Optical anisotropic layer, light guide element, and ar display device

Abstract

The present invention addresses the problem of providing an optically anisotropic layer which is capable of evening out the brightness of light emitted from a light guide plate and is has exceptional durability against external light, as well as a light guide element and an AR display device in which the optically anisotropic layer is used. The problem is solved by an optically anisotropic layer formed using a composition containing a liquid crystal compound, the optically anisotropic layer having a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned in a constant film thickness in at least a part within the plane, the cholesteric alignment region having a layer A having a helical pitch of less than 250 nm and a layer B having a helical pitch of 250 nm or greater in the thickness direction, and the ratio of the thickness of the layer A to the thickness of the cholesteric alignment region varying in the plane of the cholesteric alignment region.

Description

Optically anisotropic layer, light guide element and AR display device

[0001] The present invention relates to an optically anisotropic layer formed using a composition containing a liquid crystal compound, and to a light guide element and an AR display device using the same.

[0002] In recent years, Augmented Reality (AR) glasses, which display virtual images and various information superimposed on an actual scene, as described in Non-Patent Document 1, have been put to practical use. AR glasses are also called smart glasses, head-mounted displays (HMDs), AR glasses, etc.

[0003] As shown in Non-Patent Document 1, for example, AR glasses superimpose a virtual image on the scene actually viewed by the user by causing an image displayed by a display (optical engine) to enter one end of a light guide plate, propagate therethrough, and exit from the other end. AR glasses use a diffraction element to diffract (refract) light from the display (projected light) and cause it to enter one end of the light guide plate. This allows the light to be introduced into the light guide plate at an angle, reflecting the light at the interface (surface) of the light guide plate while propagating within the light guide plate to the other end. The light propagating through the light guide plate is diffracted by the diffraction element at the other end of the light guide plate and is then emitted from the light guide plate to the user's viewing position.

[0004] A known example of such a diffraction grating is a diffraction element using a liquid crystal. For example, Patent Document 1 describes an optical element including a plurality of stacked birefringent sublayers configured to change the direction of propagation of light passing therethrough in accordance with the Bragg condition, each stacked birefringent sublayer having a local optical axis that varies along the respective interface between adjacent stacked birefringent sublayers to define a respective grating period. The optical element described in Patent Document 1 is an optical element that diffracts transmitted light. Patent Document 1 describes a method in which light incident on a substrate (light guide plate) is diffracted by an optical element, causing the light to be incident at an angle that causes total reflection within the substrate, and the light is guided within the substrate in a direction approximately perpendicular to the direction of incidence of the light (see FIG. 8 of Patent Document 1).

[0005] Patent Document 2 describes a polarization grating comprising a photo-alignment layer that is sensitive to polarization and at least first and second liquid crystal compositions containing polymerizable mesogens arranged on the photo-alignment layer, wherein an anisotropic alignment pattern corresponding to a polarization hologram is arranged in the photo-alignment layer, the first liquid crystal composition is arranged on the alignment layer and aligned thereby, and is at least partially polymerized, and the second liquid crystal composition is arranged on the first liquid crystal composition and aligned thereby, and both liquid crystal compositions have a layer thickness d determined by d≦dmax=Λ / 2, where d is the layer thickness and Λ is the pitch of the polarization grating.

[0006] Patent Document 3 describes a reflective structure having a plurality of spiral structures each extending along a predetermined direction, a first incident surface that intersects the predetermined direction and through which light is incident, and a reflective surface that intersects the predetermined direction and reflects the light incident from the first incident surface, the first incident surface including one end of each of the plurality of spiral structures, each of the plurality of spiral structures including a plurality of structural units lined up along the predetermined direction, the plurality of structural units including a plurality of elements spirally stacked, each of the plurality of structural units having a first end and a second end, the second end of one of the structural units adjacent to each other along the predetermined direction forming the first end of the other structural unit, the orientation directions of the elements located at the first ends included in the plurality of spiral structures being aligned, the reflective surface including at least one first end included in each of the plurality of spiral structures, and the reflective surface being non-parallel to the first incident surface.

[0007] Here, it is known that in AR glasses, the diffraction efficiency of a diffraction element is adjusted so that when light propagating through a light guide plate is diffracted by the diffraction element, a portion of the light is diffracted at multiple locations and emitted outside the light guide plate, thereby expanding the viewing zone (expanding the exit pupil). For example, Patent Document 4 describes an optical waveguide that includes a step of coupling light corresponding to an image having a predetermined FOV (field of view) to the optical waveguide by an input coupler (diffraction element) of the optical waveguide, dividing the FOV of the image coupled to the optical waveguide into a first portion and a second portion, and diffracting the light toward a first intermediate component located in a first direction and a second intermediate component located in a second direction, and describes that the exit pupil is expanded by the intermediate component (diffraction element) and an output coupler (diffraction element).

[0008] Patent Publication No. 2017-522601 Patent No. 5276847 International Publication No. 2016 / 194961 International Publication No. 2017 / 180403

[0009] Bernard C. Kress et al., Towards the Ultimate Mixed Reality Experience: HoloLens Display Architecture Choices, SID 2017 DIGEST, pp.127-131

[0010] When a liquid crystal diffraction element is used as the diffraction element of the light guide element used in AR glass, and the liquid crystal diffraction element is configured to diffract part of the light at multiple points and emit it outside the light guide plate in order to expand the viewing zone of the AR glass (expand the exit pupil), there is a problem in that if the diffraction efficiency within the surface of the liquid crystal diffraction element is uniform, the brightness (amount of light) of the light emitted from the light guide plate becomes uneven.

[0011] The object of the present invention is to solve the problems of the conventional technology, and to provide an optically anisotropic layer that can make the brightness of light emitted from a light guide plate uniform, as well as a light guide element and an AR display device that use this optically anisotropic layer.

[0012] To solve this problem, the present invention has the following configuration. [1] An optically anisotropic layer formed using a composition containing a liquid crystal compound, the optically anisotropic layer having a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned at a constant film thickness in at least a part of its plane, the cholesteric alignment region having, in the thickness direction, Layer A having a helical pitch of less than 250 nm and Layer B having a helical pitch of 250 nm or more, the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region varying within the plane of the cholesteric alignment region. [2] The optically anisotropic layer according to [1], wherein, in the cholesteric alignment region, the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region gradually changes from one side to the other in at least one direction within the plane of the optically anisotropic layer. [3] The optically anisotropic layer according to [1] or [2], wherein, in the cholesteric alignment region, the helical pitch gradually changes in the thickness direction. [4] The optically anisotropic layer according to any one of [1] to [3], wherein Layer A has a constant helical pitch. [5] The optically anisotropic layer according to any one of [1] to [4], wherein the cholesteric alignment region has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. [6] The optically anisotropic layer according to [5], wherein the direction in which the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region gradually changes is parallel to the direction in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in the cholesteric alignment region. [7] The optically anisotropic layer according to any one of [1] to [6], wherein at least a part of the plane of the optically anisotropic layer, different from the cholesteric alignment region, consists solely of optically isotropic regions. [8] The optically anisotropic layer according to any one of [1] to [7], wherein at least a part of the plane of the optically anisotropic layer, different from the cholesteric alignment region, consists solely of optically anisotropic regions. [9] The optically anisotropic layer according to any one of [1] to [8], wherein the liquid crystal compound is oriented in one direction in the same plane in at least a part of the plane different from the cholesteric alignment region.

[10] The optically anisotropic layer according to [5] or [6], having in-plane regions in which the rotation directions of the optical axes derived from the liquid crystal compound in the liquid crystal alignment pattern are different from each other.

[11] The optically anisotropic layer according to any one of [1] to

[10] , having a region in which the liquid crystal compound is aligned in a right-handed helical cholesteric orientation and a region in which the liquid crystal compound is aligned in a left-handed helical cholesteric orientation.

[12] The optically anisotropic layer according to any one of [1] to

[11] , wherein the compound compositions constituting Layer A and Layer B are the same.

[13] The optically anisotropic layer according to any one of [1] to

[12] , wherein Layer A and Layer B have the same ordinary and extraordinary refractive indices.

[14] The optically anisotropic layer according to any one of [1] to

[13] , wherein the helical pitches of Layer A and Layer B differ by 20 nm or more.

[15] An optically anisotropic layer comprising a first optically anisotropic layer and a second optically anisotropic layer, each having a cholesteric liquid crystal layer, wherein at least one of the first optically anisotropic layer and the second optically anisotropic layer is the optically anisotropic layer described in any one of [1] to

[14] .

[16] The optically anisotropic layer described in

[15] , wherein the cholesteric liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while rotating continuously along at least one direction in the plane.

[17] The optically anisotropic layer described in

[16] , wherein, when the length of a 180° rotation of the direction of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern is defined as one period, the length of one period in the first optically anisotropic layer is different from that of the second optically anisotropic layer.

[18] The optically anisotropic layer according to

[16] or

[17] , wherein the first optically anisotropic layer has a region in which one direction of a liquid crystal alignment pattern that is continuously rotating in one in-plane direction differs from the one direction of a liquid crystal alignment pattern that is continuously rotating in one in-plane direction in the second optically anisotropic layer.

[19] The optically anisotropic layer according to any one of

[16] to

[18] , wherein the first optically anisotropic layer has a region in which the direction of rotation of an optical axis derived from a liquid crystal compound in the liquid crystal alignment pattern that is continuously rotating in one in-plane direction differs from the one direction of rotation of an optical axis derived from a liquid crystal compound in the liquid crystal alignment pattern that is continuously rotating in one in-plane direction in the second optically anisotropic layer.

[20] The optically anisotropic layer according to any one of

[15] to

[19] , having a region in which the helical pitch length of the cholesteric liquid crystal layer in the first optically anisotropic layer and the helical pitch length of the cholesteric liquid crystal layer in the second optically anisotropic layer are different from each other.

[21] The optically anisotropic layer according to any one of

[15] to

[20] , having a region in which the helical rotation direction of the cholesteric liquid crystal layer in the first optically anisotropic layer and the helical rotation direction of the cholesteric liquid crystal layer in the second optically anisotropic layer are different from each other.

[22] An optical element having a protective layer on at least one surface of the optically anisotropic layer according to any one of [1] to

[21] .

[23] A light guide element having a light guide plate and the optically anisotropic layer according to any one of [1] to

[21] , disposed on the surface of the light guide plate.

[24] An AR display device having the optical element according to

[22] and an image display device.

[25] A light guide element comprising: a light guide plate; and the optical element according to

[22] , which is disposed on a surface of the light guide plate.

[26] An AR display device comprising the light guide element according to

[25] and an image display device.

[0013] According to the present invention, it is possible to provide an optically anisotropic layer, a light guide element, and an AR display device that can make the brightness of light emitted from a light guide plate uniform.

[0014] FIG. 1A is a conceptual diagram of an example of a liquid crystal diffraction element having an optically anisotropic layer according to the present invention. FIG. 1B is a partially enlarged view of FIG. 1A. FIG. 2 is a top view of the optically anisotropic layer of FIG. 1. FIG. 3 is a conceptual diagram of an example of an exposure apparatus for exposing an alignment film. FIG. 4 is a diagram for explaining the function of the optically anisotropic layer of FIG. 1. FIG. 5 is a graph conceptually showing an example of the relationship between the position of the optically anisotropic layer and the diffraction efficiency. FIG. 6 is a graph conceptually showing another example of the relationship between the position of the optically anisotropic layer and the diffraction efficiency. FIG. 7 is a schematic diagram showing an example of an AR display device having the optically anisotropic layer of the present invention. FIG. 8 is a graph conceptually showing the relationship between the position in the AR display device and the emitted light. FIG. 9 is a diagram for explaining a method for measuring the intensity of emitted light in the examples. FIG. 10 is a schematic diagram for explaining a method for measuring the diffraction efficiency. FIG. 11 is a diagram illustrating an example of a method for forming a region in the in-plane direction of the optically anisotropic layer in which the ratio of the thickness of layer A with a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region gradually changes. FIG. 12 is a diagram schematically illustrating the change in thickness of layer A with a helical pitch of less than 250 nm and layer B with a helical pitch of 250 nm or more in the thickness direction of the optically anisotropic layer. FIG. 13 is a diagram illustrating the illuminance of light as a function of the position in the optically anisotropic layer. FIG. 14 is a diagram illustrating the ratio of the thickness of layer A with a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region as a function of the position in the optically anisotropic layer. FIG. 15 is a diagram illustrating the thickness distribution of a diffraction element as a function of the position in the optically anisotropic layer. FIG. 16 is a diagram schematically illustrating an example of an AR display device having a conventional liquid crystal diffraction element. FIG. 17 is a diagram illustrating an example of the in-plane distribution of diffraction efficiency using shading. FIG. 18 is a diagram conceptually illustrating an example of an optically anisotropic layer of the present invention. Fig. 19 is a diagram conceptually showing an example of the optically anisotropic layer of the present invention. Fig. 20 is a top view of Fig. 19. Fig. 21 is a diagram conceptually showing another example of the optically anisotropic layer of the present invention. Fig. 22 is a diagram conceptually showing an example of a laminate having a plurality of optically anisotropic layers of the present invention. Fig. 23 is a diagram conceptually showing a cross-sectional SEM image of a cholesteric liquid crystal layer. Fig. 24 is a diagram conceptually showing a cross-sectional SEM image of a reflective liquid crystal diffraction element.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal diffraction element, a light guide element, and an AR display device according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0016] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, "(meth)acrylate" is used to mean "either one or both of acrylate and methacrylate." In this specification, "same" is intended to include a margin of error generally accepted in the technical field. Furthermore, in this specification, when terms such as "all," "all," and "entire surface" are used, they include not only 100% but also margins of error generally accepted in the technical field, such as 99% or more, 95% or more, or 90% or more. Furthermore, "perpendicular" and "parallel" with respect to angles mean a range of ±5° from the exact angle, and "same" with respect to angles means that the difference from the exact angle is within a range of less than 5°, unless otherwise specified. The difference from the exact angle is preferably less than 4°, and more preferably less than 3°.

[0017] In this specification, visible light refers to electromagnetic waves with wavelengths visible to the human eye, in the wavelength range of 380 to 780 nm. Invisible light refers to light in the wavelength range of less than 380 nm and more than 780 nm. Furthermore, within visible light, light in the wavelength range of 420 to 490 nm is blue light, light in the wavelength range of 495 to 570 nm is green light, and light in the wavelength range of 620 to 750 nm is red light, although this is not limited thereto.

[0018] In this specification, the selective reflection central wavelength refers to the average value of two wavelengths that exhibit the half-value transmittance T1 / 2 (%), expressed by the following formula, where Tmin (%) is the minimum value of the transmittance of the target object (member). Formula for calculating half-value transmittance: T1 / 2 = 100 - (100 - Tmin) ÷ 2. Furthermore, the selective reflection central wavelengths of multiple layers being "equal" does not mean that they are strictly equal, and an error within a range that does not have an optical effect is allowed. Specifically, the selective reflection central wavelengths of multiple objects being "equal" means that the difference in the selective reflection central wavelengths between the respective objects is 20 nm or less, and this difference is preferably 15 nm or less, and more preferably 10 nm or less.

[0019] FIG. 1 conceptually shows an example of a liquid crystal diffraction element having an example of an optically anisotropic layer of the present invention. FIG. 1A is an overall view of the liquid crystal diffraction element, and FIG. 1B is a partially enlarged view of FIG. 1A. The following figures are all conceptual views for explaining the present invention. Therefore, the shape, size, thickness, length, height, and positional relationship of each component may not match the actual ones.

[0020] As shown in FIG. 1 , the liquid crystal diffraction element 10 has a structure in which a support 20, an alignment film 24, and an optically anisotropic layer 18 are laminated in this order. The optically anisotropic layer 18 is an optically anisotropic layer formed using a composition containing a liquid crystal compound, and is the optically anisotropic layer of the present invention. Therefore, the optically anisotropic layer 18 has a cholesteric alignment region in which the liquid crystal compound is cholesterically oriented at least in a portion of its plane. As is well known, cholesteric alignment is a state in which the liquid crystal compound is helically twisted and oriented along the helical axis in the thickness direction of the layer. Note that a certain thickness is acceptable within a range that achieves the effects of the present invention. For example, the error is preferably within ±5%, more preferably within ±3%, and even more preferably within ±1%.

[0021] In the optically anisotropic layer of the present invention, the cholesteric alignment region has, in the thickness direction, a layer A having a helical pitch (one pitch of helical alignment), which is the length of a 360° rotation of a cholesterically aligned liquid crystal compound in the thickness direction, of less than 250 nm, and a layer B having a helical pitch of 250 nm or more. The optically anisotropic layer 18 shown in the figure has a first layer 12 and a second layer 14 in the thickness direction. The first layer 12 is layer A in the optically anisotropic layer of the present invention, and has a helical pitch in the cholesteric alignment of less than 250 nm. On the other hand, the second layer 14 is layer B in the optically anisotropic layer of the present invention, and has a helical pitch in the cholesteric alignment of 250 nm or more. The first layer 12 corresponds to layer 328 in FIG. 12 (described later), and the second layer 14 corresponds to layer 326 in FIG. 12 (described later).

[0022] Furthermore, in the optically anisotropic layer 18 of the present invention, the ratio of the thickness of layer A to the thickness of the cholesteric alignment region varies within the plane of the cholesteric alignment region. As an example, the optically anisotropic layer 18 shown in FIG. 1A has a cholesteric alignment region over the entire surface in the plane direction, and the thickness is constant across the entire surface. That is, in the example shown in FIG. 1A, the entire optically anisotropic layer 18 is a cholesteric alignment region. This also applies to FIG. 12, which will be described later. Furthermore, in the optically anisotropic layer 18, the ratio of the thickness of the first layer 12 (layer A), i.e., the film thickness, gradually decreases linearly from right to left in the figure. Therefore, in the optically anisotropic layer 18 whose thickness is constant across the entire surface, the thickness of the second layer 14 (layer B), gradually increases linearly from right to left in the figure. As will be described later, layer A with a helical pitch of less than 250 nm basically has a selective reflection wavelength range for cholesteric alignment in the ultraviolet region, which is shorter in wavelength than visible light. On the other hand, layer B having a helical pitch of 250 nm or more basically has a selective reflection wavelength range of cholesteric alignment in the visible light region. In such an optically anisotropic layer 18, the diffraction efficiency (reflectance) of visible light gradually increases from right to left in the figure.

[0023] The optically anisotropic layer 18 of the present invention has such a configuration, and can make the brightness of light emitted from the light guide plate uniform, for example, in AR glass, etc. Each layer of the liquid crystal diffraction element 10 shown in FIG.

[0024] [Optically anisotropic layer] As described above, the optically anisotropic layer of the present invention is an optically anisotropic layer formed using a composition containing a liquid crystal compound, and the optically anisotropic layer has a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned at a constant film thickness in at least a part of its plane, and the cholesteric alignment region has, in the thickness direction, Layer A having a helical pitch of less than 250 nm and Layer B having a helical pitch of 250 nm or more, and the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region varies within the plane of the cholesteric alignment region.

[0025] One embodiment of the optically anisotropic layer of the present invention is an optically anisotropic layer having regions with different reflectances for visible light in at least a part of the plane of the optically anisotropic layer. For example, the optically anisotropic layer is an optically anisotropic layer in which the reflectance for visible light increases from one side to the other along at least one direction in the plane of the optically anisotropic layer.

[0026] Furthermore, one embodiment of the optically anisotropic layer of the present invention is an optically anisotropic layer (liquid crystal diffraction element) having regions of varying diffraction efficiency within the plane of the optically anisotropic layer when the optical axis direction derived from the liquid crystal compound has a liquid crystal orientation pattern in which the direction continuously rotates along at least one direction in the plane. As an example, the optically anisotropic layer is an optically anisotropic layer (liquid crystal diffraction element) in which the diffraction efficiency increases from one side to the other along at least one direction in the plane of the optically anisotropic layer. As will be described in detail later, the optically anisotropic layer of the present invention (liquid crystal diffraction element using the optically anisotropic layer of the present invention) has such a structure, so that when light propagating within a light guide plate is diffracted by the optically anisotropic layer and emitted from the light guide plate, the brightness of the emitted light can be made uniform. The change in diffraction efficiency may be such that the diffraction efficiency is higher in multiple directions in the plane.

[0027] Figure 17 shows an example of the in-plane distribution of diffraction efficiency in the optically anisotropic layer of the present invention. In Figure 17, the darker the black color, the higher the diffraction efficiency. However, in the optically anisotropic layer of the present invention, the in-plane distribution of diffraction efficiency is not limited to this, and various in-plane distributions of diffraction efficiency can be applied depending on the application, size, design, etc. of the optical element (optical device) using the optically anisotropic layer of the present invention, such as the design of a light guide plate or the FOV of AR glass.

[0028] FIG. 1 conceptually illustrates an example of an embodiment of the optically anisotropic layer of the present invention. As described above, FIG. 1A is an overall view of a liquid crystal diffraction element 10 using the optically anisotropic layer 18 of the present invention, and FIG. 1B is a partially enlarged view of FIG. 1A. Specifically, FIG. 1B is an enlarged view of the area indicated by the dashed circle A in FIG. 1A. Therefore, FIG. 1B shows only the first layer 14 of the optically anisotropic layer 18, which is layer B. The liquid crystal diffraction element 10 shown in FIG. 1 is an element including the optically anisotropic layer 18 of the present invention, which selectively reflects light of a specific wavelength. As will be described later, the liquid crystal diffraction element 10 shown in FIG. 1 is a reflective liquid crystal diffraction element. As described above, the liquid crystal diffraction element 10 has a configuration in which a support 20, an alignment film 24, and an optically anisotropic layer 18 formed using a composition containing a liquid crystal compound are laminated in this order.

[0029] In the present invention, the optically anisotropic layer 18 has, at least in a part of its plane, a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned at a constant film thickness. The cholesteric alignment region has, in the thickness direction, Layer A with a helical pitch of less than 250 nm and Layer B with a helical pitch of 250 nm or more. The ratio of the thickness of Layer A to the thickness of the cholesteric alignment region varies within the plane of the optically anisotropic layer, thereby realizing a configuration having regions with different diffraction efficiencies for visible light within the plane. As described above, in the optically anisotropic layer 18 shown in Figure 1, the first layer 12 is Layer A in the present invention, and the second layer 14 is Layer B in the present invention.

