Light guide element and ar display device

Abstract

The present invention provides: a light guide element that is capable of efficiently outputting light from a light guide plate; and an AR display device. Provided is a light guide element comprising a substrate and an optically anisotropic layer that is provided on at least one main surface of the substrate, wherein: the optically anisotropic layer is formed using a composition that contains a liquid crystal compound which has an ordinary light refractive index no and an extraordinary light refractive index ne and includes a region A that has an alignment pattern in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating along at least one in-plane direction; and the ordinary light refractive index no, the extraordinary light refractive index ne, and the average refractive index nBASE of the substrate satisfy the relation in the following expression (1): no < nBASE < ne.

Description

Light guide element and AR display device

[0001] The present invention relates to a light guide element and an AR display device.

[0002] In recent years, AR (Augmented Reality) 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, and the like.

[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. It describes a method in which light incident on a substrate (light guide plate) is diffracted by the 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 area (expanding the exit pupil). For example, Patent Document 4 describes an optical waveguide in which an input coupler (diffraction element) of the optical waveguide couples light corresponding to an image having a corresponding FOV (field of view) to the optical waveguide, the input coupler divides the FOV of the image coupled to the optical waveguide into first and second parts, and diffracts a portion of the light corresponding to the image in a second direction toward a second intermediate component, and the intermediate coupler (diffraction element) and the output coupler (diffraction element) perform exit pupil expansion.

[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] The inventors have studied a configuration in which a liquid crystal diffraction element is used as a diffraction element of a light guide element used in AR glasses, and the liquid crystal diffraction element diffracts a portion of light at multiple locations to emit it outside the light guide plate in order to expand the viewing zone (expand the exit pupil) of the AR glasses. As a result, they have found that there are still issues with the light utilization efficiency. Furthermore, the inventors have found that there are still issues with the light utilization efficiency when a liquid crystal diffraction element is used as the diffraction element on the side that causes light to enter the light guide plate.

[0011] The object of the present invention is to solve the problems of the conventional technology, and to provide a light-guiding element that can efficiently emit light from a light-guiding plate, and an AR display device using the same.

[0012] [1] A substrate and an optically anisotropic layer provided on at least one main surface of the substrate, the optically anisotropic layer being formed using a composition containing a liquid crystal compound having an ordinary refractive index no and an extraordinary refractive index ne, and including a region A having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and the ordinary refractive index no and the extraordinary refractive index ne and the average refractive index n of the substrate BASE and a light guide element having the relationship of the following formula (1): no < n BASE < ne (1) [2] The light guide element according to [1], wherein the extraordinary refractive index ne is 1.8 or more. [3] The light guide element according to [1] or [2], wherein the ordinary refractive index no is 1.4 or more. [4] The average refractive index n of the substrate BASEThe light guide element according to any one of [1] to [3], wherein the diffraction efficiency varies in the in-plane direction in region A. [6] The light guide element according to any one of [1] to [5], wherein region A has a region in which the diffraction efficiency gradually increases in the in-plane direction. [7] The light guide element according to any one of [1] to [6], wherein the optically anisotropic layer further has region B having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while rotating continuously along at least one direction in the plane, and the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the orientation pattern in region A is different from the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the orientation pattern in region B. [8] The light guide element according to [7], wherein one direction of the orientation pattern in region A is different from one direction of the orientation pattern in region B. [9] The light guide element according to [7] or [8], wherein the length over which the orientation of the optical axis derived from the liquid crystal compound in the orientation pattern of region A rotates 180° in the plane is different from the length over which the orientation of the optical axis derived from the liquid crystal compound in the orientation pattern of region B rotates 180° in the plane.

[10] The light guide element according to any one of [7] to [9], wherein at least one of region A and region B is a cholesteric liquid crystal layer in which the liquid crystal compound is cholesterically oriented.

[11] The light guide element according to any one of [1] to

[10] , wherein the optically anisotropic layer further includes a non-alignment pattern region having no liquid crystal alignment pattern, and at least a part of the plane of the non-alignment pattern region is optically isotropic.

[12] The light guide element according to any one of [1] to

[11] , wherein the entire optically anisotropic layer is smooth and does not have an uneven structure.

[13] The light guide element according to any one of [1] to

[11] , wherein the light guide element comprises an adhesive layer between the substrate and the optically anisotropic layer, and wherein the refractive index n of the adhesive layer is AD The light guide element according to any one of [1] to

[12] , wherein n satisfies the following formula (2): AD< ne (2)

[14] The light guide element according to any one of [1] to

[13] , comprising an adhesive layer between the substrate and the optically anisotropic layer, wherein the adhesive layer has a thickness of 0.1 μm or less.

[15] The light guide element according to any one of [1] to

[12] , wherein the substrate and the optically anisotropic layer are in direct contact with each other.

