Method for molding optical film

Abstract

The present invention can provide an optical film that prevents occurrence of light leakage when applied to a pancake-type virtual reality display device. Further, the present invention can provide a method for molding the optical film. This method for molding an optical film comprises: a step for heating an optical film having a planar shape and including at least two optical anisotropic layers; a step for pressing the optical film against a mold and deforming the optical film along the shape of the mold; and a step for cutting the deformed optical film. The mold has a substantially concave spherical shape, and when a position in a surface of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the temperature of the optical film located at the top of the concave spherical shape is higher than the temperature of the optical film located at the end of the concave spherical shape.

Description

Optical film molding method

[0001] The present invention relates to a method for forming an optical film.

[0002] A virtual reality display device is a display device that allows a user to feel as if they are immersed in a virtual world by wearing a dedicated headset and viewing images displayed through a compound lens. Virtual reality display devices generally have an image display panel and a Fresnel lens, but the distance from the image display panel to the Fresnel lens is large, which makes the headset thick and makes it difficult to wear. To address this issue, as described in Patent Documents 1 and 2, a compound lens configuration called a pancake lens has been proposed, which includes an image display panel, a reflective polarizer, and a half mirror, and reduces the overall thickness of the headset by directing light emitted from the image display panel back and forth between the reflective polarizer and the half mirror.

[0003] Here, a reflective polarizer is a polarizer that has the function of reflecting one polarized light of incident light and transmitting the other polarized light. For example, the reflected light and transmitted light by a reflective linear polarizer are linearly polarized light with orthogonal polarization states. On the other hand, the reflected light and transmitted light by a reflective circular polarizer are circularly polarized light with one rotation direction and the opposite rotation direction.

[0004] Known examples of reflective linear polarizers that produce linearly polarized transmitted and reflected light include stretched dielectric multilayer films and wire grid polarizers. Also, known examples of reflective circular polarizers that produce circularly polarized transmitted and reflected light include cholesteric liquid crystal layers having a light-reflecting layer in which a cholesteric liquid crystal phase is fixed.

[0005] Special Publication No. 2020-519964 US10394040B2

[0006] Patent Document 1 discloses a method for laminating a laminated optical body onto a spherical or aspherical curved surface of an optical lens to obtain a wide field of view, low chromatic aberration, low distortion, and an excellent MTF (modulation transfer function). However, in order to laminate a laminated optical body including an optically anisotropic layer onto a curved surface, the laminated optical body must be molded into a three-dimensional shape including a curved surface. At this time, there is a problem that the optically anisotropic layer may exhibit retardation or change in retardation due to stretching of the optically anisotropic layer. Furthermore, when molding into a three-dimensional shape including a curved surface, the laminated optical body is stretched at different stretching ratios depending on the location, resulting in different amounts of retardation exhibited and / or changed depending on the location. When the optically anisotropic layer is a retardation layer such as a λ / 4 retardation layer, the appearance of undesirable retardation may result in the retardation of the optically anisotropic layer becoming unintended. Furthermore, the optical axis of the optically anisotropic layer may change to an unintended orientation. Furthermore, even if the optically anisotropic layer is a layer that normally does not have a retardation, such as a cholesteric liquid crystal layer, stretching the optically anisotropic layer may newly exhibit a retardation. If the cholesteric liquid crystal layer exhibits a retardation, problems may occur, such as the reflected polarized light becoming elliptically polarized rather than the intended circularly polarized light. The inventors' studies have found that the appearance of such undesirable retardation and changes in retardation disrupt the polarization of light emitted from an image display device in a pancake lens, causing some of the light to leak, leading to double images and reduced contrast.

[0007] Furthermore, Patent Document 1 discloses a compound lens with a pancake lens configuration that uses a reflective linear polarizer as the reflective polarizer and includes, in this order, an image display panel, a reflective linear polarizer, and a half mirror. When including an image display panel, a reflective polarizer, and a half mirror in this order, the reflective polarizer needs to have the action of a concave mirror with respect to light rays incident from the half mirror side. In order to impart the action of a concave mirror to the reflective linear polarizer, a configuration in which the reflective linear polarizer is molded into a curved shape has been proposed. Furthermore, Patent Document 2 discloses a compound lens with a pancake lens configuration that uses a reflective linear polarizer as the reflective polarizer and includes, in this order, an image display panel, a half mirror, and a reflective linear polarizer. Patent Document 2 also proposes a configuration in which both the half mirror and the reflective polarizer are curved to improve field curvature. In this case, the reflective polarizer needs to have the action of a convex mirror. According to the investigations of the present inventors, when a reflective linear polarizer is formed into a curved shape, the phase difference of the retardation film disposed between the reflective polarizer and the half mirror, which converts circularly polarized light and linearly polarized light, changes, making it impossible to appropriately reflect and transmit incident light, and increasing light leakage. When light leakage increases, ghosts become visible.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical film that suppresses light leakage when applied to a pancake-type virtual reality display device. Another object of the present invention is to provide a molding method for the optical film.

[0009] The present inventors have conducted extensive research into the above-mentioned problems and have found that the above-mentioned problems can be solved by the following configuration.

[0010] [1] A method for molding an optical film, the method comprising the steps of: heating an optical film having a planar shape and including at least two or more optically anisotropic layers; pressing the optical film against a mold to deform it according to the shape of the mold; and cutting the deformed optical film, wherein the mold is substantially concave spherical, and when an in-plane position of the optical film is projected onto the mold from a direction normal to the surface of the optical film, the temperature of the optical film located at an apex of the concave sphere is higher than the temperature of the optical film located at an end of the concave sphere. [2] The method for molding an optical film according to [1], wherein the radius of curvature is 30 mm to 1000 mm. [3] The method for molding an optical film according to [1] or [2], wherein the two or more optically anisotropic layers are a combination of a first optically anisotropic layer having an in-plane retardation of 120 nm to 160 nm at a wavelength of 550 nm and a second optically anisotropic layer having an in-plane retardation of 200 to 320 nm. [4] The method for molding an optical film according to [3], wherein both the first optically anisotropic layer and the second optically anisotropic layer have reverse wavelength dispersion. [5] The method for molding an optical film according to [1] or [2], wherein the optical film further comprises a reflective polarizer. [6] The method for molding an optical film according to [1] or [2], wherein the heating step is a step of heating the optical film by irradiating it with infrared rays, and when a position in the plane of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the amount of infrared radiation irradiated to the optical film located at a vertex of the concave sphere is greater than the amount of infrared radiation irradiated to the optical film located at an end of the concave sphere.

[0011] According to the present invention, an optical film that suppresses light leakage when applied to a pancake-type virtual reality display device can be provided. Also, according to the present invention, a method for forming the optical film can be provided.

[0012] 1 is a schematic diagram showing an example of a laminated optical body produced by the method for molding an optical film of the present invention, showing an example of light rays of a main image. FIG. 2 is a schematic diagram showing an example of a laminated optical body produced by the method for molding an optical film of the present invention, showing an example of light rays of a ghost. FIG. 3 is a schematic diagram showing an example of a laminated optical body produced by the method for molding an optical film of the present invention. FIG. 4 is a schematic diagram showing an example of a reflective circular polarizer used in the present invention. FIG. 5 is a schematic diagram showing an example of a laminated optical body produced by the method for molding an optical film of the present invention. FIG. 6 is an example of a pattern drawn on an optical film to investigate the stretching ratios in the diameter direction and the circumferential direction in the molding method of the present invention. FIG. 7 is a diagram for explaining the molding method of the present invention. FIG. 8 is a top view of an optical film in a planar shape used in the molding method of the present invention. FIG. 9 is a diagram for explaining the ratio of stretching ratios in the plane of the optical film. FIG. 10 is a diagram for explaining the conversion effect of polarized light using a Poincare sphere. FIG. 11 is a diagram for explaining the conversion effect of polarized light using a Poincare sphere.

[0013] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0014] In this specification, the liquid crystal composition and liquid crystal compound conceptually include those that no longer exhibit liquid crystallinity due to curing or the like.

[0015] The present invention will be described in detail below with reference to the drawings. The following description of the constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0016] In this specification, "orthogonal" does not mean an angle of 90° exactly, but means 90°±10°, preferably 90°±5°. Furthermore, "parallel" does not mean an angle of 0° exactly, but means 0°±10°, preferably 0°±5°. Furthermore, "45°" does not mean an angle of 45° exactly, but means 45°±10°, preferably 45°±5°. In addition, when referring to angles, it does not mean an exact angle, but means a range of ±10°, preferably a range of ±5°.

[0017] In this specification, "absorption axis" refers to the polarization direction in which absorbance is maximized in a plane when linearly polarized light is incident. "Reflection axis" refers to the polarization direction in which reflectance is maximized in a plane when linearly polarized light is incident. "Transmission axis" refers to the direction perpendicular to the absorption axis or reflection axis in a plane. "Slow axis" refers to the direction in which refractive index is maximized in a plane.

[0018] In this specification, unless otherwise specified, phase difference refers to in-plane retardation and is referred to as Re(λ). Here, Re(λ) represents the in-plane retardation at wavelength λ, and unless otherwise specified, wavelength λ is 550 nm. Furthermore, in this specification, retardation in the thickness direction at wavelength λ is referred to as Rth(λ). Unless otherwise specified, wavelength λ is 550 nm. Re(λ) and Rth(λ) can be values ​​measured at wavelength λ using an AxoScan OPMF-1 (manufactured by OptoScience). By inputting the average refractive index ((nx + ny + nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) Rth(λ) = ((nx + ny) / 2 - nz) × d can be calculated.

[0019] In this specification, when referring to "effective in-plane retardation calculated from the change in polarization state for a predetermined polarized light," the "effective retardation" is measured as follows. That is, using a KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments), linearly polarized light with a wavelength of λ nm is incident on the optical film in the normal direction, and the transmitted light intensity of the light transmitted through the optical film is measured through an analyzer (a linear polarizer arranged at a predetermined angle). The orientations of the linear polarizer and the optical film are fixed at a predetermined angle with respect to the orientation of the optical film, and the relative angle of the analyzer is varied to perform simulations from the measured transmitted light intensity, thereby obtaining the effective in-plane retardation. The measurement wavelength λ nm can be selected by manually changing the wavelength selection filter or by converting the measured value using a program or the like. Unless otherwise specified, the measurement wavelength is λ = 550 nm. According to this measurement method, even for a composite retardation plate whose optical retardation effect changes depending on the incident polarized light, it is possible to measure the effective in-plane retardation value at each position in the plane. The effective retardation value is the in-plane retardation value of one optically anisotropic layer that causes the same optical retardation as the optical retardation caused by the laminate when linearly polarized light of a specific polarization direction is incident on the laminate (optical film) in which two or more optically anisotropic layers are stacked. Furthermore, the specific polarization direction of the linearly polarized light incident on the laminate is, for example, the polarization direction of the linearly polarized light that has passed through this linear polarizer when the optical film contains a linear polarizer. The effective retardation value of a laminate in which two or more optically anisotropic layers are stacked varies depending on the in-plane retardation value of each optically anisotropic layer and the azimuth angle of the slow axis of each optically anisotropic layer.

[0020] The effective retardation value can also be determined using AxsoScan. Specifically, using AxsoScan, light with a wavelength of λ nm is incident on the optical film from the normal direction, and the Mueller matrix of the optical film is obtained. Furthermore, from the obtained Mueller matrix, the polarization state of the emitted light when light of various polarization states is incident on the optical film can be determined, and from the change in the polarization state, the in-plane retardation value of each optically anisotropic layer and the azimuthal angle of the slow axis of each optically anisotropic layer can be determined. From these values, the effective retardation value of the optical film can be determined.

[0021] <Optical Film> The optical film produced by the optical film molding method of the present invention (hereinafter also referred to as the method of the present invention) has a non-planar shape. A non-planar shape refers to a shape other than a planar shape, such as a curved shape. The curved shape refers to a shape with a curvature greater than zero, and includes a developable curved shape and a three-dimensional curved surface shape. A developable surface is a surface that can be developed into a plane without expanding or contracting any part of the surface. Examples of developable curved surfaces include surfaces corresponding to the circumferential surfaces of a cylinder, an elliptical cylinder, a cone, and an elliptical cone, and may be either a convex or concave curved surface. A three-dimensional curved surface refers to a curved surface that cannot be formed by deforming a plane, i.e., a curved surface that is not a developable surface. Examples of three-dimensional curved surfaces include surfaces corresponding to partial spheres (spherical crown surfaces) and partial spheroids, and surfaces corresponding to curved surfaces whose cross sections form parabolas, hyperbolas, etc. (e.g., paraboloids of revolution), and may be either a convex or concave curved surface.

[0022] The curved surface shape is preferably a lens shape. Examples of the lens shape include a partial spherical shape and a partial spheroidal shape, and the shape may be a convex lens shape or a concave lens shape.

[0023] The non-planar shape of the optical film is preferably a partial spherical shape, a partial spheroidal shape, or a partial paraboloidal shape.

[0024] As described above, the optical film has a non-planar shape and exhibits a predetermined radius of curvature. That is, the portion of the optical film having a non-planar shape (a non-planar portion, preferably a curved portion) exhibits a predetermined radius of curvature. The radius of curvature is 30 to 1000 mm, and is preferably 30 to 100 mm, since this further suppresses the occurrence of light leakage when the optical film produced by the method of the present invention is applied to a pancake-type virtual reality display device (hereinafter, simply referred to as "the advantage of the present invention being superior"). The radius of curvature may be constant or may vary at any position on the optical film.

[0025] The optical film produced by the method of the present invention has a non-planar shape and includes at least two optically anisotropic layers, the details of which will be described later.

