Optical sheet, liquid crystal display device, and organic el display device

Abstract

An optical sheet (10) comprises: a first base material (11) having light-transmitting properties; and an optical functional layer (12) laminated on the first base material (11). The retardation of the first base material (11) is 6000 nm or more. The optical functional layer (12) has a light absorption part (13) and a light transmission part (14). The light absorption part (13) and the light transmission part (14) are alternately arranged along a first direction (d1) and linearly extend along a second direction (d2). The angle formed by a slow axis (11c) of the first base material (11) and the second direction (d2) is 5° or less.

Description

Optical sheet, liquid crystal display device, and organic EL display device

[0001] The present disclosure relates to an optical sheet, a liquid crystal display device, and an organic EL display device.

[0002] In display devices such as liquid crystal display devices and projection televisions, optical sheets are arranged closer to the viewer than the light source (see Patent Documents 1 and 2). These optical sheets play a role in providing high-quality images to the viewer.

[0003] Patent Documents 1 and 2 disclose an optical sheet including a base layer and an optical functional layer as one of the components constituting such an optical sheet. The optical functional layer is a layer in which light-transmitting portions (light-transmitting portions) and light-absorbing portions (louver portions, light-absorbing portions) are arranged alternately along the sheet surface.

[0004] JP 2021-060480 A JP 2016-170271 A

[0005] However, in such optical sheets, for example, when heat is applied, the base layer may thermally shrink. In this case, the pitch of the light-transmitting portions may change. Furthermore, when the base layer thermally shrinks, the viewing angle characteristics may also change. For this reason, it is necessary to suppress changes in the optical characteristics of the optical sheet.

[0006] The present disclosure has been made in consideration of these points, and aims to provide an optical sheet, a liquid crystal display device, and an organic EL display device that are capable of suppressing changes in optical properties.

[0007] Embodiments of the present disclosure relate to the following [1] to [6].

[0008] [1] An optical sheet comprising: a first substrate having optical transparency; and an optical functional layer laminated on the first substrate; wherein the retardation of the first substrate is 6000 nm or more; the optical functional layer has light-absorbing portions and light-transmitting portions; the light-absorbing portions and the light-transmitting portions are alternately arranged along a first direction and extend linearly along a second direction intersecting the first direction; and the angle formed by the slow axis of the first substrate and the second direction is 5° or less.

[0009] [2] The optical sheet according to [1], further comprising a second substrate laminated on the optical functional layer on the opposite side to the first substrate, wherein the second substrate has optical transparency, the retardation of the second substrate is 6000 nm or more, and the angle between the slow axis of the second substrate and the second direction is 5° or less.

[0010] [3] The optical sheet according to [1] or [2], wherein an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment is applied to the surface of the first substrate opposite to the optical functional layer.

[0011] [4] The optical sheet according to [2] or [3], wherein an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment is applied to the surface of the second substrate opposite to the optical functional layer.

[0012] [5] A liquid crystal display device comprising: a liquid crystal panel; an optical sheet according to any one of [1] to [4] laminated on the liquid crystal panel; and a reflective polarizing film laminated on the optical sheet.

[0013] [6] An organic EL display device comprising: the optical sheet according to any one of [1] to [4]; a circularly polarizing film laminated on the optical sheet; and an organic EL light-emitting layer laminated on the circularly polarizing film.

[0014] According to the present disclosure, changes in optical properties can be suppressed.

[0015] Fig. 1 is an exploded perspective view showing an optical sheet according to the present embodiment. Fig. 2 is a cross-sectional view (cross-sectional view taken along line II-II in Fig. 1) showing the optical sheet according to the present embodiment. Fig. 3 is a cross-sectional view showing a liquid crystal display device according to the present embodiment. Fig. 4 is a cross-sectional view showing an organic EL display device according to the present embodiment. Fig. 5 is a schematic diagram showing a method for manufacturing an optical sheet according to the present embodiment. Fig. 6 is a schematic diagram showing a method for manufacturing an optical sheet according to the present embodiment.

[0016] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings accompanying this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of illustration and understanding.

[0017] Terms used in this specification that specify shapes and geometric conditions, as well as their degrees, such as terms like "parallel," "perpendicular," and "same," and values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0018] In this specification, terms such as "film," "sheet," and "plate" are not terms that are distinguished from one another solely on the basis of differences in name. For example, a "film" cannot be distinguished from a member called a sheet or plate solely on the basis of differences in name.

[0019] 1 , the optical sheet 10 includes a first substrate 11 and an optical functional layer 12 laminated on the first substrate 11. The optical sheet 10 may further include a second substrate 16 laminated on the optical functional layer 12 on the side opposite to the first substrate 11. The optical sheet 10 is disposed so as to transmit image light from the optical functional layer 12 toward the first substrate 11, and is a member that adjusts, for example, the orientation of the image light by means of light absorbing sections 13 (described later) of the optical functional layer 12.