[0030] 1 has a support 20 and an alignment film 24, the optically anisotropic layer of the present invention may not be laminated on the support 20 or the alignment film 24. For example, the optically anisotropic layer of the present invention may be laminated on the alignment film 24 after the support 20 has been peeled off from the above-described structure. Alternatively, the support 20 and the alignment film 24 may be peeled off, and the optically anisotropic layer may be composed of only the optically anisotropic layer 18 formed using a composition containing a liquid crystal compound.

[0031] As shown in FIG. 1B , in a preferred embodiment, the optically anisotropic layer 18 has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. This applies not only to the second layer 14 (layer B) shown in FIG. 1B , but also to the first layer 12 (layer A). When the optically anisotropic layer 18 has such a liquid crystal orientation pattern, the liquid crystal diffraction element 10 (optically anisotropic layer 18) shown in FIG. 1 functions as a reflective liquid crystal diffraction element that controls the emission direction of diffracted light. However, the optically anisotropic layer of the present invention is not limited thereto, and various layer configurations can be used as long as they have regions with different diffraction efficiencies within the plane of the optically anisotropic layer, i.e., a cholesteric alignment region having layers A and B, and a region in which the thickness ratio of layer A varies within the plane of a cholesteric alignment region with a constant film thickness. The optically anisotropic layer 18 of the present invention shown in Figure 1 is, as an example, an optically anisotropic layer (liquid crystal diffraction element) having a configuration in which the diffraction efficiency increases from one side to the other side in one direction in which the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern rotates.

[0032] <Support> The support 20 is a sheet-like object (film, plate-like object) that supports the alignment film 24 and the optically anisotropic layer 18. The support 20 preferably has a transmittance of 50% or more, more preferably 70% or more, and even more preferably 85% or more, to light diffracted by the optically anisotropic layer 18.

[0033] There is no limitation on the thickness of the support 20, and it may be set appropriately to a thickness that can support the alignment film 24 and the optically anisotropic layer 18 depending on the application of the liquid crystal diffraction element 10 and the material forming the support 20. The thickness of the support 20 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0034] The support 20 may be a single layer or a multilayer. When the support 20 is a single layer, various materials used as support materials for various optical elements can be used. Specific examples of the material for the support 20 include glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin. When the support 20 is a multilayer, an example is one that includes any of the above-mentioned single-layer supports as a substrate, with another layer provided on the surface of this substrate.

[0035] <Alignment Film> An alignment film 24 is formed on the surface of the support 20. The alignment film 24 is an alignment film for orienting the liquid crystal compound 30 in a predetermined liquid crystal alignment pattern when the optically anisotropic layer 18 is formed.

[0036] As will be described later, in the liquid crystal diffraction element 10, the optically anisotropic layer 18 has a liquid crystal orientation pattern in which the orientation of the optical axis 30A (see FIG. 2 ) derived from the liquid crystal compound 30 changes while continuously rotating along one in-plane direction. In the present invention, one period (symbol Λ in FIG. 2 , also referred to as the "optical axis rotation period") is defined as the length of the rotation of the optical axis 30A by 180° in one direction in which the orientation of the optical axis 30A in the liquid crystal orientation pattern changes while continuously rotating.

[0037] In the following description, "the orientation of the optical axis 30A rotates" may also be simply referred to as "the optical axis 30A rotates."

[0038] Various known alignment films can be used, including, for example, a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film having microgrooves, and a film formed by accumulating LB (Langmuir-Blodgett) films made of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate by the Langmuir-Blodgett method.

[0039] An alignment film formed by rubbing treatment can be formed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. Preferred materials for the alignment film include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in JP-A-9-152509, and materials used to form alignment films as described in JP-A-2005-097377, JP-A-2005-099228, and JP-A-2005-128503.

[0040] In the liquid crystal diffraction element 10, a so-called photo-alignment film, which is formed by irradiating a photo-alignable material with polarized or non-polarized light, is preferably used as the alignment film. That is, in the liquid crystal diffraction element 10, a photo-alignment film formed by applying a photo-alignment material onto the support 20 is preferably used as the alignment film. Polarized light can be irradiated from a vertical direction or an oblique direction to the photo-alignment film, and non-polarized light can be irradiated from an oblique direction to the photo-alignment film.

[0041] Examples of photo-alignment materials that can be used in the photo-alignment film of the present invention include those disclosed in JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, JP-A-2007-94071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, and JP-A-2007 azo compounds described in JP-A-2009-133184, JP-A-2009-109831, JP-A-3883848 and JP-A-4151746, aromatic ester compounds described in JP-A-2002-229039, maleimides and / or copolymers having photo-alignable units described in JP-A-2002-265541 and JP-A-2002-317013 Alternatively, alkenyl-substituted nadimide compounds, photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyesters described in JP-T-2003-520878, JP-T-2004-529220 and JP-T-4162850, and photodimerizable compounds described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, WO 2010 / 150748, JP-A-2013-177561 and JP-A-2014-12823, particularly cinnamate compounds, chalcone compounds and coumarin compounds are exemplified as preferred examples. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, cinnamate compounds, and chalcone compounds are preferably used.

[0042] There is no limitation on the thickness of the alignment film, and it may be set appropriately depending on the material of which the alignment film is formed so as to obtain the necessary alignment function. The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0043] There is no limitation on the method for forming the alignment film, and various known methods can be used depending on the material for forming the alignment film. One example is a method in which an alignment film is applied to the surface of the support 20, dried, and then exposed to laser light to form an alignment pattern.

[0044] As described above, the optically anisotropic layer 18 shown in Fig. 1 has a liquid crystal orientation pattern in which the direction of the optical axis 30A (see Fig. 2) derived from the liquid crystal compound 30 changes while continuously rotating along one in-plane direction. Fig. 3 conceptually shows an example of an exposure device that exposes an alignment film to light to form an orientation pattern corresponding to this liquid crystal orientation pattern.

[0045] The exposure device 60 shown in Fig. 3 includes a light source 64 equipped with a laser 62 and a λ / 2 plate (not shown), a beam splitter 68 that splits the laser beam M emitted by the light source 64 into two beams MA and MB, mirrors 70A and 70B that are respectively arranged on the optical paths of the two split beams MA and MB, and λ / 4 plates 72A and 72B. Although not shown, the light source 64 emits linearly polarized light P0. The λ / 4 plates 72A and 72B have optical axes parallel to each other. The λ / 4 plate 72A converts the linearly polarized light P0 (beam MA) into right-handed circularly polarized light P R The λ / 4 plate 72B converts the linearly polarized light P0 (light beam MB) into left-handed circularly polarized light P L are converted to , respectively.

[0046] The support 20 having the alignment film 24 before the alignment pattern is placed in an exposure unit, and two light beams MA and MB are caused to intersect and interfere on the alignment film 24, and the alignment film 24 is irradiated with the interference light to expose it. This interference causes the polarization state of the light irradiating the alignment film 24 to periodically change in the form of interference fringes. As a result, an alignment pattern in which the alignment state periodically changes is obtained on the alignment film 24. In the exposure device 60, the period of the alignment pattern can be adjusted by changing the crossing angle α of the two light beams MA and MB. That is, in the exposure device 60, by adjusting the crossing angle α, in an alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 continuously rotates in one direction, the length of one period in which the optical axis 30A rotates 180° in one direction of the rotation of the optical axis 30A can be adjusted. By forming an optically anisotropic layer on an alignment film having such an alignment pattern in which the alignment state changes periodically, it is possible to form an optically anisotropic layer 18 having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 continuously rotates in one direction, as will be described later. In addition, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, respectively, the rotation direction of the optical axis 30A can be reversed.

[0047] In the liquid crystal diffraction element, the alignment film is provided as a preferred embodiment but is not an essential component. For example, by forming an alignment pattern on the support 20 by a method of rubbing the support 20 or a method of processing the support 20 with laser light or the like, it is possible to configure the optically anisotropic layer to have a liquid crystal alignment pattern in which the direction of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating along at least one direction in the plane.

[0048] <Optically Anisotropic Layer> An optically anisotropic layer 18 is formed on the surface of the alignment film 24. As described above, the optically anisotropic layer has a liquid crystal compound cholesterically aligned at a constant film thickness in at least a portion of its plane, and the cholesteric alignment region has, in the thickness direction, a layer A (first layer 12) having a helical pitch of less than 250 nm and a layer B (second layer 14) having a helical pitch of 250 nm or more, and the ratio of the thickness of layer A to the thickness of the cholesteric alignment region varies within the plane of the optically anisotropic layer. Furthermore, in a preferred embodiment, the optically anisotropic layer 18 (cholesteric alignment region) shown in the figure is a layer formed using a composition containing a liquid crystal compound, and has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates along at least one direction within the plane.

[0049] 1 , the optically anisotropic layer 18 has a structure in which the liquid crystal compound is cholesterically aligned. That is, the optically anisotropic layer 18 is a layer formed by fixing a cholesteric liquid crystal phase, and has a cholesteric liquid crystal structure in which the liquid crystal compound is helically twisted and aligned along the helical axis. The optically anisotropic layer 18 has a structure in which liquid crystal compounds 30 are stacked one helical rotation (360° rotation) and the liquid crystal compounds 30 are stacked one helical pitch (helical pitch), and the liquid crystal compounds 30 are stacked at multiple pitches.

[0050] The optically anisotropic layer 18 having a cholesteric liquid crystal structure has wavelength selective reflectivity. For example, when the optically anisotropic layer 18 has a selective reflection center wavelength in the green wavelength region, right-handed circularly polarized green light G R The optically anisotropic layer 18 reflects the right-handed or left-handed circularly polarized light and transmits the other light. Here, the liquid crystal compound 30 is rotated and oriented in the plane direction of the optical anisotropic layer 18, so that the incident circularly polarized light is refracted (diffracted) in a direction in which the direction of the optical axis is continuously rotating, and is reflected. At this time, the direction of diffraction differs depending on the rotation direction of the incident circularly polarized light. In other words, the optically anisotropic layer 18 reflects the right-handed or left-handed circularly polarized light of the selective reflection wavelength and diffracts this reflected light.

[0051] <<Cholesteric Liquid Crystal Phase>> Cholesteric liquid crystal phases exhibit selective reflection for either left- or right-handed circularly polarized light at a specific wavelength. The central wavelength of selective reflection (selective reflection central wavelength) λ depends on the helical pitch, i.e., the pitch P (= helical period) of the helical structure in the cholesteric liquid crystal phase, and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal phase. Therefore, the selective reflection central wavelength can be adjusted by adjusting the pitch of this helical structure. The pitch of a cholesteric liquid crystal phase depends on the type or concentration of the chiral agent used together with the liquid crystal compound when forming the optically anisotropic layer, so the desired pitch can be obtained by adjusting these factors. Details on adjusting the pitch are provided in Fujifilm Research Report No. 50 (2005), pp. 60-63. Methods for measuring the helical sense and pitch can be found in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japanese Liquid Crystal Society, Sigma Publishing, 2007, p. 46, and "Liquid Crystal Handbook," Liquid Crystal Handbook Editorial Committee, Maruzen, p. 196.

[0052] As described above, the cholesteric alignment region, i.e., the cholesteric liquid crystal layer, in the optically anisotropic layer 18 of the present invention has, in the thickness direction, layer A (first layer 12) having a helical pitch of less than 250 nm and layer B (second layer 14) having a helical pitch of 250 nm or more, and the ratio of the thickness of layer A to the thickness of the cholesteric liquid crystal layer varies within the plane of the optically anisotropic layer 18.

[0053] Whether the light reflected by a cholesteric liquid crystal phase is right-handed or left-handed circularly polarized depends on the helical twist (sense) of the cholesteric liquid crystal phase. The selective reflection of circularly polarized light by a cholesteric liquid crystal phase reflects right-handed circularly polarized light when the helical twist of the cholesteric liquid crystal phase is right-handed, and left-handed circularly polarized light when the helical twist of the cholesteric liquid crystal phase is left-handed. In the liquid crystal diffraction element 10 of FIG. 1 , the optically anisotropic layer 18 is, for example, a layer formed by fixing a right-handed cholesteric liquid crystal phase. Therefore, the optically anisotropic layer 18 selectively reflects right-handed circularly polarized light within a predetermined wavelength range. The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the optically anisotropic layer and / or the type of chiral agent added.

[0054] Furthermore, the half-width Δλ (nm) of the selective reflection band (circularly polarized light reflection band) exhibiting selective reflection depends on the Δn of the cholesteric liquid crystal phase and the helical pitch P, and follows the relationship Δλ = Δn × P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by the type of liquid crystal compound forming the optically anisotropic layer, its mixing ratio, and the temperature during alignment fixation. The half-width of the reflection wavelength region is adjusted depending on the application of the liquid crystal diffraction element 10, and may be, for example, 10 to 500 nm, preferably 20 to 300 nm, and more preferably 30 to 200 nm.

[0055] <<Method for Forming an Optically Anisotropic Layer Having a Cholesteric Liquid Crystal Structure>> An optically anisotropic layer having a cholesteric liquid crystal structure can be formed by fixing a cholesteric liquid crystal phase in a layered form. The structure in which the cholesteric liquid crystal phase is fixed may be any structure in which the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. Typically, a preferred structure is one in which a polymerizable liquid crystal compound is oriented in a cholesteric liquid crystal phase, and then polymerized and cured by ultraviolet irradiation, heating, or the like to form a non-fluid layer, while simultaneously changing to a state in which the orientation form is not changed by an external field or external force. Note that in the structure in which the cholesteric liquid crystal phase is fixed, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained; in the optically anisotropic layer, the liquid crystal compound 30 does not need to exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may be polymerized by a curing reaction and lose its liquid crystallinity.

[0056] An example of a material used to form an optically anisotropic layer formed by fixing a cholesteric liquid crystal phase is a liquid crystal composition containing a liquid crystal compound. The liquid crystal compound is preferably a polymerizable liquid crystal compound. The liquid crystal composition used to form the optically anisotropic layer may further contain a surfactant and a chiral agent.

[0057] --Polymerizable Liquid Crystal Compound-- The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a discotic liquid crystal compound. Examples of rod-shaped polymerizable liquid crystal compounds that form a cholesteric liquid crystal phase include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxy compounds, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles. Not only low-molecular-weight liquid crystal compounds but also high-molecular-weight liquid crystal compounds can be used.

[0058] A polymerizable liquid crystal compound can be obtained by introducing a polymerizable group into a liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group, with an unsaturated polymerizable group being preferred, and an ethylenically unsaturated polymerizable group being more preferred. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups contained in the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3. Examples of polymerizable liquid crystal compounds are described in Makromol. Chem. , Vol. 190, p. 2255 (1989), Advanced Materials Vol. 5, p. 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. No. 5,770,107, WO 95 / 22586, WO 95 / 24455, WO 97 / 00600, WO 98 / 23580, WO 98 / 52905, JP-A-1-272551, JP-A-6-016616, JP-A-7-110469, JP-A-11-080081, and compounds described in JP-A-2001-328973 and the like are included. Furthermore, as the rod-shaped liquid crystal compound, for example, those described in JP-A-11-513019 and JP-A-2007-279688 can also be preferably used. Two or more types of polymerizable liquid crystal compounds may be used in combination. When two or more types of polymerizable liquid crystal compounds are used in combination, the alignment temperature can be lowered.

[0059] Other examples of polymerizable liquid crystal compounds that can be used include cyclic organopolysiloxane compounds having a cholesteric phase, such as those disclosed in JP-A-57-165480. Examples of the polymeric liquid crystal compounds that can be used include polymers having mesogen groups exhibiting liquid crystallinity introduced into the main chain, side chain, or both the main chain and side chain, polymeric cholesteric liquid crystals having cholesteryl groups introduced into the side chain, liquid crystalline polymers such as those disclosed in JP-A-9-133810, and liquid crystalline polymers such as those disclosed in JP-A-11-293252.

[0060] --Discotic Liquid Crystal Compound-- As the discotic liquid crystal compound, for example, those described in JP-A Nos. 2007-108732 and 2010-244038 can be preferably used.

[0061] The amount of the polymerizable liquid crystal compound added in the liquid crystal composition is preferably 75 to 99.9 mass %, more preferably 80 to 99 mass %, and even more preferably 85 to 90 mass %, based on the solid content mass (mass excluding the solvent) of the liquid crystal composition.

[0062] From the viewpoint of achieving superior effects of the present invention and obtaining diffracted light with high diffraction efficiency at large diffraction angles, the birefringence Δn of the liquid crystal compound in the cholesteric alignment region of the optically anisotropic layer is preferably 0.15 or more, more preferably 0.20 or more, even more preferably 0.25 or more, even more preferably 0.30 or more, and most preferably 0.35 or more. The upper limit is not particularly limited, but is often 1.00 or less. Liquid crystal compounds exhibiting such high refractive index anisotropy are often compounds with normal dispersion, in which the birefringence Δn450 for incident light with a wavelength of 450 nm is greater than the birefringence Δn550 for incident light with a wavelength of 550 nm. The value of Δn450 / Δn550 is not particularly limited, but is, for example, 0.5 to 2.0, and often 1.0 to 1.5. In the case of a compound with normal dispersion, the diffraction efficiency for each wavelength can be maintained constant by adjusting the selective reflection band exhibiting the above-mentioned selective reflection, the degree of alignment described below, the thickness, etc. For example, by forming a thin layer having a selective reflection band that diffracts incident light of 450 nm and a thick layer having a selective reflection band that diffracts incident light of 550 nm, the diffraction efficiency for each wavelength can be kept constant.

[0063] From the viewpoint of achieving superior effects of the present invention and enabling AR display with a wide viewing angle, the maximum extraordinary refractive index of the liquid crystal compound in the optically anisotropic layer is preferably 1.8 or more, more preferably 1.9 or more, and even more preferably 2.0 or more. The ordinary refractive index of the liquid crystal compound in the optically anisotropic layer is preferably 1.4 or more, more preferably 1.5 or more, and even more preferably 1.6 or more.

[0064] The birefringence Δn and refractive index preferably satisfy the above-mentioned ranges over the range of 380 to 780 nm, and more preferably satisfy the above-mentioned ranges over the range of 400 to 650 nm.

[0065] From the viewpoint of achieving a more excellent effect of the present invention and of realizing an AR display having excellent transparency and high light utilization efficiency, the absorbance of the optically anisotropic layer at 450 nm is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less. In addition, the molar absorption coefficient of the liquid crystal compound used in the optically anisotropic layer at 450 nm is 100 (mol cm). -1 Preferably, 10 (mol cm) or less -1 More preferably, 1 (mol cm) or less -1 The following is even more preferred:

[0066] The absorptivity and molar extinction coefficient preferably satisfy the above-mentioned preferred ranges over the range of 380 to 780 nm, and particularly preferably satisfy the above-mentioned preferred ranges over the range of 400 to 650 nm.

[0067] Specific examples of polymerizable liquid crystal compounds having large refractive index anisotropy include those described in, for example, JP 2009-102245 A, JP 4655348 A, JP 4524827 A, JP 4720200 A, JP 2004-091380 A, JP 3972430 A, JP 4517416 A, JP 2002-128742 A, JP 4810750 A, JP 5888544 A, JP 2014-019654 A, JP 6241654 A, JP 6372060 A, JP 6323144 A, and JP 2005-015 No. 406, JP 2007-230968 A, Japanese Patent No. 6761484 A, Japanese Patent No. 6681992 A, WO 19 / 182129, CN01134217A, KR101069555B, KR101690767B, CN20120229730A, Japanese Patent No. 4053782 A, Japanese Patent No. 2009-249406 A, Japanese Patent No. 4121075 A, Japanese Patent Publication No. 2005-528416 A, US6514578 A, International Publication No. 2006 / 006819, Japanese Patent No. 2011-184417 A, Japanese Patent No. 2013-095685 A , JP 2013-103897 A, JP 2002-088008 A, JP 2002-226412 A, JP 2012-167214 A, JP 2012-167068 A, Japanese Patent Application No. 2018-084511 A, JP 2003-055317 A, JP 2 JP 001-329264 A, JP 2002-030016 A, JP 2003-055664 A, JP 2018-070889 A, CN102557896 A, US2015369982 A, JP 2020-105264 A, JP 2014-2242 No. 37, JP 2012-051862 A, JP 2010-106274 A, JP 2005-179557 A, JP 2005-035985 A, JP 2002-012579 A, ​​JP 2002-003845 A, JP 2001-233837 A, JP 2019-532167 A, JP 2016-509247 A, JP 2010-503733 A, JP 2003-533557 A, WO 2019 / 098115, WO 2018 / 034216, WO 2018 / 221236,Examples of such compounds include those described in WO 2018 / 123396, WO 2018 / 003482, WO 2017 / 086143, WO 20 / 192655, WO 2013 / 161669, and WO 2009 / 104468, and JP 2023-003351.

[0068] In addition to the above, the polymerizable liquid crystal compound also includes the compounds shown below.

[0069]

[0070]

[0071]

[0072]

[0073] --Surfactant-- The liquid crystal composition used in forming the optically anisotropic layer may contain a surfactant. The surfactant is preferably a compound that can function as an alignment control agent that contributes to stably or quickly achieving a planar aligned cholesteric liquid crystal phase. Examples of the surfactant include silicone surfactants and fluorine surfactants, with fluorine surfactants being preferred.

[0074] Specific examples of surfactants include the compounds described in paragraphs

[0082] to

[0090] of JP-A No. 2014-119605, the compounds described in paragraphs

[0031] to

[0034] of JP-A No. 2012-203237, the compounds exemplified in paragraphs

[0092] and

[0093] of JP-A No. 2005-99248, the compounds exemplified in paragraphs

[0076] to

[0078] and paragraphs

[0082] to

[0085] of JP-A No. 2002-129162, and fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of JP-A No. 2007-272185, etc. One type of surfactant may be used alone, or two or more types may be used in combination. As the fluorine-based surfactant, the compounds described in paragraphs

[0082] to

[0090] of JP-A-2014-119605 are preferred.

[0075] The amount of the surfactant added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.02 to 1% by mass, based on the total mass of the liquid crystal compound.

