Optical sheet

Abstract

Provided is an optical sheet that has a layer in which a light transmission part and a light absorption part are alternately disposed, and that is capable of suppressing warpage while securing a degree of freedom in layer configuration.　The optical sheet has a base material layer and an optical functional layer which is laminated on the base material layer and in which a light transmission part and a light absorption part are alternately disposed, wherein: the optical function layer is configured such that: the light transmission part has a predetermined cross section and extends in one direction, and a plurality of the light transmission parts are disposed at intervals in a direction different from the one direction; and the light absorption part is disposed between the light transmission parts, and when the indentation hardness of the light absorption part at a position Mb on the base material layer side is noted as Hb and the indentation hardness at a position Ma on the side opposite to the base material layer is noted as Ha, Ha > Hb is satisfied.

Description

Optical Sheet

[0001] The present invention relates to an optical sheet that controls the outgoing direction of incident light.

[0002] Patent Documents 1 and 2 disclose optical films that are less susceptible to problems caused by warping and optical adhesion.

[0003] JP 2016-105132 A JP 2017-219619 A

[0004] Conventional technology describes suppressing warpage by forming new layers or bonding layers together, but applying such additional layer configurations reduces the degree of freedom in the layer configuration, resulting in problems such as an inability to make the product thinner.

[0005] In view of the above problems, the present invention aims to provide an optical sheet that has layers in which light-transmitting sections and light-absorbing sections are arranged alternately, has flexibility in layer structure, and can suppress warping.

[0006] The present application provides an optical sheet having a base layer and an optical functional layer laminated on the base layer and including light-transmitting portions and light-absorbing portions arranged alternately, wherein the optical functional layer has a plurality of light-transmitting portions each having a predetermined cross section and extending in one direction, and the plurality of light-absorbing portions are arranged at intervals in a direction different from the one direction, and the light-transmitting portions are arranged between the light-transmitting portions, and the light-absorbing portions are arranged at a position M on the base layer side. ｂ The indentation hardness at H ｂ , a position M on the opposite side of the substrate layer ａ The indentation hardness at H ａ When this is done, H ａ >H ｂ The present invention discloses an optical sheet.

[0007] M ａ and M ｂ Position M between ｃ The indentation hardness at H ｃ When this is done, H ａ >H ｃ >H ｂ It may also be possible to use the following.

[0008] Furthermore, {(H ａ +H ｂ ) / 2}>H ｃmay be configured so that the following holds true.

[0009] Also, (H ｂ / H ａ ) × 100% may be set to be 70% or more and 85% or less.

[0010] H ａ may be set to be 212 MPa or more and 271 MPa or less.

[0011] The substrate layer may be made of a polycarbonate resin.

[0012] The light-transmitting portion may have a trapezoidal cross section with a long lower base on the side of the base layer and a short upper base on the opposite side.

[0013] The light absorbing portion may have a trapezoidal cross section with a long lower base on the upper base side of the light transmitting portion and a short upper base on the opposite side.

[0014] The light absorbing portion may be configured such that light absorbing particles made of carbon black are contained in a transparent resin.

[0015] According to the present disclosure, in an optical sheet having layers in which light-transmitting portions and light-absorbing portions are arranged alternately, the occurrence of warping can be suppressed by adjusting the indentation hardness of the light-absorbing portions, thereby increasing the degree of freedom in the layer configuration that makes up the optical sheet.

[0016] 1 is an exploded perspective view illustrating the image source unit 10. FIG. 2 is an exploded view showing a cross section of the image source unit 10. FIG. 3 is an exploded view showing another cross section of the image source unit 10. FIG. 4 is an enlarged view focusing on the optical sheet 30. FIG. 5 is a view explaining indentation hardness. FIG. 6 is a view explaining the manufacturing process of the optical sheet 30. FIG. 7 is a view explaining the manufacturing process of the optical sheet 30.

[0017] The present disclosure will be described below based on the embodiments shown in the drawings. However, the present disclosure is not limited to these embodiments. In each drawing, shapes may be enlarged, deformed, or exaggerated for clarity, and some repeated reference numerals may be omitted. Furthermore, hatching may be omitted even in cross sections for clarity.

[0018] 1. Image Source Unit FIG. 1 is a diagram illustrating one embodiment and is an exploded perspective view of an image source unit 10 including an optical sheet 30. FIG. 2 shows a portion of an exploded cross-sectional view of the image source unit 10 cut along line II-II (a vertical line) in FIG. 1, and FIG. 3 shows a portion of an exploded cross-sectional view of the image source unit 10 cut along line III-III (a horizontal line). While detailed description is omitted, this image source unit 10 is housed in a housing (not shown) together with the usual equipment required to operate the image source unit 10, such as a power source for operating the image source unit 10 and electronic circuits for controlling the image source unit 10, to form a display device. In this embodiment, a liquid crystal image source unit will be described as one embodiment of an image source unit, and a liquid crystal display device will be described as one embodiment of a display device. The image source unit 10 will be described below.

[0019] The image source unit 10 includes a liquid crystal panel 15, a surface light source device 20, and a functional film 40. In this embodiment, the optical sheet 30 is included in the surface light source device 20. Figures 1 to 3 also show the orientation of the display device when it is installed.

[0020] 1.1 Liquid Crystal Panel The liquid crystal panel 15 has an upper polarizing plate 13 arranged on the viewer side, a lower polarizing plate 14 arranged on the surface light source device 20 side, and a liquid crystal layer 12 arranged between the upper polarizing plate 13 and the lower polarizing plate 14. The upper polarizing plate 13 and the lower polarizing plate 14 have the function of decomposing incident light into two orthogonal polarized components (P waves and S waves), transmitting the polarized component in one direction (parallel to the transmission axis) (e.g., P waves) and absorbing the polarized component in the other direction (parallel to the absorption axis) orthogonal to the one direction (e.g., S waves).