[16] The light guide element according to any one of [1] to

[15] , comprising two optically anisotropic layers spaced apart from each other in the planar direction of the substrate on a main surface of the substrate, wherein an isotropic layer that is non-liquid crystalline and optically isotropic is disposed between the two optically anisotropic layers on the main surface of the substrate.

[17] The light guide element according to

[16] , wherein the isotropic layer covers the surfaces of the two optically anisotropic layers opposite to the substrate.

[18] The light guide element according to

[16] , wherein the surfaces of the isotropic layer and the two optically anisotropic layers opposite to the substrate are flush with each other.

[19] The refractive index n of the isotropic layer ISO The light guide element according to any one of

[16] to

[18] , wherein no < n satisfies the relationship of the following formula (3): ISO < ne (3)

[20] An AR display device comprising the light guide element according to any one of [1] to

[19] and an image display device.

[0013] According to the present invention, it is possible to provide a light guide element that can efficiently emit light from a light guide plate, and an AR display device that has excellent light utilization efficiency.

[0014] FIG. 1 is a conceptual diagram of an example of region A and region B of the optically anisotropic layer of the light guide element of the present invention. FIG. 2 is a top view 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 region A and / or region B of the optically anisotropic layer of FIG. 1. FIG. 5 is a graph conceptually showing an example of the relationship between position and diffraction efficiency in region A and / or region B of the optically anisotropic layer. FIG. 6 is a graph conceptually showing another example of the relationship between position and diffraction efficiency in region A and / or region B of the optically anisotropic layer. FIG. 7 is a conceptual diagram of another example of region A and region B of the optically anisotropic layer of the present invention. FIG. 8 is a top view of FIG. 7. FIG. 9 is a diagram for explaining the function of region A and / or region B of the optically anisotropic layer of FIG. 7. FIG. 10 is a diagram for explaining the function of region A and / or region B of the optically anisotropic layer of FIG. 7. FIG. 11 is a schematic diagram illustrating an example of an AR display device having a light-guiding element of the present invention. FIG. 12 is a graph conceptually illustrating the relationship between position and emitted light in an AR display device. FIG. 13 is a schematic diagram illustrating a method for measuring diffraction efficiency. FIG. 14 is a diagram illustrating an example of a method for forming a region in which the diffraction efficiency gradually changes in the in-plane direction of an optically anisotropic layer. FIG. 15 is a diagram illustrating another example of a method for forming a region in which the diffraction efficiency gradually changes in the in-plane direction of an optically anisotropic layer. FIG. 16 is a diagram illustrating the change in the amount of light irradiated depending on the position in the optically anisotropic layer. FIG. 17 is a schematic diagram illustrating an example of an AR display device having a light-guiding element of the present invention. FIG. 18 is a diagram illustrating an example of the in-plane distribution of diffraction efficiency using shading. FIG. 19 is a schematic diagram illustrating the X-Z cross section of region A and / or region B of the optically anisotropic layer. FIG. 20 is a schematic diagram illustrating the X-Z cross section of region A and / or region B of the optically anisotropic layer. Fig. 21 is a schematic diagram showing the XZ cross section of region A and / or region B of the optically anisotropic layer. Fig. 22 is a conceptual diagram showing an example of an optically anisotropic layer included in a light-guiding element of the present invention. Fig. 23 is a top view of Fig. 22. Fig. 24 is a conceptual diagram showing another example of an optically anisotropic layer included in a light-guiding element of the present invention. Fig. 25 is a conceptual diagram showing an example of a laminate having a plurality of optically anisotropic layers included in a light-guiding element of the present invention.Fig. 26 is a diagram schematically showing the change in thickness of a region with high birefringence and a region with low birefringence of a liquid crystal compound in the thickness direction of an optically anisotropic layer. Fig. 27 is a diagram schematically showing another example of a light-guiding element of the present invention. Fig. 28 is a diagram schematically showing another example of a light-guiding element of the present invention.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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, with respect to angles, "perpendicular," "parallel," and "perpendicular" refer to a range of ±5° from the exact angle, and with respect to angles, "same" means that the difference from the exact angle is within a range of less than 5 degrees, unless otherwise specified. The difference from the exact angle is preferably less than 4 degrees, and more preferably less than 3 degrees.

[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, although not limited thereto, visible 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.

[0018] In this specification, the selective reflection central wavelength refers to the average value of two wavelengths that exhibit half-value transmittance T1 / 2 (%), expressed by the following formula, when the minimum value of transmittance in the target object (member) is Tmin (%). Formula for calculating half-value transmittance: T1 / 2 = 100 - (100 - Tmin) ÷ 2

[0019] Furthermore, the term "the selective reflection central wavelengths of a plurality of layers are 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 term "the selective reflection central wavelengths of a plurality of objects are 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.