[0076] --Chiral Agents (Optically Active Compounds)--Chiral agents (chiral agents) have the function of inducing a helical structure in a cholesteric liquid crystal phase. Chiral agents can be selected according to the purpose, as the twist direction or helical pitch of the helix they induce varies depending on the compound. There are no particular limitations on the chiral agent, and known compounds (e.g., those described in "Liquid Crystal Device Handbook," Chapter 3, Section 4-3, "Chiral Agents for TN (Twisted Nematic) and STN (Super Twisted Nematic)," p. 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives can be used. Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric or planarly asymmetric compounds without an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric or planarly asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound.In this embodiment, the polymerizable group of the polymerizable chiral agent is preferably the same type of group as the polymerizable group of the polymerizable liquid crystal compound.Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group.In addition, the chiral agent may be a liquid crystal compound.

[0077] When the chiral agent has a photoisomerizable group, it is possible to form a pattern of a desired reflection wavelength corresponding to the emission wavelength by irradiating the chiral agent with actinic rays or the like through a photomask after coating and alignment. The photoisomerizable group is preferably an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0078] -Photoreactive Chiral Agent- A photoreactive chiral agent (photoreactive chiral agent) is a compound having a chiral moiety and a photoreactive moiety that undergoes a structural change upon irradiation with light, and that significantly changes the twisting power of a liquid crystal compound depending on the amount of irradiation, for example. Examples of photoreactive moieties that undergo a structural change upon irradiation with light include photochromic compounds (Kingo Uchida, Masahiro Irie, Chemical Industry, Vol. 64, p. 640, 1999; Kingo Uchida, Masahiro Irie, Fine Chemical, Vol. 28(9), p. 15, 1999). The structural change refers to decomposition, addition reaction, isomerization, racemization, [2+2] photocyclization, dimerization, and the like that occur upon irradiation of the photoreactive moiety with light, and the structural change may be irreversible. Examples of the chiral moiety include the asymmetric carbons described in Hiroyuki Nodaira, Chemistry Review, No. 22, Chemistry of Liquid Crystals, p. 73, 1994.

[0079] Examples of the photoreactive chiral agent (photoreactive chiral agent) include the photoreactive chiral agents described in paragraphs 0044 to 0047 of JP-A-2001-159709, the optically active compounds described in paragraphs 0019 to 0043 of JP-A-2002-179669, the optically active compounds described in paragraphs 0020 to 0044 of JP-A-2002-179633, the optically active compounds described in paragraphs 0016 to 0040 of JP-A-2002-179670, the optically active compounds described in paragraphs 0017 to 0050 of JP-A-2002-179668, and the optically active compounds described in paragraph 00 of JP-A-2002-180051. optically active compounds described in paragraphs 0016 to 0055 of JP-A-2002-338575, optically active isosorbide derivatives described in paragraphs 0016 to 0055 of JP-A-2002-338575, photoreactive optically active compounds described in paragraphs 0023 to 0032 of JP-A-2002-080478, photoreactive chiral agents described in paragraphs 0019 to 0029 of JP-A-2002-080851, optically active compounds described in paragraphs 0022 to 0049 of JP-A-2002-179681, optically active compounds described in paragraphs 0015 to 0044 of JP-A-2002-302487, and paragraphs optically active polyesters described in paragraphs 0015 to 0050 of JP-A-2003-055315, binaphthol derivatives described in paragraphs 0019 to 0041 of JP-A-2003-073381, optically active fulgide compounds described in paragraphs 0008 to 0043 of JP-A-2003-073381, optically active isosorbide derivatives described in paragraphs 0015 to 0057 of JP-A-2003-306490, optically active isosorbide derivatives described in paragraphs 0015 to 0041 of JP-A-2003-306491, optically active isosorbide derivatives described in paragraphs 0015 to 0049 of JP-A-2003-313187, Optically active isomannide derivatives described in paragraphs

[0015] to

[0057] of JP-A-2003-313188, optically active isosorbide derivatives described in paragraphs

[0015] to

[0049] of JP-A-2003-313189, optically active polyester / amides described in paragraphs

[0015] to

[0052] of JP-A-2003-313292, optically active compounds described in paragraphs

[0012] to

[0053] of WO 2018 / 194157, and optically active compounds described in paragraphs

[0020] to

[0049] of JP-A-2002-179682, photoreactive chiral agents described in Japanese Patent No. 7302306,Examples include the photoreactive chiral agents described in Japanese Patent No. 7141461.

[0080] Among the chiral agents, compounds having at least a photoisomerizable moiety are preferred, and the photoisomerizable moiety more preferably has a photoisomerizable double bond. As the photoisomerizable moiety having the photoisomerizable double bond, a cinnamoyl moiety, a chalcone moiety, an azobenzene moiety, or a stilbene moiety is preferred in that photoisomerization is likely to occur and the difference in helical twisting power before and after light irradiation is large, and a cinnamoyl moiety, a chalcone moiety, or a stilbene moiety is more preferred in that they have low visible light absorption. The photoisomerizable moiety corresponds to the photoreactive moiety that undergoes a structural change upon light irradiation as described above.

[0081] Furthermore, the chiral agent preferably has a trans-type photoisomerizable double bond, in that it has a high initial helical twisting power (before light irradiation) and a larger decrease in the helical twisting power due to light irradiation, and more preferably has a cis-type photoisomerizable double bond, in that it has a low initial helical twisting power (before light irradiation) and a larger increase in the helical twisting power due to light irradiation.

[0082] The chiral agent preferably has any partial structure selected from a binaphthyl partial structure, an isosorbide partial structure (a partial structure derived from isosorbide), and an isomannide partial structure (a partial structure derived from isomannide). The binaphthyl partial structure, the isosorbide partial structure, and the isomannide partial structure each refer to the following structures. The portion in the binaphthyl partial structure where the solid line and the dashed line are parallel represents a single bond or a double bond. In the structures shown below, * represents the bond position.

[0083]

[0084] The chiral agent may have a polymerizable group. The type of the polymerizable group is not particularly limited, and is preferably a functional group capable of undergoing an addition polymerization reaction, more preferably a polymerizable ethylenically unsaturated group or a ring-polymerizable group, and still more preferably a (meth)acryloyl group, a vinyl group, a styryl group, or an allyl group.

[0085] An embodiment may use two or more chiral agents, or an embodiment may use at least one photoreactive chiral agent and at least one chiral agent whose helical twisting power does not change upon irradiation with light. From the viewpoint of reducing the amount of chiral agent added, it is preferable that the helices induced by the contained chiral agents are all the same.

[0086] The molar absorption coefficient of the photoreactive chiral agent is not particularly limited, but the molar absorption coefficient at the wavelength of light irradiated in Step 3 described below (e.g., 365 nm) is preferably 100 to 100,000 L / (mol cm), and more preferably 500 to 50,000 L / (mol cm).

[0087] The content of each chiral agent in the composition layer can be appropriately set depending on the helical pitch of the optically anisotropic layer to be formed.

[0088] The total content of the chiral dopant in the composition layer is not particularly limited, but is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, and even more preferably 13.0% by mass or less, relative to the total mass of the liquid crystal compound, in order to facilitate uniform alignment of the liquid crystal compound. The lower limit is not particularly limited, but is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass.

[0089] The content of the chiral dopant in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol %, based on the molar amount of the liquid crystal compound.

[0090] --Polymerization initiator-- When the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator. In an embodiment in which the polymerization reaction is caused to proceed by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator that can initiate the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Pat. No. 2,722,512), polynuclear quinone compounds (described in U.S. Pat. Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Pat. No. 3,549,367), acridine and phenazine compounds (described in JP-A No. 60-105,667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (described in U.S. Pat. No. 4,212,970). The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, based on the content of the liquid crystal compound.

[0091] Crosslinking Agent The liquid crystal composition may optionally contain a crosslinking agent to improve the film strength and durability after curing. Suitable crosslinking agents are those that cure under ultraviolet light, heat, moisture, or the like. The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl (meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. Furthermore, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used alone or in combination of two or more. The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the mass of the solid content of the liquid crystal composition. When the content of the crosslinking agent is within the above range, the effect of improving the crosslink density is easily obtained, and the stability of the cholesteric liquid crystal phase is further improved.

[0092] --Other Additives-- If necessary, the liquid crystal composition may further contain a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, metal oxide fine particles, etc., within a range that does not impair optical performance, etc. From the viewpoint of increasing the viewing angle of AR display, high-refractive-index nanoparticles such as zirconia oxide nanoparticles and titanium oxide nanoparticles may be added.

[0093] The liquid crystal composition is preferably used as a liquid when forming an optically anisotropic layer. The liquid crystal composition may contain a solvent. The solvent is not limited and can be appropriately selected depending on the purpose, but organic solvents are preferred. The organic solvent is not limited and can be appropriately selected depending on the purpose, and examples thereof include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used alone or in combination of two or more. Among these, ketones are preferred when considering the environmental impact.

[0094] When forming an optically anisotropic layer, it is preferable to apply a liquid crystal composition to the surface on which the optically anisotropic layer is formed, align the liquid crystal compound in a cholesteric liquid crystal phase, and then harden the liquid crystal compound to form an optically anisotropic layer. That is, when forming an optically anisotropic layer on an alignment film, it is preferable to apply a liquid crystal composition to the alignment film, align the liquid crystal compound in a cholesteric liquid crystal phase, and then harden the liquid crystal compound to fix the cholesteric liquid crystal phase to form an optically anisotropic layer. The liquid crystal composition can be applied by any of printing methods such as inkjet printing and scroll printing, as well as any of known methods that can uniformly apply a liquid to a sheet-like material, such as spin coating, bar coating, and spray coating.

[0095] The coated liquid crystal composition is dried and / or heated as necessary, and then cured to form an optically anisotropic layer. During this drying and / or heating process, the liquid crystal compound in the liquid crystal composition may be oriented in a cholesteric liquid crystal phase. When heating is performed, the heating temperature is preferably 200° C. or lower, and more preferably 130° C. or lower.

[0096] The aligned liquid crystal compound is further polymerized as needed. The polymerization may be either thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. The light irradiation is preferably performed using ultraviolet light. The irradiation energy is 20 mJ / cm. 2 ~50 J / cm 2 is preferred, and 50 to 1500 mJ / cm 2In order to promote the photopolymerization reaction, the irradiation may be carried out under heated conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet light to be irradiated is preferably 250 to 430 nm.

[0097] There is no restriction on the thickness of the optically anisotropic layer, and the thickness that provides the required light reflectance can be appropriately set depending on the application of the liquid crystal diffraction element 10, the light reflectance required for the optically anisotropic layer, and the material from which the optically anisotropic layer is formed, etc.

[0098] <<Liquid Crystal Alignment Pattern of Optically Anisotropic Layer (Cholesteric Alignment Region)>> As described above, in a preferred embodiment, the optically anisotropic layer 18 has a liquid crystal alignment pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction in the plane of the optically anisotropic layer 18. In the example shown in Fig. 1 , the optical anisotropic layer has a liquid crystal alignment pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 that forms a cholesteric liquid crystal phase changes while continuously rotating in one direction in the plane of the optically anisotropic layer. In the example shown in Fig. 1 , the cholesteric alignment region of the optically anisotropic layer 18, i.e., the first layer 12 which is layer A in the cholesteric liquid crystal layer having a helical pitch of less than 250 nm, and the second layer 14 which is layer B in the cholesteric liquid crystal layer having a helical pitch of 250 nm or more, both have a liquid crystal alignment pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction in the plane. The optical axis 30A derived from the liquid crystal compound 30 is the axis along which the refractive index of the liquid crystal compound 30 is highest, that is, the so-called slow axis. For example, when the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is aligned with the long axis direction of the rod shape. In the following description, the optical axis 30A derived from the liquid crystal compound 30 is also referred to as the "optical axis 30A of the liquid crystal compound 30" or the "optical axis 30A."

[0099] Fig. 2 conceptually shows a plan view of the optically anisotropic layer 18 shown in Fig. 1. The plan view is a view of the liquid crystal diffraction element 10 in Fig. 1 as seen from above, i.e., a view of the liquid crystal diffraction element 10 as seen from the thickness direction (i.e., the stacking direction of each layer (film)). In Fig. 2, in order to clearly show the configuration of the optically anisotropic layer 18, only the liquid crystal compound 30 on the surface of the alignment film 24 is shown.

[0100] As shown in FIG. 2 , on the surface of the alignment film 24, the liquid crystal compound 30 constituting the optically anisotropic layer 18 is two-dimensionally aligned in a predetermined direction indicated by arrow X and in a direction perpendicular to this direction (arrow X direction) according to the alignment pattern formed on the underlying alignment film 24. In the following description, the direction perpendicular to the arrow X direction will be referred to as the Y direction for convenience. That is, in FIG. 1 and FIGS. 4 , 7 , 9 , and 10 described below, the Y direction is perpendicular to the paper surface. Furthermore, the liquid crystal compound 30 constituting the optically anisotropic layer 18 has a liquid crystal alignment pattern in which the direction of the optic axis 30A changes while continuously rotating along the arrow X direction within the plane of the optically anisotropic layer 18. In the example shown in FIGS. 1 and 2 , the liquid crystal compound 30 has a liquid crystal alignment pattern in which the optic axis 30A of the liquid crystal compound 30 changes while continuously rotating clockwise along the arrow X direction. The expression "the orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of arrow X (a predetermined direction)" specifically means that the angle formed between the optical axis 30A of the liquid crystal compound 30 aligned along the direction of arrow X and the direction of arrow X varies depending on the position in the direction of arrow X, and the angle formed between the optical axis 30A and the direction of arrow X sequentially changes from θ to θ+180° or θ−180° along the direction of arrow X. Note that the difference in angle between the optical axes 30A of the liquid crystal compounds 30 adjacent to each other in the direction of arrow X is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0101] On the other hand, the liquid crystal compound 30 forming the optically anisotropic layer 18 has the same orientation of the optical axis 30A in the Y direction perpendicular to the direction of the arrow X, i.e., the Y direction perpendicular to the direction in which the optical axis 30A continuously rotates. In other words, the liquid crystal compound 30 forming the optically anisotropic layer 18 has the same angle between the optical axis 30A of the liquid crystal compound 30 and the direction of the arrow X in the Y direction.

[0102] In the present invention, in the liquid crystal orientation pattern of such liquid crystal compound 30, the length (distance) over which the optical axis 30A of the liquid crystal compound 30 rotates 180° in the direction of arrow X, in which the optical axis 30A continuously rotates and changes in the plane, is defined as the length Λ of one period in the liquid crystal orientation pattern. That is, the distance between the centers of two liquid crystal compounds 30 in the direction of arrow X, which are at the same angle with respect to the direction of arrow X, is defined as the length Λ of one period. Specifically, as shown in FIG. 2, the distance between the centers of two liquid crystal compounds 30 in the direction of arrow X, in which the direction of the optical axis 30A coincides with the direction of arrow X, is defined as the length Λ of one period. In the following description, this length Λ of one period is also referred to as "one period Λ." In the liquid crystal diffraction element 10 of the present invention, the liquid crystal orientation pattern of the optically anisotropic layer repeats this one period Λ in the direction of arrow X, i.e., in one direction in which the orientation of the optical axis 30A continuously rotates and changes.

[0103] A typical cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase typically specularly reflects incident light (circularly polarized light). In contrast, an optically anisotropic layer 18 having the liquid crystal orientation pattern described above reflects incident light in a direction angled in the direction of arrow X relative to the specular reflection. For example, the optically anisotropic layer 18 does not reflect light incident from the normal direction in the normal direction, but rather reflects it at an angle in the direction of arrow X relative to the normal direction. Light incident from the normal direction is light incident from the front, that is, light incident perpendicular to the main surface. The main surface is the largest surface of the sheet-like material. The following description will be made with reference to FIG. 4.

[0104] As described above, the optically anisotropic layer 18 is an optically anisotropic layer (cholesteric liquid crystal layer) that selectively reflects one of the circularly polarized light wavelengths. For example, when the selective reflection wavelength of the optically anisotropic layer 18 is red light and the optically anisotropic layer 18 reflects right-handed circularly polarized light, the optically anisotropic layer 18 reflects the light R. R When right-handed circularly polarized red light R is incident on the optically anisotropic layer 18, the right-handed circularly polarized red light R R It reflects only light and transmits all other light.

[0105] Here, the reflection angle of light by an optically anisotropic layer in which the optical axis 30A of the liquid crystal compound 30 continuously rotates in one direction (the direction of the arrow X) varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of light, the larger the angle of the reflected light relative to the incident light. Furthermore, the reflection angle of light by an optically anisotropic layer in which the optical axis 30A of the liquid crystal compound 30 continuously rotates in the direction of the arrow X (one direction) varies depending on the length Λ of one period of the liquid crystal orientation pattern in which the optical axis 30A rotates 180° in the direction of the arrow X, i.e., one period Λ. Specifically, the shorter the one period Λ, the larger the angle of the reflected light relative to the incident light.

[0106] In the present invention, there is no limitation on one period Λ in the alignment pattern of the optically anisotropic layer, and it may be set appropriately depending on the use of the optically anisotropic layer, etc.

[0107] Here, the optically anisotropic layer of the present invention is suitably used, for example, in AR glasses as a diffraction element that reflects light propagated through a light guide plate and emits it from the light guide plate to a user's observation position. In this case, in order to reliably emit the light propagated through the light guide plate, it is necessary to reflect the light at a certain large angle relative to the incident light. Furthermore, as described above, the reflection angle of light by the optically anisotropic layer relative to the incident light can be increased by shortening one period Λ in the liquid crystal orientation pattern.

[0108] In consideration of this point, one period Λ of the liquid crystal alignment pattern of the optically anisotropic layer is preferably 50 μm or less, more preferably 10 μm or less, and even more preferably 1 μm or less. In consideration of the accuracy of the liquid crystal alignment pattern, one period Λ of the liquid crystal alignment pattern of the optically anisotropic layer is preferably 0.1 μm or more.

[0109] <<Diffraction Efficiency of Optically Anisotropic Layer>> In the present invention, the cholesteric alignment region (cholesteric liquid crystal layer) of the optically anisotropic layer has the liquid crystal alignment pattern described above as a preferred embodiment, and the cholesteric liquid crystal layer has a configuration in which the diffraction efficiency increases from one side to the other in one direction in which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern continuously rotates in the plane (hereinafter referred to as one direction in which the optical axis rotates). As described above, in the example shown in FIG. 1 (FIGS. 1A and 1B), the entire surface of the optically anisotropic layer 18 is a cholesteric alignment region (cholesteric liquid crystal layer). Therefore, the optically anisotropic layer 18 has a configuration in which the diffraction efficiency increases from one side to the other in one direction in which the optical axis rotates throughout the entire region. For example, in the case of the optically anisotropic layer 18 shown in FIGS. 1 and 2, the diffraction efficiency increases from one side to the other in the X direction.

[0110] 5 and 6 are schematic graphs showing an example of the relationship between the position in one direction (X direction) in which the optic axis of the optically anisotropic layer 18 rotates and the diffraction efficiency at that position. In the present invention, the change in the diffraction efficiency of the optically anisotropic layer 18 in the X direction may be a continuous change as shown in FIG. 5 or a stepwise change as shown in FIG. 6. The continuous change as shown in FIG. 5 may be a linear change, or may include a mixture of a curved change region and a linear change region. This change in diffraction efficiency is the same even when the optically anisotropic layer does not have a liquid crystal alignment pattern, and is also the same even when the optically anisotropic layer has a liquid crystal alignment pattern but the change in diffraction efficiency is unrelated to the one direction in which the optic axis rotates.

[0111] In the present invention, the diffraction efficiency is measured as follows. Specifically, the optically anisotropic layer 18 is transferred to a Dove prism 110 (refractive index = 1.517, inclined surface angle = 45°) as shown in FIG. 10 . Laser light of a predetermined wavelength is transmitted through a linear polarizer 112 and a λ / 4 plate 114 to become circularly polarized light (right-handed circularly polarized light in this example) in the rotation direction reflected by the optically anisotropic layer 18 (cholesteric liquid crystal layer). The angle of the laser light is set so that the diffracted light (light reflected by the optically anisotropic layer 18) emerges from a desired position on the Dove prism 110 at a desired angle, and the laser light is incident on the surface of the optically anisotropic layer 18. In the example shown in FIG. 10 , the laser light is incident on the bottom surface of the Dove prism 110, and the angle of the laser light is adjusted so that the diffracted light emerges perpendicularly from the inclined surface of the Dove prism 110, but this is not limiting. For example, as in the example described below, laser light may be incident on the inclined surface of the Dove prism and diffracted light may be emitted from the bottom surface of the Dove prism. In this case, the intensity of the diffracted light, Lr, is measured using a Newport Power Meter 1918-C, and the ratio of this intensity to the incident light, Li, is defined as (Lr / Li) x 100 [%], which is the diffraction efficiency.

[0112] The optically anisotropic layer 18 (cholesteric alignment region) in the illustrated example has a region in which the diffraction efficiency increases from one side to the other in one direction of rotation of the optical axis of the liquid crystal alignment pattern. Therefore, when the optically anisotropic layer of the present invention is used as a diffraction element in a light guide element used in an AR display device such as AR (Augmented Reality) glasses, which diffracts light propagating within a light guide plate and emits it from the light guide plate, the brightness (light amount) of the light emitted from the light guide plate can be made uniform even when the exit pupil is enlarged. This point will be described in detail later.

[0113] In the optically anisotropic layer, the direction of change in diffraction efficiency may or may not coincide with the direction in which the optical axis rotates in the liquid crystal alignment pattern. That is, the direction of change in diffraction efficiency may intersect with the direction in which the optical axis rotates. In the optically anisotropic layer of the present invention, even if the direction of change in diffraction efficiency intersects with the direction in which the optical axis rotates, it is preferable that the diffraction efficiency increases from one side to the other in the direction in which the optical axis rotates. As will be described later, the change in diffraction efficiency in the optically anisotropic layer is achieved by varying the ratio of the thickness of the layer A having a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region within the plane of the cholesteric alignment region. Therefore, when the direction of change in the ratio of the thickness of the layer A having a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region intersects with the direction in which the optical axis rotates, it is preferable that the thickness ratio of the layer A change from one side to the other in the direction in which the optical axis rotates. Furthermore, it is preferable that the direction in which the thickness ratio of layer A changes in the cholesteric orientation region is parallel to the direction in which the optical axis rotates, and in this case, it is also preferable that the thickness ratio of layer A changes as it moves from one side to the other side of the direction in which the optical axis rotates.

