> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0069] <Example 4> • First base layer 30A Material: COP Thickness: 60 μm Loss factor: 0.01677 Δxy / 250 mm: 0.0039 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0070] <Example 5> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 150 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0071] <Example 6> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 100 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0072] [Lighting devices of Comparative Examples 1 to 9] The lighting devices of Comparative Examples 1 and 2 have a different structure from the lighting device 100A_L shown in Figure 1A in the following respects. That is, the light guide layer 10 is composed of the first base material layer 30A and does not include the second base material layer 30B and the adhesive layer 52. The lighting devices of Comparative Examples 3 to 9 have substantially the same structure as the lighting device 100A_L shown in Figure 1A.

[0073] The object 70 on which the lighting devices of Comparative Examples 1 to 9 are placed is the same as the object 70 on which the lighting devices of Examples 1 to 6 are placed. The direction changing layer 60A in the lighting devices of Comparative Examples 1 to 9 is the same as the direction changing layer 60A in the lighting devices of Examples 1 to 6.

[0074] The lighting devices of Comparative Examples 1 to 9 are equipped with different light guide layers 10. The materials and parameters of the first substrate layer 30A included in the light guide layer 10 of Comparative Examples 1 and 2, and the first substrate layer 30A, second substrate layer 30B, and adhesive layer 52 included in the light guide layer 10 of Comparative Examples 3 to 9 are as follows.

[0075] <Comparative Example 1> • First substrate layer 30A Material: PMMA Thickness: 500 μm

[0076] <Comparative Example 2> • First substrate layer 30A Material: PC (polycarbonate) Thickness: 500 μm

[0077] <Comparative Example 3> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: PET (polyethylene terephthalate) Thickness: 100 μm Loss factor: 0.005699 Δxy / 250 mm: 0.039 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0078] <Comparative Example 4> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.0681348 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: PMMA Thickness: 130 μm Loss factor: 0.0687973 Δxy / 250 mm: 0.0032 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0079] <Comparative Example 5> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 188 μm Loss factor: 0.0009338 Δxy / 250 mm: 0.0039 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0080] <Comparative Example 6> • First base layer 30A Material: PMMA Thickness: 130 μm Loss factor: 0.06880 Δxy / 250 mm: 0.0032 • Second base layer 30B Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0081] <Comparative Example 7> • First base layer 30A Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Second base layer 30B Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0082] <Comparative Example 8> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 50 μm Δxy / 250 mm: 0.00031 Storage modulus: 144 kPa

[0083] <Comparative Example 9> • First base layer 30A Material: PMMA Thickness: 40 μm Loss factor: 0.06813 Δxy / 250 mm: 0.0063 • Second base layer 30B Material: COP Thickness: 130 μm Loss factor: 0.008259 Δxy / 250 mm: 0.005 • Adhesive layer 52 Material: Acrylic OCA Thickness: 200 μm Δxy / 250 mm: 0.00648 Storage modulus: 30 kPa

[0084] [Results] For the lighting devices of Examples 1 to 6 and Comparative Examples 1 to 9, the presence or absence of flexibility that allows bending with a radius of curvature of 5 mm (R5), and the color difference that occurs when light propagates through the light guide layer 10 for 250 mm are as shown in Table 1. "○" below means that there is flexibility that allows bending with a radius of curvature of 5 mm. "×" below means that there is no such flexibility.

[0085]

[0086] <Lighting devices of Comparative Examples 1 to 9> Of the lighting devices of Comparative Examples 1 to 9, the lighting devices of Comparative Examples 1, 2, and 4 to 8 did not have the flexibility to be bent with a radius of curvature of 5 mm. The light guide layer 10 of the lighting devices of Comparative Examples 1 and 2 was too thick to be bent. In the lighting device of Comparative Example 4, the second base material layer 30B cracked. This is thought to be because the thickness of the second base material layer 30B, which has a loss factor of 0.06 or more, was greater than 100 μm. The lighting device of Comparative Example 5 peeled off from the object 70. This is thought to be because the thickness of the second base material layer 30B, which has a loss factor of less than 0.06, was greater than 180 μm. In the lighting device of Comparative Example 6, the first base material layer 30A cracked. This is thought to be because the thickness of the first base material layer 30A was greater than 100 μm. The lighting device of Comparative Example 7 peeled off from the object 70. This is thought to be because the thickness of the first base material layer 30A was greater than 100 μm. In the lighting device of Comparative Example 8, creases remained. This is thought to be because the thickness of the adhesive layer 52 was less than 80 μm.