[0020] The oblique retardation Re(40) can be measured using an "Axoscan" manufactured by Axometrics, Inc. The measurement wavelength is 750 nm, and the phase difference is measured with respect to incident light from the normal direction to the sample surface. The phase difference is then measured from directions at incident angles of -40° and 40° in the slow axis plane and the fast axis plane, respectively, with respect to the detected slow axis and fast axis. The average value of the measured values ​​from the four directions is taken as the oblique retardation Re(40).

[0021] [Light Guide Element] The light guide element of the present invention includes a substrate and an optically anisotropic layer optically coupled to the substrate. The optically anisotropic layer is formed using a composition containing a liquid crystal compound and includes a region A having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane, wherein the liquid crystal compound has an ordinary refractive index no and an extraordinary refractive index ne, and the average refractive index of the substrate is n BASE and n.sub.2 are light-guiding elements that satisfy the relationship of the following formula (1): n.sub.2 < n.sub.2 BASE <ne...(1)

[0022] FIG. 11 conceptually illustrates an example of an AR display device having a light guide element of the present invention. The AR display device 50 shown in FIG. 11 includes a light guide element 45 of the present invention and an image display device 40. The light guide element 45 includes a substrate (light guide plate) 144 and an optically anisotropic layer 400. The optically anisotropic layer 400 includes a region A 45a having an orientation pattern in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane. Furthermore, in a preferred embodiment, the optically anisotropic layer 400 includes a region B 45c having an orientation pattern in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and a non-orientation pattern region 45b having no orientation pattern. The AR display device 50 will be described in detail later.

[0023] 11 , region A45a is a region that acts as an incident diffraction element that causes light emitted from image display device 40 to be incident on substrate 144, and region B45c is a region that acts as an output diffraction element that causes light guided within substrate 144 to exit substrate 144. Note that, below, an example will be described in which region A45a acts as an incident diffraction element and region B45c acts as an output diffraction element, but region A45a may act as an output diffraction element and region B45c may act as an incident diffraction element.

[0024] It is known that the internal total reflection angle of the light guide plate strongly affects the FOV of light guide type AR glasses (AR display devices). The internal total reflection angle is determined by the average refractive index of the light guide plate, so the average refractive index of the light guide plate, n BASE It is desirable that the value is high.

[0025] As mentioned in the background art, in light-guiding AR glasses, a diffraction element and a reflection element provided on or inside the light guide plate redirect part of the guided light outside the range of the internal total reflection angle and emit it. Known diffraction elements include surface relief diffraction elements, volume hologram diffraction elements, and liquid crystal diffraction elements.

[0026] Of these, liquid crystal diffraction elements exhibit excellent angular characteristics and diffraction characteristics, but the average refractive index of commercially available liquid crystal compounds is in the range of 1.4 to 1.7. Therefore, according to the inventors' studies, when a liquid crystal diffraction element is provided on a high-refractive-index light guide plate to expand the FOV, the difference in the average refractive index between the light guide plate and the liquid crystal diffraction element causes a portion of the light to be reflected, reducing the amount of light emitted along the specified optical path. That is, the liquid crystal diffraction element on the output side diffracts the light guided within the light guide plate at an angle that deviates from the total reflection condition, causing the light to exit the light guide plate. However, when a high-refractive-index light guide plate is used, the difference in the average refractive index between the light guide plate and the liquid crystal diffraction element causes a portion of the light to be reflected at the interface and not enter the liquid crystal diffraction element, thereby reducing the amount of light emitted along the specified optical path. In particular, it was found that light incident at a shallow angle on the liquid crystal diffraction element (light with a large angle of incidence with respect to the perpendicular to the main surface of the liquid crystal diffraction element) is easily reflected at the interface between the light guide plate and the liquid crystal diffraction element, resulting in a narrow FOV. That is, it was found that when a light guide plate with a high refractive index is used, the light utilization efficiency decreases and the FOV becomes narrow.

[0027] Furthermore, it was found that even in the incident-side liquid crystal diffraction element, which diffracts the light emitted from the image display device and entering the light guide plate at an angle that causes total reflection within the light guide plate, the greater the difference in average refractive index between the light guide plate and the liquid crystal diffraction element, the more the light is specularly reflected at the interface, reducing the amount of light incident on the liquid crystal diffraction element and therefore the amount of light entering the light guide plate. As a result, it was found that the ratio (utilization efficiency) of the amount of light emitted to the user's observation position relative to the amount of light emitted by the image display device decreases.