[0020] <<First Substrate>> As shown in FIG. 2, the first substrate 11 has a first surface 11a and a second surface 11b located on the opposite side to the first surface 11a.

[0021] The first substrate 11 is a member for supporting the optical function layer 12. In this embodiment, the first substrate 11 is composed of a flat, transparent member. Various materials can be used to compose the first substrate 11. For example, the first substrate 11 may be a transparent substrate having optical transparency, or may be composed of a resin. Specifically, the substrate may be composed of, for example, a polyester film. Examples of polyester resins that can be used to compose the polyester film include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Of these, the polyester film is preferably a polyethylene terephthalate film. The polyester resin may contain other copolymer components. From the viewpoint of mechanical strength, the proportion of the copolymer component may be 3 mol% or less, preferably 2 mol% or less, and more preferably 1.5 mol% or less. The above-mentioned resins have excellent transparency, thermal properties, and mechanical properties. Furthermore, the retardation Re of these resins can be easily controlled by stretching.

[0022] In this specification, "having optical transparency" means that the total light transmittance is 80% or more. A light source simulating the spectrum of D65 standard light (hereinafter referred to as the D65 light source) is used to measure the total light transmittance. Before measuring the total light transmittance, the D65 light source is turned on for 15 minutes to stabilize the output of the D65 light source. The incident angle on the sample when measuring the total light transmittance is 0°. The incident surface when measuring the total light transmittance is the light-entering surface of the optical sheet 10 (the first surface 11a in the case of the first substrate 11). The test environment for measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample is placed in the test environment for 16 hours before the test begins. Other measurement conditions for measuring the total light transmittance are in accordance with JIS K7361-1:1997. The total light transmittance is the arithmetic mean of five measured values. The five measured values ​​are measured at five measurement positions on the sample to be evaluated. The five measurement positions are to be spaced apart from each other by at least 10 mm.

[0023] The first substrate 11 may be made of a uniaxially stretched film. Uniaxially stretched polyethylene films have high transparency and excellent mechanical properties. In many resin substrates, such as polyethylene films, the stretching axis serves as the slow axis. That is, in many resin substrates, such as uniaxially stretched polyethylene films, the stretching direction serves as the slow axis. When the first substrate 11 is a uniaxially stretched film, the uniaxially stretched film is arranged so as to be stretched along the second direction d2 described below. In other words, the first substrate 11 is arranged so that the slow axis 11c (see FIG. 1 ) of the first substrate 11 extends along the second direction d2. The first substrate 11 may also be made of a biaxially stretched film. In this case, the biaxially stretched film constituting the first substrate 11 can be obtained, for example, by slightly stretching a rolled unstretched film in the longitudinal direction and then stretching it in the width direction. The width direction of the biaxially stretched film obtained in this manner serves as the slow axis.

[0024] The production conditions for obtaining a uniaxially stretched film can be appropriately set by known techniques. For example, the stretching temperature is usually 80° C. to 130° C., preferably 90° C. to 120° C. The stretching ratio is usually 1.0 to 3.5, preferably 1.0 to 3.0.

[0025] In this embodiment, the retardation Re of the first substrate 11 is 6000 nm or more. Preferably, the retardation Re of the first substrate 11 is 8000 nm or more. Preferably, the retardation Re of the first substrate 11 is 15000 nm or less, and more preferably, 12000 nm or less. Here, the retardation Re is the retardation at a wavelength of 400 nm or more and 700 nm or less, and is the retardation in the planar direction of the first substrate 11. The retardation Re can be expressed by the following formula: Re=(Nx-Ny)×d, where Nx is the maximum in-plane refractive index of the first substrate 11, and Ny is the minimum in-plane refractive index of the first substrate 11. Furthermore, d (nm) is the thickness of the first substrate 11.

[0026] When the value of retardation Re approaches the wavelength of visible light, color unevenness in the image tends to occur, coupled with the function of the reflective polarizing film 35, which aims to improve the polarization and brightness of the liquid crystal panel 31, etc., which will be described later. Therefore, by setting the retardation Re to 6000 nm or more, which is significantly different from the wavelength of visible light, color unevenness can be suppressed and a decrease in contrast can be prevented.

[0027] Furthermore, when birefringence occurs within a layer, a phase difference may occur depending on the direction of light propagation. In this case, the spectral distribution of light emitted outside the layer may vary randomly depending on the direction of light propagation. As a result, the spectrum of light emitted outside the layer may be observed as color unevenness. In particular, when the retardation Re is close to the wavelength of visible light (400 nm to 700 nm), the phase difference may become large in the range of 400 nm to 700 nm, which is the wavelength of light, and color unevenness may be significantly observed.

[0028] In contrast, in the present embodiment, the retardation Re of the first substrate 11 is 6000 nm or more, which is significantly longer than the wavelength of visible light. This makes it possible to suppress light interference and color unevenness. Furthermore, by setting the retardation Re of the first substrate 11 to 15000 nm or less, it is possible to prevent the thickness of the first substrate 11 from becoming too large.