[0021] The liquid crystal layer 12 has multiple pixels arranged vertically and horizontally along the layer surface, and an electric field can be applied to each pixel. The applied electric field changes the orientation of the pixel. As a result, the polarization direction of a polarized component (e.g., P wave) parallel to the transmission axis that passes through the lower polarizer 14 located on the surface light source device 20 side (i.e., the light incident side) is rotated by 90° when passing through a pixel to which an electric field is applied, while maintaining its polarization direction when passing through a pixel to which no electric field is applied. Therefore, depending on whether an electric field is applied to the pixel, it is possible to control whether the polarized component (e.g., P wave) that passes through the lower polarizer 14 is further transmitted through the upper polarizer 13 located on the light output side, or whether it is absorbed and blocked by the upper polarizer 13.

[0022] In this way, the liquid crystal panel 15 has a structure that controls the transmission or blocking of light from the surface light source device 20 for each pixel to display an image.

[0023] There are several types of liquid crystal panels, but in this embodiment, the type is not particularly limited, and any known type of liquid crystal panel can be used, such as TN, STN, VA, MVA, IPS, and OCB.

[0024] 1.2 Surface Light Source Device Next, the surface light source device 20 will be described. The surface light source device 20 is an illumination device that is disposed on the opposite side of the liquid crystal panel 15 from the viewer side, and emits planar light toward the liquid crystal panel 15. As can be seen from Figures 1 to 3, the surface light source device 20 of this embodiment is configured as an edge-light type surface light source device, and includes a light guide plate 21, a light source 25, a light diffusion plate 26, a prism layer 27, a reflective polarizing plate 28, an optical sheet 30, and a reflective sheet 39.

[0025] 1 to 3, the light guide plate 21 has a base 22 and rear surface optical elements 23. The light guide plate 21 is a plate-shaped member made of a light-transmitting material. In this embodiment, one plate surface of the light guide plate 21 facing the viewer is a smooth surface, and the other plate surface opposite to this is a rear surface, on which a plurality of rear surface optical elements 23 are arranged.

[0026] Various materials can be used for the base 22 and the rear optical element 23. However, it is possible to use materials that are widely used as materials for optical sheets incorporated into display devices, have excellent mechanical properties, optical properties, stability, processability, etc., and are inexpensively available. Examples of such materials include thermoplastic resins such as polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyethersulfones, as well as epoxy acrylate and urethane acrylate reactive resins (e.g., ionizing radiation curable resins).

[0027] The base 22 is a plate-like portion through which light is guided and which serves as a base for the rear optical element 23, and has a predetermined thickness.

[0028] The rear surface optical elements 23 are protruding elements formed on the rear surface side of the base 22, and in this embodiment, are triangular prism-shaped. The rear surface optical elements 23 are prism-shaped with the ridgeline of the protruding apex extending horizontally, and multiple rear surface optical elements 23 are arranged at a predetermined pitch in a direction perpendicular to the extending direction (vertical direction). In this embodiment, the rear surface optical elements 23 have a triangular cross section, but this is not limited thereto and may have any cross section shape, such as a polygonal, hemispherical, partial sphere, or lens shape. The multiple rear surface optical elements 23 are preferably arranged in the light guide direction. That is, the rear surface optical elements 23 are arranged in a direction away from the light source 25, and the ridgeline of each rear surface optical element 23 extends parallel to the arrangement direction of the light source 25 or, if a single long light source is used, the extension direction of the light source.

[0029] It should be noted that the term "triangular shape" in this specification does not only refer to a triangular shape in the strict sense, but also includes an approximately triangular shape that takes into account limitations in manufacturing technology, molding errors, etc. Similarly, terms used in this specification that specify other shapes or geometric conditions, such as "parallel," "orthogonal," "ellipse," and "circle," are also to be interpreted without being bound by their strict meanings, but with an allowance for errors that allow for the expectation of similar optical functions.

[0030] The light guide plate 21 having such a configuration can be manufactured by extrusion molding or by molding the rear optical elements 23 on the base 22. In the light guide plate 21 manufactured by extrusion molding, the base 22 and the rear optical elements 23 can be integrally formed. When the light guide plate 21 is manufactured by molding, the rear optical elements 23 may be made of the same resin material as the base 22 or a different material.

[0031] 1.2.2. Light Source The light source 25 is disposed on one of the side surfaces (end surfaces) of the base 22 of the light guide plate 21 in the direction in which the rear optical elements 23 are arranged. The type of light source is not particularly limited, and can be configured in various forms, such as a linear fluorescent lamp such as a cold cathode fluorescent tube, point-shaped LEDs (light-emitting diodes), or an incandescent bulb. In this embodiment, the light source 25 is composed of multiple LEDs, and is configured so that a control device (not shown) can individually and independently control the on / off and / or brightness of each LED when lit. While the embodiment illustrates an example in which the light source 25 is disposed on one side surface (end surface) as described above, a light source may also be disposed on the side surface (end surface) opposite to this side surface (end surface). In this case, the shape of the rear optical elements is also formed according to a known example.

[0032] 1.2.3. Light Diffuser Plate The light diffuser plate 26 is disposed on the light output side of the light guide plate 21 and is a layer that functions to diffuse and output light incident thereon. This further improves the uniformity of the light output from the light guide plate 21 and makes scratches on the light guide plate 21 less noticeable. Specific embodiments of the light diffuser plate include known light diffusers, such as a plate having a light diffusing agent dispersed in a base material. The light diffuser plate 26 can be used as a support plate for the prism layer 27, as in this embodiment. Furthermore, if the light output surface of the light guide plate 21 is smooth, the light diffuser plate 26 may be bonded to the light guide plate 21 to form an integrated structure.