[0028] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by making a certain relationship between the optical anisotropy of the material constituting the optically anisotropic layer acting as a liquid crystal diffraction element and the average refractive index of the light guide plate (substrate). Specifically, in an optically anisotropic layer formed using a composition containing a liquid crystal compound, the liquid crystal compound has an ordinary refractive index no and an extraordinary refractive index ne, and the average refractive index n of the substrate BASE and have the relationship of the following formula (1): no < nBASE <ne...(1)

[0029] In the light guide element of the present invention, the liquid crystal compound contained in the composition forming the optically anisotropic layer having a region acting as a liquid crystal diffraction element satisfies the above formula (1), so that when a high refractive index light guide plate is used, the difference in refractive index between the liquid crystal diffraction element (region) on the exit side and the light guide plate causes a portion of light to be reflected at the interface therebetween, reducing the amount of light emitted through a predetermined optical path and decreasing the light utilization efficiency, thereby preventing a narrowing of the FOV.Furthermore, in the liquid crystal diffraction element (region) on the entrance side, the interface between the light guide plate and the liquid crystal diffraction element causes a portion of light to be reflected, reducing the amount of light entering the light guide plate and preventing a decrease in the light utilization efficiency.

[0030] The ordinary refractive index no and extraordinary refractive index ne of a liquid crystal compound are measured as follows. Using ellipsometry, the complex reflectance is measured on an optically anisotropic layer while varying the angle of incidence between 50° and 70°. The complex reflectance results at angles of incidence between 50° and 70° obtained by ellipsometry are analyzed using an optical model that takes into account the anisotropy of the refractive index, and the ordinary refractive index no and extraordinary refractive index ne at a wavelength of 550 nm can be determined. Measurement devices that can be used include a Woollam RC2 and a Semilab SE-2000.

[0031] The ordinary refractive index no and the extraordinary refractive index ne of a liquid crystal compound for forming an optically anisotropic layer may be determined by preparing a uniaxially aligned liquid crystal cured layer using the liquid crystal compound and using ellipsometry in the same manner as described above.

[0032] In addition, when the optically anisotropic layer is formed using a composition containing multiple types of liquid crystal compounds, the ordinary refractive index no and extraordinary refractive index ne of the entire multiple types of liquid crystal compounds measured by the above method are taken as the ordinary refractive index no and extraordinary refractive index ne of the liquid crystal compound.

[0033] In addition, the average refractive index n BASE can be measured by, for example, spectroscopic ellipsometry.

[0034] The optically anisotropic layer, the composition for forming the optically anisotropic layer, and the components thereof will be described in detail below.

[0035] [Optically Anisotropic Layer] The optically anisotropic layer constituting the light guide element 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 region A having a liquid crystal orientation pattern (hereinafter also simply referred to as "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. As will be described later, the region A having the liquid crystal orientation pattern acts as a so-called liquid crystal diffraction element that diffracts incident light. Therefore, in other words, the optically anisotropic layer in the present invention has a region A that acts as a liquid crystal diffraction element.

[0036] In the present invention, the optically anisotropic layer may further include a region B having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The region B having the liquid crystal orientation pattern acts as a so-called liquid crystal diffraction element that diffracts incident light. Furthermore, the optically anisotropic layer may include a non-orientation pattern region (non-diffraction region) that does not have an orientation pattern.

[0037] (Region A, Region B and Non-Diffraction Region) Fig. 22 is a diagram conceptually showing a preferred embodiment of the optically anisotropic layer included in the light guide element of the present invention. Fig. 23 is a top view of Fig. 22.

[0038] 22 and 23 is formed using a composition containing a liquid crystal compound, and by varying the orientation state of the liquid crystal compound in the in-plane direction, a region A 45a, a region 45b having no liquid crystal orientation pattern (hereinafter also referred to as a non-diffraction region), and a region B 45c are formed. The non-diffraction region 45b is disposed between the region A 45a and the region B 45c. In the following description, the region A 45a and the region B 45c are also referred to as a diffraction region.

[0039] The region A45a and the region B45c each have 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 act as a liquid crystal diffraction element that diffracts incident light. Note that the liquid crystal orientation pattern of the region A45a and the liquid crystal orientation pattern of the region B45c may be the same or different.

[0040] Specifically, when an optically anisotropic layer has region A and region B, the rotation direction of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal alignment pattern of region A and the rotation direction of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal alignment pattern of region B may be different from each other.

[0041] Alternatively, one direction of the liquid crystal alignment pattern in the region A and one direction of the liquid crystal alignment pattern in the region B may be different from each other.

[0042] Alternatively, the length (one period Λ) over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern of region A rotates by 180° in the plane may be different from the length (one period Λ) over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern of region B rotates by 180° in the plane.

[0043] As will be described later, the rotation direction of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal alignment pattern is the direction of change in the angle (orientation) of the optical axis 30A of the liquid crystal compound 30 when viewed in the direction along the arrow X in Fig. 2. The one direction of the liquid crystal alignment pattern is the azimuth direction of the arrow X in Fig. 2. The length (one period Λ) over which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in the plane in the liquid crystal alignment pattern is Λ shown in Fig. 2.