[0029] The retardation Re of the first substrate 11 can be controlled within a specific range by appropriately setting the stretching ratio, stretching temperature, and thickness of the polyester film. For example, the higher the stretching ratio, the greater the retardation Re. Also, the lower the stretching temperature, the greater the retardation Re. Furthermore, the thicker the polyester film, the greater the retardation Re.

[0030] In such a first substrate 11, the surface of the first substrate 11 opposite the optical function layer 12 may be subjected to an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment. That is, the second surface 11b of the first substrate 11 may be subjected to an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment. When the second surface 11b of the first substrate 11 is subjected to an anti-glare treatment, specular reflection of light can be reduced by diffusing incident light. Furthermore, when the second surface 11b of the first substrate 11 is subjected to an anti-reflection treatment, specular reflection of light can be suppressed by utilizing interference of reflected light. Furthermore, when the second surface 11b of the first substrate 11 is subjected to a hard coat treatment, the scratch resistance of the first substrate 11 can be improved.

[0031] The thickness of the first substrate 11 may be, for example, 25 μm or more and 300 μm or less. When the thickness of the first substrate 11 is 25 μm or more, it is possible to effectively prevent wrinkles from occurring in the first substrate 11. Furthermore, when the thickness of the first substrate 11 is 300 μm or less, it is possible to easily wind up the optical sheet 10 after producing the optical sheet 10.

[0032] The refractive index of the first substrate 11 may be, for example, not less than 1.46 and not more than 1.67.

[0033] <<Optical Functional Layer>> The optical functional layer 12 has a function (light-collecting function) of intensively improving the brightness in the front direction (the normal direction of the first surface 11a of the first substrate 11) by changing the traveling direction of incident light. The optical functional layer 12 also has a function of diffusing and homogenizing light. These functions can be appropriately adjusted by the inclination angle of the interface between the light-absorbing portion 13 and the light-transmitting portion 14, which will be described later. The optical functional layer 12 also has a function (light-absorbing function) of absorbing light that is incident at a large angle with respect to the front direction.

[0034] As shown in FIG. 2 , the optical function layer 12 is laminated on the first surface 11a side of the first substrate 11. This optical function layer 12 is a so-called louver film and includes light-absorbing portions 13 and light-transmitting portions 14. The optical function layer 12 may further include land portions 15 provided between the first substrate 11 and the light-absorbing portions 13 and light-transmitting portions 14. The light-absorbing portions 13 and light-transmitting portions 14 are alternately arranged along the first direction d1. The light-absorbing portions 13 and light-transmitting portions 14 extend linearly along the second direction d2 (see FIG. 1 ). The first direction d1 and the second direction d2 are parallel to the first surface 11a and the second surface 11b of the first substrate 11. The second direction d2 intersects with the first direction d1. In other words, the second direction d2 is non-parallel to the first direction d1. The second direction d2 may be a direction perpendicular to the first direction d1.

[0035] <<<Light-Absorbing Section>>> The light-absorbing section 13 is a section that absorbs light. The light-absorbing section 13 includes a base resin (binder resin) and light-absorbing particles contained in the base resin. The material constituting the base resin is not particularly limited, but is preferably a curable resin. Specific examples of the base resin include an ionizing radiation-curable resin, a mixture of an ionizing radiation-curable resin and a solvent-drying resin, and a thermosetting resin. Among these, the ionizing radiation-curable resin is a resin that is cured by ultraviolet light or an electron beam. Furthermore, the solvent-drying resin is a resin that becomes a coating simply by drying a solvent added to adjust the solid content during application. From the viewpoint of suppressing deterioration in the optical performance of the light-absorbing section 13, the base resin is preferably an ultraviolet-curable acrylic resin, for example, an ultraviolet-curable urethane acrylate.

[0036] The light absorbing particles may be, for example, acrylic beads containing carbon black. The composition of the light absorbing portion 13 is not particularly limited. For example, the light absorbing portion 13 may be a binder resin containing a black filler.

[0037] The refractive index of the light absorbing portion 13 may be, for example, 1.47 or more and 1.65 or less, or 1.49 or more and 1.57 or less. When the refractive index of the light absorbing portion 13 is 1.47 or more, light is more likely to be totally reflected at the interface between the light absorbing portion 13 and the light transmitting portion 14. Furthermore, when the refractive index of the light absorbing portion 13 is 1.65 or less, cracking of the light absorbing portion 13 can be effectively suppressed.