[0033] 1.2.4. Prism Layer As can be seen from FIGS. 1 to 3 , the prism layer 27 is disposed closer to the liquid crystal panel 15 than the light diffusion plate 26 and includes unit prisms 27 a that are convex toward the liquid crystal panel 15. In this embodiment, each unit prism 27 a has a predetermined cross section and extends in the light guide direction of the light guide plate 21 (vertical in this embodiment). A plurality of unit prisms 27 a are arranged in a direction different from the light guide direction (horizontal, perpendicular to the light guide direction in a plan view in this embodiment). The cross-sectional shape of the unit prisms in this prism layer may be any known shape depending on the required function. This shape can further diffuse or concentrate light. Furthermore, the extension direction and arrangement direction of the unit prisms are not limited to the above-described shapes and may be other shapes. For example, each unit prism may have a predetermined cross section and extend in a direction perpendicular to the light guide direction of the light guide plate 21, and a plurality of unit prisms may be arranged in the light guide direction.

[0034] The reflective polarizing plate 28 has the function of separating incident light into two orthogonal polarized components (P and S waves), transmitting the polarized component in one direction (parallel to the transmission axis) (e.g., P waves), and reflecting the polarized component in the other direction (parallel to the reflection axis) that is orthogonal to the first direction (e.g., S waves). A known structure can be used for such a reflective polarizing plate.

[0035] 1.2.6. Optical Sheet [Structure of Optical Sheet] Next, the structure of the optical sheet 30 will be described. Fig. 4 shows an enlarged view of a portion of the optical sheet 30 taken from the perspective of Fig. 2. As can be seen from Figs. 1 to 4, the optical sheet 30 includes a base layer 31 formed in a sheet shape and an optical function layer 32 provided on one surface of the base layer 31 (the surface on the light guide plate 21 side in this embodiment).

[0036] <Substrate Layer> The substrate layer 31 is a flat sheet-like member that supports the optical functional layer 32. Various materials can be used for the substrate layer 31. However, materials that are widely used as materials for optical sheets incorporated into display devices, have excellent mechanical properties, optical properties, stability, processability, etc., and are inexpensively available can be used. Examples of such materials include transparent resin films, transparent resin plates, transparent resin sheets, and transparent glass. Suitable transparent resin films include polyester films such as triacetate cellulose (TAC) films, polyethylene terephthalate (PET), diacetyl cellulose films, acetate butyrate cellulose films, polyethersulfone films, polyacrylic resin films, polyurethane resin films, polyester films, polycarbonate films, polysulfone films, polyether films, polymethylpentene films, polyether ketone films, and (meth)acrylonitrile films. Among these, polyester films are preferred. Examples of polyester films include polyethylene terephthalate, polybutylene terephthalate, polynaphthalene terephthalate, polytrimethylene terephthalate, etc. Furthermore, for applications requiring high heat resistance, such as in-vehicle applications, polycarbonate resins with high glass transition points are desirable. Specifically, the glass transition point of polycarbonate resins is 143°C, which is generally suitable for in-vehicle applications requiring durability at 105°C.

[0037] <Optical Functional Layer> The optical functional layer 32 is a layer laminated on one surface of the base layer 31 (in this embodiment, the surface on the light guide plate 21 side), and is configured to have light-transmitting portions 33 and light-absorbing portions 34. In this embodiment, the optical functional layer 32 has a cross section shown in Figures 2 and 4 and has a shape extending toward the back / front of the page (the horizontal direction when the image source unit 10 is viewed from the front), and the light-transmitting portions 33 and the light-absorbing portions 34 are alternately arranged along the layer surface in a direction different from the extending direction (the vertical direction in this embodiment).

[0038] Light-Transmitting Section The light-transmitting section 33 is a section whose main function is to transmit light. In the cross sections shown in FIGS. 2 and 4 , the light-transmitting section 33 is an element having a generally trapezoidal cross-sectional shape with a long bottom on the base layer 31 side and a short top on the opposite side (the light guide plate 21 side). The light-transmitting sections 33 extend in one direction (the horizontal direction in this embodiment) along the layer surface of the base layer 31 while maintaining the cross-section, and are arranged at predetermined intervals in a direction different from the extending direction (the vertical direction in this embodiment). Gaps (grooves) with a generally trapezoidal cross-section are formed between adjacent light-transmitting sections 33. Therefore, the gaps (grooves) have a trapezoidal cross-section with a long bottom on the top side (the light guide plate 21 side) of the light-transmitting section 33 and a short top on the bottom side (the base layer 31 side) of the light-transmitting section 33. The light-absorbing sections 34 are formed by filling the gaps with a necessary material, which will be described later. In this embodiment, the plurality of light transmitting portions 33 are connected on their lower base side (base layer side 31) by a sheet-like base portion 32a.

[0039] The light transmitting portion 33 has a refractive index of N ｔ Such a light transmitting portion 33 can be formed by curing a light transmitting portion forming composition. ｔ Although the value of is not particularly limited, the refractive index is preferably 1.47 or more from the viewpoint of appropriately reflecting light (including total reflection) at the interface with the light absorbing portion 34 on the slope of the trapezoidal cross section, as will be described later. However, since materials with too high a refractive index are often prone to cracking, the refractive index is preferably 1.61 or less. A refractive index of 1.49 or more and 1.56 or less is more preferable, and 1.56 is even more preferable.