[0044] Furthermore, the regions A 45a, the non-diffractive regions 45b, and the regions B 45c have approximately the same thickness, and both main surfaces of the optically anisotropic layer 400 can be smooth, flat surfaces without an uneven structure.

[0045] Here, the non-diffraction region 45b does not have the above-mentioned liquid crystal orientation pattern, and is a region that does not have the function of diffracting incident light.

[0046] 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, with uniaxial or twisted orientation being preferred. 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. 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 phase difference of λ / 8 to light from at least one incident direction. As a result, for example, circularly polarized light diffracted in the incident-side region A 45 a is converted into elliptically polarized light by passing through the non-diffraction region 45 b when guided through the light guide plate, undergoes total reflection at the interface between the non-diffraction region 45 b and air, and is converted into linearly polarized light by passing through the non-diffraction region 45 b again. While the polarization state of circularly polarized light is eliminated when guided, the polarization state of linearly polarized light can be maintained when guided, making it possible to uniform the light intensity of the outgoing light in the exit-side region B 45 c.

[0047] In another preferred embodiment, although not shown, the optically anisotropic layer may be configured only with a region A having a liquid crystal orientation pattern. In yet another preferred embodiment, the region A and a region B having a liquid crystal orientation pattern different from that of the region A are adjacent in-plane, and the layer may be configured not to include a non-diffractive region.

[0048] An example of region A and / or region B will be described below with reference to Figures 1 and 2. The example shown in Figures 1 and 2 is a reflective liquid crystal diffraction element in which liquid crystal compounds are arranged in a cholesteric liquid crystal phase, and which reflects and diffracts incident light. Note that a reflective diffraction element reflects incident light in a direction different from specular reflection.

[0049] 1, the liquid crystal diffraction element 10 includes a support 20, an alignment film 24, and an optically anisotropic layer 18. The optically anisotropic layer 18 has a structure in which liquid crystal compounds 30 are cholesterically oriented. That is, the optically anisotropic layer 18 is a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase, and has a cholesteric liquid crystal structure in which the liquid crystal compounds 30 are helically twisted and oriented along a helical axis parallel to the thickness direction. The optically anisotropic layer 18 has a structure in which liquid crystal compounds 30 are stacked one helical rotation (360° rotation) to form one helical pitch, and the liquid crystal compounds 30 are stacked at multiple pitches, each pitch being a helical rotation of the liquid crystal compounds 30.

[0050] As is well known, the cholesteric liquid crystal layer has wavelength selective reflectivity. Also, the cholesteric liquid crystal layer has circularly polarized light selective reflectivity. For example, if the optically anisotropic layer 18 has a selective reflection center wavelength in the green wavelength region and reflects right-handed circularly polarized light, the optically anisotropic layer 18 will selectively reflect right-handed circularly polarized light G of green light. R The optically anisotropic layer 18 reflects the incident circularly polarized light and transmits the other light. Here, because the optically anisotropic layer 18 has a liquid crystal orientation pattern, it refracts (diffracts) and reflects the incident circularly polarized light in one direction (azimuth direction) in which the direction of the optical axis is continuously rotating. At this time, the diffracted azimuth direction differs by 180° depending on the rotation direction of the incident circularly polarized light. In other words, the optically anisotropic layer 18 reflects right-handed or left-handed circularly polarized light of the selective reflection wavelength and diffracts this reflected light. Furthermore, the optically anisotropic layer 18 changes the rotation direction of the reflected circularly polarized light to the opposite direction.

[0051] (Orientation Pattern) As described above, 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 derived from the liquid crystal compound 30 changes while continuously rotating in one direction within the plane of the optically anisotropic layer 18. In the example shown in FIG. 1 , the liquid crystal orientation 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 within the plane of the optically anisotropic layer 18. Note that 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." In the following description, "the orientation of the optical axis 30A is rotated" is also simply referred to as "the optical axis 30A is rotated." Although FIG. 1 illustrates the case where a cholesteric liquid crystal phase is formed, a composition that forms a twisted nematic liquid crystal phase, a nematic liquid crystal phase without twisting, or a smectic liquid crystal phase may alternatively be used.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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 that 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 whose optical axes 30A coincide 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, the liquid crystal orientation pattern of the optically anisotropic layer 18 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.