[0114] A configuration in which the diffraction efficiency of an optically anisotropic layer increases from one side to the other along at least one direction in the plane of the optically anisotropic layer can be achieved by a configuration in which, in a cholesteric alignment region in which a liquid crystal compound is cholesterically aligned at a constant film thickness, the cholesteric alignment region has, in the thickness direction, a layer A with a helical pitch of less than 250 nm and a layer B with a helical pitch of 250 nm or more, and the ratio of the thickness of layer A to the thickness of the cholesteric alignment region gradually changes from one side to the other along at least one direction in the plane.

[0115] Specifically, as shown in FIGS. 1 and 12 , the optically anisotropic layer 18, i.e., the cholesteric alignment region (optically anisotropic layer 324), includes, in the thickness direction, a second layer 14 (layer 326) corresponding to Layer B of the present invention and having a helical pitch of 250 nm or more, and a first layer 12 (layer 328) corresponding to Layer A of the present invention and having a helical pitch of less than 250 nm. In this description, the reference numerals in parentheses indicate the corresponding components in FIG. 12 . The total thickness of the second layer 14, which is Layer B with a helical pitch of 250 nm or more, and the first layer 12, which is Layer A with a helical pitch of less than 250 nm, i.e., the thickness of the optically anisotropic layer 18, is constant in the in-plane direction. Furthermore, the ratio of the thickness of the first layer 12, which is Layer A with a helical pitch of less than 250 nm, to the thickness of the optically anisotropic layer 18 gradually decreases from one side to the other in the in-plane direction. In the illustrated example, the thickness ratio of the first layer 12, which is layer A, gradually decreases from the right side to the left side in the drawing.

[0116] As described above, the optically anisotropic layer 18 is a cholesteric liquid crystal layer having a liquid crystal orientation pattern, i.e., a reflective liquid crystal diffraction element. Furthermore, layer B, which has a helical pitch of 250 nm or more, has a selective reflection wavelength range of the cholesteric liquid crystal layer (cholesteric liquid crystal phase) in the visible light region. On the other hand, layer A, which has a helical pitch of less than 250 nm, has a selective reflection wavelength range of the cholesteric liquid crystal layer in the ultraviolet region, which has a wavelength shorter than that of visible light. In other words, layer A hardly reflects visible light even when it is incident on it. Therefore, in an optically anisotropic layer (cholesteric liquid crystal layer) having the above-described liquid crystal orientation pattern, layer A, which has a helical pitch of less than 250 nm, has low diffraction efficiency for light with wavelengths longer than visible light. On the other hand, layer B, which has a helical pitch of 250 nm or more, has high diffraction efficiency for light with wavelengths longer than visible light. Furthermore, the reflectivity of a cholesteric liquid crystal layer generally increases with thickness.

[0117] Here, the optically anisotropic layer of the present invention is used, for example, for displaying images in AR display devices such as AR glasses. Therefore, it is important that the optically anisotropic layer of the present invention has high diffraction efficiency for visible light. That is, in the present invention, the diffraction efficiency refers to the diffraction efficiency for visible light.

[0118] Thus, in the optically anisotropic layer of the present invention, the diffraction efficiency is high in the thick region of Layer B, which has a helical pitch of 250 nm or more, and low in the thick region of Layer A, which has a helical pitch of less than 250 nm. Therefore, by configuring the optically anisotropic layer to have, in the thickness direction, Layer B, which has a helical pitch of 250 nm or more, and Layer A, which has a helical pitch of less than 250 nm, and the thickness ratio of Layer A, which has a helical pitch of less than 250 nm and has a low diffraction efficiency for visible light, gradually decrease from one side to the other along one in-plane direction, the diffraction efficiency can be configured to increase from one side to the other along at least one in-plane direction of the optically anisotropic layer. When such an optically anisotropic layer of the present invention is used in, for example, AR glass, the brightness (light amount) of light emitted from the light guide plate can be made uniform even when the exit pupil is expanded.

[0119] As described above, the optically anisotropic layer of the present invention has a cholesteric alignment region (cholesteric liquid crystal layer) with a constant film thickness, and the cholesteric alignment region has, in the thickness direction, Layer A, which has a helical pitch of less than 250 nm and selectively reflects light in the ultraviolet wavelength range or shorter, and Layer B, which has a helical pitch of 250 nm or longer and selectively reflects light in the visible wavelength range or longer. Furthermore, the optically anisotropic layer of the present invention changes its in-plane diffraction efficiency by changing the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region.

[0120] That is, the optically anisotropic layer of the present invention has, in the thickness direction in the cholesteric alignment region, a layer B having a helical pitch that selectively reflects visible light and a layer A having a helical pitch that does not reflect visible light, and the light that is not to be reflected is incident on the layer A having a helical pitch that does not reflect visible light, and the diffraction efficiency is changed in-plane by changing the thickness ratio of the layer A having a helical pitch that does not reflect visible light. In other words, the optically anisotropic layer of the present invention has, in the thickness direction in the cholesteric alignment region, a layer B that selectively reflects visible light and a layer A that does not reflect visible light, and the light that is not to be reflected by the layer B escapes to the layer B that does not reflect visible light. Here, a cholesteric liquid crystal layer having a selective reflection wavelength range in the infrared wavelength range is also considered as a cholesteric liquid crystal layer that transmits visible light without reflecting it. In a cholesteric liquid crystal layer, the shorter the wavelength of the light that is selectively reflected, the more chiral agent must be added to the composition that forms the cholesteric liquid crystal layer. Therefore, in terms of cost, a cholesteric liquid crystal layer that selectively reflects infrared light is more advantageous than a cholesteric liquid crystal layer that selectively reflects ultraviolet light. In contrast, in the optically anisotropic layer of the present invention, Layer A, which is a cholesteric liquid crystal layer that selectively reflects light with wavelengths shorter than ultraviolet light, is used as a layer that transmits visible light without reflecting it, thereby suppressing unnecessary diffraction of transmitted light.

[0121] As is well known, a cholesteric liquid crystal layer selectively reflects circularly polarized light in a specific wavelength range with a specific rotation direction, while transmitting other light. Here, a diffraction element generates diffraction by reflection and transmission. Therefore, in a cholesteric liquid crystal layer having a liquid crystal orientation pattern such as that shown in Figure 1, which is a reflective liquid crystal diffraction element, transmitted light other than the light to be reflected is diffracted and transmitted. Such unwanted transmitted diffracted light can cause a deterioration in the quality of optical devices. For example, when an optically anisotropic layer is used as a diffraction element for emitting light from a light guide plate of AR glass, the undesired diffracted light that passes through the optically anisotropic layer may become stray light and be observed by the user, resulting in a deterioration in image quality.

[0122] Here, as a result of research, the inventors have found that when light of a certain wavelength passes through a cholesteric liquid crystal layer, diffraction of the transmitted light can be suppressed if the wavelength that the cholesteric liquid crystal layer selectively reflects is shorter than the wavelength of the light.

[0123] When a cholesteric liquid crystal layer is cut in the thickness direction and the cross section is observed with a scanning electron microscope (SEM), dark regions 330 and light regions 332 parallel to the main surface are alternately observed in the thickness direction in the cross-sectional SEM image, as conceptually shown in FIG. 23 , due to the twisted orientation (cholesteric orientation) of the liquid crystal compound in the cholesteric liquid crystal layer. FIG. 12 shows the dark regions 330 and light regions 332 in this cross-sectional SEM image. Two dark regions 330 and two light regions 332 correspond to the helical pitch (pitch P) in the cholesteric orientation. Therefore, in the cross-sectional SEM image of the cholesteric liquid crystal layer, light and dark regions exist at a certain period depending on the helical pitch. Because the dark regions 330 and light regions 332 have different refractive indices, the cholesteric liquid crystal layer has a refractive index distribution at a certain period in the thickness direction.

[0124] As described above, a cholesteric liquid crystal layer (cholesteric liquid crystal phase) has a cholesteric orientation in which the liquid crystal compound is helically twisted along a helical axis in the thickness direction. Furthermore, the longer the helical pitch of the liquid crystal compound, which rotates 360° in the thickness direction, the longer the wavelength of the selectively reflected light. Therefore, the longer the wavelength of light selectively reflected by the cholesteric liquid crystal layer, the longer the refractive index period (the period between light and dark areas), and the shorter the wavelength of light selectively reflected by the cholesteric liquid crystal layer, the shorter the refractive index period. According to the inventors' studies, when light of a certain wavelength passes through the cholesteric liquid crystal layer, if the wavelength selectively reflected by the cholesteric liquid crystal layer is short, the refractive index period corresponding to the helical pitch is short relative to the wavelength of the transmitted light. Therefore, the transmitted light is less affected by the periodic change in refractive index, and the diffraction of the transmitted light is also very small. On the other hand, when light of a certain wavelength passes through a cholesteric liquid crystal layer, if the wavelength at which the cholesteric liquid crystal layer selectively reflects this transmitted light is long, the period of the refractive index corresponding to the helical pitch is long relative to the wavelength of the transmitted light, so the transmitted light is affected by the periodic change in the refractive index and is diffracted.

[0125] Furthermore, when the cholesteric liquid crystal layer (cholesteric orientation region) has a liquid crystal orientation pattern, as in this example, i.e., in the case of a reflective liquid crystal diffraction element, the dark regions 330 and the light regions 332 are tilted with respect to the main surface, as conceptually shown in FIG. 24 . Note that this cross-sectional SEM image is a cross-sectional SEM image of a section cut along one direction in which the optical axis of the liquid crystal orientation pattern rotates. The tilt angle of the dark regions 330 and the light regions 332 depends not only on the length of one period of the above-mentioned liquid crystal orientation pattern but also on the wavelength of light selectively reflected by the cholesteric liquid crystal layer. Specifically, the longer the wavelength of light selectively reflected by the cholesteric liquid crystal layer, the longer the helical pitch, and therefore the greater the tilt angle of the dark regions 330 and the light regions 332 with respect to the main surface. Therefore, compared to a cholesteric liquid crystal layer that selectively reflects ultraviolet light, a cholesteric liquid crystal layer that selectively reflects infrared light has a larger tilt angle of the dark regions 330 and the light regions 332 with respect to the main surface.

[0126] According to the inventors' investigations, the larger the angle of inclination of the dark and light regions 330 and 332 relative to the principal surface, the stronger the effect as a diffraction grating, increasing the amount of transmitted light diffraction, since the periodic distribution of refractive index also has components in the in-plane direction of the layer. Therefore, a cholesteric liquid crystal layer that selectively reflects infrared light has a large effect on transmitted light, causing it to diffract. In contrast, a cholesteric liquid crystal layer that selectively reflects ultraviolet light has a large effect on transmitted light, causing it to diffract.

[0127] That is, the optically anisotropic layer of the present invention can change the diffraction efficiency in the plane while suppressing transmission diffraction by providing, in the thickness direction, a layer B that selectively reflects visible light and a layer A that selectively reflects light of wavelengths shorter than ultraviolet light in a cholesteric alignment region having a constant film thickness.

[0128] In addition, in the optically anisotropic layer of the present invention, Layer B (second layer 14 (layer 326 in FIG. 12 )) of the cholesteric alignment region is usually the incident side for the target visible light. For example, when the optically anisotropic layer of the present invention is used as an output diffraction element from a light guide plate in AR glass, Layer B of the cholesteric alignment region faces the light guide plate. That is, in the optically anisotropic layer of the present invention, Layer A (first layer 12 (layer 328 in FIG. 12 )) of the cholesteric alignment region is the incident side for the ambient light. As described above, Layer A selectively reflects light with wavelengths equal to or shorter than ultraviolet light. Therefore, in the optically anisotropic layer of the present invention, by selecting the helical pitch of Layer A, ultraviolet light contained in ambient light can be reflected by Layer A, and the ultraviolet light incident on Layer B can be reduced. Therefore, the optically anisotropic layer of the present invention can suppress deterioration of Layer B (decomposition of the liquid crystal compound in Layer B) due to ultraviolet light, and improve weather resistance (durability).

[0129] In the examples shown in FIGS. 1 and 12 above, the cholesteric alignment region, i.e., the cholesteric liquid crystal layer, has a liquid crystal alignment pattern in which the optical axis changes while continuously rotating in one direction (at least one direction). However, the present invention is not limited thereto. That is, the cholesteric alignment region, i.e., the cholesteric liquid crystal layer, of the optically anisotropic layer of the present invention does not have to have a liquid crystal alignment pattern. In other words, the optically anisotropic layer of the present invention does not have to be a diffraction element. Even in this case, the reflectance can be changed in-plane by keeping the film thickness of the cholesteric alignment region constant and varying the thickness ratio of layer A in-plane. Preferably, as in the above example, the thickness ratio of layer A can be gradually decreased from one side to the other along one direction in the plane of the cholesteric alignment region, thereby increasing the reflectance from one side to the other along one direction.

[0130] Here, if the cholesteric alignment region, i.e., the cholesteric liquid crystal layer, does not have a liquid crystal alignment pattern, the diffraction of transmitted light as described above does not occur. However, if layer A is a cholesteric liquid crystal layer that selectively reflects light with wavelengths equal to or greater than infrared, when light is incident from an oblique direction, a so-called blue shift occurs, in which the selectively reflected wavelength becomes shorter, and layer A may unnecessarily reflect the incident visible light. In contrast, if layer A is a cholesteric liquid crystal layer that selectively reflects light with wavelengths equal to or less than ultraviolet, layer A will not unnecessarily reflect the incident visible light even if light is incident from an oblique direction and a blue shift occurs. Furthermore, even if the cholesteric alignment region does not have a liquid crystal alignment pattern, layer A's reflection of ultraviolet light can similarly improve the weather resistance of the optically anisotropic layer (cholesteric alignment region).

[0131] In the optically anisotropic layer of the present invention, it is preferable that, in the cholesteric alignment region, the thickness ratio of the layer A having a helical pitch of less than 250 nm gradually decreases from one side to the other along one in-plane direction, as described above. For example, in the examples shown in Figures 1 and 12, as a preferred embodiment, the thickness ratio of the layer A having a helical pitch of less than 250 nm in the cholesteric alignment region gradually decreases from one side to the other along one in-plane direction. However, the optically anisotropic layer of the present invention is not limited thereto. That is, in the cholesteric alignment region of the optically anisotropic layer of the present invention, for example, the thickness ratio of the layer A having a helical pitch of less than 250 nm may be configured to change stepwise, or regions having different thickness ratios of the layer A having a helical pitch of less than 250 nm may be scattered like islands in a sea. That is, as shown above in the in-plane distribution of diffraction efficiency, in the optically anisotropic layer of the present invention, the change in the thickness ratio of layer A in the plane of the cholesteric alignment region can be made in various modes depending on the application, size, and design of the optical element (optical device) using the optically anisotropic layer of the present invention, for example, the design of a light guide plate, the FOV in AR glass, etc. Note that, as mentioned above, when the cholesteric alignment region (cholesteric liquid crystal layer) of the optically anisotropic layer has a liquid crystal alignment pattern, it is preferable that one direction in which the optical axis rotates in the liquid crystal alignment pattern and one in-plane direction in which the diffraction efficiency gradually changes, i.e., one in-plane direction in which the thickness ratio of layer A gradually changes, are parallel.

[0132] In the plane of the optically anisotropic layer (cholesteric alignment region), the maximum thickness of Layer B having a helical pitch of 250 nm or more is preferably 0.1 to 10 μm, more preferably 0.3 to 8 μm, and even more preferably 0.5 to 5 μm. In the plane of the optically anisotropic layer, the minimum thickness of Layer B having a helical pitch of 250 nm or more is preferably 0.0 to 5 μm, more preferably 0.0 to 3 μm, and even more preferably 0.0 to 1 μm. In the optically anisotropic layer of the present invention, the cholesteric alignment region is, as described above, a region having a constant film thickness, comprising Layer A and Layer B, and further having a different thickness ratio of Layer A to the thickness of the cholesteric alignment region within the plane. That is, in the present invention, such a cholesteric alignment region may partially have regions where the thickness of Layer B is zero, i.e., regions where Layer B is absent. The maximum thickness of Layer A having a helical pitch of less than 250 nm in the plane of the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.3 to 8 μm, and even more preferably 0.5 to 5 μm. The minimum thickness of Layer A having a helical pitch of less than 250 nm in the plane of the optically anisotropic layer is preferably 0.0 to 5 μm, more preferably 0.0 to 3 μm, and even more preferably 0.0 to 1 μm. That is, in the present invention, the cholesteric alignment region may partially have a region where the thickness of Layer A is zero, i.e., a region where Layer A is absent. The maximum ratio of the thickness of Layer A having a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region is preferably 0.1 to 1.0, more preferably 0.3 to 1.0, and even more preferably 0.5 to 1.0. The minimum value of the ratio of the thickness of the layer A having a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region is preferably 0.0 to 0.5, more preferably 0.0 to 0.3, and even more preferably 0.0 to 0.1. As mentioned above, in the present invention, the cholesteric alignment region may partially have a region in its plane where the thickness of the layer A is zero.

[0133] From the viewpoints of making the diffraction efficiency uniform over wavelength and in-plane and suppressing decomposition of the liquid crystal compound, the helical pitch of Layer A having a helical pitch of less than 250 nm is preferably 100 to 240 nm, more preferably 140 to 230 nm, and even more preferably 180 to 220 nm. The helical pitch of Layer B having a helical pitch of 250 nm or more can be selected arbitrarily.

[0134] In the examples shown in Figures 1 and 12, in the cholesteric alignment region, both layer B, which has a helical pitch of 250 nm or more, and layer A, which has a helical pitch of less than 250 nm, have a constant helical pitch. However, the present invention is not limited to this, and the helical pitch may vary in the thickness direction in layer A and / or layer B. For example, by keeping the helical pitch of layer A constant and gradually increasing the helical pitch of layer B in the thickness direction, the wavelength range of visible light reflected by layer B can be broadened. Alternatively, as in the optically anisotropic layer 340 conceptually shown in Figure 18, the helical pitch of both layer A and layer B may gradually vary in the thickness direction, and this variation may differ in the in-plane direction, resulting in a cholesteric alignment region in which the proportion of layer A with a helical pitch of less than 250 nm varies in the plane. 18 is a diagram showing a cross section of the optically anisotropic layer in the thickness direction, and the helical pitch at each position is expressed as density, with the darker the black, the longer the helical pitch. In other words, in this example, as in the examples shown in FIGS. 1 and 12, the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region gradually decreases from right to left in the figure.

[0135] In the optically anisotropic layer of the present invention, the difference between the helical pitch of Layer A, which has a helical pitch of less than 250 nm, and the helical pitch of Layer B, which has a helical pitch of 250 nm or more, is not limited, as long as both are within a predetermined helical pitch range. Here, if the helical pitches of Layer A, which has a helical pitch of less than 250 nm, and Layer B, which has a helical pitch of 250 nm or more, are close to each other, the diffraction efficiency for blue light will inevitably be high, making it difficult to diffract visible light uniformly. Therefore, in order to make the diffraction efficiency uniform across wavelength and in-plane, the difference in the helical pitch between Layer A and Layer B is preferably 20 nm or more, more preferably 40 nm or more. There is no particular upper limit to the difference in the helical pitch between Layer A and Layer B, but it is usually less than 1000 nm.

[0136] In the optically anisotropic layer of the present invention, the liquid crystal compound constituting Layer A, which has a helical pitch of less than 250 nm, and the liquid crystal compound constituting Layer B, which has a helical pitch of 250 nm or more, are not limited, and the liquid crystal compounds described above can be used, for example. Here, from the viewpoint of equalizing the refractive indexes of Layer A and Layer B and suppressing reflection at the interface between Layer A and Layer B, it is preferable that the compound compositions constituting Layer A and Layer B be identical (or substantially identical). In particular, in a configuration in which the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region in the optically anisotropic layer gradually changes, the interface between Layer A and Layer B becomes non-parallel to the cholesteric alignment region, the optically anisotropic layer, and the light guide plate. In this case, it has been found that interfacial reflection due to the difference in refractive index between Layer A and Layer B generates reflected light that is non-parallel to the guided light, resulting in stray light (scattering). Considering this point, it is preferable that the compound compositions constituting Layer A and Layer B be identical. The compound composition can be confirmed by, for example, TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry). Even if Layer A and / or Layer B contain a compound having stereoisomers or geometric isomers and the abundance ratio of the isomers differs between Layer A and Layer B, the compound compositions are considered to be equal if the sum of the contents of the isomers is equal and the contents of other compounds are also equal. In this case, the content of each compound in Layer A is preferably within ±10% of the content of each compound in Layer B.

[0137] In the cholesteric alignment region of the optically anisotropic layer, it is preferable that Layer A, which has a helical pitch of less than 250 nm, and Layer B, which has a helical pitch of 250 nm or more, have the ordinary refractive index of Layer A equal to that of Layer B in the in-plane and thickness directions, and that the extraordinary refractive index of Layer A equal to that of Layer B. This configuration is advantageous in that it prevents interfacial reflection at the interface between Layer A and Layer B. The ordinary and extraordinary refractive indices of Layer A and Layer B can be measured, for example, using ellipsometry. In this case, it is preferable that the ordinary and extraordinary refractive indices of Layer A are within ±10% of the ordinary and extraordinary refractive indices of Layer B, and in this case, the above-mentioned condition that the ordinary and extraordinary refractive indices are equal is satisfied.

[0138] Here, the optically anisotropic layer of the present invention may have a region different from the cholesteric alignment region in the in-plane direction. As described above, the cholesteric alignment region is a diffraction region that diffracts (reflects and diffracts) light. The optically anisotropic layer of the present invention may have such a diffraction region and a region that does not have a diffraction effect (hereinafter also referred to as a non-diffraction region).