[0087] The lighting device of Comparative Example 3 had flexibility that allowed it to be bent with a radius of curvature of 5 mm. However, the color difference that occurred when light propagated 250 mm through the second substrate layer 30B was Δxy > 0.03. The color difference that occurred when light propagated 250 mm through the light guide layer 10 was Δxy > 0.2. Therefore, the lighting device of Comparative Example 3 did not have the transparency necessary to clearly see the object 70.

[0088] The lighting device of Comparative Example 9 had flexibility that allowed it to be bent with a radius of curvature of 5 mm. However, the color difference that occurred when light propagated 250 mm through the adhesive layer 52 was Δxy > 0.006. The color difference that occurred when light propagated 250 mm through the light guide layer 10 was Δxy > 0.2. Therefore, the lighting device of Comparative Example 9 did not have the transparency necessary to clearly see the object 70.

[0089] <Lighting devices of Examples 1 to 6> The lighting devices of Examples 1 to 6 were flexible and could be bent with a radius of curvature of 5 mm. In the lighting devices of Examples 1 to 6, the thickness of the direction changing layer 60A was 100 μm or less. The thickness of the first base material layer 30A was 100 μm or less. When the loss coefficient of the second base material layer 30B was less than 0.06, the thickness of the second base material layer 30B was 180 μm or less. When the loss coefficient of the second base material layer 30B was 0.06 or more, the thickness of the second base material layer 30B was 100 μm or less. The thickness of the adhesive layer 52 was 80 μm or more. The storage modulus of the adhesive layer 52 was 300 kPa or less.

[0090] More specifically, in the lighting devices of Examples 1 to 6, the thickness of the direction changing layer 60A was 80 μm or less. The thickness of the first substrate layer 30A was 80 μm or less, and furthermore, 60 μm or less. When the loss coefficient of the second substrate layer 30B was less than 0.06, the thickness of the second substrate layer 30B was 150 μm or less, and furthermore, 130 μm or less. When the loss coefficient of the second substrate layer 30B was 0.06 or more, the thickness of the second substrate layer 30B was 50 μm or less. The thickness of the adhesive layer 52 was 100 μm or more. The storage modulus of the adhesive layer 52 was 200 kPa or less, and furthermore, 150 kPa or less.

[0091] Furthermore, the lighting devices of Examples 1 to 6 had transparency that allowed the object 70 to be clearly visible. In the lighting devices of Examples 1 to 6, the color difference that occurred when light propagated 250 mm through the direction conversion layer 60A was Δxy ≤ 0.03. The color difference that occurred when light propagated 250 mm through the first substrate layer 30A was Δxy ≤ 0.03. The color difference that occurred when light propagated 250 mm through the second substrate layer 30B was Δxy ≤ 0.03. The color difference that occurred when light propagated 250 mm through the adhesive layer 52 was Δxy ≤ 0.006. The color difference that occurred when light propagated 250 mm through the light guide layer 10 was Δxy ≤ 0.2.

[0092] More specifically, in the lighting devices of Examples 1 to 6, the color difference that occurred while light propagated 250 mm through the direction conversion layer 60A was Δxy ≤ 0.01. The color difference that occurred while light propagated 250 mm through the first substrate layer 30A was Δxy ≤ 0.01. The color difference that occurred while light propagated 250 mm through the second substrate layer 30B was Δxy ≤ 0.01. The color difference that occurred while light propagated 250 mm through the adhesive layer 52 was Δxy ≤ 0.001. The color difference that occurred while light propagated 250 mm through the light guide layer 10 was Δxy ≤ 0.1.

[0093] [Measurement Methods for Thickness, Loss Factor, Elastic Modulus, and Color Difference Δxy] The measuring instruments, samples, and measurement methods for thickness, loss factor, elastic modulus, and color difference Δxy are as follows.

[0094] <Thickness> • Measuring instrument and sample measuring instrument: Constant pressure thickness measuring instrument (TechLock Corporation) Sample: 10 mm x 10 mm cut piece cut from film • Measurement method The sample was placed on the stage of the measuring instrument, and the thickness of the sample was measured by the measuring instrument.