[0026] The in-plane variation of the effective in-plane retardation value calculated from the change in the polarization state of the optical film with respect to a predetermined polarized light is preferably less than 5%. In particular, less than 3% is preferable, and less than 1% is more preferable, in terms of more excellent effects of the present invention. The lower limit is not particularly limited, but may be 0%. The in-plane variation of the effective in-plane retardation value calculated from the change in the polarization state of the optical film with respect to a predetermined polarized light is calculated by the following method. In this specification, the following method is also referred to as "specific method 1." First, when the optical film is applied to a virtual reality display device, the optical film is viewed in plan from the normal direction to the exit surface of the image display panel, and the intersection of the optical film viewed in plan with an axis extending in the normal direction through the center of the exit surface is defined as the center of the optical film. Furthermore, for example, when the optical film has a partial spherical surface, the optical film is basically positioned such that the vertex position of the partial spherical surface coincides with the center of the exit surface of the image display panel in the in-plane direction, and therefore the vertex position of the partial spherical surface is the center of the optical film. Next, in a projected image obtained by viewing the optical film in a planar view, a line passing through the center and extending in one in-plane direction is defined as a first line, a line passing through the center and rotating the first line 45° clockwise is defined as a second line, a line passing through the center and rotating the second line 45° clockwise is defined as a third line, and a line passing through the center and rotating the third line 45° clockwise is defined as a fourth line. Next, a circle is drawn within the projected image obtained by viewing the optical film in a planar view, with the center of the optical film as its center. In this case, the inscribed circle that can be drawn with the largest radius is defined as the first circle, and a circle with half the radius of the first circle is defined as the second circle.Next, the effective in-plane retardation at a position of the optical film corresponding to the center of the optical film in plan view, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the first straight line and the first circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the first straight line and the second circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the second straight line and the first circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the second straight line and the second circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the third straight line and the first circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the third straight line and the second circle, the effective in-plane retardation at a position of the optical film corresponding to two intersections of the fourth straight line and the first circle, and the effective in-plane retardation at a position of the optical film corresponding to two intersections of the fourth straight line and the second circle are measured. The position of the optical film corresponding to the center of the optical film in planar view corresponds to the intersection of the optical film with an axis that passes through the center of the projected image obtained by viewing the optical film in planar view and extends in the normal direction of the projected image. In other words, the center position in the projected image is reflected in the position of the optical film to calculate the effective in-plane retardation at that position of the optical film. The position of the optical film corresponding to the intersection corresponds to the intersection of the optical film with an axis that passes through the selected intersection position in the projected image obtained by viewing the optical film in planar view and extends in the normal direction of the projected image. In other words, the position of the intersection position in the projected image is reflected in the position of the optical film to calculate the effective in-plane retardation at that position of the optical film. According to the above procedure, the effective in-plane retardation of the optical film is measured at 17 locations. Next, the maximum, minimum, and average values ​​of the obtained measured values ​​are calculated, and the in-plane variation (%) of the effective retardation is calculated using the following formula: In-plane variation (%) = {(maximum value - minimum value) / average value} × 100.

[0027] In the present invention, the shape of the outer peripheral edge of the optical film is not particularly limited, and may be, for example, a perfect circle, an ellipse, or an irregular shape. The shape of the outer peripheral edge refers to the shape of the outer peripheral edge of the optical film when the optical film is applied to a virtual reality display device and the optical film is observed from the normal direction of the exit surface of the image display panel.

[0028] In the present invention, the in-plane variation in the film thickness of the optical film is not particularly limited. However, a value of less than 5% is preferred, and less than 3% is more preferred, as this provides better effects of the present invention. The lower limit is not particularly limited, but can be 0%. To measure the in-plane variation in film thickness, the film thickness is measured at 17 locations where the effective in-plane retardation was measured when calculating the in-plane variation in retardation described above. The maximum, minimum, and average values ​​of the obtained measurements are calculated, and the in-plane variation in retardation (%) is calculated using the following formula: In-plane variation (%) = {(maximum value - minimum value) / average value} × 100. The film thickness at each location is measured by cutting the optical film with a microtome to expose a cross section, and then observing the cross section with a scanning electron microscope (SEM) at an appropriate magnification (20,000 to 50,000 times) to determine the film thickness of the optical film. To facilitate cross-section observation, the measurement sample may be subjected to appropriate treatments such as carbon deposition and etching. The acceleration voltage is preferably optimized at 1 to 10 kV. In this specification, the above method of measuring the in-plane variation in film thickness is also referred to as "specifying method 2."

[0029] In the present invention, the optical film includes at least two optically anisotropic layers. Examples of the optically anisotropic layer include a retardation film. In the present invention, the optical film preferably includes at least one or more retardation films as the optically anisotropic layers. In addition, in the present invention, the optical film may have a configuration including a retardation film and a linear polarizer. In addition, in the present invention, the optical film may have a configuration including a plurality of retardation films and a linear polarizer. For example, the optical film may have two retardation films and a linear polarizer. Hereinafter, the retardation film will be first described in detail.

[0030] <Retardation Film (hereinafter also referred to as "Retardation Layer")> The retardation layer has the function of changing the polarization state when polarized light is incident. For example, when circularly polarized light is incident, the retardation layer converts the emitted light into approximately linearly polarized light, and when linearly polarized light is incident, the retardation layer converts the emitted light into approximately circularly polarized light. In this case, for example, a retardation layer having an Re of approximately 1 / 4 wavelength at any wavelength in the visible range can be used. In this case, the effective in-plane retardation Re(550) at a wavelength of 550 nm is preferably 120 nm to 160 nm, more preferably 125 nm to 145 nm, and even more preferably 135 nm to 142 nm. Retardation layers having an Re of approximately 3 / 4 wavelength and approximately 5 / 4 wavelength are also preferable because they can convert linearly polarized light into circularly polarized light. In addition, the retardation layer may have the function of rotating the polarization direction of incident linearly polarized light by approximately 90 degrees. In this case, for example, a retardation layer having Re of approximately 1 / 2 wavelength at any wavelength in the visible range can be used, and in this case, the effective in-plane retardation Re(550) at a wavelength of 550 nm is preferably 200 nm to 320 nm, more preferably 250 nm to 300 nm, and further preferably 270 nm to 290 nm.

[0031] Furthermore, the retardation layer preferably has reverse dispersion with respect to wavelength. Having reverse dispersion is preferable because it makes it possible to convert circularly polarized light into linearly polarized light over a wide wavelength range in the visible range. Here, having reverse dispersion with respect to wavelength means that the value of the retardation at that wavelength increases as the wavelength increases. A retardation layer having reverse dispersion can be produced by uniaxially stretching a polymer film such as a modified polycarbonate resin film having reverse dispersion, for example, with reference to JP 2017-049574 A.

[0032] It is also preferable that the retardation layer has a layer formed by fixing a uniformly aligned liquid crystal compound. For example, a layer in which a rod-shaped liquid crystal compound is uniformly aligned horizontally relative to the in-plane direction, and a layer in which a discotic liquid crystal compound is uniformly aligned perpendicularly to the in-plane direction, etc. can be used. Furthermore, for example, referring to JP-A-2020-084070, a retardation layer having reverse dispersion can also be produced by uniformly aligning and fixing a rod-shaped liquid crystal compound having reverse dispersion.

[0033] In addition, the retardation layer also preferably has the layer that is made by fixing the liquid crystal compound that is twisted and aligned with thickness direction as helical axis.For example, as disclosed in Japanese Patent No. 5753922 and Japanese Patent No. 5960743, the retardation layer can also have the layer that is made by fixing the rod-shaped liquid crystal compound or discotic liquid crystal compound that is twisted and aligned with thickness direction as helical axis, and in this case, the retardation layer can be regarded as having substantially reverse dispersion, so it is preferable.

[0034] The thickness of the retardation layer is not particularly limited, but from the viewpoint of thinning, it is preferably 0.1 to 8 μm, more preferably 0.3 to 5 μm.

[0035] In addition, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the retardation layer is preferably transparent to near-infrared light.

[0036] In the present invention, the optical film preferably has two or more optically anisotropic layers, each of which is a combination of a first optically anisotropic layer having an in-plane retardation of 120 to 160 nm at a wavelength of 550 nm and a second optically anisotropic layer having an in-plane retardation of 200 to 320 nm. For example, as disclosed in Japanese Patent No. 6259925, a combination of a retardation layer having an Re of approximately ¼ wavelength and a retardation layer having an Re of approximately ½ wavelength is laminated such that the slow axes of the two layers form an angle of approximately 60°. In this case, even if the quarter-wave retardation layer and the half-wave retardation layer each have normal dispersion (the retardation value at the wavelength decreases as the wavelength increases), it is known that they can convert circularly polarized light into linearly polarized light over a wide wavelength range in the visible region and can be considered to have substantially reverse dispersion. However, it is more preferable that these first and second optically anisotropic layers each have reverse wavelength dispersion, as this approaches ideal wavelength dispersion.

[0037] Furthermore, the optical film preferably has a linear polarizer in addition to the quarter-wave retardation layer and the half-wave retardation layer. The linear polarizer is preferably disposed on the side of the half-wave retardation layer opposite to the quarter-wave retardation layer. In this case, when viewed from the direction perpendicular to the main surface of the optical film (stacking direction), it is preferable that the slow axis of the half-wave retardation layer is at an angle of approximately 15° with respect to the transmission axis of the linear polarizer, and the slow axis of the quarter-wave retardation layer is at an angle of approximately 75° with respect to the transmission axis of the linear polarizer. It is also preferable that the slow axis of the half-wave retardation layer is at an angle of approximately 75° with respect to the transmission axis of the linear polarizer, and the slow axis of the quarter-wave retardation layer is at an angle of approximately 15° with respect to the transmission axis of the linear polarizer. As a result, light incident from the linear polarizer side is converted by the linear polarizer into linearly polarized light having a polarization direction parallel to the transmission axis of the linear polarizer, and then incident on the laminate of the half-wave retardation layer and the quarter-wave retardation layer to be converted into circularly polarized light. That is, a laminate of a half-wave retardation layer and a quarter-wave retardation layer laminated at the above-mentioned axial angle functions as a λ / 4 plate when linearly polarized light is incident on the laminate, the polarization direction of which is 15° with respect to the slow axis of the half-wave retardation layer and at an angle of 75° with respect to the slow axis of the quarter-wave retardation layer, or when linearly polarized light is incident on the laminate, the polarization direction of which is 75° with respect to the slow axis of the half-wave retardation layer and at an angle of 15° with respect to the slow axis of the quarter-wave retardation layer.

[0038] In the method of the present invention, since the optical film is molded into a curved surface, each layer of the optical film is stretched, resulting in a change in thickness. Generally, when the thickness of a retardation layer changes, the in-plane retardation changes. Therefore, for example, in the case of a quarter-wave retardation layer that converts linearly polarized light into circularly polarized light, the converted linearly polarized light is not completely converted into circularly polarized light due to a change in thickness, and becomes elliptically polarized light (the ellipticity of the converted polarized light decreases). On the other hand, in the case of a configuration in which a half-wave retardation layer and a quarter-wave retardation layer are stacked to function as a λ / 4 plate, even if the optical film is stretched by molding and the thicknesses of the half-wave retardation layer and the quarter-wave retardation layer change, the changes in the effects of the half-wave retardation layer and the quarter-wave retardation layer due to the change in the film thickness of each layer cancel each other out, so that the optical film functions properly as a λ / 4 plate. This point will be described in detail later.

[0039] In addition, in the present invention, the retardation layer may be formed of a plurality of layers.For example, two 1 / 4 wavelength retardation layers may be laminated with the direction of the slow axis aligned to form a 1 / 2 wavelength retardation layer.For example, in the case of the configuration in which the 1 / 2 wavelength retardation layer and the 1 / 4 wavelength retardation layer are laminated, the first 1 / 4 wavelength retardation layer is laminated so that the slow axis is 15° with respect to the transmission axis of the linear polarizer, the second 1 / 4 wavelength retardation layer is laminated so that the slow axis is 15° with respect to the transmission axis of the linear polarizer, and the third 1 / 4 wavelength retardation layer is laminated so that the slow axis is 75° with respect to the transmission axis of the linear polarizer.

[0040] <Laminated Optical Body> One embodiment of the laminated optical body (optical film) has at least a cholesteric liquid crystal layer and a retardation layer that converts circularly polarized light and linearly polarized light into each other. One embodiment of the laminated optical body has at least a cholesteric liquid crystal layer, a retardation layer that converts circularly polarized light and linearly polarized light into each other, and a linear polarizer, in this order. One embodiment of the laminated optical body has at least a linearly polarized reflective polarizer and a retardation layer that converts circularly polarized light and linearly polarized light into each other. One embodiment of the laminated optical body has at least a retardation layer that converts circularly polarized light and linearly polarized light into each other, a linearly polarized reflective polarizer, and a linear polarizer, in this order. The retardation layer included in the laminated optical body is as described above. Other components that may be included in the laminated optical body will be described in detail below.

[0041] [Cholesteric Liquid Crystal Layer] A cholesteric liquid crystal layer is an optical element that separates incident light into right-handed circularly polarized light and left-handed circularly polarized light, specularly reflecting one circularly polarized light and transmitting the other circularly polarized light. Furthermore, as is well known, cholesteric liquid crystal layers have wavelength-selective reflectivity. For example, JP 2020-060627 A and the like disclose a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase. Films formed by fixing a cholesteric liquid crystal phase are preferred because they have a high degree of polarization of transmitted light despite being thin. Cholesteric liquid crystal layers are preferred as films used for curved surface molding because they suppress a decrease in polarization degree and / or distortion of the polarization axis when stretched or molded into a three-dimensional shape. Furthermore, a decrease in polarization degree due to distortion of the polarization axis is less likely to occur.

[0042] The cholesteric liquid crystal layer preferably has a blue light-reflecting layer with a reflectance of 40% or more at a wavelength of 460 nm, a green light-reflecting layer with a reflectance of 40% or more at a wavelength of 550 nm, a yellow light-reflecting layer with a reflectance of 40% or more at a wavelength of 600 nm, and a red light-reflecting layer with a reflectance of 40% or more at a wavelength of 650 nm. This configuration is preferable because it can exhibit high reflection characteristics over a wide wavelength range in the visible range. The reflectances described above are those when unpolarized light is incident on the cholesteric liquid crystal layer at each wavelength. Furthermore, the blue light-reflecting layer, green light-reflecting layer, yellow light-reflecting layer, and red light-reflecting layer, each formed by fixing a cholesteric liquid crystal phase, may have a pitch gradient layer in which the helical pitch of the cholesteric liquid crystal phase is continuously changed in the thickness direction. For example, referring to JP 2020-060627 A, etc., the green light-reflecting layer and the yellow light-reflecting layer can be continuously produced.

[0043] It is also preferable that the cholesteric liquid crystal layer has a light-reflecting layer formed by fixing a cholesteric liquid crystal phase containing a rod-shaped liquid crystal compound, and a light-reflecting layer formed by fixing a cholesteric liquid crystal phase containing a discotic liquid crystal compound. With such a configuration, the cholesteric liquid crystal phase containing the rod-shaped liquid crystal compound has a positive Rth, whereas the cholesteric liquid crystal phase containing the discotic liquid crystal compound has a negative Rth, so that the Rths cancel each other out, thereby suppressing the occurrence of ghosts even with respect to light incident from an oblique direction, which is preferable.