[0139] Fig. 19 is a conceptual diagram illustrating another example of the optically anisotropic layer of the present invention. Fig. 20 is a top view of Fig. 19. The optically anisotropic layer 400 shown in Figs. 19 and 20 is formed using a composition containing a liquid crystal compound, and the liquid crystal compound is oriented in different in-plane directions to form a first diffraction region 45a, a non-diffraction region 45b, and a second diffraction region 45c. The non-diffraction region 45b is disposed between the first diffraction region 45a and the second diffraction region B 45c. In the following description, when it is not necessary to distinguish between the first diffraction region 45a, the second diffraction region 45c, and a third diffraction region 45d (see Fig. 21) described later, they are also simply referred to as diffraction regions.

[0140] As described above, the diffraction region has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and functions as a liquid crystal diffraction element that diffracts incident light. The configurations of the liquid crystal orientation pattern and the like of each diffraction region may be the same or different. At least one of the diffraction regions has a cholesteric orientation region in which the liquid crystal compound is cholesterically oriented at a constant film thickness. The cholesteric orientation region has, in the thickness direction, a layer A having a helical pitch of less than 250 nm and a layer B having a helical pitch of 250 nm or more, and the ratio of the thickness of layer A to the thickness of the cholesteric orientation region varies within the plane of the cholesteric orientation region. That is, at least one of the diffraction regions is a cholesteric orientation region in the optically anisotropic layer of the present invention.

[0141] The first diffractive region 45a, the non-diffractive region 45b, and the second diffractive region 45c have approximately the same thickness, and the optically anisotropic layer 400 has both main surfaces that are smooth and flat without any uneven structure.

[0142] The non-diffraction region 45b may be a non-oriented region in which the liquid crystal compound is not oriented, i.e., an optically isotropic region, or a region in which the liquid crystal compound is oriented in one direction in the same plane. In the non-diffraction region 45b, the liquid crystal compound may be uniaxially oriented, twisted, or cholesterically oriented in the thickness direction. In the case of cholesteric orientation, a helical pitch of less than 250 nm is preferable in order to prevent reflection of visible light. Furthermore, the non-diffraction region 45b may have a structure in which a region in which the liquid crystal compound is uniaxially oriented, twisted, or cholesterically oriented in the thickness direction and an isotropic region are stacked.

[0143] When the non-diffraction region 45b is a region in which the liquid crystal compound is oriented in one direction in the same plane, the non-diffraction region 45b preferably functions as a retardation region. The retardation region preferably imparts a retardation of λ / 8 to light from at least one incident direction. As a result, for example, when the optically anisotropic layer 400 is laminated to a light guide plate as described below, circularly polarized light that is diffracted by the first diffraction region 45a on the incident side and enters the light guide plate is converted into elliptically polarized light by passing through the non-diffraction region 45b during light guide within the light guide plate, undergoes total reflection at the interface between the non-diffraction region 45b and air, and is then converted into linearly polarized light by passing through the non-diffraction region 45b again. While the polarization state of circularly polarized light is eliminated during light guide, linearly polarized light can maintain its polarization state during light guide, making it possible to uniform the light intensity of the output light from the second diffraction region 45c on the output side.

[0144] 19 and 20 , the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal orientation pattern of the first diffraction region 45 a and the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal orientation pattern of the second diffraction region 45 c may be the same or different. Furthermore, the direction of rotation of the optical axis in the liquid crystal orientation pattern of the first diffraction region 45 a and the direction of rotation of the optical axis in the liquid crystal orientation pattern of the second diffraction region 45 c may be the same or different. Furthermore, the length (length of one period Λ) over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern of the first diffraction region 45 a rotates 180° in the plane may be the same as or different from the length (length of one period Λ) over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern of the second diffraction region 45 c rotates 180° in the plane.

[0145] As will be described later, when the optically anisotropic layer is combined with a light guide plate and used as a light guide element, for example, the first diffraction region 45a acts as an incident diffraction element for making light incident on the light guide plate, and the second diffraction region 45c acts as an exit diffraction element for making light exit from the light guide plate. Therefore, the first diffraction region 45a and the second diffraction region 45c have different diffraction performances required. Therefore, the first diffraction region 45a and the second diffraction region 45c only need to be set according to the required diffraction performance, such as the rotation direction, one period, and one direction of the optical axis direction derived from the liquid crystal compound in the liquid crystal orientation pattern. The liquid crystal orientation pattern in the first diffraction region 45a and the liquid crystal orientation pattern in the second diffraction region 45c may be different.

[0146] 19 and 20 , the first diffraction region 45 a and the second diffraction region 45 c may be cholesteric liquid crystal layers that reflect and diffract light, respectively, or the first diffraction region 45 a may be a cholesteric liquid crystal layer and the second diffraction region 45 c may be an optically anisotropic layer that transmits and diffracts light (also referred to as a transmission diffraction layer), or the first diffraction region 45 a may be a transmission diffraction layer and the second diffraction region 45 c may be a cholesteric liquid crystal layer. In either configuration, at least one cholesteric liquid crystal layer is a cholesteric alignment region in the optically anisotropic layer of the present invention, which has the above-mentioned layer A and layer B, as described above.

[0147] 19 and 20, when the first diffraction region 45a and the second diffraction region 45c are cholesteric liquid crystal layers, the helical pitch length of the cholesteric liquid crystal layer in the first diffraction region 45a and the helical pitch length of the cholesteric liquid crystal layer in the second diffraction region 45c may be different from each other. For example, when the optically anisotropic layer is combined with a light guide plate and the first diffraction region 45a is used as an input diffraction element and the second diffraction region 45c is used as an output diffraction element, light is incident on the first diffraction region 45a from a substantially perpendicular direction, while light is incident on the second diffraction region 45c from an oblique direction. As described above, the cholesteric liquid crystal layer has wavelength-selective reflectivity, but when light is incident from an oblique direction, a so-called blue shift occurs, in which the selectively reflected wavelength is shortened. Therefore, even if the first diffraction region 45a and the second diffraction region 45c diffract light of the same wavelength, it is preferable to set an appropriate spiral pitch length for each region depending on the incident angle of the light, etc.

[0148] Furthermore, when the first diffraction region 45 a and the second diffraction region 45 c are cholesteric liquid crystal layers, the direction of rotation of the helix of the cholesteric alignment in the first diffraction region 45 a may be different from the direction of rotation of the helix of the cholesteric alignment in the second diffraction region 45 c. That is, the direction of rotation of the circularly polarized light reflected by the first diffraction region 45 a may be different from the direction of rotation of the circularly polarized light reflected by the second diffraction region 45 c. For example, when the optically anisotropic layer is combined with a light guide plate, and the first diffraction region 45 a is used as an input diffraction element and the second diffraction region 45 c is used as an output diffraction element, even if right-handed circularly polarized light is incident on the light guide plate from the first diffraction region 45 a, the light may be depolarized while being totally reflected and guided within the light guide plate and enter the second diffraction region 45 c, and may become unpolarized or light containing a left-handed circularly polarized component such as elliptically polarized light. Therefore, the circularly polarized light reflected and diffracted by the second diffraction region 45c may be different from the circularly polarized light reflected and diffracted by the first diffraction region 45a.

[0149] 19 and 20, the optically anisotropic layer has two diffraction regions, but this is not limiting. That is, the optically anisotropic layer of the present invention may further have a third diffraction region 45d having a diffractive effect in the in-plane direction of the same optically anisotropic layer.

[0150] Fig. 21 is a plan view conceptually illustrating another example of the optically anisotropic layer of the present invention. The optically anisotropic layer 450 shown in Fig. 21 has a first diffraction region 45a, a second diffraction region 45c, a third diffraction region 45d, and a non-diffraction region 45b. As shown in Fig. 21, the first diffraction region 45a and the third diffraction region 45d are spaced apart in the left-right direction in the figure, and the third diffraction region 45d and the second diffraction region 45c are spaced apart in the up-down direction in the figure. Non-diffraction regions 45b are formed between the first diffraction region 45a and the third diffraction region 45d, and between the third diffraction region 45d and the second diffraction region 45c.

[0151] Like the first and second diffraction regions 45a and 45c, the third diffraction region 45d has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one in-plane direction. Like the first and second diffraction regions 45a and 45c, the third diffraction region 45d may be a cholesteric liquid crystal layer or a transmissive diffraction layer. The liquid crystal orientation pattern in the third diffraction region 45d may be the same as or different from the liquid crystal orientation patterns in the first and second diffraction regions 45a and 45c, respectively. However, as described above, at least one of the three diffraction regions in the optically anisotropic layer 450 is a cholesteric orientation region in the optically anisotropic layer of the present invention, which includes the above-described Layer A and Layer B. This also applies to optically anisotropic layers of the present invention having four or more diffraction regions.

[0152] Thus, the optically anisotropic layer 450 further including the third diffraction region 45d has three diffraction regions that diffract light. Such an optically anisotropic layer 450 is used in combination with a light guide plate to form a light guide element. In this case, as described below, for example, the first diffraction region 45a acts as an incident diffraction element for directing light into the light guide plate, the second diffraction region 45c acts as an exit diffraction element for directing light out of the light guide plate, and the third diffraction region 45d acts as an intermediate diffraction element that diffracts light incident from the first diffraction region 45a toward the second diffraction region 45c. In this way, the third diffraction region 45d, acting as an intermediate diffraction element, can diffract a portion of the light at multiple locations and emit it out of the light guide plate, thereby achieving an exit pupil expansion. Furthermore, when the third diffraction region 45d is a cholesteric alignment region according to the present invention, it is preferable that the third diffraction region 45d has a region with different diffraction efficiency in the in-plane direction, and that the diffraction efficiency gradually changes in this region.

[0153] In the optically anisotropic layer of the present invention, the cholesteric alignment region may have an optically isotropic region in a part of the thickness direction.

[0154] [Laminate] The laminate is a laminate formed by stacking two or more of the optically anisotropic layers described above. FIG. 22 is a conceptual diagram illustrating an example of a laminate. The laminate 500 shown in FIG. 22 has a first optically anisotropic layer 400a and a second optically anisotropic layer 400b. The first optically anisotropic layer 400a has a first diffraction region 410a having a liquid crystal alignment pattern, a second diffraction region 410c, and a non-diffraction region 410b. The second optically anisotropic layer 400b has a first diffraction region 420a having a liquid crystal alignment pattern, a second diffraction region 420c, and a non-diffraction region 420b. The basic configurations of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b are the same as those of the optically anisotropic layer 400 shown in FIGS. 19 and 20 .

[0155] 22, the first diffraction region 410a of the first optically anisotropic layer 400a and the first diffraction region 420a of the second optically anisotropic layer 400b are arranged in an overlapping position. The non-diffraction region 410b of the first optically anisotropic layer 400a and the non-diffraction region 420b of the second optically anisotropic layer 400b are also arranged in an overlapping position. The second diffraction region 410c of the first optically anisotropic layer 400a and the second diffraction region 420c of the second optically anisotropic layer 400b are also arranged in an overlapping position.

[0156] 22, the laminate is configured to have two optically anisotropic layers stacked, but is not limited to this and may have three or more optically anisotropic layers stacked. Even in the case of a configuration in which three or more optically anisotropic layers are stacked, it is preferable that the first diffraction regions, second diffraction regions, and non-diffraction regions of each optically anisotropic layer are stacked in positions where they overlap.

[0157] 21 may be a laminate of two or more optically anisotropic layers each having a third diffraction region 45d, in which case the third diffraction regions of the optically anisotropic layers are preferably stacked so as to overlap each other.

[0158] In the laminate having the optically anisotropic layer of the present invention, it is preferable that all the optically anisotropic layers are the optically anisotropic layers of the present invention having the cholesteric alignment regions including the above-mentioned Layer A and Layer B. However, there is no limitation thereto, and it is sufficient that at least one of the optically anisotropic layers is the optically anisotropic layer of the present invention. In other words, at least one of the optically anisotropic layers constituting the laminate is the cholesteric alignment region in the optically anisotropic layer of the present invention, in which at least one diffraction region has the above-mentioned Layer A and Layer B.

[0159] 22 preferably satisfies at least one of the following conditions A and B. Condition A is that the first diffraction region 410a of the first optically anisotropic layer 400a and the first diffraction region 420a of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the helical pitch length of the cholesteric liquid crystal layer in the first diffraction region 410a of the first optically anisotropic layer 400a is different from the helical pitch length of the cholesteric liquid crystal layer in the first diffraction region 420a of the second optically anisotropic layer 400b. On the other hand, condition B is that the second diffraction region 410c of the first optically anisotropic layer 400a and the second diffraction region 420c of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the length of the helical pitch of the cholesteric liquid crystal layer in the second diffraction region 410c of the first optically anisotropic layer 400a is different from the length of the helical pitch of the cholesteric liquid crystal layer in the second diffraction region 420c of the second optically anisotropic layer 400b.

[0160] As described above, the cholesteric liquid crystal layer reflects light of a specific wavelength depending on the length of the helical pitch. By making the helical pitch lengths of the first diffraction regions 45a and / or the second diffraction regions 45c of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b different, the first diffraction regions 45a and / or the second diffraction regions 45c of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b reflect and diffract light of different wavelengths. As will be described later, when a light guide element combining the laminate 500 with a light guide plate is used in an AR display device or the like, if the AR display device displays a color image, the light guide element needs to guide light of two or more wavelengths, for example, R (red), G (green), and B (blue). Therefore, the laminate is preferably configured by laminating optically anisotropic layers having a first diffraction region and a second diffraction region (and a third diffraction region) that reflect and diffract light of these wavelengths. For example, the first diffraction region and the second diffraction region of the first optically anisotropic layer may be configured as cholesteric liquid crystal layers having a selective reflection wavelength in the red wavelength range, and the first diffraction region and the second diffraction region of the second optically anisotropic layer may be configured as cholesteric liquid crystal layers having a selective reflection wavelength in the green wavelength range.

[0161] 22 preferably satisfies at least one of the following conditions C and D. Condition C is that the first diffraction region 410a of the first optically anisotropic layer 400a and the first diffraction region 420a of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the direction of helical rotation of the cholesteric liquid crystal layer in the first diffraction region 410a of the first optically anisotropic layer 400a is different from the direction of helical rotation of the cholesteric liquid crystal layer in the first diffraction region 420a of the second optically anisotropic layer 400b. On the other hand, condition D is that the second diffraction region 410c of the first optically anisotropic layer 400a and the second diffraction region 420c of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the direction of rotation of the spiral of the cholesteric liquid crystal layer in the second diffraction region 410c of the first optically anisotropic layer 400a is different from the direction of rotation of the spiral of the cholesteric liquid crystal layer in the second diffraction region 420c of the second optically anisotropic layer 400b.

[0162] As described above, the cholesteric liquid crystal layer has circular polarization selectivity depending on the rotation direction of the helix in the helical structure. By making the rotation directions of the helices of the first diffraction regions and / or the second diffraction regions of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b different from each other, it is possible to achieve a configuration in which, for example, the first diffraction region 410a of the first optically anisotropic layer 400a reflects and diffracts right-handed circularly polarized light of a certain wavelength, the first diffraction region 420a of the second optically anisotropic layer 400b reflects and diffracts left-handed circularly polarized light of the same wavelength, and / or the second diffraction region 410c of the first optically anisotropic layer 400a reflects and diffracts right-handed circularly polarized light of a certain wavelength, and the second diffraction region 420c of the second optically anisotropic layer 400b reflects and diffracts left-handed circularly polarized light of the same wavelength.

[0163] Here, in a laminate using the optically anisotropic layer of the present invention, one or more of the diffraction regions of each optically anisotropic layer may have a liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound described above changes while continuously rotating in at least one direction.

[0164] In the laminate 500 shown in Fig. 22, when at least one of the diffraction regions of each optically anisotropic layer has a liquid crystal orientation pattern, it is preferable to satisfy at least one of the following conditions E and F. Condition E is that the length of one period in which the orientation of the optical axis derived from the liquid crystal compound of the liquid crystal orientation pattern in the first diffraction region 410a of the first optically anisotropic layer 400a rotates 180° in the plane is different from the length of one period in the first diffraction region 420a of the second optically anisotropic layer 400b. On the other hand, Condition F is that the length of one period in which the orientation of the optical axis derived from the liquid crystal compound in the second diffraction region 410c of the first optically anisotropic layer 400a rotates 180° in the plane is different from the length of one period in the second diffraction region 420c of the second optically anisotropic layer 400b.

[0165] As described above, the diffraction angles in the first diffraction region and the second diffraction region are determined according to the length of one period in the liquid crystal orientation pattern. Furthermore, even if the length of one period is the same, the diffraction angles will differ depending on the wavelength of light. Therefore, for example, as described above, if the first diffraction regions and / or the second diffraction regions of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b have different helical pitch lengths, and the first optically anisotropic layer 400a and the second optically anisotropic layer 400b reflect and diffract light of different wavelengths, if the lengths of one period in the liquid crystal orientation pattern are the same, the diffraction angles will be different, and the light will be emitted in different directions. Therefore, it is preferable to make the length of one period of the liquid crystal orientation pattern different between the first diffraction regions and / or the second diffraction regions of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b so that the diffraction angles of light by the first diffraction regions and / or the second diffraction regions of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b are the same.

[0166] 22 , when at least one of the diffraction regions of each optically anisotropic layer has a liquid crystal orientation pattern, it is preferable to satisfy at least one of the following conditions G and H. Condition G requires that one direction of the liquid crystal orientation pattern in the first diffraction region 410a of the first optically anisotropic layer 400a is different from one direction of the liquid crystal orientation pattern in the first diffraction region 420a of the second optically anisotropic layer 400b. On the other hand, Condition H requires that one direction of the liquid crystal orientation pattern in the second diffraction region 410c of the first optically anisotropic layer 400a is different from one direction of the liquid crystal orientation pattern in the second diffraction region 420c of the second optically anisotropic layer 400b.

[0167] This allows, for example, light diffracted in the first diffraction region 410a of the first optically anisotropic layer 400a to be selectively diffracted in the second diffraction region 410c of the first optically anisotropic layer 400a. Similarly, light diffracted in the first diffraction region 420a of the second optically anisotropic layer 400b to be selectively diffracted in the second diffraction region 420c of the second optically anisotropic layer 400b. In other words, it is possible to selectively diffract light in each of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b. This makes it possible to avoid color crosstalk, for example, when it is desired to diffract light of different wavelengths in the first optically anisotropic layer 400a and the second optically anisotropic layer 400b.

[0168] Furthermore, in the laminate 500 shown in Figure 22, when at least one of the diffraction regions of each optically anisotropic layer has a liquid crystal orientation pattern, it is preferable to satisfy at least one of the following conditions I and J. Condition I is that the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern in the first diffraction region 410a of the first optically anisotropic layer 400a is different from the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern in the first diffraction region 420a of the second optically anisotropic layer 400b. On the other hand, Condition J is that the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern in the second diffraction region 410c of the first optically anisotropic layer 400a is different from the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern in the second diffraction region 420c of the second optically anisotropic layer 400b.

[0169] [Light Guide Element and AR Display Device] The light guide element of the present invention includes the above-described optically anisotropic layer of the present invention and a light guide plate. The AR (Augmented Reality) display device of the present invention includes the light guide element of the present invention and an image display device.

[0170] An example of an embodiment of the AR display device of the present invention is conceptually shown in Fig. 7. The AR display device 50 shown in Fig. 7 has a display (image display device) 40 and a light guide element 45.

[0171] Light guide element 45 is a light guide element of the present invention, and includes optically anisotropic layer 400 of the present invention shown in FIGS. 19 and 20 and light guide plate 144. The light guide element of the present invention may also have a configuration including a laminate having multiple optically anisotropic layers and a light guide plate. In other words, the light guide element of the present invention may have multiple optically anisotropic layers. Furthermore, the light guide element of the present invention is not limited to a configuration including an optically anisotropic layer having multiple diffraction regions, and may also have a configuration in which a single optically anisotropic layer is disposed at the incident position and the exit position on the surface of the light guide plate, as shown in FIG. 16 .

[0172] As described above, the optically anisotropic layer 400 is a single optically anisotropic layer formed of three regions: the first diffraction region 45a, the non-diffraction region 45b, and the second diffraction region 45c. In the first diffraction region 45a and the second diffraction region 45c, the direction in which the optical axis of the liquid crystal alignment pattern rotates is the direction of arrow X, as described above. The light guide plate 144 has a rectangular parallelepiped shape that is elongated in one direction and guides light therein. As shown in FIG. 7 , the first diffraction region 45a of the optically anisotropic layer 400 is disposed on the surface (main surface) of the light guide plate 144 at one end in the longitudinal direction. Furthermore, the second diffraction region 45c of the optically anisotropic layer 400 is disposed on the surface of the light guide plate 144 at the other end. The position of the first diffraction region 45a of the optically anisotropic layer 400 corresponds to the position of light incidence on the light guide plate 144, and the position of the second diffraction region 45c of the optically anisotropic layer 400 corresponds to the position of light emission on the light guide plate 144. In addition, an optically isotropic non-diffraction region 45b is formed between the first diffraction region 45a and the second diffraction region 45c.

[0173] The first diffraction region 45a of the optically anisotropic layer 400 is an incident diffraction element region that diffracts light that is irradiated from the display 40 and enters the light guide plate 144 so as to be totally reflected within the light guide plate 144. The second diffraction region 45c of the optically anisotropic layer 400 is an output diffraction element region that diffracts light that has been guided within the light guide plate 144 so as to be output from the light guide plate 144.

[0174] There are no particular limitations on the light guide plate 144, and any conventional light guide plate known in the art and used in image display devices and the like can be used.

[0175] Various materials used as materials for light guide plates in optical elements can be used for the light guide plate 144. Specifically, examples of materials for the light guide plate 144 include glass, acrylic, polycarbonate, polystyrene, urethane, polyolefin, polyvinyl chloride, polyethylene terephthalate (PET), and triacetyl cellulose (TAC).

[0176] There are no limitations on the thickness of the light guide plate 144, and it may be set appropriately taking into consideration the thickness that can support the optically anisotropic layer, the light weight of the light guide plate, the uniformity of the brightness (amount of light) of the light emitted from the light guide plate, and the like. The thickness of the light guide plate 144 is preferably 0.02 to 2.0 mm, more preferably 0.05 to 1.0 mm, and even more preferably 0.1 to 0.5 μm. The refractive index of the light guide plate is preferably 1.5 or more, more preferably 1.8 or more, and even more preferably 2.0 or more. The difference between the extraordinary refractive index of the liquid crystal compound inside the optically anisotropic layer and the refractive index of the light guide plate is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less.