[0056] When the X-Z plane of an optically anisotropic layer 18 having a liquid crystal orientation pattern in which the direction of the optical axis 30A derived from the liquid crystal compound 30 changes by continuous rotation, as in the liquid crystal diffraction element 10 shown in FIG. 1, is observed with a scanning electron microscope (SEM), a striped pattern is observed in which the orientation direction of the alternating bright and dark regions 42 and 44 is tilted at a predetermined angle relative to the principal surface (X-Y plane), as conceptually shown in FIG. 19. In the following description, the optically anisotropic layer 18 will also be referred to as a liquid crystal layer 18. In such an SEM cross section, the spacing between adjacent bright and dark regions 42 or 44 in the normal direction of the line formed by the bright and dark regions 42 or 44 corresponds to the ½ tilted plane pitch. When the optical axis 30A of the liquid crystal compound 30 is aligned parallel to the principal surface (X-Y plane) of the liquid crystal layer 18, one helical pitch corresponds to the pitch P shown in FIG. 1, as described above. On the other hand, when the liquid crystal compound 30 is tilted with respect to the principal surface of the liquid crystal layer 18, particularly when the tilt angle of the liquid crystal compound 30 with respect to the principal surface of the liquid crystal layer 18 is equal to the angle between the line formed by the light portions 42 or the dark portions 44 and the principal surface of the liquid crystal layer 18, two light portions 42 and two dark portions 44 correspond to one pitch of the spiral (one winding of the spiral), as shown by P in Figure 19.

[0057] 1, the liquid crystal compound 30 is configured such that its optical axis 30A is aligned parallel to the main surface (X-Y plane) in the X-Z plane of the liquid crystal layer 18. However, the present invention is not limited to this. For example, as shown in FIG. 20, the liquid crystal compound 30 may be configured such that its optical axis 30A is aligned at an angle to the main surface (X-Y plane) in the X-Z plane of the liquid crystal layer 18.

[0058] 20, the tilt angle (tilt angle) of the liquid crystal compound 30 relative to the main surface (X-Y plane) in the X-Z plane of the liquid crystal layer 18 is uniform in the thickness direction (Z direction), but the present invention is not limited to this. The liquid crystal layer 18 may have a region in which the tilt angle of the liquid crystal compound 30 varies in the thickness direction. For example, the example shown in FIG. 21 shows a configuration in which the optical axis 30A of the liquid crystal compound 30 is parallel to the main surface (pretilt angle is 0°) at the interface on the alignment film 24 side of the liquid crystal layer 18, and the tilt angle of the liquid crystal compound 30 increases with increasing distance in the thickness direction from the interface on the alignment film 24 side, and thereafter the liquid crystal compound is aligned at a constant tilt angle up to the other interface (air interface).

[0059] In this way, in the liquid crystal layer 18, the optical axis 30A of the liquid crystal compound 30 may have a pretilt angle at one of the upper and lower interfaces, or may have a pretilt angle at both interfaces. The pretilt angles may also be different at both interfaces. When the liquid crystal compound 30 has a tilt angle (is tilted) in this way, the effective birefringence of the liquid crystal compound increases when light is diffracted, thereby improving the diffraction efficiency.

[0060] The average angle (average tilt angle) between the optical axis 30A of the liquid crystal compound 30 and the principal surface (X-Y plane) is preferably 5 to 80°, more preferably 10 to 50°. The average tilt angle can be measured by observing the X-Z plane of the liquid crystal layer 18 with a polarizing microscope. In particular, in the X-Z plane of the liquid crystal layer 18, the optical axis 30A of the liquid crystal compound 30 is preferably tilted in the same direction with respect to the principal surface (X-Y plane). The tilt angle is the arithmetic average of the angles between the optical axis 30A of the liquid crystal compound 30 and the principal surface measured at any five or more positions in polarizing microscope observation of the cross section of the optically anisotropic layer.

[0061] Light incident perpendicularly to the liquid crystal diffraction element (liquid crystal layer 18) is subjected to a bending force in an oblique direction within the liquid crystal layer 18, and travels obliquely. As light travels within the liquid crystal layer 18, deviations from conditions such as the diffraction period, which are originally set to obtain a desired diffraction angle for perpendicular incidence, occur, resulting in diffraction loss. When the liquid crystal compound 30 is tilted, there is an orientation in which a higher birefringence occurs relative to the light diffracting orientation compared to when it is not tilted. In this orientation, the effective extraordinary refractive index increases, resulting in a higher birefringence, which is the difference between the extraordinary refractive index and the ordinary refractive index. By setting the tilt angle orientation to match the desired diffraction orientation, deviations from the original diffraction conditions at that orientation can be suppressed, and as a result, it is believed that using a liquid crystal compound with a tilt angle can achieve higher diffraction efficiency.