[0040] Light-absorbing section The light-absorbing section 34 functions as a gap formed by filling a material into the above-mentioned gap (groove) between adjacent light-transmitting sections 33, and has a basic structure with a cross-sectional shape similar to that of the gap. Therefore, in this embodiment, the short upper base faces the liquid crystal panel 15 side (substrate layer 31 side), and the long lower base faces the light guide plate 21 side. The light-absorbing section 34 has a refractive index of N ｒ Specifically, the refractive index is N ｒ Light absorbing particles are dispersed in a transparent resin having a refractive index N ｒis the refractive index N of the light transmitting portion 33 ｔ In this way, by making the refractive index of the light absorbing portion 34 (transparent resin) smaller than that of the light transmitting portion 33, light incident on the light transmitting portion 33 under predetermined conditions can be appropriately totally reflected at the interface with the light absorbing portion 34. Even when the total reflection condition is not satisfied, some light is reflected at the interface. Refractive index N ｒ The value of is not particularly limited, and is preferably 1.47 or more, provided that the total reflection can be performed appropriately. However, since materials with too high a refractive index are often prone to cracking, the refractive index is preferably 1.61 or less. More preferably, it is 1.49 or more and 1.56 or less, and even more preferably 1.49. The refractive index N of the light transmitting portion 33 ｔ and the refractive index N of the light absorbing portion 34 ｒ The difference in refractive index between the film and the base is not particularly limited, but is preferably greater than 0 and equal to or less than 0.14, and more preferably 0.05 or greater and 0.14 or less. By increasing the difference in refractive index, more light can be totally reflected.

[0041] The light absorbing portion 34 has interfaces 34a and 34b with the light transmitting portion 33, and the interface angle of the interface 34a is θ １１ The interface angle of the interface 34b is shown in FIG. １２ The angle θ is an angle formed with the normal to the layer surface of the optical function layer 32. There are no particular limitations on the angle, but it is preferably between 0° and 10°. This makes it possible to increase the brightness in the front direction. １１ , θ １２ When θ is 0°, the cross section of the light transmitting portion and the light absorbing portion becomes rectangular. １１ and θ １２ The angles may be the same or different.

[0042] Also, in FIG. ａThe pitch of the light transmitting portions 33 and the light absorbing portions 34, represented by "D", is preferably 20 μm or more and 100 μm or less, and more preferably 30 μm or more and 100 μm or less. The thickness of the light absorbing portions 34, represented by "D" in FIG. 4, is preferably 50 μm or more and 150 μm or less, and more preferably 60 μm or more and 150 μm or less. By setting the thickness within these ranges, it is possible to achieve a more appropriate balance between light transmission and light absorption.

[0043] The light absorption property of the light absorbing section 34 can be adjusted by the content ratio of the light absorbing particles in the light absorbing section 34. Specifically, the content ratio of the light absorbing particles relative to the entire composition (transparent resin + light absorbing particles) constituting the light absorbing section is preferably greater than 10% by mass and equal to or less than 30% by mass. If the content ratio is 10% by mass or less, there is a risk that the light absorbing performance (light blocking property) of the light absorbing section will be insufficient, and if the content ratio is greater than 30% by mass, there is a risk that the curability of the light absorbing section will be insufficient, increasing the possibility of problems such as the light absorbing particles falling off.

[0044] In this embodiment, an example has been shown in which the interfaces 34a, 34b between the light transmitting portion 33 and the light absorbing portion 34 are linear in cross section, but the present invention is not limited to this and may be polygonal, have a convex curved surface, a concave curved surface, etc. Furthermore, the cross-sectional shapes of the plurality of light transmitting portions 33 and light absorbing portions 34 may be the same, or may be different cross-sectional shapes with a predetermined regularity.

[0045] The light absorbing portions 34 further have the following characteristics. An explanatory diagram is shown in Fig. 5. Fig. 5 is a cross section of one light absorbing portion 34, and is a cross section from the same viewpoint as Fig. 4 (a cross section perpendicular to the direction in which the light absorbing portions 34 extend). In the optical sheet 30 of this embodiment, the light absorbing portions 34 are aligned at a position M ａ Indentation hardness H ａ But, position M ｂ Indentation hardness H ｂ That is, H ａ >H ｂ Also, at position M ａ and position M ｂ Position M located between ｃ Indentation hardness H ｃIn the relationship including the indentation hardness is also H ａ and H ｂ It is preferable that the relationship is between H ａ >H ｃ >H ｂ It is preferable that H ｃ Is H ａ and H ｂ That is, H ａ >H ｂ At the same time, ａ +H ｂ ) / 2}>H ｃ It can be said that:

[0046] Also, H ａ >H ｂ Regarding (H ｂ / H ａ ) × 100(%) is preferably 70% or more and 85% or less. ｂ / H ａ ) × 100(%) is 70% or more and 85% or less, the following effect is obtained in addition to suppressing warpage. An optical sheet having an optical function layer laminated on a base layer and having light-transmitting portions and light-absorbing portions alternately arranged therein as disclosed herein can be stored in a rolled state (a state in which a long strip-shaped sheet before being cut into the size of the optical sheet is wound into a roll) after the light-absorbing portions are formed. In this case, if the light-transmitting portion has a trapezoidal cross section with a long lower base on the base layer side and a short upper base on the opposite side, the light-absorbing portion will be located on the base layer side (M ｂ side, H ｂ It has a trapezoidal cross section with a short upper base on the side, ｂ (H ｂ The light absorbing part on the side M is required to have adequate flexibility against the stress caused by the roll due to the short upper base. ｂ (H ｂ The light absorbing portion of the upper base, which is the shorter portion on the side of the H, is required to have an appropriate indentation hardness. If the indentation hardness is not within an appropriate range, cracks or peeling may occur at the interface between the upper base side, which is the shorter portion of the light absorbing portion, and the lower base side, which is the longer portion of the light transmitting portion. ｂ (H ｂ / H ａ) × 100(%) satisfies 70% or more and 85% or less, or, as shown below, it is preferable that the ratio is 145 MPa or more and 177 MPa or less.