[0177] As shown in Figure 7, the display 40 is disposed facing one end of the light guide plate 144, on the surface opposite to the surface on which the optically anisotropic layer 400 is disposed. The user U's observation position is on the surface of one end of the light guide plate 144 opposite to the surface on which the optically anisotropic layer 400 is disposed. In the following description, the longitudinal direction of the light guide plate 144 is referred to as the X direction, and the direction perpendicular to the X direction and perpendicular to the surface of the optically anisotropic layer is referred to as the Z direction. The Z direction is also the thickness direction of each layer in the optically anisotropic layer (see Figure 1). There are no limitations on the display 40, and various known displays used in AR display devices such as AR glasses can be used. Examples of the display 40 include a liquid crystal display (including LCOS (Liquid Crystal On Silicon) and the like), an organic electroluminescence display, a DLP (Digital Light Processing), a μLED (Micro Light Emitting Diode) display, a laser beam scanning system using a MEMS (Micro-Electro-Mechanical Systems) mirror, etc. The display 40 may be one that displays monochrome images, two-color images, or color images.

[0178] In the optically anisotropic layer of the present invention, a display that emits polarized light is preferably used because the cholesteric liquid crystal layer, such as a cholesteric alignment region, has polarization selectivity. For example, a display that displays red and blue images by emitting right-handed circularly polarized light and green images by emitting left-handed circularly polarized light may be used, and an optically anisotropic layer (diffraction region) that diffracts corresponding right-handed circularly polarized red light, an optically anisotropic layer (diffraction region) that diffracts left-handed green circularly polarized light, and an optically anisotropic layer (diffraction region) that diffracts right-handed blue circularly polarized light may be laminated on a light guide plate. This results in different polarization states for adjacent wavelengths of red and green, and green and blue, making it possible to avoid color crosstalk. Furthermore, for example, by using a display that displays an image corresponding to an FOV of 0 to 50° by emitting right-handed circularly polarized light and an image corresponding to an FOV of −50 to 0° by emitting left-handed circularly polarized light, and laminating an optically anisotropic layer (diffraction region) that diffracts the corresponding right-handed circularly polarized light and an optically anisotropic layer (diffraction region) that diffracts the corresponding left-handed circularly polarized light on a light guide plate, the FOV can be expanded by two times compared to when no polarized light is used.

[0179] In the AR display device 50 configured as described above, light displayed by the display 40 enters the light guide plate 144 from one end of the light guide plate 144, on the surface opposite to the surface on which the optically anisotropic layer 400 is disposed, as indicated by the arrow. The light that enters the light guide plate 144 is reflected by the first diffraction region 45a of the optically anisotropic layer 400. At this time, due to the diffraction effect of the first diffraction region 45a, the light is not specularly reflected (regularly reflected), but is reflected in a direction at an angle different from the specular reflection direction. In the example shown in FIG. 7 , the light enters the first diffraction region 45a of the optically anisotropic layer 400 from a direction approximately perpendicular (Z direction) and is reflected in a direction tilted at a large angle from the perpendicular direction toward the longitudinal direction (X direction) of the light guide plate 144.

[0180] Because the light reflected by the first diffraction region 45a of the optically anisotropic layer 400 is reflected at a large angle relative to the angle of the incident light, the angle of the light's traveling direction with respect to the surface of the light guide plate 144 becomes small, and the light is totally reflected by the surface of the light guide plate 144 or the surface of the region 45b of the optically anisotropic layer 400, and is guided in the longitudinal direction (X direction) of the light guide plate 144. The guided light is reflected by the second diffraction region 45c of the optically anisotropic layer 400 at the other end of the longitudinal direction of the light guide plate 144. At this time, due to the diffraction effect of the second diffraction region 45c of the optically anisotropic layer 400, the light is not specularly reflected, but is reflected in a direction at an angle different from the specular reflection direction. In the example shown in FIG. 7 , light is incident on the second diffraction region 45c of the optically anisotropic layer 400 from an oblique direction and is reflected in a direction perpendicular to the surface of the second diffraction region 45c of the optically anisotropic layer 400.

[0181] The light reflected by the second diffraction region 45c of the optically anisotropic layer 400 reaches the surface of the light guide plate 144 opposite to the surface on which the optically anisotropic layer 400 is disposed, but because it is incident on this surface approximately perpendicularly, it is not totally reflected and is emitted to the outside of the light guide plate 144. In other words, the light is emitted to the observation position of the user U. In this way, the AR display device 50 displays a virtual image superimposed on the scene actually viewed by the user U by causing the image displayed by the display 40 to enter one end of the light guide plate 144, propagate therethrough, and emit from the other end.

[0182] Here, the second diffraction region 45c of the optically anisotropic layer 400 is configured such that when light propagating through the light guide plate 144 is diffracted by the second diffraction region 45c of the optically anisotropic layer 400, a portion of the light is diffracted at multiple locations and emitted to the outside of the light guide plate 144, thereby expanding the viewing zone (exit pupil expansion). Specifically, in Fig. 7, light I propagating through the light guide plate 144 is repeatedly reflected by both surfaces (interfaces) of the light guide plate 144 and reaches the position of the second diffraction region 45c of the optically anisotropic layer 400. The light I that has reached the position of the second diffraction region 45c of the liquid crystal diffraction element is partially diffracted in a region P1 close to the incident side and is emitted from the light guide plate 144 (emitted light R1). The undiffracted light I further propagates within the light guide plate 144, and a portion of the light R is diffracted again at a position P of the second diffraction region 45 c of the optically anisotropic layer 400 to be emitted from the light guide plate 144. The undiffracted light I further propagates within the light guide plate 144, and a portion of the light R is diffracted again at a position P of the second diffraction region 45 c of the optically anisotropic layer 400 to be emitted from the light guide plate 144. The undiffracted light I further propagates within the light guide plate 144, and a portion of the light R is diffracted again at a position P of the second diffraction region 45 c of the optically anisotropic layer 400 to be emitted from the light guide plate 144.

[0183] In this way, by configuring the light propagating within the light guide plate 144 to be diffracted at multiple locations by the second diffraction region 45c of the optically anisotropic layer 400 and emitted outside the light guide plate 144, the viewing area can be expanded (exit pupil expansion).

[0184] Let us now consider a case where the diffraction efficiency of the optically anisotropic layer (liquid crystal diffraction element) on the exit side is constant within the plane. When the diffraction efficiency is constant, the light intensity (light amount) of incident light I0 is large at position P1 close to the entrance side, and therefore the intensity of exiting light R1 is also large. Next, the undiffracted light I1 propagates through the light guide plate 144 and is diffracted again at position P2 of the liquid crystal diffraction element, resulting in a portion of light R2 being emitted. However, because light I1 has a lower light intensity than light I0, even though it is diffracted with the same diffraction efficiency, the light intensity of light R2 is smaller than the light intensity of light R1 reflected in the region close to the entrance side. Similarly, the undiffracted light I2 propagates through the light guide plate 144 and is diffracted again at position P3 of the liquid crystal diffraction element, resulting in a portion of light R3 being emitted. However, because light I2 has a lower light intensity than light I1, even though it is diffracted with the same diffraction efficiency, the light intensity of light R3 is smaller than the light intensity of light R2 reflected at position P2. Furthermore, the light intensity of light R4 reflected at position P4, which is farther from the incident side, is smaller than the light intensity of light R3. Thus, if the diffraction efficiency of the liquid crystal diffraction element is constant within the plane, light with a high light intensity will be emitted at positions close to the incident side, and light with a low light intensity will be emitted at positions farther from the incident side, as shown by the dashed lines in Figure 8. This causes the problem of the emitted light intensity being non-uniform depending on the position.

[0185] In contrast, the second diffraction region 45c in the illustrated optically anisotropic layer 400 is a cholesteric alignment region in the optically anisotropic layer of the present invention, and is configured such that the diffraction efficiency increases from one side to the other in one direction of rotation of the optical axis in the liquid crystal alignment pattern. Preferably, the second diffraction region 45c is configured such that the diffraction efficiency increases in the direction of light propagation within the light guide plate 144. That is, in the example shown in Figure 7, the second diffraction region 45c of the optically anisotropic layer 400 is configured such that the diffraction efficiency increases from left to right in Figure 7. Specifically, in the second diffraction region 45c, which is a cholesteric alignment region in the optically anisotropic layer 400, the ratio of the thickness of layer A having a helical pitch of less than 250 nm to the thickness of the optically anisotropic layer 400 (cholesteric alignment region) gradually or stepwise decreases from left to right in Figure 7. That is, in the second diffraction region 45c, which is a cholesteric alignment region, the thickness of the layer B, which has a helical pitch of 250 nm or more and selectively reflects visible light, increases gradually or in steps from left to right in Fig. 7. In the example shown in Fig. 7, with this configuration, the diffraction efficiency in the second diffraction region 45c of the optically anisotropic layer 400 increases from left to right in Fig. 7.

[0186] In this case, at position P1 close to the incident side, the light intensity (light amount) of incident light I0 is high, but because the diffraction efficiency is low, the intensity of emitted light R1 is limited to a certain level. Next, the undiffracted light I1 propagates through the light guide plate 144 and is again diffracted at position P2 of the second diffraction region 45c of the optically anisotropic layer 400, resulting in a portion of light R2 being emitted. At this time, light I1 has a lower light intensity than light I0, but because the diffraction efficiency at position P2 is higher than that at position P1, the light intensity of light R2 can be made equal to the light intensity of light R1 reflected at position P1. Similarly, the undiffracted light I2 propagates through the light guide plate 144 and is again diffracted at position P3 of the second diffraction region 45c of the optically anisotropic layer 400, resulting in a portion of light R3 being emitted. In this case, although the light intensity of light I2 is lower than that of light I1, the diffraction efficiency at position P3 is higher than that at position P2, so the light intensity of light R3 can be made equal to the light intensity of light R2 reflected at position P2. Furthermore, the diffraction efficiency at position P4, which is farther from the incident side, is higher than that at position P3, so the light intensity of light R4 can be made equal to the light intensity of light R3 reflected at position P3. In this way, by configuring the second diffraction region 45c of the optically anisotropic layer 400 so that the diffraction efficiency increases from one side to the other in one direction of rotation of the optic axis, light with a constant light intensity can be emitted from any position of the second diffraction region 45c of the optically anisotropic layer 400. Therefore, when the diffraction efficiency is uniform in the plane, the light intensity of the emitted light, which varies depending on the position of the second diffraction region 45c as shown by the dashed line in FIG. 8, can be made uniform regardless of the position of the second diffraction region 45c as shown by the solid line in FIG. 8.

[0187] Although light is indicated by arrows in Figure 7, the light emitted from the display 40 is usually planar, and the planar light propagates through the light guide plate 144 while maintaining its positional relationship, and is diffracted by the second diffraction region 45c of the optically anisotropic layer 400 before being emitted.

[0188] Furthermore, in the light guide element of the present invention having an optically anisotropic layer, it is preferable to use a single optically anisotropic layer having multiple diffraction regions, as in the optically anisotropic layer 400 shown in FIGS. 19 and 20 . However, the light guide element of the present invention having an optically anisotropic layer is not limited thereto. It may have incident-side and output-side diffraction elements spaced apart, with the optically anisotropic layer of the present invention being used as at least one of the diffraction elements, preferably the output-side diffraction element. Consider a light guide element of the present invention in which the optically anisotropic layer (diffraction region) is not integrally formed, but has two optically anisotropic layers, an incident-side optically anisotropic layer 46 and an output-side optically anisotropic layer 47, as shown in FIG. 16 . In this case, a portion of the light diffracted by the optically anisotropic layer 46 may be scattered by the element end face X of the optically anisotropic layer 46 and / or the element end face Y of the optically anisotropic layer 47. Such scattered light can cause a decrease in image clarity in an AR display device. In contrast, by configuring the optically anisotropic layer so that two or more diffractive regions and a non-diffractive region are integrally formed, as in the optically anisotropic layer 400 shown in Figures 19 and 20, when combined with a light guide plate, it is possible to prevent light guided within the light guide plate from being scattered at the end faces of the diffractive regions, and it is possible to emit a highly clear image from the light guide plate, which is preferable.

[0189] Although FIG. 7 illustrates the light guide element 45 having a single optically anisotropic layer 400 with multiple diffraction regions, as described above, the light guide element 45 of the present invention may have multiple optically anisotropic layers. Alternatively, the light guide element of the present invention may have a configuration in which multiple single optically anisotropic layers are stacked on each of the incident and exit sides. When the light guide element 45 has multiple optically anisotropic layers, it is preferable to have multiple optically anisotropic layers with different selective reflection wavelengths. For example, it may have optically anisotropic layers that selectively reflect red, green, and blue light, respectively. This allows the optically anisotropic layer (or its laminate) to diffract red, green, and blue light, respectively, and the light guide element can appropriately guide light for the display 40 that displays color images. To accommodate such color image display, it is preferable to appropriately change the length of one period of the liquid crystal orientation pattern in the cholesteric liquid crystal layer depending on the selective reflection wavelength of each layer. It is also preferable that the helical pitch of the cholesteric liquid crystal layer is appropriately changed depending on the selective reflection wavelength of each layer.

[0190] Furthermore, when the light guide element of the present invention has multiple optically anisotropic layers, it may be configured to have two optically anisotropic layers that reflect circularly polarized light with the same selective reflection wavelength but opposite rotation directions. For example, it may be configured to have an optically anisotropic layer that reflects right-handed circularly polarized red light and an optically anisotropic layer that reflects left-handed circularly polarized red light. This allows the laminate of optically anisotropic layers to diffract right-handed and left-handed circularly polarized light, respectively, and the light guide element to guide right-handed and left-handed circularly polarized light, thereby improving light utilization efficiency. Alternatively, the light guide element of the present invention may be configured to have two optically anisotropic layers that reflect circularly polarized light with the same selective reflection wavelength but opposite rotation directions, and in which the helical pitch of the cholesteric liquid crystal layer, such as a cholesteric alignment region, is different. This allows the optically anisotropic layer (or its laminate) to diffract right-handed circularly polarized light and left-handed circularly polarized light, and the light-guiding element to guide right-handed circularly polarized light and left-handed circularly polarized light that are incident at different angles and emit the guided light at different angles, thereby increasing the FOV (Field of View).

[0191] 7, the optically anisotropic layer 400 has a first diffraction region 45a on the incident side, a second diffraction region 45c on the exit side, and an isotropic non-diffraction region 45b, but is not limited thereto and may have an intermediate diffraction region (third diffraction region) as described above, for example, as shown in Fig. 21. That is, light diffracted by the incident diffraction region (first diffraction region) and entering the light guide plate may be diffracted by the intermediate diffraction region (third diffraction region) to bend the traveling direction of the light within the light guide plate, and then diffracted by the exit-side diffraction region (second diffraction region) to emit the light outside the light guide plate. In this case, the first diffraction region on the incident side and the intermediate third diffraction region can be formed in a single optically anisotropic layer, the intermediate third diffraction region and the second diffraction region on the exit side can be formed in a single optically anisotropic layer, or all diffraction regions can be formed in a single optically anisotropic layer. However, from the viewpoint of improving image clarity, it is preferable to form as many diffraction regions as possible used in the light guide plate in a single optically anisotropic layer. Furthermore, when the optically anisotropic layer of the present invention has an intermediate diffraction region, it is preferable to configure the efficiency of the intermediate diffraction region to increase from one side to the other in order to uniform the light intensity of the emitted light. Furthermore, when the cholesteric orientation region in the optically anisotropic layer of the present invention is used as the intermediate diffraction region and / or the exit-side diffraction region, it is also preferable to configure the in-plane distribution of the diffraction efficiency of the intermediate diffraction region and the exit-side diffraction region to be different in order to uniform the light intensity of the emitted light.

[0192] Furthermore, when the optically anisotropic layer has an intermediate diffraction region, it is preferable to use a configuration in which the length of one period over which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in-plane is shorter than that of the incident-side diffraction region. This allows light diffracted by the incident diffraction region and entering the light guide plate to be diffracted by the intermediate diffraction region, thereby increasing the angle at which the light's traveling direction within the light guide plate is bent, thereby enabling the light guide plate to be made more compact. Furthermore, when one period of the intermediate diffraction region is shorter than that of the incident-side diffraction region, it is preferable to make the helical pitch of the cholesteric liquid crystal layer larger in the intermediate diffraction region than in the incident-side diffraction region. This allows the intermediate diffraction region to efficiently bend the traveling direction of light within the light guide plate. Furthermore, it is preferable that the intermediate diffraction region has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in-plane, which is different from that of the incident-side diffraction region. This allows the light to bend efficiently in the intermediate diffraction region. Light that is diffracted by the incident diffraction region and enters the light guide plate can be diffracted by the intermediate diffraction region, changing the direction in which the light travels within the light guide plate, and the light can be appropriately guided toward the output diffraction region.

[0193] In addition, multiple incident diffraction regions and intermediate diffraction regions may be arranged in the plane. The multiple incident diffraction regions have different directions of the liquid crystal orientation pattern continuously rotating along one direction in the plane, and the light incident on the incident diffraction region is guided in different directions within the light guide plate, diffracted by the intermediate diffraction regions arranged at different positions in the plane, and the light traveling direction within the light guide plate is bent. Then, the guided light can be emitted at different angles by the diffraction region on the output side, thereby increasing the FOV (Field of View). For example, as described in International Publication No. 2020 / 122128, the incident diffraction region and intermediate diffraction region have the length of one period in which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in the plane, the direction of rotation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern continuously rotating in one direction in the plane, and in the case of a cholesteric liquid crystal layer, the length of the helical pitch and the direction of helical twist rotation in the thickness direction can be appropriately set. In the multiple incident-side diffraction regions, the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that is continuously rotating in one direction in the plane can be appropriately set, and in the multiple incident-side diffraction regions, the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that is continuously rotating in one direction in the plane can be made different. Furthermore, when the diffraction region (optically anisotropic layer) is a cholesteric liquid crystal layer, the direction of the spiral twist rotation in the thickness direction of the multiple incident-side diffraction regions (the rotation direction of the reflected circularly polarized light) can be appropriately set, and specifically, the multiple incident-side diffraction regions may be a region in which the cholesteric liquid crystal layer is right-handed helical cholesterically oriented and a region in which the cholesteric liquid crystal layer is left-handed helical cholesterically oriented. Furthermore, the intermediate diffraction region can preferably be configured to have a shorter length of one period in which the orientation of the optical axis derived from the liquid crystal compound rotates by 180° in the plane compared to the diffraction region on the incident side.If one period of the intermediate diffraction region is shorter than that of the diffraction region on the incident side, it is preferable that the helical pitch of the cholesteric liquid crystal layer in the intermediate diffraction region be larger than that of the diffraction region on the incident side, as described above.Furthermore, even in such a configuration, when the optically anisotropic layer of the present invention is used as an intermediate diffraction region and / or an exit-side diffraction region, a configuration in which the in-plane distribution of the diffraction efficiency in the intermediate diffraction region and the exit-side diffraction region is different can also be preferably used in order to make the light intensity of the exiting light uniform.

[0194] Furthermore, as described above, when multiple optically anisotropic layers are stacked, it is also preferable to stack multiple optically anisotropic layers with different selective reflection wavelengths (helical pitches). This allows the stack of optically anisotropic layers to diffract light of different colors (wavelengths), and the light-guiding element can appropriately guide light for color display on the display 40. In this case, the length of one period of the liquid crystal orientation pattern in each diffraction region is preferably set appropriately according to the selective reflection wavelength of each diffraction region of each layer. Alternatively, a configuration may be used in which two optically anisotropic layers are stacked, each having a diffraction region that reflects circularly polarized light with the same selective reflection wavelength but opposite rotation directions. For example, a configuration may be used in which an optically anisotropic layer having a diffraction region that reflects right-handed circularly polarized light of red light is stacked on another optically anisotropic layer having a region that reflects left-handed circularly polarized light of red light. This allows the stack of optically anisotropic layers to diffract right-handed and left-handed circularly polarized light, respectively, and the light-guiding element to guide right-handed and left-handed circularly polarized light, thereby improving light utilization efficiency. Alternatively, two optically anisotropic layers may be laminated, each having the same selective reflection wavelength but opposite helical pitches, and each reflecting circularly polarized light having an opposite rotation direction. This allows the laminate of optically anisotropic layers to diffract right-handed and left-handed circularly polarized light, and the light guide element to guide right-handed and left-handed circularly polarized light incident at different angles and emit the guided light at different angles, thereby increasing the FOV. Furthermore, as described in, for example, International Publication Nos. WO 2020 / 122128, WO 2020 / 075738, WO 2020 / 226078, and WO 2021 / 060528, when multiple optically anisotropic layers are stacked, it is also preferable to stack multiple optically anisotropic layers having diffraction regions (incident diffraction region, intermediate diffraction region, output diffraction region) of each optically anisotropic layer that have different lengths of one period of the liquid crystal orientation pattern, one direction of the liquid crystal orientation pattern that is continuously rotating in one direction in the plane, and the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that is continuously rotating in one direction in the plane.In addition, when the diffraction region is a cholesteric liquid crystal layer, it is also preferable to stack multiple optically anisotropic layers having diffraction regions with different helical pitches and helical twist rotation directions in the thickness direction (rotation direction of reflected circularly polarized light), and this can be appropriately set according to the purpose.In addition, even when multiple optically anisotropic layers are stacked, when the optically anisotropic layer of the present invention is used as an intermediate diffraction region and / or an output diffraction region, in order to make the light intensity of the output light uniform, a configuration in which the in-plane distribution of the diffraction efficiency in the intermediate diffraction region and the output diffraction region is different can also be preferably used.Furthermore, when multiple optically anisotropic layers of the present invention are stacked, a configuration in which the in-plane distribution of the diffraction efficiency in the diffraction region is different in each intermediate diffraction region and each output diffraction region can also be preferably used.