[0044] The manner in which Rth is cancelled out can be expressed by the following formula. In an optical laminate film having n light-reflecting layers, when the light-reflecting layers are named L1, L2, L3, ..., Ln in order from the light source side, the sum of the Rth of each layer from light-reflecting layer L1 to light-reflecting layer Li is SRthi. Specifically, it is expressed by the following formula: SRth1=Rth1 SRth2=Rth1+Rth2... SRthi=Rth1+Rth2... +Rthi... SRthn=Rth1+Rth2... +Rthi... +Rthn The absolute values ​​of all these SRthi (SRth1 to SRthn) are preferably 0.3 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less. The Rthi of each layer in the above formula is determined by the above-mentioned formula for calculating Rth.

[0045] The thickness of the cholesteric liquid crystal layer is not particularly limited, but from the viewpoint of thinning, it is preferably 30 μm or less, and more preferably 15 μm or less.

[0046] Furthermore, when the cholesteric liquid crystal layer is stretched or molded, the reflection wavelength range of the cholesteric liquid crystal layer may shift, so it is preferable that the reflection wavelength range be selected in advance, taking into account this wavelength shift. For example, since the film may be stretched by stretching or molding, which may result in a smaller helical pitch of the cholesteric liquid crystal phase, it is preferable to set the helical pitch of the cholesteric liquid crystal phase to a larger value in advance. Furthermore, in anticipation of a short-wavelength shift in the reflection wavelength range due to stretching or molding, it is also preferable that the cholesteric liquid crystal layer have an infrared light-reflecting layer with a reflectance of 40% or more at a wavelength of 800 nm. Furthermore, if the stretching ratio during stretching, molding, etc. is not uniform in the plane, an appropriate reflection wavelength range may be selected for each location in the plane according to the wavelength shift due to stretching. That is, before an optical film including a cholesteric liquid crystal layer is molded onto a curved surface, the cholesteric liquid crystal layer may have regions with different reflection wavelength ranges in the plane. Furthermore, in anticipation of different stretching ratios in each location in the plane, it is also preferable to set the reflection wavelength range in advance to be wider than the required wavelength range.

[0047] (Method for Producing a Cholesteric Liquid Crystal Layer) A cholesteric liquid crystal layer can be formed by coating a liquid crystal composition, which is prepared by dissolving a liquid crystal compound, a chiral agent, a polymerization initiator, and optionally a surfactant, in a solvent, on a support or on an underlayer formed on a support, drying the coating to obtain a coating film, orienting the liquid crystal compound in the coating film, and irradiating the coating film with actinic rays to harden the liquid crystal composition. This allows the formation of a cholesteric liquid crystal layer having a cholesteric liquid crystal structure with fixed cholesteric regularity.

[0048] [Coating Method] Examples of the method for coating the liquid crystal composition include known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet printing.

[0049] [Method of Giving In-Plane Distribution to Helical Pitch] As a method of giving an in-plane distribution to the helical pitch of a cholesteric liquid crystal layer, for example, there is a method of using a chiral agent whose HTP changes upon photoisomerization.

[0050] Details will be explained. A cholesteric liquid crystal layer is aligned by applying (and optionally subsequently heating) a liquid crystal composition containing a chiral agent whose HTP changes upon photoisomerization. Irradiating the layer with light corresponding to the photoisomerization changes the HTP of the chiral agent, thereby changing the helical pitch of the cholesteric liquid crystal layer and thereby changing the reflection wavelength. By utilizing this property, the aligned cholesteric liquid crystal layer is subjected to patterned light irradiation using an exposure mask or the like to cause photoisomerization, thereby obtaining a pattern in which the reflection wavelength is changed only in the light-irradiated region. After obtaining the pattern, the entire cholesteric liquid crystal layer is exposed to light to harden the liquid crystal composition, polymerizing the liquid crystal composition, ultimately obtaining a cholesteric liquid crystal layer with an in-plane distribution of helical pitch (patterned cholesteric liquid crystal layer). After hardening, the patterned cholesteric liquid crystal layer no longer undergoes photoisomerization and has stable properties.

[0051] To effectively form this pattern, it is preferable to be able to separate the light irradiation for photoisomerization from the light irradiation for curing, in other words, to prevent the progress of either the photoisomerization or the curing as much as possible while the other is progressing. Measures for separating the two include, for example, separation based on oxygen concentration and separation based on exposure wavelength.

[0052] First, regarding oxygen concentration, photoisomerization is less susceptible to the effect of oxygen concentration, but curing becomes less likely to occur as the oxygen concentration increases (although this depends on the initiator used). Therefore, photoisomerization is carried out under conditions of high oxygen concentration, for example, in air, and curing is carried out under conditions of low oxygen concentration, for example, in a nitrogen atmosphere with an oxygen concentration of 300 volume ppm or less, which makes it easier to distinguish between photoisomerization and curing.

[0053] Regarding the exposure wavelength, photoisomerization of the chiral agent occurs at the absorption wavelength of the chiral agent, and curing occurs at the absorption wavelength of the photopolymerization initiator. Therefore, if the chiral agent and the photopolymerization initiator are selected so that their absorption wavelengths differ, it becomes possible to distinguish between photoisomerization and curing depending on the exposure wavelength.

[0054] If necessary, one or both of the photoisomerization and curing may be carried out under heating, preferably at a temperature of 25 to 140°C, more preferably at 30 to 100°C.

[0055] As an alternative to the method using a chiral agent whose HTP changes upon photoisomerization, there is also a method in which the material is first cured in a pattern and then the uncured regions are isomerized. That is, the aligned cholesteric liquid crystal phase is first irradiated with light for curing in a pattern using an exposure mask or the like. Then, by irradiating the entire surface with light for photoisomerization, a pitch change due to photoisomerization occurs only in the uncured regions (since the previously cured regions can no longer undergo pitch change due to photoisomerization), resulting in a change in the reflection wavelength. In this case, after obtaining the pattern, the entire cholesteric liquid crystal layer is exposed to light for curing the liquid crystal composition, and the liquid crystal composition is polymerized, thereby obtaining the final patterned cholesteric liquid crystal layer.

[0056] [Direct Coating of Each Layer] It is preferable that adjacent layers are formed directly between each light-reflecting layer of the cholesteric liquid crystal layer without an adhesive layer. When forming a layer, the adhesive layer can be eliminated by directly coating the adjacent layer that has already been formed. Furthermore, in order to reduce the refractive index difference in all in-plane directions, it is preferable to arrange the liquid crystal compounds so that the alignment direction (slow axis direction) of the liquid crystal compounds changes continuously at the interface. For example, when forming a light-reflecting layer formed using a rod-shaped liquid crystal compound on a light-reflecting layer formed using a discotic liquid crystal compound, a coating liquid containing the rod-shaped liquid crystal compound can be directly coated, and the alignment force of the discotic liquid crystal compound in the light-reflecting layer containing the discotic liquid crystal compound can be used to align the slow axis direction continuously at the interface.

[0057] [Method of Adhesion of Each Layer] The cholesteric liquid crystal layer is preferably a laminate consisting of multiple light-reflecting layers. The layers can be bonded by any adhesive method, such as a pressure-sensitive adhesive or adhesive. Any commercially available pressure-sensitive adhesive can be used. In particular, from the viewpoint of thinning and reducing the surface roughness Ra of the laminated optical body, the thickness of the adhesive layer is preferably 25 μm or less, more preferably 15 μm or less, and most preferably 6 μm or less. Furthermore, it is preferable that the adhesive is less likely to outgas. In particular, when stretching or molding is performed, a vacuum process or a heating process may be used, and it is preferable that the adhesive does not outgas even under these conditions. Any commercially available adhesive can be used as the adhesive, such as an epoxy resin adhesive or an acrylic resin adhesive. From the viewpoint of thinning and reducing the surface roughness Ra of the cholesteric liquid crystal layer, the thickness of the adhesive layer is preferably 25 μm or less, more preferably 5 μm or less, and most preferably 1 μm or less. Furthermore, from the viewpoint of thinning the adhesive layer and applying the adhesive to the adherend with a uniform thickness, the viscosity of the adhesive is preferably 300 cP or less, more preferably 100 cP or less. Furthermore, if the adherend has surface irregularities, the adhesive and adhesive can be selected with appropriate viscoelasticity or thickness so as to embed the surface irregularities of the layer to be adhered, in order to reduce the surface roughness Ra of the cholesteric liquid crystal layer. From the viewpoint of embedding the surface irregularities, the adhesive and adhesive preferably have a viscosity of 50 cP or more. Furthermore, the thickness is preferably greater than the height of the surface irregularities. Examples of methods for adjusting the viscosity of the adhesive include using a solvent-containing adhesive. In this case, the viscosity of the adhesive can be adjusted by adjusting the ratio of the solvent. Furthermore, the thickness of the adhesive can be further reduced by drying the solvent after applying the adhesive to the adherend.

[0058] In order to reduce unnecessary reflection and suppress a decrease in the degree of polarization of transmitted light in a cholesteric liquid crystal layer, it is preferable that the adhesive or pressure-sensitive adhesive used to bond each layer has a small refractive index difference with adjacent layers. The liquid crystal molecules constituting the liquid crystal layer have refractive index anisotropy (birefringence), and the refractive index in the no-axis (normal axis) direction and the refractive index in the ne-axis (extraordinary axis) direction of the liquid crystal molecules are different. Therefore, when the average refractive index (nave) of the liquid crystal layer is calculated by adding the refractive index in the no-axis direction and the refractive index in the ne-axis direction and dividing the sum by 2, the difference in refractive index between adjacent adhesive or pressure-sensitive adhesive layers and nave is preferably 0.075 or less, more preferably 0.05 or less, and even more preferably 0.025 or less. The refractive index of the adhesive or pressure-sensitive adhesive can be adjusted by mixing, for example, titanium oxide fine particles or zirconia fine particles. Furthermore, the cholesteric liquid crystal layer, retardation layer, and linear polarizer have in-plane refractive index anisotropy, and the refractive index difference between adjacent layers is preferably 0.10 or less in all directions in the plane. Therefore, the pressure-sensitive adhesive and adhesive may have in-plane refractive index anisotropy. Furthermore, a refractive index adjustment layer having a smaller difference between the refractive index in the fast axis direction and the refractive index in the slow axis direction than the cholesteric liquid crystal layer may be provided between the cholesteric liquid crystal layer and the pressure-sensitive adhesive, or between the cholesteric liquid crystal layer and the adhesive. In this case, the refractive index adjustment layer preferably contains cholesteric liquid crystal. By providing the refractive index adjustment layer, interfacial reflection can be further suppressed, and the occurrence of ghosts can be further suppressed. Furthermore, it is more preferable that the average refractive index of the refractive index adjustment layer be smaller than the average refractive index of the cholesteric liquid crystal layer. Furthermore, the central wavelength of the reflected light from the refractive index adjustment layer may be smaller than 430 nm or larger than 670 nm, and is more preferably smaller than 430 nm.

[0059] It is also preferable that the adhesive layer between each layer has a thickness of 100 nm or less. When the adhesive layer is 100 nm or less, the refractive index difference is less noticeable for visible light, thereby suppressing unnecessary reflection. The adhesive layer thickness is more preferably 50 nm or less, and even more preferably 30 nm or less. Examples of methods for forming an adhesive layer having a thickness of 100 nm or less include vapor deposition of a ceramic adhesive such as silicon oxide (SiOx layer) onto the bonding surface. The bonding surface of the bonding member can be subjected to surface modification treatments such as plasma treatment, corona treatment, and saponification treatment before bonding, or a primer layer can be applied. Furthermore, when there are multiple bonding surfaces, the type and thickness of the adhesive layer can be adjusted for each bonding surface. Specifically, an adhesive layer having a thickness of 100 nm or less can be formed, for example, by the following steps (1) to (3): (1) The layers to be laminated are bonded to a temporary support made of a glass substrate. (2) A SiOx layer having a thickness of 100 nm or less is formed on both the surface of the layer to be laminated and the surface of the layer to be laminated by vapor deposition or the like. Vapor deposition can be performed using, for example, a vapor deposition device manufactured by ULVAC (model number ULEYES) using SiOx powder as a vapor deposition source. It is also preferable to subject the surface of the formed SiOx layer to plasma treatment. (3) After the formed SiOx layers are bonded together, the temporary support is peeled off. The bonding is preferably performed at a temperature of, for example, 120°C.

[0060] The coating, adhesion, or lamination of each layer may be performed by roll-to-roll or sheet-to-sheet. The roll-to-roll method is preferred from the viewpoint of improving productivity and reducing axial misalignment of each layer. On the other hand, the sheet-to-sheet method is preferred because it is suitable for small-lot, high-mix production and because it allows the selection of a special adhesion method such as the above-mentioned adhesive layer thickness of 100 nm or less. Furthermore, methods for applying the adhesive to the adherend include, for example, known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet printing.

[0061] Furthermore, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the cholesteric liquid crystal layer is preferably transparent to near-infrared light.

[0062] <Linear Polarizer> A linear polarizer is an absorption-type polarizer that absorbs linearly polarized light in the absorption axis direction of incident light and transmits linearly polarized light in the transmission axis direction. A typical linear polarizer can be used as the linear polarizer. For example, a polarizer obtained by dyeing a dichroic material onto polyvinyl alcohol or other polymer resin and stretching it to orient it, or a polarizer obtained by aligning a dichroic material by utilizing the orientation of a liquid crystal compound, may be used. From the viewpoints of availability and increasing the degree of polarization, a polarizer obtained by dyeing polyvinyl alcohol with iodine and stretching it is preferred. The thickness of the linear polarizer is preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less. A thin linear polarizer can prevent cracking and breakage of the film when stretching or molding a laminated optical body. The single-plate transmittance of the linear polarizer is preferably 40% or more, more preferably 42% or more. The degree of polarization is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more. In this specification, the single-plate transmittance and degree of polarization of the linear polarizer are measured using an automatic polarizing film measuring device: VAP-7070 (manufactured by JASCO Corporation). The direction of the transmission axis of the linear polarizer preferably coincides with the direction of the polarization axis of light converted into linearly polarized light by the retardation layer. For example, when an optical film has one retardation layer and a linear polarizer, and the retardation layer is a layer having a retardation of ¼ wavelength, the angle between the transmission axis of the linear polarizer and the slow axis of the retardation layer is preferably approximately 45°.

[0063] The linear polarizer is also preferably a light-absorbing anisotropic layer containing a liquid crystal compound and a dichroic material. Linear polarizers containing a liquid crystal compound and a dichroic material are preferred because they can be made thin and are less likely to crack or break even when stretched or molded. The thickness of the light-absorbing anisotropic layer is not particularly limited, but from the viewpoint of thinning, it is preferably 0.1 to 8 μm, more preferably 0.3 to 5 μm. Linear polarizers containing a liquid crystal compound and a dichroic material can be produced, for example, with reference to JP 2020-023153 A. From the viewpoint of improving the polarization degree of the linear polarizer, the light-absorbing anisotropic layer preferably has an orientation degree of the dichroic material of 0.95 or more, more preferably 0.97 or more.