[0047] Indentation hardness H ａ Although there are no particular limitations on the magnitude of the indentation hardness H, it is preferable that the indentation hardness H is 212 MPa or more and 271 MPa or less. This makes it possible to more reliably suppress the occurrence of warping of the optical sheet. ａ The magnitude of the indentation hardness H is 212 MPa or more and 254 MPa or less. ｂ The magnitude of H ｂ is preferably 145 MPa or more and 177 MPa or less, more preferably 160 MPa or more and 177 MPa or less. c The magnitude of H ｃ is preferably 149 MPa or more and 213 MPa or less, more preferably 162 MPa or more and 213 MPa or less. ａ and indentation hardness H ｂ The combination with ａ >H ｂ That would be good, but among them, H ａ is 158 MPa or more and 271 MPa or less, and H ｂ is preferably 145 MPa or more and 177 MPa or less.

[0048] Here, position M ａ , M ｂ , M ｃ are defined as follows: The center of the bottom (short upper base) of the light absorbing portion 34 on the base layer 31 side is C １ , the center of the bottom (long bottom) of the light absorbing portion 34 on the side opposite to the base material layer 31 is C ２ Then, C １ and C ２ When the line connecting these points is C, the position M ａ , M ｂ , M ｃ In addition, if the shape of the bottom of the light transmitting portion 34 is not a straight line, the center C is located on a straight line connecting the ends of the bottom. １ , C ２Also, let the length of C be L Ａ When M ａ is C ２ From 0.1L Ａ Located at a distance of M ｂ is C １ Distance from 0.1L Ａ Located in. M ｃ is M ａ and M ｂ However, the position M ａ , M ｂ , M ｃ If there is a light absorbing particle at the position, the position closest to the position where the light absorbing particle is not present is used.

[0049] Indentation hardness H is also called indentation hardness, and is defined in ISO 14577-1 by the following formula: Indentation hardness (H) = F ｍａｘ / A ｐ However, F ｍａｘ is the maximum load (N), and A ｐ is the contact area between the indenter and the test piece at the maximum load (mm ２ ) and the unit of indentation hardness is N / mm ２ The indentation hardness specified in ISO 14577-1 is measured in accordance with ISO 14577-1 2002-10-01 Part 1, and can be measured, for example, using an ultra-microindentation hardness tester (nanoindentation tester) ENT1100a manufactured by Elionix Co., Ltd., with an indentation load of 10 mgf (divided into 250 steps) and a test load holding time of 1 second.

[0050] In this way, by adjusting the indentation hardness of the light absorbing portion, it is possible to suppress the occurrence of warping of the optical sheet.

[0051] [Optical Sheet Manufacturing Method] The optical sheet 30 as described above can be manufactured, for example, as follows.

[0052] <Formation of Light-Transmitting Portion> First, the light-transmitting portion 33 is formed on one surface of the base layer 31. As shown in FIG. 6 , a base sheet 31' that will become the base layer 31 is inserted between a mold roll 52 having a surface shape that can transfer the shape of the light-transmitting portion 33 and a nip roll 51 that is disposed opposite the mold roll 52. At this time, a predetermined gap is provided between the mold roll 52 and the nip roll 51, forming a base portion 32a. The mold roll 52 and the nip roll 51 are then rotated while a composition that will form the light-transmitting portion is supplied from a supply device 55 between the base sheet 31' and the mold roll 52. As a result, the composition that will form the light-transmitting portion fills the grooves (shapes that are the inverse of the shape of the unit light-transmitting elements) formed on the surface of the mold roll 52 that correspond to the unit light-transmitting elements, and the composition conforms to the surface shape of the mold roll 52. Here, examples of the composition that will form the light-transmitting portion include ionizing radiation-curable resins such as epoxy acrylates, urethane acrylates, polyether acrylates, polyester acrylates, and polythiols.

[0053] The composition that constitutes the light-transmitting portion, which is sandwiched between the mold roll 52 and the base sheet 31' and filled therein, is irradiated with light for hardening from the base sheet side by a light irradiation device 54. This hardens the composition and fixes its shape. Then, the base layer 31 and the molded light-transmitting portion 33 are released from the mold roll 52 by a release roll 53.

[0054] <Formation of Light-Absorbing Portions> Next, the light-absorbing portions 34 are formed. To form the light-absorbing portions 34, first, the ink composition 57 that will form the light-absorbing portions is filled into the gaps (grooves) between the light-transmitting portions 33 formed above. Thereafter, as shown in FIG. 7 , excess composition is scraped off with a doctor blade 58 or the like. Then, the remaining ink composition is cured by irradiating it with ultraviolet light from the unit light-transmitting element 33 side, thereby forming the light-absorbing portions 34. Specifically, this can be done, for example, as follows.

[0055] An ink composition 57 containing a transparent ionizing radiation resin composition and light-absorbing particles is filled into the grooves 33' between the parallel light-transmitting portions 33. The ink composition 57 can be filled into the wedge-shaped grooves by, for example, dropping with a dispenser, applying with a die head, or using a finisher roll.