[0195] It should be noted that, when the optically anisotropic layer of the present invention has a plurality of diffraction regions, regardless of the number of diffraction regions, there is no limitation on the arrangement of each diffraction region, and as necessary, can be suitably arranged in-plane, thickness direction (lamination).In addition, when the optically anisotropic layer of the present invention has a plurality of diffraction regions, all diffraction regions are not limited to the structure of the cholesteric alignment region of the optically anisotropic layer of the present invention, which has layer A and layer B, and has in-plane distribution of diffraction efficiency, and can also comprise the normal reflective liquid crystal diffraction element and transmission diffraction element, which do not have in-plane distribution of diffraction efficiency, as mentioned above.That is, when the optically anisotropic layer of the present invention has a plurality of diffraction regions, it is sufficient that at least one diffraction region is the cholesteric alignment region of the optically anisotropic layer of the present invention, which has layer A and layer B, and has in-plane distribution of diffraction efficiency.

[0196] Furthermore, when multiple optically anisotropic layers are laminated, a diffraction region that also serves as both an intermediate diffraction region and an output diffraction region may be laminated. The intermediate diffraction region and the output diffraction region may each be configured by laminating optically anisotropic layers in which the direction of a liquid crystal orientation pattern that continuously rotates along one in-plane direction is different from each other. In this case, it is preferable that the input diffraction region uses multiple input diffraction regions in which the direction of a liquid crystal orientation pattern that continuously rotates along one in-plane direction is different from each other, and guides light that has entered the input diffraction region into different directions within the light guide plate. The multiple input regions may be arranged at different positions within the plane, or may be configured by laminating them. Light that has been diffracted by the input diffraction region and entered the light guide plate is diffracted by the intermediate diffraction region to bend the traveling direction of the light within the light guide plate, and then diffracted by the output diffraction region laminated with the intermediate diffraction region to emit the light outside the light guide plate. The light diffracted by the separate incident diffraction region and entering the light guide plate functions as an intermediate diffraction region, diffracting the light to bend its traveling direction within the light guide plate, and the intermediate diffraction region functions as an exit diffraction region, enabling the guided light to exit at a different angle. This allows a compact light guide plate to have a larger FOV than when the intermediate diffraction region and the exit diffraction region are located at different positions within the plane. Furthermore, for example, as described in International Publication No. 2021 / 201218 and International Publication No. 2021 / 256453, when stacking multiple optically anisotropic layers, if a diffraction region that serves as both an intermediate diffraction region and an output diffraction region is stacked, it is also preferable to stack multiple optically anisotropic layers that differ in the length of one period of the liquid crystal orientation pattern, one direction of the liquid crystal orientation pattern that is continuously rotating in one direction in the plane, and the direction of rotation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that is continuously rotating in one direction in the plane, and when the diffraction region is a cholesteric liquid crystal layer, it is also preferable to stack multiple optically anisotropic layers that differ in the helical pitch and the direction of helical twist rotation in the thickness direction (the rotation direction of the reflected circularly polarized light), and can be set appropriately depending on the purpose.

[0197] In addition, when multiple optically anisotropic layers of the present invention are stacked, even in a configuration in which a diffraction region that serves as both an intermediate diffraction region and an output diffraction region is stacked, a configuration in which the in-plane distribution of the diffraction efficiency in each diffraction region is different can also be preferably used in order to make the light intensity of the output light uniform.

[0198] 7, the optically anisotropic layer 400 has a reflective diffraction region, but the present invention is not limited to this, and as mentioned above, an optically anisotropic layer having a transmissive diffraction region may be partially used. That is, the optically anisotropic layer (its diffraction region on the incident side) may be arranged on the surface of the light guide plate 144 that faces the display 40.

[0199] [Method for Forming Optically Anisotropic Layer (Cholesteric Alignment Region)] In the optically anisotropic layer of the present invention, there is no particular limitation on the method for forming a cholesteric alignment region having regions with different diffraction efficiencies in its plane, i.e., a cholesteric alignment region having Layer A and Layer B, where the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region is different within the plane of the cholesteric alignment region. Here, a formation method including Steps 1 to 3 is preferred, in terms of efficient production of an optically anisotropic layer. Step 1: Forming a coating film using a composition containing a liquid crystal compound having a polymerizable group and a chiral agent, and cholesterically aligning the liquid crystal compound in the formed coating film. Step 2: Polymerizing the liquid crystal compound so as to form regions with different polymerization rates of the liquid crystal compound in the in-plane and thickness directions of the coating film. Step 3: Changing the helical twisting force of the chiral agent by light and / or heat, and forming regions with different helical pitches depending on the polymerization rate in Step 2. Steps 1 to 3 are described in detail below.

[0200] (Step 1) Step 1 is a step of forming a coating film using a composition containing a liquid crystal compound having a polymerizable group and a chiral agent, and orienting the liquid crystal compound in the formed coating film. By carrying out this step, a coating film containing an aligned liquid crystal compound is formed. In one preferred embodiment of this step, a coating film is formed by applying the composition onto an alignment film of a support having a support and an alignment film, and the liquid crystal compound in the coating film is preferably aligned. By carrying out this preferred embodiment, a laminate is formed, including a support 320, an alignment film 322, and a coating film 324, as shown in FIG. 11 . The coating film 324 will become a cholesteric alignment region of the optically anisotropic layer in a subsequent step.

[0201] The composition containing a liquid crystal compound having a polymerizable group used in this step is as described above. The liquid crystal compound used in this step is preferably a liquid crystal compound having a radical polymerizable group or a cation polymerizable group, and more preferably a liquid crystal compound having a radical polymerizable group.

[0202] The composition can be applied by various known methods used for applying liquids, such as bar coating, gravure coating, and spray coating. Next, the coating film formed by application is subjected to an alignment treatment to align the liquid crystal compound. By performing the alignment treatment, the liquid crystal compound in the coating film is oriented in a predetermined alignment state according to the orientation pattern of the alignment film. As the alignment treatment, a heat treatment is preferred. The heating conditions are not particularly limited, but the heating temperature is preferably 50 to 140°C, and the heating time is preferably 0.5 to 20 minutes.

[0203] (Step 2) Step 2 is a step of polymerizing the liquid crystal compound so as to form regions with different polymerization rates of the liquid crystal compound in the in-plane and thickness directions of the coating film. The procedure of this step is not particularly limited, but by carrying out this step, regions with different degrees of curing of the liquid crystal compound are formed in at least a part of the plane of the coating film in the in-plane and thickness directions.

[0204] An example of a method for forming regions in which the degree of cure of the liquid crystal compound varies in the in-plane direction is a method of performing exposure through a photomask (Method 1). For example, by using a photomask whose transmittance gradually changes from one side to the other, it is possible to form an optically anisotropic layer in which the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region gradually changes from one side to the other.

[0205] Examples of means for forming regions in the thickness direction in which the degree of cure of the liquid crystal compound varies include a method of performing exposure or heat treatment in an atmosphere containing components that inhibit polymerization, such as oxygen and moisture (Method 2), and a method of forming a coating film using a composition containing a compound that absorbs ultraviolet light at the exposure wavelength, such as an ultraviolet absorber, and then exposing the formed coating film to light (Method 3).

[0206] A method for forming a cholesteric alignment region having a layer A with a helical pitch of less than 250 nm and a layer B with a helical pitch of 250 nm or more, in which the ratio of the thickness of layer A to the thickness of the cholesteric alignment region gradually changes from one side to the other within the plane of the optically anisotropic layer, includes a method that combines a method for forming a region in which the liquid crystal compound has a different degree of hardening in the thickness direction with a method for forming a region in which the liquid crystal compound has a different degree of hardening in the in-plane direction.

[0207] For example, a combination of Method 1 and Method 2 will be described with reference to FIG. 11 . In FIG. 11 , reference numeral 329 denotes a photomask. In this photomask 329, white areas represent high transmittance, and black areas represent low transmittance. When exposure is performed from the direction indicated by the white arrow indicated by reference numeral 327, the first region 326 on the alignment film 322 side of the coating film 324 is not in contact with the atmosphere, so oxygen supply from the atmosphere is slow and polymerization proceeds sufficiently. On the other hand, the second region 328 on the opposite side of the alignment film 322 side of the coating film 324 is in contact with the atmosphere, so oxygen supply from the atmosphere is fast and polymerization does not proceed. At this time, the thickness of region 326 gradually changes depending on the transmittance of the photomask 329. That is, polymerization proceeds more in regions with higher transmittance (white areas) of the photomask 329, so region 326 becomes thicker, and as the transmittance decreases, region 326 becomes thinner. In step 3 described below, the helical pitch of region 328 changes relatively more significantly than that of region 326, so that the ratio of the two layers with different helical pitches gradually changes due to the thickness gradient between the two.

[0208] Next, we will explain a combination of the above-mentioned methods 1 and 3. When a coating film 324 is formed using a composition containing an ultraviolet absorber, the ultraviolet absorber is dispersed throughout the thickness of the coating film. When such a coating film is exposed to light from the direction indicated by the white arrow 327 in FIG. 11 , as described above, the exposure energy is strong on the alignment film 322 side of the coating film 324, resulting in sufficient polymerization of the liquid crystal compound. Meanwhile, due to the influence of the ultraviolet absorber in the coating film 324, the exposure energy gradually decreases in the depth direction, and therefore the side of the coating film 324 opposite the alignment film 322 side is not irradiated with enough energy to sufficiently promote polymerization of the liquid crystal compound. As a result, the polymerization rate of the liquid crystal compound in the coating film 324 gradually changes from the alignment film 322 side toward the side opposite the alignment film 322. Furthermore, the polymerization rate of the liquid crystal compound in the coating film 324 gradually changes in the in-plane direction depending on the transmittance of the photomask 329. Region 326 represents a region where the polymerization rate is equal to or greater than a certain threshold, and region 328 represents a region where the polymerization rate is less than a certain threshold, and the thickness of region 326 gradually changes depending on the transmittance of photomask 329. That is, the higher the transmittance of upper photomask 329 (white portion), the more polymerization progresses, and as the transmittance decreases, the polymerization progresses more slowly, and region 326 becomes thinner. Since the helical pitch of region 328 changes significantly relative to region 326 through step 3 described below, the ratio of the two layers with different helical pitches gradually changes due to the thickness gradient between the two. Step 2 may also be performed by other methods.

[0209] Whether or not a region with a different polymerization rate of the liquid crystal compound is formed in the thickness direction of the coating film can be determined, for example, by cutting the coating film in the thickness direction, analyzing the exposed cross section of the coating film using infrared absorption spectroscopy or the like, and calculating the residual rate of the polymerizable group in the thickness direction of the coating film.

[0210] In the method of forming a coating film using a composition containing the liquid crystal compound having a polymerizable group and then exposing the formed coating film, ultraviolet irradiation treatment is preferred as the exposure treatment. The optimum conditions for the ultraviolet irradiation treatment are appropriately selected depending on the coating film to be used, and the irradiation dose is preferably 0.1 to 3000 mJ / cm.2 is preferred, and 1 to 1000 mJ / cm 2 The illuminance is more preferably 0.1 to 1000 mW / cm. 2 is preferred, and 1 to 300 mW / cm 2 is more preferred.

[0211] (Step 3) Step 3 is a step of changing the helical twisting force of the chiral agent in the coating film obtained in step 2 by light and / or heat, thereby forming regions with different helical pitches depending on the polymerization rate in step 2. The coating film obtained in step 2 includes regions with different polymerization rates of the liquid crystal compound in the in-plane and thickness directions of the coating film. In such a coating film, when the helical twisting force of the chiral agent in the coating film is changed, the helical pitch of the liquid crystal compound is maintained in regions with a high polymerization rate of the liquid crystal compound. On the other hand, in regions with a low polymerization rate of the liquid crystal compound, the liquid crystal compound reorients in accordance with the change in helical twisting force, thereby changing the helical pitch. For example, when the helical twisting force is increased by light and / or heat, performing this step results in regions with a high polymerization rate of the liquid crystal compound having a large helical pitch, and regions with a low polymerization rate of the liquid crystal compound having a small helical pitch. As shown in layer 326 and layer 328 in Fig. 12, the region with a large helical pitch is layer B (layer 326) in the cholesteric alignment region, where the helical pitch is 250 nm or more, and the region with a small helical pitch is layer A (layer 326) in the cholesteric alignment region, where the helical pitch is less than 250 nm. Note that Fig. 12 is the above-mentioned cross-sectional SEM image in which dark areas 330 and light areas 332 resulting from cholesteric alignment (cholesteric liquid crystal phase) are observed. As mentioned above, the longer the helical pitch, the wider the interval between dark areas 330 and light areas 332.

[0212] The preferred range of the exposure treatment carried out in this step is the same as that in step 2. Steps 2 and 3 may proceed simultaneously. That is, the helical twisting power of the chiral agent may be changed by the exposure treatment in step 2. The conditions for the heat treatment carried out in this step are not particularly limited, and optimal conditions are selected depending on the coating film to be used. The heating temperature during the heat treatment is preferably 30 to 200°C, more preferably 50 to 150°C. The heating time at the heating temperature is preferably 0.5 to 30 minutes, more preferably 1 to 5 minutes. From the viewpoint of sufficiently changing the orientation of the liquid crystal compound by the heat treatment, it is preferable that the heat treatment be carried out after the exposure treatment in this step, or that the exposure treatment and the heat treatment be carried out simultaneously.

[0213] After carrying out step 3, step 4 may be carried out, if necessary, in which the optically anisotropic layer obtained in step 3 is subjected to an exposure treatment. By carrying out the exposure treatment, unreacted polymerizable groups can be polymerized. As the exposure treatment, ultraviolet irradiation treatment is preferred. The optimum conditions for the ultraviolet irradiation treatment are appropriately selected depending on the coating film to be used, and the irradiation dose is 50 to 2000 mJ / cm. 2 is preferred, and 100 to 1000 mJ / cm 2 The ultraviolet irradiation treatment is preferably carried out in an atmosphere with a low oxygen concentration, and more preferably in a nitrogen atmosphere.

[0214] In the optically anisotropic layer of the present invention described above, in any of the cholesteric liquid crystal layers (diffraction regions) such as the cholesteric alignment region having a liquid crystal alignment pattern, the optical axis 30A of the liquid crystal compound 30 in the liquid crystal alignment pattern continuously rotates only along the direction of the arrow X. However, the present invention is not limited thereto, and various configurations of the cholesteric liquid crystal layer (diffraction region) such as the cholesteric alignment region having a liquid crystal alignment pattern can be used as long as the optical axis 30A of the liquid crystal compound 30 continuously rotates along at least one direction.

[0215] As described above, the optically anisotropic layer of the present invention can also be formed into a laminate by laminating multiple optically anisotropic layers. There are no limitations on the lamination method, and various methods can be used. Examples include a method in which a liquid crystal composition is directly applied onto a first optically anisotropic layer to form a second optically anisotropic layer, a method in which an alignment film is applied onto the first optically anisotropic layer, followed by an alignment treatment, and then a liquid crystal composition is applied, and a method in which an optically anisotropic layer provided on another substrate is laminated. Furthermore, in the diffraction region of each optically anisotropic layer, the grating pitch (e.g., one period in the liquid crystal alignment pattern), the grating angle, and the helical pitch of the cholesteric alignment region can be adjusted as desired.

[0216] In the optically anisotropic layer of the present invention, when a cholesteric liquid crystal layer (reflective liquid crystal diffraction element) such as a cholesteric alignment region is used in the diffraction region, it is preferable that the helical pitch length of the cholesteric liquid crystal layer varies within the region, and more preferably that the helical pitch length varies continuously within the region. By varying the helical pitch length, the diffraction efficiency can be controlled according to the incident angle of light. Therefore, as shown in Figure 7, by designing the helical pitch so that light with a specific incident angle is selectively diffracted at positions P1, P2, P3, and P4 of the second diffraction region 45c, the amount of light reaching the eye can be increased, thereby improving the brightness of the AR glasses.

[0217] In addition, when preparing the optically anisotropic layer of the present invention, an optically anisotropic layer having multiple cholesteric alignment regions (diffraction regions) may be formed on a single support, and then cut into individual regions to prepare multiple optically anisotropic layers. Furthermore, a single substrate may be formed with multiple units, each unit consisting of at least a first diffraction region, a second diffraction region, and a non-diffraction region, and then the unit may be cut into multiple units to prepare multiple optically anisotropic layers. By forming multiple optically anisotropic layers on a single substrate, productivity can be improved not only in the process of forming the optically anisotropic layer of the present invention, but also in downstream processes.

[0218] Next, a method for calculating the thickness ratio of layer A with a helical pitch of less than 250 nm in a cholesteric alignment region will be described with reference to FIG. 12 . As described above, in a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned, dark areas 330 and light areas 332 resulting from the cholesteric alignment are observed in an SEM image of the exposed coating film when the optically anisotropic layer 324 (cholesteric alignment region) is cut in the thickness direction. Furthermore, the number of dark areas 330 and the number of light areas 332 is equal to the helical pitch of the cholesteric liquid crystal layer. Therefore, in layer 326, which is layer B with a helical pitch of 250 nm or more, the light areas 330 and the dark areas 332 resulting from the cholesteric alignment of the liquid crystal compound appear at an interval of 125 nm (half of 250 nm) or more. On the other hand, in layer 328, which is layer A with a helical pitch of less than 250 nm, the light areas 330 and the dark areas 332 appear at an interval of less than 125 nm. Therefore, the ratio of the thickness of layer A having a helical pitch of less than 250 nm to the thickness of the cholesteric alignment region can be determined by measuring the thickness of layer 328. When a cholesteric liquid crystal layer such as a cholesteric alignment region is a diffraction element, the helical pitch can be determined from a cross-sectional SEM image by cutting the optically anisotropic layer parallel to the direction in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating.

[0219] <Adhesive Layer (Pressure-Sensitive Adhesive Layer), Adhesive> The laminate and the light guide element of the present invention may include an adhesive layer for bonding the optically anisotropic layers together and / or the optically anisotropic layer to the light guide plate. In this specification, the term "adhesion" is used to include the concept of "sticking." Examples of adhesives include water-soluble adhesives, UV-curable adhesives, emulsion adhesives, latex adhesives, mastic adhesives, multilayer adhesives, paste-like adhesives, foam adhesives, supported film adhesives, thermoplastic adhesives, hot-melt adhesives, heat-setting adhesives, heat-activated adhesives, heat-seal adhesives, thermosetting adhesives, contact adhesives, pressure-sensitive adhesives (i.e., pressure-sensitive adhesives), polymerization adhesives, solvent-based adhesives, solvent-activated adhesives, and ceramic adhesives. Specific examples include an aqueous solution of a boron compound, a curable adhesive of an epoxy compound that does not contain an aromatic ring in the molecule, as disclosed in JP 2004-245925 A, an active energy ray-curable adhesive described in JP 2008-174667 A, which contains as essential components a photopolymerization initiator having a molar absorption coefficient of 400 or more at a wavelength of 360 to 450 nm and an ultraviolet-curable compound, and an active energy ray-curable adhesive described in JP 2008-174667 A, which contains, per 100 parts by mass of the total amount of (meth)acrylic compounds, (a) a (meth)acrylic compound having two or more (meth)acryloyl groups in the molecule, (b) a (meth)acrylic compound having a hydroxyl group in the molecule and only one polymerizable double bond, and (c) a phenol ethylene oxide-modified acrylate or nonylphenol ethylene oxide-modified acrylate. These various adhesives may be used alone or, if necessary, may be used in combination.

[0220] In the laminate and the light guide element of the present invention, from the viewpoint of reducing unnecessary reflection, it is preferable that the adhesive layer have a small difference in refractive index from the adjacent layer. Specifically, the difference in refractive index between the adhesive layer and the adjacent layer is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.01 or less. There are no particular limitations on the method for adjusting the refractive index of the adhesive layer, but known methods can be used, such as adding zirconia-based, silica-based, acrylic, acrylic-styrene-based, or melamine-based fine particles, adjusting the resin refractive index, and the method described in JP-A-11-223712. Furthermore, if the adhesive layer and the adjacent layer have in-plane refractive index anisotropy, the difference in refractive index between the adhesive layer and the adjacent layer in all directions in the plane is preferably 0.2 or less, more preferably 0.1 or less, and even more preferably 0.05 or less. Therefore, the adhesive layer may have in-plane refractive index anisotropy. If the refractive index difference between the interfaces to be bonded is large, the interface reflectance can be reduced by providing a refractive index distribution in the thickness direction of the adhesive layer. Methods for imparting a refractive index distribution in the thickness direction include providing multiple adhesive layers, mixing the interfaces between multiple adhesive layers, and controlling the uneven distribution of materials within the adhesive layers to impart a refractive index distribution.

[0221] The adhesive layer can be provided on one or both of the members to be bonded by any method such as coating, vapor deposition, or transfer. From the viewpoint of increasing adhesive strength, post-treatment such as heat treatment and ultraviolet irradiation can be carried out depending on the type of adhesive. The thickness of the adhesive layer can be adjusted as desired, but is preferably 20 μm or less, more preferably 0.1 μm or less, and even more preferably 0.01 μm or less. Methods for forming an adhesive layer of 0.1 μm or less include silicon oxide (SiO x One example is a method of depositing a ceramic adhesive such as a ceramic adhesive layer (a ceramic adhesive layer) on 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, and 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.

[0222] <Cutting of Optically Anisotropic Layer and Laminate> The prepared optically anisotropic layer and / or laminate can be cut to a predetermined size. There are no limitations on the method for cutting the optically anisotropic layer and / or laminate, and various known methods can be used, such as physical cutting using a blade such as a Thomson blade or cutting by irradiating a laser. When using a laser, it is preferable to select the pulse width (nanoseconds, picoseconds, femtoseconds) and wavelength taking into consideration cutting properties and damage to the material. Furthermore, after processing the optically anisotropic layer and / or laminate into a predetermined shape, for example, polishing of the end faces may be performed. From the viewpoints of improving processability during cutting and suppressing dust generation, cutting can also be performed with a peelable protective film attached. Furthermore, by cutting while observing the liquid crystal alignment pattern, for example, according to the method disclosed in JP 2004-141889 A, the cutting position can be determined arbitrarily. In this case, observation can be performed through a polarizing plate, a retardation film, or the like to make the liquid crystal alignment pattern more visible. Furthermore, when a plurality of units are provided on one substrate, it is preferable to cut out each unit.