[0064] Furthermore, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the linear polarizer is preferably transparent to near-infrared light.

[0065] <Other Functional Layers> The laminated optical body may have other functional layers in addition to the above-described cholesteric liquid crystal layer, retardation layer, and linear polarizer.

[0066] Furthermore, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, it is preferable that the other functional layers be transparent to near-infrared light.

[0067] <Positive C Plate> The laminated optical body preferably further includes a positive C plate. Here, the positive C plate is a retardation layer having an Re of substantially zero and an Rth of a negative value. The positive C plate can be obtained, for example, by vertically aligning a rod-shaped liquid crystal compound. For details of the manufacturing method of the positive C plate, see, for example, JP 2017-187732 A, JP 2016-053709 A, and JP 2015-200861 A. The positive C plate functions as an optical compensation layer to increase the degree of polarization of transmitted light with respect to obliquely incident light. The positive C plate can be installed at any position in the laminated optical body, and multiple positive C plates may be installed.

[0068] The positive C plate may be disposed adjacent to or within the cholesteric liquid crystal layer. For example, when a light-reflecting layer formed by immobilizing a cholesteric liquid crystal phase containing a rod-shaped liquid crystal compound is used as the cholesteric liquid crystal layer, the light-reflecting layer has a positive Rth. In this case, when light is incident obliquely onto the cholesteric liquid crystal layer, the Rth may change the polarization state of the reflected light and transmitted light, potentially reducing the degree of polarization of the transmitted light. Having a positive C plate within or near the cholesteric liquid crystal layer is preferable because it can suppress changes in the polarization state of obliquely incident light and reduce the degree of polarization of the transmitted light. The positive C plate is preferably disposed on the side of the blue light-reflecting layer opposite the green light-reflecting layer, but may be disposed elsewhere. In this case, the Re of the positive C plate is preferably approximately 10 nm or less, and the Rth is preferably -600 to -100 nm, more preferably -400 to -200 nm.

[0069] The positive C plate may be disposed adjacent to the retardation layer or inside the retardation layer (between two retardation layers). For example, when a layer formed by immobilizing a rod-shaped liquid crystal compound is used as the retardation layer, the retardation layer has a positive Rth. In this case, when light is incident on the retardation layer from an oblique direction, the polarization state of the transmitted light may change due to the action of Rth, resulting in a decrease in the degree of polarization of the transmitted light. Having a positive C plate inside or near the retardation layer is preferable because it can suppress changes in the polarization state of obliquely incident light and suppress a decrease in the degree of polarization of the transmitted light. The positive C plate is preferably disposed on the side of the retardation layer opposite the linear polarizer, but may be disposed elsewhere. In this case, the Re of the positive C plate is preferably approximately 10 nm or less, and the Rth is preferably -90 to -40 nm.

[0070] <Anti-Reflection Layer> It is also preferable that the laminated optical body (optical film) has an anti-reflection layer on its surface. Laminated optical bodies have the function of reflecting specific circularly polarized light and transmitting circularly polarized light with the opposite rotation. However, reflection on the surface of the laminated optical body generally includes reflection of unintended polarized light, thereby reducing the polarization degree of the transmitted light. Therefore, it is preferable that the laminated optical body has an anti-reflection layer on its surface. The anti-reflection layer may be installed on only one surface of the laminated optical body or on both surfaces. The type of anti-reflection layer is not particularly limited, but from the viewpoint of further reducing the reflectance, moth-eye films and AR films are preferred. Furthermore, when the laminated optical body is stretched or molded, moth-eye films are preferred because they can maintain high anti-reflection performance even if the film thickness changes due to stretching. Furthermore, when the anti-reflection layer includes a support and stretching or molding is performed, the support preferably has a Tg peak temperature of 170°C or less, more preferably 130°C or less, from the viewpoint of facilitating stretching and / or molding. Specifically, for example, PMMA film is preferred.

[0071] <Second Retardation Layer> It is also preferable that the laminated optical body further has a second retardation layer in addition to the above-mentioned retardation layer. For example, the laminated optical body may include a cholesteric liquid crystal layer, a retardation layer, a linear polarizer, and a second retardation layer in this order. The second retardation layer preferably converts linearly polarized light into circularly polarized light, and for example, a retardation layer having a quarter wavelength Re is preferred. The reason for this will be explained below. Light that enters the laminated optical body from the cholesteric liquid crystal layer side and passes through the cholesteric liquid crystal layer, the retardation layer, and the linear polarizer becomes linearly polarized light, and a portion of it is reflected by the outermost surface on the linear polarizer side and then exits again from the surface on the cholesteric liquid crystal layer side. Such light is unnecessary reflected light and can be a factor in reducing the degree of polarization of the reflected light, so it is preferable to reduce it. Therefore, there is a method of laminating an antireflection layer to suppress reflection on the outermost surface on the linear polarizer side. However, when the laminated optical body is used by being attached to a medium such as glass or plastic, even if an antireflection layer is provided on the attachment surface of the laminated optical body, reflection on the surface of the medium cannot be suppressed, and therefore, antireflection effect cannot be obtained. On the other hand, when a second retardation layer that converts linearly polarized light into circularly polarized light is provided, the light that reaches the outermost surface on the linear polarizer side becomes circularly polarized light and is converted into reverse circularly polarized light when reflected on the outermost surface of the medium. After that, when the light passes through the second retardation layer again and reaches the linear polarizer, the light becomes linearly polarized light in the absorption axis direction of the linear polarizer and is absorbed by the linear polarizer. Therefore, unnecessary reflection can be prevented. From the viewpoint of more effectively suppressing unnecessary reflection, it is preferable that the second retardation layer has substantially reverse dispersion.

[0072] <Support> The laminated optical body may further have a support. The support can be installed in any location. For example, when the cholesteric liquid crystal layer, the retardation layer, or the linear polarizer is a film to be transferred from a temporary support, the support can be used as the transfer destination. The type of support is not particularly limited, but it is preferably transparent. For example, films such as cellulose acylate, polycarbonate, polysulfone, polyethersulfone, polyacrylate and polymethacrylate, cyclic polyolefin, polyolefin, polyamide, polystyrene, and polyester can be used. Among these, cellulose acylate film, cyclic polyolefin film, polyacrylate film, and polymethacrylate film are preferred. Commercially available cellulose acetate films (for example, "TD80U" and "Z-TAC" manufactured by Fujifilm Corporation) can also be used. Furthermore, it is preferable that the support has a small retardation from the viewpoint of suppressing adverse effects on the polarization degree of transmitted light and from the viewpoint of facilitating optical inspection of the laminated optical body. Specifically, the magnitude of Re is preferably 10 nm or less, and the absolute value of the magnitude of Rth is preferably 50 nm or less.

[0073] When the laminated optical body is to be stretched or molded, the support preferably has a tan δ peak temperature of 170° C. or less. From the viewpoint of enabling molding at low temperatures, the tan δ peak temperature is preferably 150° C. or less, and more preferably 130° C. or less.

[0074] Here, the method for measuring tan δ will be described. Using a dynamic viscoelasticity measuring device (DVA-200, manufactured by IT Measurement Control Co., Ltd.), E" (loss modulus) and E' (storage modulus) are measured under the following conditions for a film sample that has been conditioned in advance for at least two hours in an atmosphere at a temperature of 25°C and a humidity of 60% Rh, and tan δ (= E" / E') is the calculated value. Device: DVA-200, manufactured by IT Measurement Control Co., Ltd. Sample: 5 mm, length 50 mm (gap 20 mm) Measurement conditions: tension mode Measurement temperature: -150°C to 220°C Heating conditions: 5°C / min Frequency: 1 Hz Note that, in general, resin substrates that have been subjected to a stretching treatment are often used in optical applications, and the peak temperature of tan δ often becomes high due to the stretching treatment. For example, the peak temperature of tan δ for a TAC (triacetyl cellulose) substrate (TG40, manufactured by Fujifilm Corporation) is 180°C or higher.

[0075] As a support having a tan δ peak temperature of 170°C or less, various resin substrates can be used without any particular limitation. Examples include polyolefins such as polyethylene, polypropylene, and norbornene-based polymers; cyclic olefin-based resins; polyvinyl alcohol; polyethylene terephthalate; acrylic resins such as polymethacrylic acid esters and polyacrylic acid esters; polyethylene naphthalate; polycarbonate; polysulfone; polyethersulfone; polyether ketone; polyphenylene sulfide, and polyphenylene oxide. Among these, in terms of easy commercial availability and excellent transparency, cyclic olefin-based resins, polyethylene terephthalate, and acrylic resins are preferred, and cyclic olefin-based resins and polymethacrylic acid esters are particularly preferred.

[0076] Examples of commercially available resin substrates include Technolloy S001G, Technolloy S014G, Technolloy S000, Technolloy C001, and Technolloy C000 (Sumika Acrylic Sales Co., Ltd.), Lumirror U Type, Lumirror FX10, and Lumirror SF20 (Toray Industries, Inc.), HK-53A (Higashiyama Films Co., Ltd.), Teflex FT3 (Teijin DuPont Films Co., Ltd.), S-Cina and SCA40 (Sekisui Chemical Co., Ltd.), Zeonor Film (Optes Co., Ltd.), and Arton Film (JSR Corporation).

[0077] The thickness of the support is not particularly limited, but is preferably from 5 to 300 μm, more preferably from 5 to 100 μm, and even more preferably from 5 to 30 μm.

[0078] <Method of Adhesion of Each Layer> The laminated optical body is a laminate composed of multiple layers. Each layer can be bonded by any adhesive method, for example, a pressure-sensitive adhesive and / or adhesive. Any commercially available pressure-sensitive adhesive can be used as the pressure-sensitive adhesive. From the viewpoint of thinning and reducing the surface roughness Ra of the laminated optical body, the thickness of the adhesive layer is preferably 25 μm or less, more preferably 15 μm or less, and even more preferably 6 μm or less. It is also preferable that the pressure-sensitive adhesive is one that is less likely to outgas. In particular, when performing stretching and molding, etc., vacuum processes and heating processes may be used, and it is preferable that the pressure-sensitive adhesive does not outgas even under these conditions. Any commercially available adhesive can be used as the adhesive, for example, an epoxy resin-based adhesive or an acrylic resin-based adhesive can be used. From the viewpoint of thinning and reducing the surface roughness Ra of the laminated optical body, the thickness of the adhesive layer is preferably 25 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. In addition, from the viewpoint of thinning the adhesive layer and applying the adhesive to the adherend with a uniform thickness, the viscosity of the adhesive is preferably 300 cP or less, more preferably 100 cP or less, and even more preferably 10 cP or less. Furthermore, when the adherend has surface irregularities, the adhesive and adhesive can be selected with appropriate viscoelasticity or thickness so as to embed the surface irregularities of the layer to be adhered, in order to reduce the surface roughness Ra of the laminated optical body. From the viewpoint of embedding the surface irregularities, the adhesive and adhesive preferably have a viscosity of 50 cP or more. Furthermore, the thickness is preferably greater than the height of the surface irregularities. Examples of methods for adjusting the viscosity of the adhesive include using an adhesive containing a solvent. In this case, the viscosity of the adhesive can be adjusted by adjusting the ratio of the solvent. Furthermore, the thickness of the adhesive can be further reduced by applying the adhesive to the adherend and then drying the solvent.

[0079] In a laminated optical body, from the viewpoint of reducing unnecessary reflection and suppressing a decrease in the degree of polarization of transmitted light and reflected light, it is preferable that the pressure-sensitive adhesive or adhesive used to bond each layer has a small refractive index difference with adjacent layers. Specifically, the refractive index difference between adjacent layers is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.01 or less. The refractive index of the pressure-sensitive adhesive or adhesive can be adjusted, for example, by mixing titanium oxide fine particles and zirconia fine particles. Furthermore, the cholesteric liquid crystal layer, retardation layer, and linear polarizer have in-plane refractive index anisotropy, but it is preferable that the refractive index difference with adjacent layers is 0.05 or less in all directions in the plane. Therefore, the pressure-sensitive adhesive and / or adhesive may have in-plane refractive index anisotropy.

[0080] It is also preferable that the adhesive layer between each layer has a thickness of 100 nm or less. When the adhesive layer is 100 nm or less, the refractive index difference is less noticeable for visible light, thereby suppressing unnecessary reflection. The adhesive layer thickness is more preferably 50 nm or less. An example of a method for forming an adhesive layer having a thickness of 100 nm or less is a method of depositing a ceramic adhesive such as silicon oxide (SiOx layer) on the bonding surface. The bonding surface of the bonding member can be subjected to a surface modification treatment such as plasma treatment, corona treatment, or saponification treatment before bonding, and a primer layer can be applied. Furthermore, when there are multiple bonding surfaces, the type or thickness of the adhesive layer can be adjusted for each bonding surface. Specifically, an adhesive layer having a thickness of 100 nm or less can be formed, for example, by the following steps (1) to (3): (1) The layers to be laminated are bonded to a temporary support made of a glass substrate. (2) A SiOx layer having a thickness of 100 nm or less is formed on both the surface of the layer to be laminated and the surface of the layer to be laminated by vapor deposition or the like. Vapor deposition can be performed using, for example, a vapor deposition device manufactured by ULVAC (model number ULEYES) using SiOx powder as the vapor deposition source. It is also preferable to subject the surface of the formed SiOx layer to plasma treatment. (3) After the formed SiOx layers are bonded together, the temporary support is peeled off. The bonding is preferably performed at a temperature of, for example, 120°C.

[0081] The coating, adhesion, or lamination of each layer may be performed by roll-to-roll or sheet-to-sheet. The roll-to-roll method is preferred from the viewpoint of improving productivity and reducing axial misalignment of each layer. On the other hand, the sheet-to-sheet method is preferred because it is suitable for small-lot, high-mix production and because it allows the selection of a special adhesion method such as the above-mentioned adhesive layer thickness of 100 nm or less. Furthermore, methods for applying the adhesive to the adherend include, for example, known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet printing.

[0082] <Direct Coating of Each Layer> It is also preferable that there is no adhesive layer between each layer of the laminated optical body. When forming a layer, the adhesive layer can be eliminated by directly coating the layer on an adjacent layer that has already been formed. Furthermore, when one or both of the adjacent layers contain a liquid crystal compound, it is preferable that the alignment direction of the liquid crystal compound continuously changes at the interface in order to reduce the refractive index difference in all in-plane directions. For example, a retardation layer containing a liquid crystal compound can be directly coated on a linear polarizer containing a liquid crystal compound and a dichroic material, and the liquid crystal compound of the retardation layer can be continuously aligned at the interface due to the alignment regulating force of the liquid crystal compound of the linear polarizer.