[0056] The ink composition contains a transparent ionizing radiation-curable resin composition and light-absorbing particles as components. The ionizing radiation-curable resin composition may be any of the ionizing radiation-curable resin compositions used in conventional visibility-improving sheets, viewing angle-improving sheets, etc. For example, a resin having an acrylate-based functional group may be suitably used. Specific examples include oligomers or prepolymers such as (meth)acrylates of relatively low-molecular-weight polyester resins, polyether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiolpolyene resins, and polyhydric alcohols or other polyfunctional compounds. Furthermore, a reactive diluent may be added to the resin composition. As such a reactive diluent, monofunctional monomers and polyfunctional monomers such as ethyl (meth)acrylate, ethylhexyl (meth)acrylate, styrene, methylstyrene, and N-vinylpyrrolidone may be used. Specific examples of the reactive diluent include trimethylolpropane tri(meth)acrylate, hexanediol (meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. To convert an ionizing radiation-curable resin composition into an ultraviolet-curable resin composition, a photopolymerization initiator such as acetophenones, benzophenones, Michler's benzoyl benzoate, α-amyloxime ester, tetramethylthuram monosulfide, or thioxanthones, or a photosensitizer such as n-butylamine, triethylamine, or poly-n-butylphosphine can be mixed into the composition. In particular, in the present invention, it is preferable to mix urethane acrylate as an oligomer and dipentaerythritol hexa(meth)acrylate as a monomer.

[0057] The light-absorbing particles may be resin beads or glass beads, and may be colored particles capable of selectively absorbing specific wavelengths in accordance with the characteristics of the image light. Alternatively, colorants such as carbon black, graphite, fibrous carbon, metal salts such as black iron oxide, dyes, or pigments may be kneaded into the resin beads or glass beads. From the viewpoint of ease of kneading the colorant, resin beads are preferred. Suitable resin beads include melamine beads, acrylic beads, acrylic-styrene beads, polycarbonate beads, polyethylene beads, polystyrene beads, and PVC beads. Urethane crosslinked microparticles and silicone-based beads are also suitable. These resin beads preferably have a refractive index difference of approximately 0.1 with respect to the ionizing radiation-curable resin composition described above. While transparent resins can be used as the resin before the colorant is kneaded into the resin, it is preferable to use resins colored with pigments or dyes. While the resin may be capable of selectively absorbing specific wavelengths in accordance with the characteristics of the image light, black-colored resin beads are preferred. The average particle diameter of the light-absorbing particles is preferably 1.0 μm or more and 20 μm or less, more preferably 1.0 μm or more and 10 μm or less, and even more preferably 1.0 μm or more and 4.0 μm or less. Here, the "average particle diameter" refers to the diameter obtained by observing 100 light-absorbing particles with an electron microscope, measuring their diameters, and calculating the arithmetic mean.

[0058] Of the above-mentioned colorants, carbon black is preferably used as the colorant. The amount of carbon black kneaded into the resin beads is approximately 0.1 to 0.7 parts by mass, preferably 0.15 to 0.5 parts by mass, and more preferably 0.2 to 0.35 parts by mass, per 1 part by mass of the resin beads. If the amount of carbon black kneaded into the resin beads is more than 0.7 parts by mass, the resin beads may be prone to cracking. On the other hand, if the amount of carbon black kneaded into the resin beads is less than 0.1 parts by mass, fine particles having the desired black color may not be obtained. Carbon black having an average particle size of 10 to 500 nm is preferably used, and examples of such carbon black include furnace black, acetylene black, channel black, thermal black, carbon nanotubes, and carbon fiber. Commercially available carbon blacks can also be used, such as the HCF series, MCF series, RCF series, and LFF series (all manufactured by Mitsubishi Chemical Corporation), the Vulcan series (manufactured by Cabot Corporation), and the Ketjen series (manufactured by Lion Corporation). The average particle size here refers to the arithmetic mean diameter determined by observing carbon black particles under an electron microscope. To improve the dispersibility of light-absorbing particles in an ionizing radiation-curable resin composition, the particles can be surface-treated. Examples of surface treatments include conventional hydrophilic treatments using silica coating and surface modification using plasma, etc. An ink composition containing the above-mentioned components is prepared by mixing a predetermined amount of light-absorbing particles with an ionizing radiation-curable resin composition and optionally adding a polymerization initiator, etc. The amount of colored fine particles added is preferably in the range of 15 to 35% based on the total mass of the ink composition. This range enables the realization of a visibility-enhancing sheet with superior contrast. If the content of light-absorbing particles is too low, the light-blocking properties of the light-absorbing portion may be insufficient, while if the content of light-absorbing particles is too high, the resin beads may come into contact with each other, easily causing cracking or chipping.

[0059] After filling the ink composition 57 into the grooves 33' as described above, excess ink composition 57 is scraped off with a doctor blade 58 as shown in FIG. 7, so that the ink composition 57 fills the grooves 33'.

[0060] Here, the ink composition 57 is scraped off by the doctor blade 58 by pressing the doctor blade 58 against the light-transmitting portion 33 with a predetermined pressure (pressing force) while moving the laminate of the base material layer 31 and the light-transmitting portion 33 at a predetermined speed V.

[0061] After scraping, the ionizing radiation-curable resin in the ink composition is cured. This can be achieved by irradiation with electron beams or ultraviolet light. For example, in the case of electron beam curing, electron beams having an energy of 50 to 1000 keV, preferably 100 to 300 keV, emitted from various electron beam accelerators, such as Cockcroft-Walton, Van de Graaff, resonant transformer, insulating core transformer, linear, dynamitron, and high-frequency types, are used. In the case of ultraviolet light curing, ultraviolet light emitted from light beams such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arcs, xenon arcs, and metal halide lamps can be used. Here, in order to achieve the above-described relationship in the indentation hardness of the light-absorbing portion, the dose of electron beam or ultraviolet light can be reduced and the irradiation time can be adjusted.