[0095] <Loss Factor and Elastic Modulus> • Measuring instrument and sample measuring instrument: Dynamic viscoelasticity measuring device (TA Instruments Co., Ltd.: Product name RSA-G2) Sample: 10 mm x 50 mm cut piece from film • Measurement method The dynamic viscoelasticity (storage modulus and loss modulus) of the sample was measured by the measuring instrument at a temperature of 25°C. The loss factor was obtained from the dynamic viscoelasticity.

[0096] <Color Difference (Substrate Layers 30A, 30B, Directional Conversion Layer 60A)> Referring to Figure 5A, a method for measuring the color difference that occurs when light propagates 250 mm through the substrate layers 30A, 30B, or directional conversion layer 60A will be explained. Figure 5A is a diagram illustrating a method for measuring the color difference that occurs when light propagates 250 mm through the substrate layers 30A, 30B, or directional conversion layer 60A.

[0097] ・Measuring instrument 72 and sample measuring instrument 72: Total luminous flux measurement system (Otsuka Electronics Co., Ltd.) Sample: A laminate formed by bonding a base layer 30A, 30B or a direction changing layer 60A to an acrylic plate 82 (material: Acrylite Ex) with a thickness of 2 mm, a width of 120 mm and a length of 250 mm via an adhesive layer 84 (material: acrylic OCA) with a thickness of 25 μm. ・Measurement method As shown in Figure 5A, the measuring instrument 72 has an integrating sphere 72a and a light receiver 72b. The sample has two sides that are opposite to each other in the longitudinal direction. Of these two sides, one side is located outside the integrating sphere 72a and the other side is located inside the integrating sphere 72a. The measuring instrument 72 is mounted inside the integrating sphere 72a so as to face the other side. When light emitted from the light source LS (LED, FKK Corporation: product name FB-120-NZ-K) was incident on one side of the sample, more specifically on the side of the acrylic plate 82, light leaked from the other side of the sample. The luminance of the leaked light was measured by a photodetector. Based on the luminance measurement, the change in the color coordinates between the light emitted from the light source LED and the leaked light was defined as Δxy. The color difference Δxy that occurs when light propagates 250 mm through the adhesive layer 84 was 0.0003, which was negligibly small compared to the color difference Δxy that occurs when light propagates 250 mm through the substrate layers 30A, 30B, or the direction conversion layer 60A.

[0098] <Color Difference (Adhesive Layer 52)> Referring to Figure 5B, the method for measuring the color difference that occurs when light propagates through the adhesive layer 52 for 250 mm will be explained. Figure 5B is a diagram illustrating the method for measuring the color difference that occurs when light propagates through the adhesive layer 52 for 250 mm.

[0099] - Measuring instrument 72 and sample measuring instrument 72: Total luminous flux measurement system (Otsuka Electronics Co., Ltd.) Sample: A laminate formed by bonding only an adhesive layer 52 to an acrylic plate 82 (material: Acrylite Ex) with a thickness of 2 mm, a width of 120 mm and a length of 250 mm. - Measurement method: The method is as described with reference to Figure 5A, except that the sample shown in Figure 5B is different from the sample shown in Figure 5A.

[0100] <Color Difference (Light Guide Layer 10)> Referring to Figure 5C, the method for measuring the color difference that occurs when light propagates through the light guide layer 10 for 250 mm will be explained. Figure 5C is a diagram illustrating the method for measuring the color difference that occurs when light propagates through the light guide layer 10 for 250 mm.

[0101] ・Measuring instrument and sample measuring instrument 74: Two-dimensional radiance meter (Topcon Techno House Co., Ltd.: product name SR-5000) Sample: Light guide layer 10 with a width of 120 mm and a length of 300 mm, including a direction conversion layer 60A, a first substrate layer 30A, an adhesive layer 52, and a second substrate layer 30B in that order. ・Measurement method As shown in Figure 5C, the sample has two sides that are opposite to each other in the longitudinal direction. When light emitted from the light source LS is incident on one side of the sample, more specifically the side of the second substrate layer 30B, light leaks from the light emission surface of the direction conversion layer 60A. The luminance of the leaked light was measured by the measuring instrument at a light guide distance of 250 mm. Based on the luminance measurement, the change in the color coordinates of the light emitted from the light source LED and the color coordinates of the leaked light was defined as Δxy.

[0102] The light guide member and lighting device according to the embodiment of the present invention are transparent and flexible. The light guide member and lighting device according to the embodiment of the present invention can be used, for example, as a front light for a flexible display device.