[0083] <Lamination Order of Each Layer> The laminated optical body is composed of many layers, but the order of the lamination process is not particularly limited and can be selected arbitrarily. For example, when transferring a functional layer from a film consisting of a temporary support and a functional layer, wrinkles, cracks, etc. during transfer can be prevented by adjusting the lamination order so that the thickness of the transfer film is 10 μm or more. In addition, from the viewpoint of reducing the surface roughness Ra of the laminated optical body, if another layer is laminated on a layer with large surface irregularities, the surface irregularities may be further amplified, so it is preferable to laminate the layers in order from the layer with the smallest surface roughness Ra. In addition, the lamination order can also be selected from the viewpoint of quality evaluation in the manufacturing process of the laminated optical body. For example, layers other than the cholesteric liquid crystal layer can be laminated and quality evaluation can be performed using a transmission optical system, and then the cholesteric liquid crystal layer can be laminated and quality evaluation can be performed using a reflection optical system. In addition, the lamination order can be selected from the viewpoint of improving the manufacturing yield of the laminated optical body and reducing costs.

[0084] As a suitable example of the use of the retardation film used in the present invention, the laminated optical body including the retardation film, and the composite lens including the laminated optical body, a virtual reality display device using the laminated optical body will be taken up, and the function of the laminated optical body will be described in detail.

[0085] FIG. 1 shows a virtual reality display device using a laminated optical body. As shown in FIG. 1, a light ray 1000 emitted from an image display panel 500 passes through a circular polarizer 400 to become circularly polarized light, and then passes through a half mirror 300. The light ray then passes through a lens 200, enters a laminated optical body 100, is reflected, passes through the lens 200 again, is reflected again by the half mirror 300, passes through the lens 200 again, and enters the laminated optical body 100. At this time, the circular polarization state of the light ray 1000 does not change when reflected by the laminated optical body 100, but when reflected by the half mirror, it changes to circular polarization in the opposite direction to the circular polarization when it entered the laminated optical body 100. Therefore, the light ray 1000 passes through the laminated optical body 100 and is visually recognized by the user. Furthermore, when the light ray 100 is reflected by the half mirror 300, the image is magnified due to the half mirror's concave mirror shape, allowing the user to view a magnified virtual image. The above-described mechanism is called a reciprocating optical system, a folding optical system, or the like. Meanwhile, FIG. 2 is a schematic diagram showing a case where a light ray 2000 is transmitted without being reflected when it first enters the laminated optical body 100, resulting in leakage light. As can be seen from the figure, in this case, the user will see an unmagnified image. This image is called a ghost, and it is necessary to reduce it. Since the laminated optical body 100 satisfies the requirements of the present invention, it can reduce leakage of transmitted light (i.e., ghost) when a light ray enters the laminated optical body 100 for the first time. Furthermore, since the laminated optical body 100 satisfies the requirements of the present invention, it can increase the transmittance when a light ray enters the laminated optical body 100 for the second time, improving the brightness of the virtual image and further suppressing coloring of the virtual image.

[0086] As shown in Figures 1 and 2, the laminated optical body 100 may be molded onto a curved surface such as a lens. This can suppress field curvature and improve pupil swimming. It also provides effects such as reduced aberration and a wider viewing angle. For example, a laminated optical body in which a reflective circular polarizer and a retardation layer having a quarter-wave retardation are laminated is less likely to suffer from a decrease in polarization degree due to stretching and / or molding because the cholesteric liquid crystal layer does not have an optical axis.

[0087] FIG. 3 shows the layer structure of one embodiment of the laminated optical body (100). Note that in FIG. 3, the non-planar shape of the laminated optical body, which is an optical film, is not shown, and for simplification, it is shown as a planar shape. A cholesteric liquid crystal layer (101), a positive C plate (102), a retardation layer (103), a linear polarizer (104), a retardation layer (105), and an anti-reflection film (106) are arranged in this order. Note that when the laminated optical body is stretched or molded, there is a concern that the slow axis of the retardation layer and / or the absorption axis of the linear polarizer may be distorted. However, as described above, the cholesteric liquid crystal layer maintains a high degree of polarization even after stretching and / or molding, and the amount of light leaking from the cholesteric liquid crystal layer is small, so the increase in leaked light is kept to a minimum. FIG. 4 shows an example of the layer structure of the cholesteric liquid crystal layer (101) used in the second embodiment of the present invention. A first light-reflecting layer (131), a second light-reflecting layer (132), a third light-reflecting layer (133), and a fourth light-reflecting layer (134) are arranged in this order. Note that in Figure 4, the non-planar shape of the cholesteric liquid crystal layer that may be included in the optical film is not shown, and for simplification, it is shown as a planar shape.

[0088] Another different layer structure of the laminated optical body (100B) is shown in Figure 5. In Figure 5, the non-planar shape of the laminated optical body, which is an optical film, is not shown, and for simplification, it is shown as a planar shape. In the laminated optical body (100B), a positive C plate (111), a retardation layer (112), a linear polarization type reflective polarizer (113), a linear polarizer (114), a retardation layer (115), and an anti-reflection film (116) are arranged in this order.

[0089] Furthermore, the laminated optical body preferably has a surface roughness Ra of 100 nm or less. A small Ra is preferable because it can improve the sharpness of images, for example, when the laminated optical body is used in a virtual reality display device, etc. The inventors have estimated that when light is reflected from the laminated optical body, if there are irregularities, the angle of the reflected light is distorted, leading to image distortion and blurring. The Ra of the laminated optical body is preferably 50 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. Furthermore, the laminated optical body is produced by stacking multiple layers. When another layer is stacked on an irregular layer, the irregularities may be amplified. Therefore, it is preferable that the Ra of all layers in the laminated optical body is small. Each layer of the laminated optical body preferably has an Ra of 50 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. Furthermore, from the viewpoint of improving the image sharpness of the reflected image, it is particularly preferable that the Ra of the cholesteric liquid crystal layer is small. The surface roughness Ra can be measured, for example, using a non-contact surface / layer cross-sectional shape measurement system, VertScan (manufactured by Ryoka Systems Co., Ltd.). Since VertScan is a surface shape measurement method that utilizes the phase of reflected light from a sample, when measuring a cholesteric liquid crystal layer consisting of a light-reflecting layer formed by fixing a cholesteric liquid crystal phase, reflected light from within the film may be superimposed, making it impossible to accurately measure the surface shape. In this case, a metal layer may be formed on the surface of the sample to increase the surface reflectance and further suppress reflection from within. The main method for forming a metal layer on the surface of a sample is sputtering. Examples of sputtering materials include Au, Al, and Pt.

[0090] It is preferable that the number of point defects per unit area of ​​a laminated optical body is small. Since a laminated optical body is produced by stacking a large number of layers, it is preferable that the number of point defects in each layer is also small in order to reduce the number of point defects in the entire laminated optical body. Specifically, the number of point defects in each layer is preferably 20 or less per square meter, more preferably 10 or less, and even more preferably 1 or less. For the entire laminated optical body, the number of point defects is preferably 100 or less per square meter, more preferably 50 or less, and even more preferably 5 or less. Point defects lead to a decrease in the degree of polarization of transmitted light and a decrease in image sharpness, so it is preferable that there are few point defects. Here, point defects include foreign matter, scratches, dirt, film thickness fluctuations, and poor alignment of liquid crystal compounds. Furthermore, it is preferable that the number of point defects described above is counted as the number of point defects with a size of preferably 100 μm or more, more preferably 30 μm or more, and most preferably 10 μm or more.

[0091] Furthermore, in order to minimize the influence on various sensors that use near-infrared light as a light source, such as those for eye tracking, facial expression recognition, and iris authentication, which are incorporated into optical systems such as virtual reality display devices and electronic viewfinders, the laminated optical body is preferably transparent to near-infrared light.

[0092] <Composite Lens> One embodiment of a compound lens includes a lens and an optical film produced by the method of the present invention. A half mirror may be formed on one side of the lens. Convex and concave lenses can be used as lenses. Convex lenses can be biconvex lenses, plano-convex lenses, and convex meniscus lenses. Concave lenses can be biconcave lenses, plano-concave lenses, and concave meniscus lenses. Lenses used in virtual reality display devices are preferably convex meniscus lenses or concave meniscus lenses to expand the viewing angle, and more preferably concave meniscus lenses to minimize chromatic aberration. Lens materials that are transparent to visible light, such as glass, crystal, and plastic, can be used. Because birefringence in lenses can cause rainbow unevenness or light leakage, smaller birefringence is preferable, and zero-birefringence materials are more preferable.

[0093] One embodiment of a virtual reality display device includes an image display device that emits at least polarized light and a compound lens that includes the optical film produced by the method of the present invention. The virtual reality display device may also include additional optical components such as a half mirror and a diopter adjustment lens.

[0094] <Image Display Device> The image display device used in the second embodiment of the present invention can be a known image display device. Examples include organic electroluminescence display devices, LED (Light Emitting Diode) display devices, and display devices in which self-luminous fine light emitters are arranged on a transparent substrate, such as micro-LED display devices. These self-luminous display devices typically have a (circular) polarizing plate attached to the display surface to prevent reflection on the display surface. Therefore, the emitted light is polarized. Another example of an image display device is a liquid crystal display device. Liquid crystal display devices also have a polarizing plate on their surface, so the emitted light is polarized. In the following description, an organic electroluminescence display device will also be referred to as an OLED. OLED is an abbreviation for "organic light emitting diode."

[0095] <Molding method> The method for manufacturing the optical film having the above-mentioned non-planar shape is not particularly limited. In particular, the method for molding the optical film of the present invention preferably includes a step of heating the optical film having a planar shape, a step of pressing the heated optical film against a mold to deform it according to the shape of the mold, and a step of cutting the optical film. Each step will be described in detail below.

[0096] (Step of heating an optical film having a planar shape) The optical film used in this step has a planar shape including at least two or more optically anisotropic layers. As will be described later, a predetermined shape is transferred to this optical film having a planar shape, and an optical film having the above-mentioned non-planar shape is obtained. The optical film having a planar shape includes various components (e.g., a retardation film, etc.) that can be included in the optical film having the above-mentioned non-planar shape. However, the various components included in the optical film having a planar shape have a planar shape.

[0097] Methods for heating an optical film having a planar shape include heating by contacting it with a heated solid, heating by contacting it with a heated liquid, heating by contacting it with a heated gas, heating by irradiating it with infrared rays, and heating by irradiating it with microwaves. Of these, heating by irradiating it with infrared rays is preferred, as it allows heating to be performed remotely immediately before molding.

[0098] The wavelength of the infrared rays used for heating is preferably 1.0 μm to 30.0 μm, more preferably 1.5 μm to 5 μm. Examples of IR (infrared) light sources that can be used include near-infrared lamp heaters with a tungsten filament sealed in a quartz tube and wavelength-controlled heaters with multiple quartz tubes and a mechanism for cooling a portion of the space between the quartz tubes with air. Furthermore, by creating a distribution of infrared irradiation dose on the optical film, the physical properties during molding can be controlled according to the purpose. Methods for creating an intensity distribution include varying the density of IR light sources and placing a filter with a patterned infrared transmittance between the IR light source and the optical film. Examples of filters with a patterned transmittance include those made by vapor-depositing metal on glass, those made by converting the reflection band of a cholesteric liquid crystal layer to infrared, those made by converting the reflection band to infrared using a dielectric multilayer film, and those made by applying infrared-absorbing ink to glass. The temperature of the optical film is controlled by the intensity of infrared radiation, and by the infrared radiation exposure time and / or illuminance of infrared radiation. The temperature of the optical film can be monitored using a non-contact radiation thermometer and a thermocouple, etc., and it is possible to mold the optical film at a target temperature.

[0099] (Step of Pressing the Optical Film Against the Mold and Deforming it to Fit the Shape of the Mold) The heated optical film can be pressed against the mold and deformed to fit the shape of the mold by reducing the pressure and / or increasing the pressure in the molding space. Alternatively, a mold pressing method can be used.

[0100] One form of molding apparatus used in this process consists of box 1 with an opening at the top and box 2 with an opening at the bottom. To form the molding space, the openings of box 1 and box 2 are aligned directly or via a jig to form a sealed molding space. A mold (also called an adherend) with the shape to be molded and the film to be molded are placed in the molding space. The film to be molded acts as a partition, dividing the molding space consisting of box 1 and box 2 into two spaces. The mold is placed on the box 1 side, below the film to be molded. Furthermore, the vacuum molding apparatus has multiple heating elements dispersedly arranged to heat the film to be molded. The heating elements may be placed inside the molding space, or they may be placed outside the molding space and heat the film to be molded through a transparent window.

[0101] (Step of Cutting Optical Film) The molded optical film can be cut into any desired shape using a cutter, scissors, a cutting plotter, a laser cutter, or the like.

[0102] <Concept of molding method that does not generate retardation distribution> In order to mold an optical film having a planar shape to obtain an optical film having the above-mentioned non-planar shape and an in-plane variation of effective retardation of less than 5%, it is preferable that an in-plane distribution of effective retardation does not occur during molding. Hereinafter, the concept of the molding method that does not generate an effective retardation distribution will be described in detail, taking a retardation film included in the optical film as an example.

[0103] As described above, it is preferable that no in-plane distribution of the effective retardation occurs when a retardation film is molded onto a curved surface. This makes it possible to suppress the occurrence of ghosts even when a retardation film molded onto a curved surface is used for a pancake lens in a virtual reality display device. The reason why an in-plane distribution occurs in the effective retardation of an optical film is that the film thickness d after molding varies depending on the location, and in the case of a layered retardation film, the relative relationship between the slow axes of each optically anisotropic layer changes with deformation. Note that the methods for calculating the diameter stretching ratio and the circumferential stretching ratio will be described in detail later.

[0104] In the method for forming the optical film of the present invention, an optical film including two or more optically anisotropic layers is formed so that the ratio of the stretching ratio in the diameter direction to the stretching ratio in the circumferential direction is in the range of 0.95 to 1.05. By doing so, the relative relationship between the slow axes of the first and second optical anisotropies can be maintained, and the effective in-plane retardation value can be kept within a certain range even after forming. The ratio of the stretching ratio in the diameter direction to the stretching ratio in the circumferential direction is more preferably in the range of 0.98 to 1.02.