[0038] As shown in FIG. 2 , the cross-sectional shape of the light absorbing section 13 in this embodiment is a trapezoid tapered toward the light exit side. The light exit side is the first substrate 11 side as viewed from the light absorbing section 13, which is the lower side in FIG. 2 . Therefore, the width of the light absorbing section 13 in the first direction d1 gradually increases with increasing distance from the first substrate 11. Meanwhile, the cross-sectional shape of the light transmitting section 14 is a trapezoid tapered toward the light entrance side (upper side in FIG. 2 ). In this case, the interface between the light absorbing section 13 and the light transmitting section 14 extends in a straight line. The cross-sectional shapes of the light absorbing section 13 and the light transmitting section 14 are not particularly limited. Various shapes may be adopted for the cross-sectional shapes of the light absorbing section 13 and the light transmitting section 14 depending on the required function, and may be, for example, rectangular. Furthermore, the cross-sectional shapes of the light absorbing sections 13 and the light transmitting sections 14 may be the same or different from each other. When the cross-sectional shapes of the light absorbing portions 13 and the light transmitting portions 14 are different from each other, the cross-sectional shapes may vary with a predetermined regularity. Furthermore, the interface between the light absorbing portions 13 and the light transmitting portions 14 may extend in a polygonal or curved line shape, for example.

[0039] The pitch P (see FIG. 2 ) of such light-absorbing portions 13 may be, for example, 30 μm or more and 100 μm or less. This allows the optical function layer 12 to effectively exhibit the function of a louver film. Furthermore, the length L (see FIG. 2 ) of the light-absorbing portions 13 may be, for example, 60 μm or more and 150 μm or less.

[0040] The maximum width W (see FIG. 2) of the light absorbing portion 13 in the first direction d1 may be, for example, 5 μm or more and 15 μm or less, which can improve the optical performance of the optical function layer 12.

[0041] As described above, the cross-sectional shape of the light absorbing portion 13 is a trapezoid that tapers toward the light exit side. In this case, the inclination angle θ (see FIG. 2 ) of the legs of the trapezoid with respect to the front direction (the normal direction to the first surface 11 a of the first base material 11) may be 1° or more and 10° or less. This makes it possible to maintain a good balance between light transmission and light absorption.

[0042] <<<Light-Transmitting Portion>>> The light-transmitting portion 14 is a portion that transmits light. The light-transmitting portion 14 is made of, for example, a resin that is transparent to visible light. The material that constitutes the light-transmitting portion 14 is not particularly limited, but is preferably a curable resin. Specifically, examples of the material that constitutes the light-transmitting portion 14 include an ionizing radiation-curable resin, a mixture of an ionizing radiation-curable resin and a solvent-drying resin, and a thermosetting resin.

[0043] The material constituting the light-transmitting portion 14 may be the same as the material constituting the land portion 15. In this embodiment, the land portion 15 is bonded to the first substrate 11. Therefore, it is desirable that the material constituting the light-transmitting portion 14 (land portion 15) be compatible with the material constituting the first substrate 11 in order to improve the bonding strength with the first substrate 11. Furthermore, gaps are provided between the light-transmitting portions 14 to form the light-absorbing portions 13. These gaps are formed, for example, by a mold (not shown). Therefore, it is desirable that the material constituting the light-transmitting portion 14 have good releasability, for example, by containing a release agent. For example, if the first substrate 11 is composed of a material primarily composed of polycarbonate, a material containing phenoxyethyl acrylate and a phosphate ester can be suitably used as the material constituting the light-transmitting portion 14. This effectively satisfies the two requirements described above (i.e., improved bonding strength and good releasability). The inclusion of phenoxyethyl acrylate in the material improves bonding strength. Furthermore, since the material contains phosphate ester, good releasability can be ensured. From the viewpoint of suppressing deterioration of the optical performance of the light transmitting portion 14, the material constituting the light transmitting portion 14 is preferably an ultraviolet-curable acrylic resin, for example, an ultraviolet-curable urethane acrylate.

[0044] The refractive index of the light transmitting portion 14 may be, for example, 1.47 or more and 1.65 or less, or 1.49 or more and 1.57 or less. When the refractive index of the light transmitting portion 14 is 1.47 or more, light is more likely to be totally reflected at the interface between the light absorbing portion 13 and the light transmitting portion 14. Furthermore, when the refractive index of the light transmitting portion 14 is 1.65 or less, cracking of the light transmitting portion 14 can be effectively suppressed.

[0045] Furthermore, the refractive index of the light-transmitting portion 14 may be higher than the refractive index of the light-absorbing portion 13. When the refractive index of the light-transmitting portion 14 is higher than the refractive index of the light-absorbing portion 13, an optical design utilizing total reflection of light traveling from the light-transmitting portion 14 toward the light-absorbing portion 13 becomes possible. This makes it possible to improve, for example, the light utilization efficiency. In this case, the difference between the refractive index of the light-transmitting portion 14 and the refractive index of the light-absorbing portion 13 is not particularly limited, but is preferably 0.05 or more and 0.14 or less. When the refractive index difference is large, more light can be totally reflected.

[0046] <<<Land Portion>>> The land portion 15 is a member that supports the light absorbing portion 13 and the light transmitting portion 14. The land portion 15 is formed integrally with each of the light transmitting portions 14 so as to span across the plurality of light transmitting portions 14. The material that constitutes this land portion 15 may be the same as the material that constitutes the light transmitting portions 14. The thickness t of the land portion 15 (see FIG. 2) may be 10 μm or more and 50 μm or less, and may be 25 μm, for example. The optical function layer 12 may not have the land portion 15.