[0062] The tilt angle may also be controlled by treating the interface of the liquid crystal layer 18. At the interface on the support side, the tilt angle of the liquid crystal compound 30 can be controlled by performing a pretilt treatment on the alignment film. For example, during the formation of the alignment film, a pretilt angle can be generated in the liquid crystal compound 30 in the liquid crystal layer 18 formed on the alignment film by exposing the alignment film to UV light from the front and then obliquely exposing it. In this case, the liquid crystal compound 30 is pretilted in a direction that allows the uniaxial side of the liquid crystal compound 30 to be viewed relative to the second irradiation direction. However, the liquid crystal compound 30 oriented perpendicular to the second irradiation direction does not pretilt, resulting in in-plane pretilted and non-pretilted regions. This contributes to the greatest birefringence in the desired direction when diffracting light in that direction, and is therefore suitable for improving diffraction efficiency. Furthermore, an additive that promotes the pretilt angle can be added to the liquid crystal layer 18 or the alignment film. In this case, the additive can be used as a factor to further enhance diffraction efficiency. This additive can also be used to control the pretilt angle at the air-side interface.

[0063] In a cross section of the liquid crystal layer 18 observed with an SEM, the bright and dark regions 42 and 44 resulting from the cholesteric liquid crystal phase are tilted relative to the principal surface. When the retardation of the liquid crystal layer 18 is measured from the normal direction and from a direction tilted relative to the normal, the direction in either the slow axis plane or the fast axis plane in which the retardation is minimized is preferably tilted relative to the normal. Specifically, the absolute value of the measurement angle between the normal and the direction in which the retardation is minimized is preferably 5° or greater. In other words, the liquid crystal compound 30 of the liquid crystal layer 18 is preferably tilted relative to the principal surface, and the tilt direction preferably substantially coincides with the bright and dark regions 42 and 44 of the liquid crystal layer 18. The normal direction is a direction perpendicular to the principal surface. The liquid crystal layer 18 having such a configuration can diffract circularly polarized light with higher diffraction efficiency than a liquid crystal layer in which the liquid crystal compound 30 is parallel to the principal surface.

[0064] In a configuration in which the liquid crystal compound 30 of the liquid crystal layer 18 is tilted with respect to the principal surface and the tilt direction is substantially aligned with the bright and dark portions 42 and 44, the bright and dark portions corresponding to the reflective surfaces are aligned with the optical axis 30A of the liquid crystal compound 30. This increases the effect of the liquid crystal compound on the reflection (diffraction) of light, thereby improving the diffraction efficiency. As a result, the amount of reflected light relative to incident light can be further increased.

[0065] In the fast axis plane or slow axis plane of the liquid crystal layer 18, the absolute value of the optical axis tilt angle of the liquid crystal layer 18 is preferably 5° or more, more preferably 15° or more, and even more preferably 20° or more. By setting the absolute value of the optical axis tilt angle to 15° or more, it is possible to more suitably align the directions of the liquid crystal compound 30 with the bright and dark areas, which is preferable in that the diffraction efficiency can be improved.

[0066] A typical optically anisotropic layer formed by fixing a cholesteric liquid crystal phase typically specularly reflects incident light (circularly polarized light). In contrast, the 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, 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. Below, we will explain this with reference to Figure 4.

[0067] As described above, the optically anisotropic layer 18 is an optically anisotropic 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 right-handed circularly polarized light is reflected, 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.

[0068] 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.

[0069] In the liquid crystal diffraction element 10, 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 application of the liquid crystal diffraction element 10, etc.

[0070] Here, as an example, the liquid crystal diffraction element 10 is suitably used as a diffraction element in AR glasses, which reflects light propagated through a light guide plate and outputs it to a user's observation position. In this case, in order to reliably output 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 mentioned above, the reflection angle of light by the optically anisotropic layer relative to the incident light can be increased by shortening one period Λ of the liquid crystal orientation pattern.

[0071] 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.

[0072] In the present invention, the optically anisotropic layer preferably has a structure 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 rotates continuously in the plane (hereinafter referred to as one direction in which the optical axis rotates). For example, in the case of the optically anisotropic layer shown in Figures 1 and 2, it is preferable that the diffraction efficiency increases from one side to the other in the X direction.

[0073] 5 and 6 are schematic graphs showing 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 X direction, the diffraction efficiency of the optically anisotropic layer 18 may be configured to change continuously as shown in Fig. 5, or may be configured to change stepwise as shown in Fig. 6.

[0074] Here, the diffraction efficiency is the intensity ratio of outgoing light (diffracted light) to incident light, and is measured as follows: As shown in Figure 13, the optically anisotropic layer 18 is transferred to a Dove prism 110 (refractive index = 1.517, oblique surface angle = 45°), and a laser of a predetermined wavelength is transmitted through a linear polarizer 112 and a λ / 4 plate 114 to become circularly polarized light, and the angle is set so that the diffracted light is emitted perpendicularly from the oblique surface, and the incident light is incident on the surface of the optically anisotropic layer 18. The outgoing light intensity Lr is measured using a Newport Power Meter 1918-C, and the ratio of the outgoing light intensity Lr to the incident light intensity Li (Lr / Li × 100 [%]) is taken as the diffraction efficiency.