[0105] <Method of Installing the Mold> The method of installing the mold in the molding apparatus is not particularly limited. For example, a movable stage with a horizontal top plate can be installed in the box 1 below the above-mentioned molding apparatus, and the mold can be installed on the stage. In this case, the interior of the molding apparatus is evacuated, and then the movable stage is raised to press the mold against the film to be molded. Furthermore, one or more molds may be installed on the stage. From the viewpoint of improving productivity, it is also possible to use a film to be molded having an area larger than the area of ​​the mold, install multiple molds, and simultaneously produce multiple molded bodies.

[0106] <Jig for Gripping the Mold> It is also preferable to grip the mold using a jig having a recess into which the mold can be fitted to prevent the mold from moving on the stage. This allows the mold to be fixed so that it does not move on the stage. It is also preferable that the jig for gripping the mold covers the surfaces of the mold other than the molding surface (the surface to which the molded film is attached). If the molded film attempts to cover the mold's edge surface in addition to the molding surface, the molded film will be significantly stretched, which may result in significant non-uniformity in the film's thickness and optical properties. Therefore, it is preferable to use a jig that covers the surfaces of the mold other than the molding surface to prevent the molded film from contacting the surfaces other than the molding surface. It is also preferable that the jig has a horizontal surface that is approximately the same height as the molding surface of the mold in the area where the mold is not present. This can prevent the molded film from being stretched in areas other than the molding surface of the mold, thereby improving the uniformity of the film's thickness and optical properties. Furthermore, when forming the film to be formed into the mold, it is preferable to raise the movable stage on which the jig and mold are placed so that the position of the forming surface of the mold is approximately equal to the position of the film to be formed. This prevents the film to be formed from contacting the edge of the jig and being significantly stretched. The jig may be integrated with the stage.

[0107] <Method of bonding optical film to adherend> The method of bonding the optical film to the adherend is not particularly limited. For example, the optical film may be formed into a curved shape by any of the methods described above, and then adhered to an adherend such as a lens using an adhesive or the like. From the viewpoint of simplifying the process, it is preferable to previously bond a pressure-sensitive adhesive sheet to the surface of the optical film that will come into contact with the mold, and then bond the optical film to the curved surface of the mold at the same time as forming the optical film into a curved shape.

[0108] <Method for Evaluating Stretch Ratio> In order to evaluate the stretch ratio at each location of an optical film molded into a curved surface shape by the above-mentioned molding method, for example, a pattern such as that shown in Figure 6 is drawn on the film before molding. One example of this pattern is a pattern of equally spaced circles drawn at intervals of 1 / 4 of the radius of the inscribed circle (the circle with the largest radius that can be drawn) drawn on the film before molding (for example, in Figure 6, the radius of the inscribed circle shown by the solid line is 20 mm, and circles shown by the dashed line at 5 mm radius intervals are drawn), and equally spaced straight lines (straight dashed lines in Figure 6) drawn in the azimuthal direction at 45° intervals. The center of the circle corresponds to the center of gravity of the film. Furthermore, all of the above straight lines pass through the center of the circle. The coordinates of the intersections of this pattern are measured before and after molding, and the rate of change in the distance between adjacent intersections on each line is calculated, thereby evaluating the stretch ratio in the diametric direction. More specifically, if the distance between two points located in the diametric direction before molding is L0 and the distance between the two points after molding is L1, the stretch ratio can be obtained by calculating L1 / L0. Following the above procedure, 32 L1 / L0 values ​​are calculated and used as the diametric stretch ratio for each point. The circumferential stretch ratio can also be evaluated by using the coordinates of each intersection point relative to the center of the circle. More specifically, if the distance from the center before molding is r0 and the distance between the center and the intersection point when projected onto a plane parallel to the tangent plane of the center after molding is r1, the circumferential length of the circle drawn at that distance changes from 2πr0 to 2πr1, and the circumferential stretch ratio can be calculated as r1 / r0. r0 and r1 can be calculated from the x, y, and z coordinates of each point (center is the origin 0,0,0) using r0 = sqrt(x02 + y02) and r1 = sqrt(x12 + y12). According to the above procedure, r0 is appropriately changed, and r1 / r0 is calculated at each of the 32 points where the diameter-direction stretching ratios were calculated, and this is taken as the circumferential stretching ratio at each point. The product of the diameter-direction stretching ratio at each of the 32 points calculated above and the circumferential stretching ratio (direction perpendicular to the diameter direction) is calculated, and the maximum, minimum, and average values ​​are determined to calculate the in-plane variation (%) described above.

[0109] [Example of a molding method that does not generate a retardation distribution] Another example of a molding method that does not generate a retardation distribution is a molding method for an optical film, including a step of heating an optical film having a planar shape, a step of pressing the heated optical film against a mold to deform it according to the shape of the mold, and a step of cutting the deformed optical film, wherein the heating step is a step of irradiating the optical film with infrared rays, and the infrared irradiation amount has an in-plane distribution of the optical film. In particular, in the molding method, it is preferable that the mold is substantially concave spherical, and when an in-plane position of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the infrared irradiation amount irradiated to the optical film located at the vertex of the concave sphere is greater than the infrared irradiation amount irradiated to the optical film located at the end of the concave sphere. Furthermore, in the molding method, it is preferable that the mold is substantially concave spherical, and when an in-plane position of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the temperature of the optical film located at the vertex of the concave sphere is higher than the temperature of the optical film located at the end of the concave sphere. This allows the forming characteristic to be imparted in which the stretch ratio in the diameter direction decreases with increasing distance from the center, thereby making it possible to suppress the ratio of the stretch ratio in the diameter direction to the stretch ratio in the circumferential direction to be 0.95 times or more and 1.05 times or less.

[0110] A preferred embodiment of the above-described method will be described in more detail below. As described above, when a molding die having a concave molding surface is used, the ratio of the stretching ratio in the diameter direction to the stretching ratio in the circumferential direction is likely to be distorted in the peripheral portion. Therefore, in a preferred embodiment of the above-described molding method, as shown in FIGS. 7 and 8 , the heating temperature of the central portion 242C of a planar optical film 242 placed on a molding die 240 having a concave molding surface is set higher by infrared irradiation than the heating temperature of the peripheral portion 242R by infrared irradiation, thereby making it easier for the central portion 242C to stretch when the optical film 242 is deformed along the molding surface. By changing the heating conditions for the central portion and the peripheral portion, the peripheral portion is made more difficult to stretch and the central portion is made more easily stretched, thereby maintaining a uniform ratio of the stretching ratio in the diameter direction to the stretching ratio in the circumferential direction within the plane.

[0111] [Another Example of Molding Method That Does Not Generate Retardation Distribution] Another example of a molding method that does not generate a retardation distribution is a method for molding an optical film, comprising the steps of heating an optical film that includes at least two or more optically anisotropic layers and has a planar shape, pressing the heated optical film against a mold to deform it according to the shape of the mold, and cutting the deformed optical film, in which the mold is substantially concave spherical, and when an in-plane position of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the temperature of the optical film located at a vertex of the concave sphere is higher than the temperature of the optical film located at an end of the concave sphere.

[0112] The temperature distribution within the plane of the optical film preferably becomes gradually lower from the apex of the concave spherical surface toward the end portion.

[0113] Furthermore, the heating step is a step of heating the optical film by irradiating it with infrared rays, and it is preferable that the amount of infrared radiation has a distribution within the plane of the optical film. Specifically, when the in-plane positions of the optical film are projected onto the mold from the normal direction of the plane of the optical film, it is preferable that the amount of infrared radiation irradiated to the optical film located at the apex of the concave sphere is greater than the amount of infrared radiation irradiated to the optical film located at the end of the concave sphere, and it is preferable that the amount of infrared radiation irradiated to the optical film gradually decreases from the apex to the end of the concave sphere.

[0114] In the forming method of this example, the mold is substantially concave spherical, and when an in-plane position of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the temperature of the optical film located at the apex of the concave sphere is higher than the temperature of the optical film located at the end of the concave sphere, so that a molding characteristic can be imparted in which the stretch ratio in the diameter direction decreases with increasing distance from the center, thereby making it possible to suppress the ratio of the stretch ratio in the diameter direction to the stretch ratio in the circumferential direction to be 0.95 or more and 1.05 or less.

[0115] Hereinafter, the preferred embodiment of the above-mentioned method will be described by taking the structure of laminating the above-mentioned 1 / 2 wavelength retardation layer and 1 / 4 wavelength retardation layer as an example.When laminating the structure of 1 / 2 wavelength retardation layer and 1 / 4 wavelength retardation layer, the angle relationship (60 °) between the slow axis of 1 / 2 wavelength retardation layer and 1 / 4 wavelength retardation layer is important.In addition, when further having a linear polarizer, the angle relationship (15 °) between the transmission axis of linear polarizer and the slow axis of 1 / 2 wavelength retardation layer, and the angle relationship (75 °) between the transmission axis of linear polarizer and the slow axis of 1 / 4 wavelength retardation layer are important.

[0116] However, when an optical film is molded into a curved surface using a concave spherical mold, as shown in FIG. 7 , a flat optical film is placed in contact with the edge of the concave spherical mold, and molding is performed. Therefore, at the edge of the concave spherical mold, the optical film is fixed and difficult to stretch in the circumferential direction. Therefore, when the temperature of the optical film is made uniform in the plane, the stretching ratios in the circumferential direction and the diametric direction tend to differ near the edge. On the other hand, near the apex, the optical film is not restricted, so the difference between the stretching ratio in the circumferential direction and the diametric direction becomes small (isotropically stretched). If the stretching ratios differ between the circumferential direction and the diametric direction, at least one of the following changes occurs: the relationship between the slow axis of the half-wave retardation layer and the quarter-wave retardation layer; the relationship between the transmission axis of the linear polarizer and the slow axis of the half-wave retardation layer; and the relationship between the transmission axis of the linear polarizer and the slow axis of the quarter-wave retardation layer. As a result, the above-mentioned effect cannot be properly obtained.

[0117] In contrast, in the method of the present invention, when an optical film is molded into a curved shape using a concave spherical mold, the temperature of the optical film located at the apex of the concave spherical shape (region 242C) is set higher than the temperature of the optical film located at the end of the concave spherical shape (region 242R). This makes it difficult for the optical film to be stretched in the diametric direction near the end of the concave spherical shape, thereby reducing the difference between the circumferential stretching ratio and the diametric stretching ratio (see FIG. 9 , where the length of the arrow in FIG. 9 indicates the magnitude of the stretching ratio). Meanwhile, near the center of the concave spherical shape, the optical film is easily stretched in both the diametric and circumferential directions, thereby reducing the difference between the circumferential stretching ratio and the diametric stretching ratio (see FIG. 9 ). That is, although the stretching ratios are different near the center and near the end, the difference between the circumferential stretching ratio and the diametric stretching ratio can be reduced at each position. Therefore, in the method of the present invention, the optical film can be isotropically stretched at any position in the plane. Therefore, in the optical film after molding, at any position in the plane, the relationship between the angles of the slow axes of the half-wave retardation layer and the quarter-wave retardation layer, the relationship between the angle between the transmission axis of the linear polarizer and the slow axis of the half-wave retardation layer, and the relationship between the transmission axis of the linear polarizer and the slow axis of the quarter-wave retardation layer all maintain predetermined relationships.

[0118] In the method of the present invention, since the temperature of the optical film is high near the vertices, the optical film is easily stretched in both the diametric and circumferential directions, and although the difference in stretching ratio is small, the stretching ratio is higher near the ends (see Figure 9). Therefore, the film thickness of the optical film after molding is thinner near the vertices than near the ends. However, as described above, in a laminate in which a half-wave retardation layer and a quarter-wave retardation layer are stacked with their slow axes at a predetermined angle (60°), the changes in the effects of the layers due to the change in thickness cancel each other out, and the laminate can function properly as a λ / 4 plate at any position in the plane.

[0119] This point will be explained with reference to Figures 10 and 11. Figures 10 and 11 are diagrams showing the polarized light conversion effect of the retardation layer on the Poincare sphere.

[0120] The trajectory indicated by V1 in Fig. 10 is a trajectory when linearly polarized light is converted into circularly polarized light by one quarter-wave retardation layer. When the quarter-wave retardation layer before molding has a film thickness that converts linearly polarized light into circularly polarized light, if the film thickness is reduced by stretching through molding, the trajectory becomes shorter as indicated by V4 in Fig. 11, and linearly polarized light is not sufficiently converted into circularly polarized light, resulting in elliptically polarized light (the ellipticity of the polarized light after conversion becomes low).

[0121] On the other hand, the trajectories shown by V2 and V3 in Fig. 10 are the trajectories when linearly polarized light is converted into circularly polarized light by a laminate of a half wavelength retardation layer and a quarter wavelength retardation layer.When the laminate of a half wavelength retardation layer and a quarter wavelength retardation layer before molding has a thickness that converts linearly polarized light into circularly polarized light, when the thickness of each layer is thinned by molding and stretched, as shown in Fig. 11, the trajectory of polarization conversion by the half wavelength retardation layer becomes short as shown by V5, and the trajectory of polarization conversion by the quarter wavelength retardation layer becomes short as shown by V6.However, as shown in Fig. 11, the trajectories of the half wavelength retardation layer and the quarter wavelength retardation layer due to the thickness change cancel each other out, and the laminate of a half wavelength retardation layer and a quarter wavelength retardation layer that is thinned by molding and stretched can also convert linearly polarized light into circularly polarized light appropriately (the ellipticity of the polarized light after conversion can be increased). Therefore, even if the thickness of the optical film varies (is non-uniform) within the plane, the optical film can function as a λ / 4 plate at any position within the plane and can convert linearly polarized light into circularly polarized light appropriately. Therefore, when the optical film formed by the method of the present invention is applied to a pancake-type virtual reality display device, the occurrence of light leakage can be suppressed.

[0122] In this example, it is preferable that the half-wave retardation layer and the quarter-wave retardation layer each have reverse wavelength dispersion, so that the trajectory changes caused by the half-wave retardation layer and the quarter-wave retardation layer can be more effectively canceled out.

[0123] In the method of the present invention, the radius of curvature of the concave spherical mold is preferably 30 mm to 1000 mm, more preferably 30 to 100 mm.

[0124] The features of the present invention will be explained in more detail below with reference to examples. Note that the materials, amounts used, ratios, processing details, processing procedures, etc. shown below can be changed as appropriate without departing from the spirit of the present invention. Furthermore, configurations other than those shown below can also be used without departing from the spirit of the present invention.