[0047] 2 , the second substrate 16 has a third surface 16 a and a fourth surface 16 b located on the opposite side of the third surface 16 a. The third surface 16 a is the surface on the optical function layer 12 side, and the fourth surface 16 b is the surface on the opposite side of the optical function layer 12.

[0048] The second substrate 16 is a member for supporting the optical function layer 12. This second substrate 16 may be a transparent substrate having optical transparency, similar to the first substrate 11. The second substrate 16 may also be made of a uniaxially stretched film. When the second substrate 16 is a uniaxially stretched film, the uniaxially stretched film is arranged so as to be stretched along the second direction d2. In other words, the uniaxially stretched film is arranged so that the slow axis 16c (see FIG. 1 ) of the second substrate 16 extends along the second direction d2. The second substrate 16 may also be made of a biaxially stretched film.

[0049] The retardation Re of the second substrate 16 is 6000 nm or more. This makes it possible to suppress light interference and color unevenness. The retardation Re of the second substrate 16 is preferably 8000 nm or more. The retardation Re of the second substrate 16 is preferably 15000 nm or less, and more preferably 12000 nm or less. In this way, by making the retardation Re of the second substrate 16 15000 nm or less, it is possible to prevent the thickness of the second substrate 16 from becoming too thick.

[0050] The second substrate 16 is disposed opposite the first substrate 11 so as to sandwich the optical function layer 12 between them. This makes it possible to suppress optical interference while increasing the rigidity of the optical sheet 10 compared to when the first substrate 11 is used alone.

[0051] In such a second substrate 16, the surface of the second substrate 16 opposite the optical function layer 12 may be subjected to an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment. That is, the fourth surface 16b of the second substrate 16 may be subjected to an anti-glare treatment, an anti-reflection treatment, or a hard coat treatment. When the fourth surface 16b of the second substrate 16 is subjected to an anti-glare treatment, specular reflection of light can be reduced by diffusing incident light. Furthermore, when the fourth surface 16b of the second substrate 16 is subjected to an anti-reflection treatment, specular reflection of light can be suppressed by utilizing the interference of reflected light. Furthermore, when the fourth surface 16b of the second substrate 16 is subjected to a hard coat treatment, the scratch resistance of the second substrate 16 can be improved.

[0052] The second base material 16 may be bonded to the optical function layer 12 using, for example, an adhesive including an acrylic adhesive or an adhesive sheet (not shown).

[0053] The other configurations of the second substrate 16 are the same as those of the first substrate 11, and therefore detailed description thereof will be omitted here.

[0054] In this optical sheet 10, the angle θ1 between the slow axis 11c of the first substrate 11 and the second direction d2 is 5° or less. The angle θ1 between the slow axis 11c of the first substrate 11 and the second direction d2 is preferably 3° or less, and more preferably 1° or less. As described below, when forming the light-transmitting portions 14 of the optical sheet 10, the first substrate 11 is irradiated with ultraviolet light or the like. After the optical sheet 10 is incorporated into a liquid crystal display device 30 or an organic EL display device 40, a reliability test may be performed. In this case, heat may be applied to the optical sheet 10. When heat is applied to the optical sheet 10, the first substrate 11 thermally shrinks. In this case, the first substrate 11 of the optical sheet 10 thermally shrinks along the stretching direction (the direction in which the slow axis 11c extends). Furthermore, when the first base material 11 thermally shrinks, there is a possibility that the optical function layer 12 will also shrink in the direction in which the first base material 11 shrinks.

[0055] In contrast, in the present embodiment, as described above, the angle θ1 between the slow axis 11c of the first substrate 11 and the second direction d2 is 5° or less. As a result, when the first substrate 11 thermally shrinks, the first substrate 11 thermally shrinks along a direction substantially parallel to the second direction d2. Therefore, when the first substrate 11 thermally shrinks, the optical function layer 12, like the first substrate 11, shrinks along a direction substantially parallel to the second direction d2. As a result, even when the optical function layer 12 shrinks, changes in the dimensions of the optical function layer 12 in the first direction d1 can be suppressed. Therefore, even when the optical function layer 12 shrinks, changes in the pitch P of the light absorbing portions 13, the maximum width W of the light absorbing portions 13, and the like can be suppressed. As a result, changes in the optical properties of the optical sheet 10 can be suppressed.

[0056] Furthermore, the angle θ2 formed between the slow axis 16c of the second substrate 16 and the second direction d2 is 5° or less. Furthermore, the angle θ2 formed between the slow axis 16c of the second substrate 16 and the second direction d2 is preferably 3° or less, and more preferably 1° or less. Even in this case, when the second substrate 16 thermally shrinks, the second substrate 16 thermally shrinks along a direction substantially parallel to the second direction d2. Therefore, when the second substrate 16 thermally shrinks, the optical function layer 12 shrinks along a direction substantially parallel to the second direction d2, similar to the second substrate 16. As a result, even when the optical function layer 12 shrinks, changes in the pitch P of the light absorbing portions 13, the maximum width W of the light absorbing portions 13, and the like can be suppressed.