[0062] 1 to 3, the reflective sheet 39 of the surface light source device 20 will be described. The reflective sheet 39 is a member that reflects light emitted from the rear surface of the light guide plate 21 and causes the light to enter the light guide plate 21 again. The reflective sheet 39 can preferably be a sheet that enables so-called specular reflection, such as a sheet made of a material with high reflectivity such as metal, or a sheet that includes a thin film made of a material with high reflectivity (e.g., a metal thin film) as a surface layer.

[0063] 1.3 Functional Film The functional film 40 is disposed on the light-emitting side of the liquid crystal panel 15 and has the function of improving the quality of the image light and protecting the image source unit 10. Examples of such films include an anti-reflection film, an anti-glare film, a hard coat film, a color correction film, and a light diffusion film, and these may be used alone or in combination.

[0064] 2. Effects, etc. Next, the function of the optical sheet 30 having the above-described configuration will be described for the image source unit 10, showing examples of optical paths. However, these optical path examples are conceptual examples for the purpose of explanation, and do not strictly represent the degree of reflection or refraction.

[0065] First, as shown in Fig. 2, light emitted from the light source 25 enters the light guide plate 21 from a light entrance surface, which is a side surface (end surface) of the light guide plate 21. Fig. 2 shows, as an example, an example of the optical paths of light L21 and L22 incident on the light guide plate 21 from the light source 25.

[0066] As shown in Figure 2, light L21 and L22 incident on the light guide plate 21 undergoes repeated total reflection due to the difference in refractive index between the light guide plate 21 and air at the light-emitting side surface and the back surface opposite the light guide plate 21, and travels in the light guide direction (downward in the plane of the paper in Figure 2).

[0067] However, a rear optical element 23 is disposed on the rear surface of the light guide plate 21. Therefore, as shown in Fig. 2, the direction of light L21 and L22 traveling within the light guide plate 21 is changed by the rear optical element 23, and the light may be incident on the light output surface and the rear surface at an incident angle less than the critical angle of total reflection. In this case, the light may be emitted from the light output surface of the light guide plate 21 and the rear surface on the opposite side.

[0068] The light beams L21 and L22 emitted from the light output surface proceed toward the light diffusion plate 26 disposed on the light output side of the light guide plate 21. On the other hand, the light beams emitted from the rear surface are reflected by the reflective sheet 39 disposed on the rear surface of the light guide plate 21, and then enter the light guide plate 21 again to travel within the light guide plate 21.

[0069] Light traveling within the light guide plate 21 and light that is redirected by the rear optical element 23 and reaches the light output surface at an incident angle less than the critical angle for total reflection are generated in each region along the light guide direction within the light guide plate 21. Therefore, the light traveling within the light guide plate 21 is gradually emitted from the light output surface. This makes it possible to uniformize the light amount distribution along the light guide direction of the light that is emitted from the light output surface of the light guide plate 21.

[0070] The light emitted from the light guide plate 21 then reaches the light diffusion plate 26, where its uniformity is improved. The light is then diffused or concentrated as necessary by the prism layer 27, and the light that exits the prism layer 27 reaches the reflective polarizing plate 28. Here, light polarized along the transmission axis of the reflective polarizing plate 28 passes through the reflective polarizing plate 28 and proceeds toward the optical sheet 30. Meanwhile, light polarized along the reflection axis of the reflective polarizing plate 28 is reflected as shown by the dotted arrows in FIG. 2 and returned to the light guide plate 21. The returned light is reflected by the light guide plate 21, the rear optical element 23, or the reflective sheet 39 and travels again toward the reflective polarizing plate 28. During this reflection, the polarization direction of some of the light changes, and some of this light passes through the reflective polarizing plate 28. The other light is returned again to the light guide plate. In this way, the light reflected by the reflective polarizing plate 28 also becomes able to pass through the reflective polarizing plate 28 through repeated reflections. This increases the utilization efficiency of light from the light source 25. Here, the polarization direction of the light emitted from the reflective polarizing plate 28 is aligned with the transmission axis of the lower polarizing plate 14 , and the light passes through the lower polarizing plate 14 as polarized light.

[0071] The light emitted from the reflective polarizing plate 28 reaches the optical sheet 30. The light incident on the optical sheet 30 travels along the following optical path. An example of the optical path in the optical sheet 30 is shown in FIG.

[0072] With respect to the direction in which the light transmitting portions 33 and the light absorbing portions 34 are alternately arranged (the vertical direction in this embodiment), light L21 and light L22 shown in FIG. 2 and light L41 and light L42 shown in FIG. 4 are directed toward the interface between the light transmitting portions 33 and the light absorbing portions 34. Then, light is totally reflected at the interface, and the light is controlled to be directed in a desired direction so as to limit the viewing angle. Note that the angle of the interface between the light transmitting portions 33 and the light absorbing portions 34 (θ in FIG. 4) can be adjusted as needed. １１ , θ １２ ) can be adjusted to direct the light in a direction having a desired angle with respect to the normal direction (i.e., the front direction) of the optical sheet.

[0073] 4 travels at an angle that transmits the interface between the light-transmitting portion 33 and the light-absorbing portion 34 without being totally reflected at the interface, and is therefore transmitted through the interface and absorbed by the light-absorbing portion 34. This makes it possible to efficiently absorb and block light that is emitted at a viewing angle equal to or greater than a predetermined angle, thereby limiting the viewing angle. Furthermore, since such light is likely to enter the liquid crystal panel and cause problems such as a decrease in contrast and color inversion, it is possible to absorb such light.