[0125] [Preparation of Cellulose Acylate Film A1] (Preparation of Core Layer Cellulose Acylate Dope) The following composition was charged into a mixing tank and stirred to dissolve each component, thereby preparing a cellulose acetate solution to be used as the core layer cellulose acylate dope. -------------------------------- Core Layer Cellulose Acylate Dope------------------------------------------------ - 100 parts by mass of cellulose acetate having an acetyl substitution degree of 2.88 - 12 parts by mass of polyester compound B described in the examples of JP 2015-227955 A - 2 parts by mass of compound F below - 430 parts by mass of methylene chloride (first solvent) - 64 parts by mass of methanol (second solvent)------------------------------------------------

[0126] Compound F

[0127]

[0128] (Preparation of Outer Layer Cellulose Acylate Dope) 10 parts by weight of the following matting agent solution was added to 90 parts by weight of the above core layer cellulose acylate dope to prepare a cellulose acetate solution to be used as the outer layer cellulose acylate dope.

[0129] ------------------------------------------------------------------ Matting agent solution -------------------------------------------------- Silica particles with an average particle size of 20 nm (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.) 2 parts by mass Methylene chloride (first solvent) 76 parts by mass Methanol (second solvent) 11 parts by mass The above-mentioned cellulose acylate dope for the core layer 1 part by mass ------------------------------------------------------------------

[0130] (Preparation of Cellulose Acylate Film A1) The core layer cellulose acylate dope and the outer layer cellulose acylate dope were filtered through a filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm. The core layer cellulose acylate dope and the outer layer cellulose acylate dope on both sides were simultaneously cast onto a drum at 20°C through a casting nozzle (band caster). The film was then peeled off while still containing approximately 20% solvent by weight. Both ends of the film in the width direction were fixed with tenter clips, and the film was stretched transversely at a stretch ratio of 1.1 times while being dried. The film was then transported between the rolls of a heat treatment device and further dried to produce an optical film with a thickness of 40 μm, which was designated as cellulose acylate film A1. The in-plane retardation of the resulting cellulose acylate (TAC) film A1 was 0 nm.

[0131] [Preparation of Retardation Film 1 Having Positive A Plate] A coating solution E1 for forming a photo-alignment layer having the following composition was continuously applied onto the above-mentioned cellulose acylate film A1 using a wire bar. The support on which the coating film was formed was dried with hot air at 140°C for 120 seconds, and then the coating film was irradiated with polarized ultraviolet light (10 mJ / cm ２ , using an ultra-high pressure mercury lamp) to form a photo-alignment film E1 with a thickness of 0.2 μm, thereby obtaining a TAC film with a photo-alignment film.

[0132] -------------------------------------------------- Coating liquid E1 for forming photoalignment film -------------------------------------------------- Polymer PA-2 (shown below) 100.00 parts by mass Acid generator PAG-1 (shown below) 5.00 parts by mass Acid generator CPI-110TF (shown below) 0.005 parts by mass Isopropyl alcohol 16.50 parts by mass Butyl acetate 1072.00 parts by mass Methyl ethyl ketone 268.00 parts by mass --------------------------------------------------

[0133] Acid generator PAG-1

[0134]

[0135] Acid generator CPI-110TF

[0136]

[0137] Polymer PA-2

[0138]

[0139] Composition F1 having the following composition was applied onto the photo-alignment film E1 using a bar coater. The coating film formed on the photo-alignment film E1 was heated to 120°C with hot air, then cooled to 60°C, and then irradiated with 100 mJ / cm2 at a wavelength of 365 nm using a high-pressure mercury lamp under a nitrogen atmosphere. ２ The coating film was irradiated with ultraviolet light of 500 mJ / cm 2 while being heated to 120°C. ２ The coating film was irradiated with ultraviolet light of 1000 nm, thereby fixing the alignment of the liquid crystal compound, and a retardation film 1 having a positive A plate F1 was produced. The thickness of the positive A plate F1 was 2.5 μm, and the Re(550) was 141 nm. The positive A plate also satisfied the relationship Re(450)≦Re(550)≦Re(650), and had reverse wavelength dispersion. The Re(450) / Re(550) was 0.82.

[0140] -------------------------------- Composition F1------------------------------------------------ 43.50 parts by mass of polymerizable liquid crystal compound LA-1 described below 43.50 parts by mass of polymerizable liquid crystal compound LA-2 described below 8.00 parts by mass of polymerizable liquid crystal compound LA-3 described below 5.00 parts by mass of polymerizable liquid crystal compound LA-4 described below 0.55 parts by mass of polymerization initiator PI-1 described below 0.20 parts by mass of leveling agent T-1 described below 235.00 parts by mass of cyclopentanone --------------------------------

[0141] Polymerizable liquid crystal compound LA-1 (tBu represents a tertiary butyl group)

[0142]

[0143] Polymerizable liquid crystal compound LA-2

[0144]

[0145] Polymerizable liquid crystal compound LA-3

[0146]

[0147] Polymerizable liquid crystal compound LA-4 (Me represents a methyl group)

[0148]

[0149] Polymerization initiator PI-1

[0150]

[0151] Leveling agent T-1

[0152]

[0153] [Preparation of Retardation Film 2 Having a Positive C Plate] The above-described cellulose acylate film A1 was used as a temporary support. The cellulose acylate film A1 was passed through a dielectric heating roll at a temperature of 60°C to raise the surface temperature of the film to 40°C, and then an alkaline solution having the composition shown below was applied to one side of the film using a bar coater in an amount of 14 ml / m. ２ The film was heated to 110°C and transported for 10 seconds under a steam-type far-infrared heater manufactured by Noritake Co., Ltd. Next, pure water was applied to the film at a rate of 3 ml / m using the same bar coater. ２ Next, after repeating washing with water using a fountain coater and draining with an air knife three times, the film was transported to a drying zone at 70° C. for 10 seconds and dried to prepare an alkali-saponified cellulose acylate film A1.

[0154] ---------------------------------------------------------------- (Alkaline solution) ---------------------------------------------------------------- Potassium hydroxide 4.7 parts by mass Water 15.8 parts by mass Isopropanol 63.7 parts by mass Fluorine-containing surfactant SF-1 (C １４ H ２９ O (CH ２ CH ２ O) ２０ H) 1.0 part by mass Propylene glycol 14.8 parts by mass

[0155] An alignment film-forming coating solution G1 having the following composition was continuously applied onto the above-mentioned alkali-saponified cellulose acylate film A1 using a #8 wire bar, and the resulting film was dried with hot air at 60°C for 60 seconds and then with hot air at 100°C for 120 seconds to form an alignment film G1.

[0156] ------------------------------------------------------------------ Coating liquid G1 for forming alignment film -------------------------------------------------- Polyvinyl alcohol (PVA103, manufactured by Kuraray) 2.4 parts by mass Isopropyl alcohol 1.6 parts by mass Methanol 36 parts by mass Water 60 parts by mass ------------------------------------------------------------------

[0157] A coating solution H1 for forming a positive C plate having the following composition was applied onto the alignment film G1, and the resulting coating film was aged at 60° C. for 60 seconds, and then irradiated with 70 mW / cm 2 ２ An air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) was used, and the light output was 1000 mJ / cm ２ The alignment state was fixed by irradiating the liquid crystal compound with ultraviolet light of 1000 nm to vertically align the liquid crystal compound, thereby producing a retardation film 2 having a positive C plate H1 with a thickness of 0.8 μm. The Rth(550) of the obtained positive C plate was −80 nm.

[0158] -------------------------------- Coating liquid H1 for forming positive C-plate -------------------------------- 80 parts by mass of the following liquid crystal compound LC-1 20 parts by mass of the following liquid crystal compound LC-2 1 part by mass of the following vertical alignment liquid crystal compound promoter S01 8 parts by mass of ethylene oxide-modified trimethylolpropane triacrylate (V#360, manufactured by Osaka Organic Chemical Industry Co., Ltd.) 3 parts by mass of Irgacure 907 (manufactured by BASF) 1 part by mass of Kayacure DETX (manufactured by Nippon Kayaku Co., Ltd.) 0.4 parts by mass of the following compound B03 170 parts by mass of methyl ethyl ketone 30 parts by mass of cyclohexanone --------------------------------

[0159] Liquid crystal compound LC-1

[0160]

[0161] Liquid crystal compound LC-2

[0162]

[0163] Vertical alignment liquid crystal compound promoter S01

[0164]

[0165] Compound B03

[0166]

[0167] [Preparation of Retardation Film 3 Having Positive A Plate] The above-mentioned TAC film A1 was used as a temporary support.

[0168] The coating solution 1 for forming an alignment layer, which will be described later, was continuously applied onto the TAC film A1 using a wire bar of #2.4. The support on which the coating film was formed was dried with hot air at 140°C for 120 seconds, and then the coating film was irradiated with polarized ultraviolet light (10 mJ / cm ２, an ultra-high pressure mercury lamp was used) to form a photo-alignment layer 1, thereby obtaining a TAC film with the photo-alignment layer 1. -------------------------------------------------- Coating liquid 1 for forming alignment layer -------------------------------------------------- Polymer PA-1 below: 100.00 parts by mass Acid generator PAG-1 above: 1.00 part by mass Isopropyl alcohol: 16.50 parts by mass Butyl acetate: 1,072.00 parts by mass Methyl ethyl ketone: 268.00 parts by mass

[0169] Polymer PA-1

[0170]

[0171] Next, the following coating liquid A-1 for forming a positive A plate was prepared. ------------------------------------------------ Coating liquid A-1 for forming a positive A plate ------------------------------------------------ Liquid crystal compound L-1 (below) 70.00 parts by mass Liquid crystal compound L-2 (below) 30.00 parts by mass Polymerization initiator PI-1 (below) 0.60 parts by mass Leveling agent (compound LT-1 (below)) 0.10 parts by mass Methyl ethyl ketone (solvent) 200.00 parts by mass Cyclopentanone (solvent) 200.00 parts by mass

[0172] Liquid crystal compound L-1

[0173]

[0174] Liquid crystal compound L-2

[0175]

[0176] Leveling agent LT-1 (the numerical value for each repeating unit represents the content (mass%) relative to all repeating units, the content of the repeating unit on the left side was 32.5 mass%, and the content of the repeating unit on the right side was 67.5 mass%)

[0177]

[0178] Next, using a bar coater, coating solution A-1 for forming a positive A plate was applied onto the photo-alignment layer 1. The resulting coating film was heated and aged at a film surface temperature of 100°C for 20 seconds, cooled to 90°C, and then irradiated with 300 mJ / cm using an air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) under air. ２ The nematic alignment state was fixed by irradiating the film with ultraviolet light of 1000 kJ / cm2 to prepare a retardation film 3 having a positive A plate A-1.

[0179] The positive A plate A-1 had a thickness of 3.0 μm, Re(550) of 141 nm, Re(550) / Re(450) of 1.18, and Re(650) / Re(550) of 1.03, indicating reverse wavelength dispersion. The liquid crystal compound was homogeneously aligned.

[0180] [Preparation of Linear Polarizer]

[0181] <Formation of Photo-Alignment Layer PA1>

[0182] The above-mentioned cellulose acylate film A1 was used as a temporary support. The alignment layer forming coating liquid S-PA-1 described later was continuously applied onto the above-mentioned cellulose acylate film A1 using a wire bar. The support on which the coating film was formed was dried with hot air at 140°C for 120 seconds, and then the coating film was irradiated with polarized ultraviolet light (10 mJ / cm ２ A photo-alignment layer PA1 was formed by irradiating the substrate with light (using an ultra-high pressure mercury lamp). The film thickness was 0.3 μm.

[0183] -------------------------------------------------- (Coating liquid for forming alignment layer S-PA-1) -------------------------------------------------- Polymer M-PA-1 shown below: 100.00 parts by mass Acid generator PAG-1 described above: 5.00 parts by mass Acid generator CPI-110TF described above: 0.005 parts by mass Xylene: 1,220.00 parts by mass Methyl isobutyl ketone: 122.00 parts by mass

[0184] Polymer M-PA-1

[0185]

[0186] <Formation of Optically Absorbent Anisotropic Layer> The following coating solution SP-1 for forming an optically absorbent anisotropic layer was continuously applied onto the obtained alignment layer PA1 using a wire bar. The coating layer P1 was then heated at 140°C for 30 seconds and cooled to room temperature (23°C). It was then heated at 90°C for 60 seconds and cooled again to room temperature. Thereafter, an LED lamp (center wavelength 365 nm) was used to apply the coating solution SP-1 continuously onto the obtained alignment layer PA1 using a wire bar. The coating layer P1 was then heated at 140°C for 30 seconds and cooled to room temperature again. The coating layer P1 was then heated at 90°C for 60 seconds and cooled again to room temperature. Thereafter, the coating layer P1 was heated at an illuminance of 200 mW / cm ２ An optically absorptive anisotropic layer was formed on the alignment layer PA1 by irradiating the layer for 2 seconds under the irradiation conditions of 1.6 μm. The film thickness was 1.6 μm. In this way, an absorptive linear polarizer P1 was produced.

[0187] 0.25 parts by mass of dichroic substance D-1 below 0.36 parts by mass of dichroic substance D-2 below 0.59 parts by mass of dichroic substance D-3 below 2.21 parts by mass of polymer liquid crystal compound M-P-1 below 1.36 parts by mass of low molecular weight liquid crystal compound M-1 below 0.200 parts by mass of polymerization initiator IRGACURE OXE-02 (manufactured by BASF) 0.026 parts by mass of surfactant F-1 below 46.00 parts by mass of cyclopentanone 46.00 parts by mass of tetrahydrofuran 46.00 parts by mass of benzyl alcohol ----------------------------------------------------------------------------------

[0188] Dichroic substance D-1

[0189]

[0190] Dichroic substance D-2

[0191]

[0192] Dichroic substance D-3

[0193]

[0194] Polymer liquid crystal compound M-P-1

[0195]

[0196] Low molecular liquid crystal compound M-1

[0197]

[0198] Surfactant F-1

[0199]

[0200] [Preparation of Laminated Optical Body 1] The retardation film 1 was bonded to a PMMA film "Technoloy S001G" manufactured by Sumika Acrylic Sales Co., Ltd. using an adhesive sheet "NCF-D692 (5)" manufactured by Lintec Corporation, and the temporary support of the retardation film 1 (TAC film with a photo-alignment film) was peeled off. Next, a second retardation film 1 was bonded to the first retardation film 1 so that the slow axis orientation coincided, and the temporary support was peeled off. Furthermore, a third retardation film 1 was bonded to the second retardation film 1 so that the slow axis orientation was 60 ° relative to each other, and the temporary support was peeled off. Furthermore, the retardation film 2 was bonded to the third retardation film 1, and the temporary support was peeled off. In this way, a laminated optical body 1 was obtained. In addition, in the laminated optical body 1, of the three laminated retardation films 1, the first retardation film 1 and the second retardation film 1 have the same slow axis orientation, so they can be collectively regarded as a first optically anisotropic layer. Furthermore, the third retardation film 1 can be regarded as a second optically anisotropic layer. In this case, the first optically anisotropic layer has an in-plane retardation of 282 nm, and the second optically anisotropic layer has an in-plane retardation of 141 nm. That is, the first optically anisotropic layer is a half-wave retardation layer, and the second optically anisotropic layer is a quarter-wave retardation layer. Furthermore, both the first optically anisotropic layer and the second optically anisotropic layer have reverse wavelength dispersion.