[0057] Such an optical sheet 10 may be incorporated into a liquid crystal display device 30 as shown in Fig. 3. Alternatively, the optical sheet 10 may be incorporated into an organic EL display device 40 as shown in Fig. 4. The liquid crystal display device 30 and the organic EL display device 40 may be provided in the interior of an automobile and function as part of a navigation device. The liquid crystal display device 30 and the organic EL display device 40 may be housed in a housing (not shown) together with a power supply, electronic circuits, etc. Here, the liquid crystal display device 30 will first be described.

[0058] <Liquid Crystal Display Device> The liquid crystal display device 30 includes a liquid crystal panel 31, the above-described optical sheet 10 laminated on the liquid crystal panel 31, and a reflective polarizing film 35 laminated on the optical sheet 10. The liquid crystal display device 30 may further include a light guide plate 36 laminated on the reflective polarizing film 35.

[0059] The liquid crystal panel 31 has a liquid crystal layer 32, a first polarizing plate 33, and a second polarizing plate 34. The liquid crystal layer 32 contains a liquid crystal compound and is disposed between the first polarizing plate 33 and the second polarizing plate 34. The first polarizing plate 33 is disposed closer to the viewer than the second polarizing plate 34.

[0060] The first polarizing plate 33 and the second polarizing plate 34 have the function of separating incident light into two orthogonal polarized components (P waves and S waves). The first polarizing plate 33 and the second polarizing plate 34 transmit the polarized component (e.g., P waves) in one direction (parallel to the transmission axis) and absorb the polarized component (e.g., S waves) in the other direction (parallel to the absorption axis) that is orthogonal to the one direction.

[0061] Such a liquid crystal panel 31 is configured to control the transmission or blocking of light from the light guide plate 36 and provide an image to the viewer. There are no particular limitations on the type of liquid crystal panel 31, and any known type of liquid crystal panel can be used. For example, the liquid crystal panel 31 may be configured to have a liquid crystal layer 32 of a TN type, STN type, VA type, MVA type, IPS type, OCB type, or the like.

[0062] The reflective polarizing film 35 has the function of separating incident light into two orthogonal polarized components (P waves and S waves). The reflective polarizing film 35 transmits the polarized component (e.g., P waves) in one direction (parallel to the transmission axis) and reflects the polarized component (e.g., S waves) in the other direction (parallel to the reflection axis) that is orthogonal to the first direction. Any known reflective polarizing film 35 can be used as this type of reflective polarizing film 35.

[0063] The light guide plate 36 serves to guide light from a light source (not shown). A known light guide plate can be used as the light guide plate 36.

[0064] In addition, the liquid crystal display device 30 may further include a light diffusion plate that diffuses incident light and emits it, a prism layer that concentrates light, or a functional film that protects the liquid crystal panel while improving the quality of the image light.

[0065] <Organic EL Display Device> The organic EL display device 40 includes the above-described optical sheet 10, a circularly polarizing film 41 laminated on the optical sheet 10, and an organic EL light-emitting layer 42 laminated on the circularly polarizing film 41.

[0066] The circular polarizing film 41 is a member formed by laminating a polarizing member and a phase difference member. The circular polarizing film 41 serves to suppress the occurrence of interference fringes (moiré) caused by the periodic brightness and darkness generated by the light absorbing portions 13 and the light transmitting portions 14 of the optical function layer 12 themselves and the periodic brightness and darkness generated when the periodic brightness and darkness are reflected by the organic EL light emitting layer 42. A known circular polarizing plate can be used as the circular polarizing film 41. The circular polarizing film 41 may be bonded to the optical sheet 10 using, for example, an adhesive or an adhesive sheet (not shown) including an acrylic adhesive or the like.

[0067] The organic EL light-emitting layer 42 has a pair of electrodes (not shown) and a light-emitting layer (not shown) made of an organic material provided between the pair of electrodes. The organic EL light-emitting layer 42 may be a known one.

[0068] The organic EL display device 40 may further include a functional layer having a predetermined function.

[0069] <Method for Manufacturing Optical Sheet> Next, a method for manufacturing the optical sheet 10 according to this embodiment will be described.

[0070] First, prepare the first substrate 11. The first substrate 11 has a first surface 11a and a second surface 11b located on the opposite side of the first surface 11a.

[0071] Next, a plurality of light-transmitting portions 14 spaced apart from one another are formed on the first substrate 11. At this time, the light-transmitting portions 14 are formed on the first surface 11a of the first substrate 11. In this case, first, as shown in FIG. 5 , the first substrate 11 is inserted between a mold roll 20 and a nip roll 21 arranged opposite the mold roll 20. Concave and convex portions (not shown) corresponding to the shape of the light-transmitting portions 14 are formed on the surface of the mold roll 20. At this time, the mold roll 20 and the nip roll 21 are rotated while supplying material 14a constituting the light-transmitting portions 14 between the first substrate 11 and the mold roll 20. As a result, the material 14a constituting the light-transmitting portions 14 is filled into the concave portions (grooves) of the concave and convex portions formed on the surface of the mold roll 20. At this time, the material 14a is also supplied to positions corresponding to the land portions 15 (i.e., between the concave portions (not shown) and the first substrate 11).