[0223] <Other Treatments> Marks of any shape can be provided as needed for the purposes of accurately installing the optically anisotropic layer (or laminate) on various devices (e.g., light guide plates), improving the accuracy of the axis and cutting position during cutting, etc. The type of mark can be selected as desired, and can be a method of physically providing the mark using a laser, inkjet method, etc., a method of partially changing the alignment state of the liquid crystal, a method of providing a partially bleached or dyed region, or the like.

[0224] Furthermore, for the purpose of protecting the optically anisotropic layer, a protective layer (such as a gas barrier layer, a moisture-blocking layer, an ultraviolet absorbing layer, a scratch-resistant layer, or a transparent colored layer) may be provided on at least one side of the optically anisotropic layer, as needed. The protective layer may be formed directly on the optically anisotropic layer, or may be provided via another optical film such as a pressure-sensitive adhesive layer. Furthermore, an antireflection layer (such as a low-reflection (LR) layer, an anti-reflection (AR) layer, or a moth-eye layer) may be provided to reduce the surface reflectance. Various protective layers can be appropriately selected from known materials. When a gas barrier layer is provided, polyvinyl alcohol, glass, or the like are preferred. Polyvinyl alcohol can also function as a polarizer. The ultraviolet absorbing layer is a layer containing an ultraviolet absorber. The ultraviolet absorber preferably has excellent absorption ability for ultraviolet light with a wavelength of 370 nm or less and, from the viewpoint of good display performance, has little absorption of visible light with a wavelength of 400 nm or more. Only one ultraviolet absorber may be used, or two or more ultraviolet absorbers may be used in combination. Examples of such ultraviolet absorbers include those described in Japanese Patent Application Laid-Open No. 2001-072782 and Japanese Patent Application Laid-Open No. 2002-543265. Specific examples of ultraviolet absorbers include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylic acid ester-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, and nickel complex salt-based compounds. The transparent colored layer is a layer that absorbs or reflects at least a portion of visible light. By combining a transparent colored layer with an optically anisotropic layer, the external color of an optical element including an optically anisotropic layer can be adjusted. For example, if the optically anisotropic layer is colored, the color can be adjusted to a neutral color by combining a transparent colored layer.

[0225] The optically anisotropic layer of the present invention can be used for various applications that reflect (diffract) light at an angle other than specular reflection, such as an optical path changing element in an optical device, a light concentrating element, a light diffusing element in a predetermined direction, a diffraction element, etc.

[0226] In the above examples, the optically anisotropic layer of the present invention is used in a liquid crystal diffraction element that mainly reflects visible light, but the present invention is not limited to this and various configurations can be used. For example, the optically anisotropic layer of the present invention may be configured to mainly reflect infrared or ultraviolet light, or may be configured to mainly reflect only light other than visible light.

[0227] The optically anisotropic layer, the light-guiding element, and the AR display device of the present invention have been described in detail above. However, the present invention is not limited to the above-described examples, and various improvements and modifications may be made within the scope of the present invention.

[0228] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, and treatment procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0229] Example 1 (Formation of Alignment Film) A glass substrate was prepared as a support. The following coating liquid for forming an alignment film was applied to the support by spin coating. The support on which the coating film of the coating liquid for forming an alignment film had been formed was dried on a hot plate at 60°C for 60 seconds to form an alignment film.

[0230] Coating liquid for forming alignment film ------------------------------------------------ Photoalignment material below: 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass ------------------------------------------------------------------

[0231] -Material for photo alignment-

[0232] (Exposure of Alignment Film) Using the exposure device shown in Figure 3, exposure was performed on Region 1 and Region 2 of the alignment film, respectively, to form an alignment film P-1 having an alignment pattern. At this time, the orientation of the alignment film in Region 2 was rotated 180° relative to Region 1 before exposure, thereby inverting the alignment patterns in Regions 1 and 2 by 180°. In the exposure device, a laser emitting laser light with a wavelength (325 nm) was used. The exposure dose by interference light was 300 mJ / cm. 2 The period (length for which the optical axis rotates 180°) Λ of the orientation pattern formed by the interference of the two laser beams was controlled to be 0.43 μm by changing the crossing angle (crossing angle α) of the two beams. In the regions other than Region 1 and Region 2, linearly polarized light was applied at 300 mJ / cm. 2 Irradiated.

[0233] (Formation of Optically Anisotropic Layer) The following composition LC-1 was prepared as a liquid crystal composition for forming an optically anisotropic layer. Composition LC-1: Rod-shaped liquid crystal compound L-1 80.00 parts by mass Rod-shaped liquid crystal compound L-2 20.00 parts by mass Polymerization initiator (manufactured by BASF, Omnirad (registered trademark) OXE01) 3.00 parts by mass Chiral agent Ch-1 9.50 parts by mass Chiral agent Ch-2 4.50 parts by mass Leveling agent T-1 0.14 parts by mass Cyclopentanone 306.45 parts by mass

[0234] Rod-shaped liquid crystal compound L-1 Rod-shaped liquid crystal compound L-2

[0235] Chiral agent Ch-1 Chiral agent Ch-2

[0236] Leveling agent T-1

[0237] The prepared composition LC-1 was applied onto the alignment film P-1 to form a composition layer. The coating was performed using a spin coater at 1500 rpm, resulting in a smooth coating film of 1.5 μm. The support having the composition layer was heated on a hot plate at 90°C for 1 minute. Subsequently, a mask MK-1 was placed on the composition layer, and ultraviolet light having a wavelength of 365 nm was irradiated at 100 mW / cm using a 365 nm LED UV exposure device at 30°C under atmospheric conditions through the mask MK-1. 2 The composition layer was exposed to light at an illuminance of 300 mJ / cm for 3 seconds (corresponding to the exposure treatments in steps 2 and 3). The amount of ultraviolet light irradiated onto the composition layer through mask MK-1 and the positional relationship between region 1 and region 2 of the alignment film are shown in FIG. 13. Subsequently, a heat treatment was carried out at 80°C for 1 minute (corresponding to the heat treatment in step 3). Subsequently, ultraviolet light with a wavelength of 365 nm was irradiated at 300 mJ / cm using a 365 nm LED UV exposure device in a nitrogen atmosphere at 30°C. 2 The coating film was irradiated with a dose of 1000 u / s, thereby fixing the alignment of the liquid crystal compound and forming an optically anisotropic layer. The optically anisotropic layer was cut in the direction in which the optical axis of the liquid crystal alignment pattern rotated, and the cross section was observed with an SEM to obtain a cross-sectional SEM image. The cross-sectional SEM image revealed that the entire optically anisotropic layer exhibited smooth cholesteric alignment, and contained a layer with a helical pitch of 206 nm (corresponding to Layer A, which had a helical pitch of less than 250 nm) and a layer with a helical pitch of 324 nm (corresponding to Layer B, which had a helical pitch of 250 nm or more). In Region 2, the thickness of the layer with a helical pitch of 206 nm gradually changed. Figure 14 shows the ratio of the thickness of the layer with a helical pitch of 206 nm to the thickness of the cholesteric alignment layer. Both the layer with a helical pitch of 206 nm and the layer with a helical pitch of 324 nm were cholesteric liquid crystal layers that selectively reflected right-handed circularly polarized light.

[0238] [Evaluation] (Evaluation of Diffraction Efficiency) The optically anisotropic layer 18 prepared as described above was placed on the surface of a Dove prism as shown in Figure 10, and the diffraction efficiency was evaluated for each position on the optically anisotropic layer. A glass Dove prism with a refractive index of 1.5 was used as the Dove prism 110. The optically anisotropic layer was peeled off from the glass substrate before use. The optically anisotropic layer and the Dove prism were bonded together using a heat-sensitive adhesive.

[0239] 10 , an optically anisotropic layer 18 was placed on the top surface of a Dove prism 110, a laser was placed facing the inclined surface of the Dove prism 110, and a linear polarizer 112 and a λ / 4 plate 114 were placed between the laser light source and the Dove prism 110. The transmission axis and slow axis of the linear polarizer 112 and the λ / 4 plate 114 were set so that the light transmitted through the λ / 4 plate 114 became right-handed circularly polarized light.

[0240] When laser light is emitted from the laser light source, it passes through linear polarizer 112 and λ / 4 plate 114 to become right-handed circularly polarized light, enters Dove prism 110, propagates through Dove prism 110, and enters optically anisotropic layer 18. The diffracted light reflected and diffracted by optically anisotropic layer 18 propagates through Dove prism 110 in the direction opposite to the surface on which the optically anisotropic layer is disposed. The diffracted light (laser light) that has propagated through Dove prism 110 reaches the lower surface of Dove prism 110 and is emitted.

[0241] In Figure 13, the position of the end of the optically anisotropic layer on the side where the laser light is incident is defined as 0 mm, and laser light was incident on the optically anisotropic layer at positions 25 mm, 35 mm, and 45 mm to measure the diffraction efficiency at each position. The wavelength of the laser light was 532 nm, and the angle of incidence of the laser light on the optically anisotropic layer was set so that the light was incident at an angle of 55.6° relative to the normal direction of the optically anisotropic layer. The light was reflected and diffracted by the optically anisotropic layer, and the light intensity of the light emitted in the normal direction of the optically anisotropic layer (the normal direction to the lower surface of the Dove prism 110) was measured. The intensity of the light emitted from the lower surface of the Dove prism 110 was measured using a Newport Power Meter 1918-C.

[0242] The diffraction efficiency Deff of the produced optically anisotropic layer was calculated using the following formula, where Li is the light intensity of the laser light incident on the Dove prism 110 (incident light intensity) and Lr is the light intensity of the light diffracted by the optically anisotropic layer and emitted from the Dove prism 110 (emitted light intensity): Diffraction efficiency Deff = (Lr / Li) × 100 [%] Note that when calculating the diffraction efficiency, the transmittance loss at the interface when light is incident on and emitted from the Dove prism 110 was excluded.

[0243] The diffraction efficiency of the optically anisotropic layer prepared by the above method was evaluated, and the results were 13% at a position of 25 mm, 21% at a position of 35 mm, and 58% at a position of 45 mm. As a result, it was confirmed that the prepared optically anisotropic layer (cholesteric orientation region) had an in-plane distribution in the diffraction efficiency.

[0244] [Evaluation] (Durability evaluation) PVA103 was laminated to a thickness of 2 μm on the optically anisotropic layer, and the layer was irradiated with Xe light for 3 days using a low-temperature cycle xenon weather meter (XL75Z, Suga Test Instruments Co., Ltd.) through an ultraviolet absorption filter SC40 (manufactured by Fujifilm). No change in diffraction efficiency was observed.

[0245] (Evaluation of Emitted Light Intensity Distribution) As conceptually shown in Fig. 9, a light guide element was produced by disposing the optically anisotropic layer 18 produced as described above on the surface of a light guide plate 144. In Fig. 9, a glass light guide plate with a refractive index of 1.5 and a thickness of 1 mm was used as the light guide plate 144. The optically anisotropic layer 18 was peeled off from the glass substrate before use. The optically anisotropic layer 18 and the light guide plate 144 were bonded together using a heat-sensitive adhesive.

[0246] As shown in FIG. 9 , a laser light source was placed facing the end of the light guide plate 144 on the side where region 1 was located, opposite the side where the optically anisotropic layer 18 was located, and a linear polarizer 100 and a λ / 4 plate 102 were placed between the laser light source and the light guide plate 144. A power meter (not shown) was placed 10 cm from the optically anisotropic layer, facing the end of the light guide plate 144 on the side where region 2 was located, opposite the side where the optically anisotropic layer 18 was located. The wavelength of the laser light was 532 nm, and the beam diameter of the laser light was 1 mm. The power meter used was a Newport Power Meter 1918-C. The transmission axis and slow axis of the linear polarizer 100 and the λ / 4 plate 102 were set so that the light transmitted through the λ / 4 plate 102 became right-handed circularly polarized light.

[0247] When laser light is emitted from the laser light source, it passes through linear polarizer 100 and λ / 4 plate 102 to become right-handed circularly polarized light and enters light guide plate 144. The light that enters light guide plate 144 enters region 1 of optically anisotropic layer 18. Due to the diffraction and selective reflection effects of region 1 of optically anisotropic layer 18, the diffracted light is reflected and propagated within light guide plate 144. The light that propagates within light guide plate 144 is diffracted and reflected by region 2 of optically anisotropic layer 18 and is emitted in the direction of the power meter.

[0248] A light-shielding plate 104 was placed between the light guide plate 144 and the power meter, facing the surface opposite to the surface on which the optically anisotropic layer 18 was placed. A pinhole 104a having a diameter of 2 mm was formed in the light-shielding plate 104.

[0249] The intensity of light emitted from the light guide plate 144 (emitted light intensity) was measured through the pinhole 104a of the light blocking plate 104. By changing the position of the pinhole 104a, the emitted light intensity was measured for each position of the region 2 using a power meter.

[0250] When the amount of light emitted from the light guide plate 144 was checked, it was confirmed that the emission intensity was uniform.

[0251] Example 2 (Formation of Optically Anisotropic Layer) The following composition LC-2 was prepared as a liquid crystal composition for forming an optically anisotropic layer. Composition LC-2 ----------------------------------- Rod-shaped liquid crystal compound L-3 50.00 parts by mass Rod-shaped liquid crystal compound L-4 50.00 parts by mass Polymerization initiator (manufactured by BASF, Omnirad (registered trademark) OXE01) 3.00 parts by mass Chiral agent Ch-1 9.50 parts by mass Chiral agent Ch-2 4.50 parts by mass Leveling agent T-1 0.14 parts by mass Cyclopentanone 406.45 parts by mass

[0252] Rod-shaped liquid crystal compound L-3 Rod-shaped liquid crystal compound L-4

[0253] An optically anisotropic layer having a thickness of 1.0 μm was formed in the same manner as in Example 1, except that composition LC-2 was used. A cross-sectional SEM image obtained in the same manner as in Example 1 revealed that the entire optically anisotropic layer was smoothly cholesterically aligned, and contained a layer with a helical pitch of 205 nm (corresponding to Layer A, which had a helical pitch of less than 250 nm) and a layer with a helical pitch of 325 nm (corresponding to Layer B, which had a helical pitch of 250 nm or more). In Region 2, the thickness of the layer with a helical pitch of 205 nm gradually changed. The thickness of the layer with a helical pitch of 205 nm relative to the thickness of the cholesteric alignment layer was approximately the same as that shown in FIG. 14 .

[0254] Next, similarly to Example 1, the diffraction efficiency of the optically anisotropic layer was evaluated. The diffraction efficiency was 13% at a position of 25 mm, 21% at a position of 35 mm, and 58% at a position of 45 mm. This confirmed that the prepared optically anisotropic layer (cholesteric alignment region) had an in-plane distribution of diffraction efficiency. Furthermore, similarly to Example 1, a light guide element was prepared, and the amount of emitted light was measured. It was confirmed that the emitted intensity was uniform. The optically anisotropic layers of Examples 1 and 2 were both smooth, with an in-plane film thickness distribution within ±50 nm. No scattered light due to the unevenness of the optically anisotropic layer was observed. Furthermore, the compound compositions, ordinary and extraordinary refractive indices of Layer A and Layer B were identical, and no scattered light due to interfacial reflection was observed.

[0255] Comparative Example 1 An alignment film prepared in the same manner as in Example 1 was exposed to light using the exposure device shown in FIG. 3 to form an alignment film P-2 having a single alignment pattern. The exposure device used a laser that emitted laser light with a wavelength of 325 nm. The exposure dose by the interference light was 300 mJ / cm. 2The period (length for which the optical axis rotates 180°) Λ of the alignment pattern formed by the interference of the two laser beams was controlled to be 0.43 μm by changing the crossing angle (crossing angle α) of the two beams. As in Example 1, composition LC-1 was applied to the alignment film P-2 to form a composition layer. The application was carried out using a spin coater at 1500 rpm. The support having the composition layer was heated on a hot plate at 90°C for 1 minute. Subsequently, without using a mask, ultraviolet light with a wavelength of 365 nm was applied at 300 mJ / cm using a 365 nm LED UV exposure machine in a nitrogen atmosphere at 90°C. 2 The coating film was irradiated with an irradiation amount of 1000 ppm, whereby the orientation of the liquid crystal compound was fixed, and an optically anisotropic layer was formed.

[0256] Subsequently, the diffraction efficiency of the optically anisotropic layer was evaluated in the same manner as in Example 1. The diffraction efficiency was found to be 58% regardless of position. Cross-sectional SEM images obtained in the same manner as in Example 1 confirmed that the optically anisotropic layer contained only a layer with a helical pitch of 324 nm (corresponding to Layer B with a helical pitch of 250 nm or more). PVA103 was laminated to a thickness of 2 μm on the optically anisotropic layer, and the layer was irradiated with Xe light for 3 days using a low-temperature cycle xenon weather meter (XL75Z, Suga Test Instruments Co., Ltd.) via an ultraviolet absorption filter SC40 (manufactured by Fujifilm). A decrease of approximately 1% in the diffraction efficiency was observed.

[0257] Next, the optically anisotropic layer was cut out, peeled off from the glass substrate, and placed on the surface of the light guide plate to achieve the thickness distribution shown in Figure 15. In Figure 15, reference numeral 241 denotes a region where the optically anisotropic layer was cut out and placed. Reference numeral 242 denotes a region where the optically anisotropic layer was cut out and placed in a direction inverted 180° from reference numeral 241. No optically anisotropic layer was placed in reference numeral 243, and the optically anisotropic layers corresponding to reference numerals 241 and 242 were not continuous. That is, as shown in Figure 16, the optically anisotropic layer on the incident side and the optically anisotropic layer on the output side were not continuous. Next, as in Example 1, laser light was incident on the optically anisotropic layer on the incident side of the light guide element, and the amount of light emitted was confirmed. It was confirmed that the output intensity was non-uniform. It was also confirmed that scattered light was generated when the laser hit the thickness step.

[0258] The present invention can be suitably used for various applications that reflect light in optical devices, such as a diffraction element that causes light to enter and exit an AR glass light guide plate.

[0259] REFERENCE SIGNS LIST 10 Liquid crystal diffraction element 12 First layer (layer A) 14 Second layer (layer B) 18 Optically anisotropic layer 20 Support 24 Alignment film 30 Liquid crystal compound 30A Optical axis 40 Display (image display device) 45 Light guide element 45a First diffraction region 45b Non-diffraction region 45c Second diffraction region 45d Third diffraction region 50 AR display device 60 Exposure device 62 Laser 64 Light source 68 Beam splitter 70A, 70B Mirror 72A, 72B λ / 4 plate 100 Linear polarizer 102 λ / 4 plate 104 Light shielding plate 104a Pinhole 110 Dove prism 112 Linear polarizer 114 λ / 4 plate 144 Light guide plate 320 Support 322 Alignment film 324 Optically anisotropic layer (coating film) 326 Layer with helical pitch of 250 nm or more 328 Layer with helical pitch of less than 250 nm 329 Photomask 330 Dark area 332 Light area 340, 400, 450 Optically anisotropic layer 400a First optically anisotropic layer 400b Second optically anisotropic layer 450 Optically anisotropic layer 410a, 420a First diffraction area 410b, 420b Non-diffraction area 410c, 420c Second diffraction area 500 Laminate M Laser light MA, MB Light ray P O Linear polarized light P R Right circular polarization P L Left circularly polarized light α Crossing angle L1, L4 Incident light L2, L5 Reflected light R R Right-handed circularly polarized red light I0 to I3 Light propagating within the light guide plate P1 to P4 Position R1 to R4 Light

Claims

1. An optically anisotropic layer formed using a composition containing a liquid crystal compound, the optically anisotropic layer having a cholesteric alignment region in which the liquid crystal compound is cholesterically aligned at a constant film thickness in at least a part of its plane, the cholesteric alignment region having, in the thickness direction, Layer A with a helical pitch of less than 250 nm and Layer B with a helical pitch of 250 nm or more, and the ratio of the thickness of Layer A to the thickness of the cholesteric alignment region differs within the plane of the cholesteric alignment region.

2. The optically anisotropic layer according to claim 1, wherein in the cholesteric alignment region, the ratio of the thickness of the layer A to the thickness of the cholesteric alignment region gradually changes from one side to the other in at least one direction within the plane of the optically anisotropic layer.

3. The optically anisotropic layer according to claim 1, wherein the helical pitch gradually changes in the thickness direction in the cholesteric alignment region.

4. The optically anisotropic layer according to claim 1, wherein the helical pitch in said layer A is constant.

5. The optically anisotropic layer according to claim 1, wherein the cholesteric alignment region has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while rotating continuously along at least one direction in the plane.

6. An optically anisotropic layer according to claim 5, wherein in the cholesteric alignment region, the direction in which the ratio of the thickness of said layer A to the thickness of the cholesteric alignment region gradually changes is parallel to the direction in which the orientation of the optical axis derived from said liquid crystal compound changes while continuously rotating.

7. The optically anisotropic layer according to claim 1, wherein at least a part of the plane of the optically anisotropic layer, which is different from the cholesteric alignment region, consists solely of an optically isotropic region.

8. The optically anisotropic layer according to claim 1, wherein at least a part of the plane of the optically anisotropic layer, which is different from the cholesteric alignment region, consists solely of an optically anisotropic region.

9. The optically anisotropic layer according to claim 1, wherein in at least a part of the plane different from the cholesteric alignment region, the liquid crystal compound is aligned in one direction in the same plane.

10. The optically anisotropic layer according to claim 5, wherein the optically anisotropic layer has regions in the plane where the rotation directions of the optical axes derived from the liquid crystal compound in the liquid crystal alignment pattern are different from each other.

11. The optically anisotropic layer according to claim 1, wherein the liquid crystal compound has a region in which it is aligned in a right-handed helical cholesteric orientation and a region in which it is aligned in a left-handed helical cholesteric orientation.

12. The optically anisotropic layer according to claim 1, wherein the compound compositions constituting said Layer A and said Layer B are the same.

13. The optically anisotropic layer according to claim 1, wherein the ordinary refractive index and the extraordinary refractive index of said layer A and said layer B are the same.

14. The optically anisotropic layer according to claim 1, wherein the helical pitch of said layer A and that of said layer B differ by 20 nm or more.

15. A light guide element comprising: a light guide plate; and the optically anisotropic layer according to any one of claims 1 to 14, disposed on the surface of said light guide plate.

16. An AR display device comprising the light guide element according to claim 15 and an image display device.

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