[0201] [Preparation of Laminated Optical Body 2] The liquid crystal display of an Apple iPad tablet computer was removed, and a linearly polarized reflective polarizer (3M trademark APF) made of a wideband dielectric multilayer film was peeled off from the polarizing plate attached to the back of the liquid crystal display. Next, a retardation film 1 was attached to one side of the peeled APF using a Lintec adhesive sheet "NCF-D692 (5)", and the temporary support of the retardation film 1 was peeled off. At this time, the reflection axis orientation of the APF and the slow axis orientation of the retardation film 1 were adjusted to be 75° to each other. Next, a second retardation film 1 was attached to the first retardation film 1 so that the slow axis orientation coincided, and the temporary support was peeled off. Next, a third retardation film 1 was attached to the second retardation film 1 so that the slow axis orientations were 60° to each other, and the temporary support was peeled off. At this time, the reflection axis orientation of the APF and the slow axis orientation of the three retardation films 1 were 15° to each other. Furthermore, the retardation film 2 was bonded to the third retardation film 1, and the temporary support was peeled off. Furthermore, an absorbing linear polarizer P1 was bonded to the opposite surface of the APF, and the temporary support was peeled off. At this time, the reflection axis orientation of the APF and the absorption axis orientation of the absorbing linear polarizer P1 were adjusted to coincide. Thus, a laminated optical body 2 was obtained. Of the three laminated retardation films 1, the first retardation film 1 and the second retardation film 1 have the same slow axis orientation, so they can be collectively regarded as a first optically anisotropic layer. Furthermore, the third retardation film 1 can be regarded as a second optically anisotropic layer. In this case, the first optically anisotropic layer has an in-plane retardation of 282 nm, and the second optically anisotropic layer has an in-plane retardation of 141 nm. Both the first optically anisotropic layer and the second optically anisotropic layer have reverse wavelength dispersion.

[0202] [Preparation of Laminated Optical Body 3] The retardation film 1 was bonded to a PMMA film "Technoloy S001G" manufactured by Sumika Acrylic Sales Co., Ltd. using an adhesive sheet "NCF-D692(5)" manufactured by Lintec Corporation, and the temporary support of the retardation film 1 was peeled off. This was used as a laminated optical body 3.

[0203] [Preparation of Laminated Optical Body 4] The liquid crystal display of an Apple iPad tablet computer was removed, and a linearly polarized reflective polarizer (3M trademark APF) made of a wideband dielectric multilayer film was peeled off from the polarizing plate attached to the back of the liquid crystal display. Next, a retardation film 1 was attached to one side of the peeled APF using a Lintec adhesive sheet "NCF-D692 (5)", and the temporary support of the retardation film 1 was peeled off. At this time, the reflection axis orientation of the APF and the slow axis orientation of the retardation film 1 were adjusted to be 45° to each other. Next, an absorbing linear polarizer P1 was attached to the opposite side of the APF, and the temporary support was peeled off. At this time, the reflection axis orientation of the APF and the absorption axis orientation of the absorbing linear polarizer P1 were adjusted to coincide. In this way, a laminated optical body 4 was obtained.

[0204] [Preparation of Laminated Optical Body 5] Laminated optical body 5 was prepared in the same manner as laminated optical body 2, except that retardation film 1 was changed to retardation film 3.

[0205] [Example 1]

[0206] [Molding Method 1] The laminated optical body 1 was set in a molding device. The molding space in the molding device consisted of box 1 and box 2, separated by the laminated optical body 1. In box 1 below the laminated optical body 1, a Thorlab convex meniscus lens LE1076-A (diameter 2 inches, focal length 100 mm, radius of curvature on the concave side 65 mm) with aluminum vapor deposition on the convex side was placed with the concave side facing up. In addition, a transparent window was installed on the top of box 2 above the laminated optical body 1, and an IR light source for heating the laminated optical body 1 was installed outside this window. Between the IR light source and the laminated optical body 1, a circular patterned infrared reflective filter obtained by cutting a cholesteric liquid crystal layer that reflects infrared rays with a wavelength of 2.2 μm to 3.0 μm with a reflectance of approximately 50% into a circle with a diameter of 1 inch was placed. In this case, the center of the patterned infrared reflective filter was positioned so that it was at the center of the mold when viewed from directly above. Next, a vacuum pump was used to evacuate the inside of box 1 and box 2 to a pressure of 0.1 atmospheres or less. Next, as a step of heating the laminated optical body 1, infrared rays were irradiated and the laminated optical body 1 was heated until the center of the laminated optical body 1 reached 108 ° C and the ends reached 99 ° C. Since the glass transition temperature Tg of the PMMA film used as the support was 105 ° C, the aim was to make the center easily stretchable and the ends difficult to stretch during molding. Next, as a step of pressing the laminated optical body 1 against the mold and deforming it according to the shape of the mold, gas was flowed into box 2 from a gas cylinder to pressurize it to 300 kPa, and the laminated optical body 1 was pressure-bonded to the mold. Finally, the laminated optical body 1 was removed from the lens, which was the mold. As a result, a laminated optical body 1 molded into a curved surface was obtained as Example 1.

[0207] [Example 2]

[0208] Laminated optical body 1 was replaced with laminated optical body 2, and molding was carried out in the same manner as in Example 1. An adhesive sheet "NCF-D692(15)" manufactured by Lintec Corporation was attached to the surface of laminated optical body 2 that came into contact with the mold, and was attached to the lens at the same time as molding. In this way, a composite lens 2 used in Example 2 was obtained.

[0209] [Example 3]

[0210] A composite lens 3 used in Example 3 was obtained in the same manner as in Example 2, except that the laminated optical body 2 was changed to the laminated optical body 5 .

[0211] [Comparative Example 1]

[0212] A laminated optical body 3 of Comparative Example 1 was obtained by molding in the same manner as in Example 1, except that the laminated optical body 1 was changed to the laminated optical body 3.

[0213] [Comparative Example 2]

[0214] Laminated optical body 1 was replaced with laminated optical body 4, and molding was carried out in the same manner as in Example 1. An adhesive sheet "NCF-D692(15)" manufactured by Lintec Corporation was attached to the surface of laminated optical body 4 that came into contact with the mold, and was attached to the lens at the same time as molding. In this way, a composite lens 4 used in Comparative Example 2 was obtained.

[0215] [Comparative Example 3]

[0216] [Molding method 2] A Lintec adhesive sheet "NCF-D692 (15)" was attached to the surface of the laminated optical body 2 facing the retardation film 1, and the laminated optical body 2 was set in a molding device. The molding space in the molding device consisted of a box 1 and a box 2 separated by the laminated optical body 2. In box 1 below the laminated optical body 2, a Thorlab convex meniscus lens LE1076-A (diameter 2 inches, focal length 100 mm, radius of curvature on the concave side 65 mm) was placed with the concave side facing up, with aluminum vapor deposition applied to the convex side. In addition, a transparent window was installed on the top of box 2 above the laminated optical body 2, and an IR light source for heating the laminated optical body 2 was installed on the outside of this window. Next, a vacuum pump was used to evacuate box 1 and box 2 to a pressure of 0.1 atmospheres or less. Next, as a step of heating the laminated optical body 2, infrared rays were irradiated and the laminated optical body 2 was heated uniformly to 108 ° C. Next, in a step of pressing the laminated optical body 2 against the mold and deforming it to conform to the shape of the mold, gas was flowed into the box 2 from a gas cylinder to pressurize it to 300 kPa, and the laminated optical body 2 was pressed against the mold. In this way, the laminated optical body 2 was molded and simultaneously bonded to the lens, thereby obtaining the composite lens 5 used in Comparative Example 3.

[0217] [Evaluation of molded retardation film] The effective retardation of the laminated optical body 1 molded on the curved surface of Example 1 was Re = 140 nm before molding. In addition, the effective in-plane retardation value at each position in the plane of the laminated optical body 1 molded on the curved surface in Example 1 was measured using the above-mentioned specific method 1. After molding, the effective retardation at the center was Re = 138 nm, and the in-plane variation of the effective retardation was 2.8%. This confirmed that the laminated optical body 1 molded on the curved surface by the method of the present invention has a small in-plane variation of the effective retardation. The positions at which the in-plane variation was measured were positions corresponding to the intersections of the pattern shown in FIG. 6, and a total of 17 points were measured: the central point, circles equally spaced at 10 mm radius intervals in the diameter direction, and the intersections of lines equally spaced at 45 degree intervals in the azimuth angle direction. The in-plane variation was calculated from the average, maximum, and minimum values ​​of these 17 points.

[0218] The effective retardation of the laminated optical body 3 molded on the curved surface of Comparative Example 1 was Re = 141 nm before molding. After molding, the effective retardation at the center was Re = 125 nm, and the in-plane variation of the effective retardation was 8.8%. This confirmed that the laminated optical body 3 molded on the curved surface had a large in-plane variation of the effective retardation.

[0219] [Fabrication of Virtual Reality Display Devices of Examples 2 and 3] A virtual reality display device "Huawei VR Glass" manufactured by Huawei, which is a virtual reality display device employing a reciprocating optical system, was disassembled, and all of the compound lenses were removed. Instead, compound lens 2 of Example 2 was incorporated into the main body to fabricate a virtual reality display device of Example 2. In the fabricated virtual reality display device, a black and white checkered pattern was displayed on the image display panel, and ghost visibility was visually evaluated using the following four-point scale. The virtual reality display device of Example 3 was also fabricated in the same manner as Example 2, except that compound lens 3 of Example 3 was used.

[0220] [Fabrication of Virtual Reality Display Device of Comparative Example 2] A virtual reality display device of Comparative Example 2 was fabricated in the same manner as in Example 2, except that composite lens 2 was replaced with composite lens 4. In the fabricated virtual reality display device, a black and white checkered pattern was displayed on the image display panel, and ghost visibility was visually evaluated using the following four-point scale.

[0221] [Fabrication of Virtual Reality Display Device of Comparative Example 3] A virtual reality display device of Comparative Example 3 was fabricated in the same manner as in Example 2, except that composite lens 2 was replaced with composite lens 5. In the fabricated virtual reality display device, a black and white checkered pattern was displayed on the image display panel, and ghost visibility was visually evaluated using the following four-point scale.

[0222] <Ghost Evaluation> A: Slight ghosting is visible, but not bothersome. B: Weak ghosting is visible. C: Slightly strong ghosting is visible. D: Strong ghosting is visible. Table 1 shows the molding method and type of optical film used in each example. Table 2 also shows the evaluation results. As a result, the virtual reality display devices of Examples 2 and 3 had good ghosting across the entire viewing area. Furthermore, the color change in the white parts of the black and white checkered pattern was not bothersome.

[0223] Table 1. Molding methods and optical film types used in the examples

[0224]

[0225] Table 2 Evaluation results of the examples

[0226]

[0227] REFERENCE SIGNS LIST 100 Laminated optical body 100B Laminated optical body 101 Cholesteric liquid crystal layer 102 Positive C plate 103 Retardation layer 104 Linear polarizer 105 Retardation layer 106 Antireflection film 111 Positive C plate 112 Retardation layer 113 Linear polarization type reflective polarizer 114 Linear polarizer 115 Retardation layer 116 Antireflection film 131 First light-reflecting layer 132 Second light-reflecting layer 133 Third light-reflecting layer 134 Fourth light-reflecting layer 200 Lens 240 Mold 242 Optical film 242C Central portion of optical film 242R Peripheral portion of optical film 300 Half mirror 400 Circularly polarizing plate 500 Image display panel 1000 Light ray 2000 Light ray

Claims

1. A step of heating an optical film having a planar shape and including at least two or more optically anisotropic layers, The process of pressing the optical film onto the mold and deforming it to conform to the shape of the mold, A method for forming an optical film, comprising the step of cutting the deformed optical film, The mold is substantially concave and spherical, and when a position within the plane of the optical film is projected onto the mold from the direction normal to the plane of the optical film, The temperature of the optical film located at the apex of the concave sphere is greater than the temperature of the optical film located at the edge of the concave sphere. A method for forming optical films.

2. A method for forming an optical film according to claim 1, wherein the radius of curvature is 30 mm to 1000 mm.

3. The method for forming an optical film according to claim 1 or 2, wherein the two or more optical anisotropic layers are a combination of a first optical anisotropic layer having an in-plane phase difference at a wavelength of 550 nm in the range of 120 nm to 160 nm and a second optical anisotropic layer having an in-plane phase difference value of 200 to 320 nm.

4. The method for forming an optical film according to claim 3, wherein both the first optical anisotropy layer and the second optical anisotropy layer have reverse wavelength dispersion properties.

5. The method for forming an optical film according to claim 1 or 2, wherein the optical film further includes a reflective polarizer.

6. The heating step is a step of heating the optical film by irradiating it with infrared light, A method for forming an optical film according to claim 1 or 2, wherein when a position within the plane of the optical film is projected onto the mold from the normal direction of the surface of the optical film, the amount of infrared radiation irradiated onto the optical film at the vertex of the concave sphere is greater than the amount of infrared radiation irradiated onto the optical film at the end of the concave sphere.

7. The two or more optical anisotropic layers are a combination of a first optical anisotropic layer having an in-plane phase difference at a wavelength of 550 nm in the range of 120 nm to 160 nm and a second optical anisotropic layer having an in-plane phase difference value of 200 to 320 nm. Both the first optical anisotropy layer and the second optical anisotropy layer have inverse wavelength dispersion properties. The method for forming an optical film according to claim 1 or 2, wherein both the first optical anisotropy layer and the second optical anisotropy layer are layers on which a liquid crystal compound is immobilized.

8. The method for forming an optical film according to claim 1 or 2, wherein the optical film has a support, and if the glass transition temperature of the support is Tg, the temperature at the apex of the optical film during the heating step is Tg or higher, and the temperature at the end is Tg or lower.

9. The method for forming an optical film according to claim 6, wherein in the heating step, an infrared intensity distribution is created by irradiating infrared light through a filter with a patterned transmittance to infrared light.