[0072] Next, the light irradiation device 23 irradiates the material 14a with light L from the first substrate 11 side. This hardens the material 14a. In this manner, the light-transmitting portions 14 and the land portions 15 are formed. At this time, gaps G (see FIG. 6 ) for forming the light-absorbing portions 13 are formed between the light-transmitting portions 14. The gaps G are formed to have a shape corresponding to the convex portions of the uneven portion formed on the surface of the mold roll 20.

[0073] Then, the first substrate 11 , the land portion 15 and the light transmitting portion 14 are released from the mold roll 20 by a release roll 24 provided downstream of the mold roll 20 .

[0074] Next, the light absorbing portions 13 are formed between the light transmitting portions 14 .

[0075] When forming the light-absorbing portions 13, first, a composition 13d containing a light-absorbing material is supplied between the light-transmitting portions 14. In this case, as shown in Fig. 6, the composition 13d containing the light-absorbing material is supplied into the gaps G formed between the light-transmitting portions 14. Next, as shown in Fig. 6, excess composition 13d is scraped off with a doctor blade 25 or the like.

[0076] Next, the composition 13d is exposed to light to cure the composition 13d. At this time, the composition 13d is irradiated with light using a light irradiation device (not shown). This cures the composition 13d. In this way, an optical function layer 12 is obtained in which the light absorbing portions 13 are formed between the light transmitting portions 14.

[0077] Next, the second substrate 16 is attached to the optical function layer 12. At this time, the optical function layer 12 and the second substrate 16 may be bonded to each other using, for example, an adhesive including an acrylic adhesive or an adhesive sheet (not shown).

[0078] In this way, the optical sheet 10 is produced. Thereafter, the optical sheet 10 is processed to an appropriate size by punching or the like, as necessary.

[0079] As described above, according to the present embodiment, the optical sheet 10 includes the first substrate 11 having optical transparency and the optical function layer 12 laminated on the first substrate 11. The retardation Re of the first substrate 11 is 6000 nm or more. This makes it possible to suppress light interference and color unevenness.

[0080] The optical functional layer 12 includes light-absorbing portions 13 and light-transmitting portions 14. The light-absorbing portions 13 and light-transmitting portions 14 are alternately arranged along the first direction d1 and extend linearly along a second direction d2 intersecting the first direction d1. The angle θ1 between the slow axis 11c of the first substrate 11 and the second direction d2 is 5° or less. As a result, when the first substrate 11 thermally shrinks, the first substrate 11 thermally shrinks along a direction substantially parallel to the second direction d2. Therefore, when the first substrate 11 thermally shrinks, the optical functional layer 12, like the first substrate 11, shrinks along a direction substantially parallel to the second direction d2. As a result, even when the optical functional layer 12 shrinks, changes in the dimensions of the optical functional layer 12 in the first direction d1 can be suppressed. Therefore, even when the optical functional layer 12 shrinks, changes in the pitch P of the light-absorbing portions 13, the maximum width W of the light-absorbing portions 13, and the like can be suppressed. As a result, changes in the optical properties of the optical sheet 10 can be suppressed.

[0081] In the present embodiment, as described above, even when the optical function layer 12 shrinks, the change in the pitch P of the light-absorbing portions 13 can be suppressed. Therefore, the change in the viewing angle characteristics caused by the change in the pitch P can be suppressed. Furthermore, as described above, the optical sheet 10 is incorporated into a liquid crystal display device 30 or an organic EL display device 40. In this case, the pitch P of the light-absorbing portions 13 can be designed taking into account the pitch of pixels (not shown) so as to prevent appearance unevenness (moiré (interference fringes)) from occurring. In the present embodiment, the change in the pitch P of the light-absorbing portions 13 can be suppressed, and therefore appearance unevenness (moiré) in the liquid crystal display device 30 or the organic EL display device 40 can be effectively suppressed.

[0082] Next, the operation of the above-described embodiment will be specifically described.

[0083] Example An optical sheet 10 shown in FIG. 1 was produced.

[0084] First, the mold roll 20 shown in FIG. 5 was produced. The cross-sectional shape of the convex portion of the mold corresponding to the gap G, which was a cross-sectional shape along the radial direction, was a trapezoid tapered toward the radially outward direction. The width of the upper base (radially outer side) of the trapezoid was 4 μm, the width of the lower base (radially inner side) of the trapezoid was 10 μm, the height of the trapezoid was 102 μm, the pitch of the trapezoid was 39 μm, and the inclination angle of the legs of the trapezoid relative to the radial direction was 3°. The width of the lower base (radially inner side), the height of the trapezoid, the pitch of the trapezoid, and the inclination angle of the legs of the trapezoid relative to the radial direction correspond to the maximum width W of the light absorbing portion 13 in the first direction d1, the length L of the light absorbing portion 13, the pitch P of the light absorbing portion 13, and the inclination angle θ of the legs of the trapezoid, respectively.