[0103] 10: Light guide layer, 12a: First main surface, 12b: Second main surface, 30A: First base layer, 30B: Second base layer, 30C: Third base layer, 52, 54, 56: Adhesive layer, 60A, 60B: Direction change layer, 62: Shaping film, 64: Internal space, recess, 72, 74: Measuring instrument, 72a: Integrating sphere, 72b: Photodetector, 82: Acrylic plate, 84: Adhesive layer, 100A, 100B: Light guide member, 100A_L, 100B_L: Lighting device, ISa: First inclined surface, ISb: Second inclined surface, LRa: Irradiated light, LRb: Reflected light, LS: Light source

Claims

1. A light guide member for a lighting device having an emission surface, comprising: a light receiving portion that receives light emitted from a light source; a light guide layer having a first main surface on the emission surface side and a second main surface on the opposite side of the emission surface; and a direction changing layer disposed on the side of the first main surface or the second main surface of the light guide layer, which directs a portion of the light propagating through the light guide layer toward the emission surface, wherein the light guide layer comprises a first base material layer, an adhesive layer, and a second base material layer laminated in order from the emission surface side, the first main surface being the surface of the first base material layer opposite to the adhesive layer, the direction changing layer, the first base material layer, and the second base material layer being formed from resin, the thickness of the direction changing layer being 100 μm or less, and the thickness of the first base material layer being 100 μm or less. A light guide member for a lighting device, wherein when the loss coefficient (loss modulus / storage modulus) of the second substrate layer is less than 0.06, the thickness of the second substrate layer is 180 μm or less; when the loss coefficient of the second substrate layer is 0.06 or more, the thickness of the second substrate layer is 100 μm or less; the thickness of the adhesive layer is 80 μm or more; the storage modulus of the adhesive layer is 300 kPa or less; the color difference that occurs when light propagates 250 mm through the first substrate layer is Δxy ≤ 0.03; the color difference that occurs when light propagates 250 mm through the second substrate layer is Δxy ≤ 0.03; the color difference that occurs when light propagates 250 mm through the adhesive layer is Δxy ≤ 0.006; and the color difference that occurs when light propagates 250 mm through the light guide layer is Δxy ≤ 0.

2.

2. The light guide member for a lighting device according to claim 1, wherein the thickness of the direction conversion layer is 60 μm or less, the thickness of the first substrate layer is 60 μm or less, and if the loss coefficient (loss modulus / storage modulus) is less than 0.06, the thickness of the second substrate layer is 130 μm or less, and if the loss coefficient is 0.06 or more, the thickness of the second substrate layer is 50 μm or less.

3. The light guide member for a lighting device according to claim 1 or 2, wherein the color difference that occurs when light propagates 250 mm through the first substrate layer is Δxy ≤ 0.01, the color difference that occurs when light propagates 250 mm through the second substrate layer is Δxy ≤ 0.01, and the color difference that occurs when light propagates 250 mm through the adhesive layer is Δxy ≤ 0.

001.

4. The light guide member for a lighting device according to claim 1 or 2, wherein the color difference that occurs while light propagates through the light guide layer for 250 mm is Δxy ≤ 0.

1.

5. The light guide member for a lighting device according to claim 1 or 2, wherein the thickness of the adhesive layer is 100 μm or more, and the storage modulus of the adhesive layer is 200 kPa or less.

6. The light guide member for a lighting device according to claim 1 or 2, wherein the first base layer is formed from an acrylic resin or a cycloolefin resin, and the second base layer is formed from an acrylic resin or a cycloolefin resin.

7. The light guide member for a lighting device according to claim 1 or 2, wherein the adhesive layer is formed from an optically transparent adhesive.

8. The light guide member for a lighting device according to claim 1 or 2, wherein the direction changing layer has a plurality of internal spaces that totally reflect a portion of the light propagating through the light guide layer and direct it toward the emission surface.

9. A light guide member for a lighting device according to claim 1 or 2, which does not break even when bent with a radius of curvature of 5 mm.

10. The light guide member for a lighting device according to claim 1 or 2, wherein when light is incident from the first main surface side and viewed from the second main surface side, the visible light transmittance is 60% or more and the haze value is less than 30%.

11. The light guide member for a lighting device according to claim 1 or 2, wherein the total thickness of the light guide layer and the direction changing layer is 600 μm or less.

12. A lighting device comprising: a light guide member for a lighting device according to claim 1 or 2; and a light source that emits the light toward the light receiving portion.

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