[0074] Light emitted from the optical sheet 30 is incident on the lower polarizer 14 of the liquid crystal panel 15. The lower polarizer 14 transmits one polarized component of the incident light and absorbs the other polarized component. The light that passes through the lower polarizer 14 is selectively transmitted through the upper polarizer 13 depending on the state of the electric field applied to each pixel. In this way, the liquid crystal panel 15 selectively transmits light from the surface light source device 20 pixel by pixel, allowing a viewer of the liquid crystal display device to view an image. At this time, the image light is provided to the viewer via the functional film 40, improving the quality of the image.

[0075] Here, according to the optical sheet of the present disclosure, warpage can be suppressed by adjusting the indentation hardness of the light-absorbing portion. If warpage can be suppressed by the light-absorbing portion in this way, a surface light source device can be constructed without adding additional layers, even if additional layers are added, without adding thick layers, and without necessarily bonding layers together, thereby enabling a thin design and high flexibility in layer configuration. However, this does not prevent the application of warpage suppression by conventional means in addition to the application of the configuration of the present disclosure.

[0076] 3. Examples In the examples, optical sheets having a distribution in the indentation hardness of the light-absorbing portions were fabricated following the example of the optical sheet 30, and tests were conducted. On the other hand, as Comparative Example 1, an example having an indentation hardness distribution opposite to that of the present disclosure was tested. Each example is as follows.

[0077] Base material layer: Thickness: 250 μm, Material: Polycarbonate Light-transmitting part material: Epoxy acrylate Light-absorbing part shape: Lower base (W ｂ ) 22 μm, top bottom (Wａ ) 3 μm, height (D) 120 μm, inclination angle (θ １１ , θ １２ ) 4.5° isosceles trapezoid Pitch of light absorbing part ａ Material of light absorbing portion: Acrylic beads (black) dispersed in acrylic resin binder Acrylic beads: average particle size 4 μm, 2 parts by mass per 100 parts by mass of binder

[0078] The optical sheet was manufactured according to the procedure described above. The indentation hardness of the light absorbing portion in each example was adjusted by changing the amount of ultraviolet light irradiation (low-pressure mercury lamp) performed from both the upper and lower sides of the light absorbing portion. The specific irradiation amounts are shown in Table 1. In Table 1, the amounts are expressed as a ratio when the amount of ultraviolet light irradiation in Comparative Example 1 is set to 1.

[0079] The indentation hardness was measured as described above, and the average value of five measurements was used. The warpage of the optical sheet was measured by exposing the optical sheet to an air atmosphere at a temperature of 70°C and a humidity of 95% for 1000 hours, and then leaving it on a flat table at room temperature and humidity for 24 hours, and measuring the distances from the surface of the table to the four corners of the optical film using a JIS Class 1 straightedge.

[0080] The results are also shown in Table 1. Table 1 shows the results, including the indentation hardness (MPa) and H ａ The ratio (%) of the indentation hardness at each position when the value is 100, the warpage (mm), and H ｂ / H ａ The values ​​are expressed as ×100%.

[0081]

[0082] As can be seen from Table 1, in Examples 1 to 7, H ａ >H ｂ The warpage was reduced compared to Comparative Example 1, where this relationship did not hold. ａ >H ｃ >H ｂ In Examples 1 to 5 and Example 7, in which the above condition was met, the warpage was further reduced compared to Example 6, in which the above condition was not met.

[0083] 10...image source unit, 15...liquid crystal panel, 20...surface light source device, 21...light guide plate, 25...light source, 26...light diffusion plate, 27...prism layer, 28...reflective polarizing plate, 30...optical sheet, 31...base material layer, 32...optical function layer, 33...light transmitting portion, 34...light absorbing portion

Claims

1. An optical sheet having a base layer and an optical functional layer laminated on the base layer and having light transmitting portions and light absorbing portions arranged alternately, wherein the optical functional layer has the light transmitting portions each having a predetermined cross section and extending in one direction, and a plurality of light absorbing portions are arranged at intervals in a direction different from the one direction, and the light absorbing portions are arranged between the light transmitting portions, and the light absorbing portions are arranged at a position M on the base layer side. ｂ The indentation hardness at H ｂ , a position M on the opposite side to the base layer ａ The indentation hardness at H ａ When this is done, H ａ >H ｂ That is, the optical sheet.

2. Said M ａ and the above M ｂ Position M between ｃ The indentation hardness at H ｃ When this is done, H ａ >H ｃ >H ｂ The optical sheet according to claim 1 , 3. Furthermore, ａ +H ｂ ) / 2}>H ｃ 3. The optical sheet according to claim 2, wherein the following expression is satisfied.

4. (H ｂ / H ａ 2. The optical sheet according to claim 1, wherein the ratio of the refractive index to the refractive index of the optical sheet is 70% or more and 85% or less.

5. The above H ａ The optical sheet according to any one of claims 1 to 4, wherein the compressive strength is 212 MPa or more and 271 MPa or less.

6. The optical sheet according to any one of claims 1 to 5, wherein the base layer is made of a polycarbonate resin.

7. An optical sheet according to any one of claims 1 to 6, wherein said light transmitting portion has a trapezoidal cross section with a long lower base on the side of said base layer and a short upper base on the opposite side.

8. The optical sheet according to claim 7, wherein said light absorbing portion has a trapezoidal cross section with a long lower base on the upper base side of said light transmitting portion and a short upper base on the opposite side.

9. An optical sheet according to any one of claims 1 to 8, wherein the light absorbing portion comprises a transparent resin containing light absorbing particles made of carbon black.

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