[0085] Next, a light-transmitting portion 14 was formed on the first substrate 11 using the mold roll 20 prepared by the method shown in FIG. 5 . At this time, ultraviolet light was irradiated as the light L. A polyester film (Cosmoshine (registered trademark), ultra-birefringent type, SRF (product name), thickness 80 μm, manufactured by Toyobo Co., Ltd.) was used as the first substrate 11. Furthermore, ultraviolet-curable urethane acrylate (refractive index 1.57) was used as the material 14a for forming the light-transmitting portion 14. The light-transmitting portion 14 was formed so that the angle (i.e., angle θ1) between the ultra-stretching direction of the polyester film (the direction in which the slow axis 11c extends) and the direction in which the convex portion of the mold extends was 5° or less. The thickness t of the land portion 15 was 25 μm.

[0086] Next, the light-absorbing portion 13 was formed by the method shown in Fig. 6. At this time, ultraviolet light was irradiated onto the composition 13d constituting the light-absorbing portion 13. Furthermore, a material in which black beads were contained in ultraviolet-curable urethane acrylate (refractive index 1.49) was used as the composition 13d constituting the light-absorbing portion 13. At this time, beads in which carbon black was provided on the surface layer of acrylic beads with an average particle size of 4 µm were used as the black beads. Furthermore, the content of black beads in the composition 13d was 20 mass%.

[0087] (Comparative Example) An optical sheet was produced in the same manner as in the Example, except that the light-transmitting portion 14 was formed so that the angle between the ultra-stretching direction of the polyester film (the direction in which the slow axis 11c extends) and the direction in which the convex portion of the mold extends (i.e., angle θ1) was 89° or more and 91° or less.

[0088] Next, the optical sheet 10 according to the example and the optical sheet according to the comparative example were left in an environment of 105°C for 1000 hours to perform a reliability test. After that, the rate of change in the pitch P of the light-absorbing portions 13 was measured. In addition, a 12.3-inch IPS liquid crystal display (LA123WF1-SR03 (product name) manufactured by LG Display) was used to check for changes in viewing angle characteristics and the presence or absence of appearance unevenness. At this time, the optical sheet 10 according to the example and the optical sheet according to the comparative example were incorporated between a liquid crystal panel and a reflective polarizing film.

[0089] The results are shown in Table 1.

[0090]

[0091] As a result, as shown in Table 1, the rate of change in pitch P was 0.7% in the optical sheet according to the comparative example. In contrast, the rate of change in pitch P was 0.1% in the optical sheet 10 according to the example. Thus, it was found that the rate of change in pitch P can be reduced in the optical sheet 10 according to the present embodiment.

[0092] Furthermore, as shown in Table 1, the optical sheet 10 according to the example was able to suppress changes in the viewing angle characteristics and the occurrence of uneven appearance. Therefore, it was found that the optical sheet 10 according to the present embodiment was able to suppress changes in the optical characteristics of the optical sheet 10.

[0093] The components disclosed in the above-described embodiment and each modification may be combined as needed, or some components may be omitted from all the components shown in the above-described embodiment and each modification.

Claims

1. An optical sheet comprising: a first substrate having optical transparency; and an optical functional layer laminated on said first substrate; wherein the retardation of said first substrate is 6000 nm or more; said optical functional layer has light absorbing portions and light transmitting portions; said light absorbing portions and said light transmitting portions are alternately arranged along a first direction and extend linearly along a second direction intersecting said first direction; and wherein an angle formed between the slow axis of said first substrate and said second direction is 5° or less.

2. An optical sheet according to claim 1, further comprising a second substrate laminated on the optical functional layer on the opposite side to the first substrate, wherein the second substrate is optically transparent, the retardation of the second substrate is 6000 nm or more, and the angle between the slow axis of the second substrate and the second direction is 5° or less.

3. The optical sheet according to claim 1, wherein the surface of the first substrate opposite to the optical functional layer is subjected to anti-glare treatment, anti-reflection treatment, or hard coat treatment.

4. The optical sheet according to claim 2, wherein the surface of the second substrate opposite to the optical functional layer is subjected to anti-glare treatment, anti-reflection treatment, or hard coat treatment.

5. A liquid crystal display device comprising: a liquid crystal panel; an optical sheet according to any one of claims 1 to 4 laminated on said liquid crystal panel; and a reflective polarizing film laminated on said optical sheet.

6. An organic EL display device comprising: an optical sheet according to any one of claims 1 to 4; a circularly polarizing film laminated on said optical sheet; and an organic EL light-emitting layer laminated on said circularly polarizing film.

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