[0075] The liquid crystal diffraction element preferably has an optically anisotropic layer configured such that the diffraction efficiency increases from one side to the other in one direction of rotation of the optical axis. That is, in region A and / or region B of the optically anisotropic layer, or further in region C described below, the diffraction efficiency preferably increases from one side to the other in one direction of rotation of the optical axis. As a result, in a light guide element used in an AR display device such as AR (Augmented Reality) glasses, when the liquid crystal diffraction element is used as a diffraction element that 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.

[0076] In addition, if the direction in which regions with constant diffraction efficiency are arranged in the optically anisotropic layer is defined as the direction in which the diffraction efficiency changes, this direction in which the diffraction efficiency changes may or may not coincide with the direction in which the optical axis rotates. That is, the direction in which the diffraction efficiency changes may intersect with the direction in which the optical axis rotates. Even in a configuration in which the direction in which the diffraction efficiency changes intersects with the direction in which the optical axis rotates, the diffraction efficiency increases from one side to the other in the direction in which the optical axis rotates.

[0077] In addition, the optically anisotropic layer (at least one of region A, region B, and region C) may be configured to have regions with different diffraction efficiency in the in-plane direction, or may be configured so that the diffraction efficiency gradually changes in one in-plane direction, or may be configured so that the diffraction efficiency gradually increases (or decreases) in one in-plane direction.

[0078] A configuration in which the diffraction efficiency of the optically anisotropic layer increases from one side to the other in one direction in which the orientation of the optical axis derived from the liquid crystal compound rotates continuously in the plane can be realized by the optically anisotropic layer having either of the following configurations (i) and (ii), with configuration (ii) being preferred in terms of the smoothness of the optically anisotropic layer: (i) a configuration in which the film thickness increases from one side to the other in one direction in which the optical axis rotates; and (ii) a configuration in which the thickness direction retardation Rth increases from one side to the other in one direction in which the optical axis rotates.

[0079] In an optically anisotropic layer, the diffraction efficiency is high in a thick region and low in a thin region, so that the diffraction efficiency can be changed by configuring the optically anisotropic layer so that the thickness increases from one side to the other in one direction of rotation of the optic axis.

[0080] As described above, in the optically anisotropic layer, the liquid crystal compound is aligned in a desired orientation pattern. In regions where this alignment is not disordered, light can be diffracted appropriately, resulting in high diffraction efficiency. Furthermore, in regions where the alignment of the liquid crystal compound is not disordered, the thickness direction retardation Rth is high. On the other hand, in regions where the alignment of the liquid crystal compound is disordered, light is not diffracted appropriately, resulting in low diffraction efficiency. Furthermore, in regions where the alignment of the liquid crystal compound is disordered, the thickness direction retardation Rth is low. Therefore, by configuring the optically anisotropic layer so that the thickness direction retardation Rth increases from one side to the other in one direction of rotation of the optical axis, the diffraction efficiency can be changed. Examples of methods for forming such optically anisotropic layers include the methods described in WO2020 / 122119.

[0081] A method for detecting whether the thickness retardation Rth varies at each in-plane position will be described. Since the oblique retardation Re(40) is proportional to the thickness retardation Rth, by confirming whether the oblique retardation Re(40) varies in the plane, it is possible to detect whether the thickness retardation Rth varies in the plane. Furthermore, by confirming that the oblique retardation Re(40) varies gradually in the plane, it is possible to detect whether the thickness retardation Rth varies gradually in the plane.

[0082] In addition, in the optically anisotropic layer, in thickness direction, there are a region with high birefringence and a region with low birefringence, and the ratio of the thickness of the region with high birefringence to the thickness of the optically anisotropic layer is made different in the plane of the optically anisotropic layer, so that the diffraction efficiency can be changed.In the thickness direction of the optically anisotropic layer, the ratio of the thickness of the region with high birefringence is higher, the diffraction efficiency becomes higher, and the ratio of the thickness of the region with high birefringence is lower, the diffraction efficiency becomes lower.In the thickness direction, the region with low birefringence can preferably be made to include an optically isotropic region.

[0083] A method for detecting differences in birefringence at different positions in the thickness direction at a certain position in the plane is described with reference to FIG. 26 . In an optically anisotropic layer in which liquid crystal compounds are cholesterically oriented, when the optically anisotropic layer 324 is cut in the thickness direction and an SEM image of the exposed optically anisotropic layer 324 is analyzed, bright and dark areas resulting from the cholesteric orientation of the liquid crystal compounds are clearly visible in the high birefringence region 326. On the other hand, in the low birefringence region 328, the contrast between the bright and dark areas is small, and the bright and dark areas are not visible, particularly when the region 328 is optically isotropic. Therefore, the film thickness of the high birefringence region can be determined by measuring the thickness of the region where the bright and dark areas are clearly visible.

[0084] However, when the liquid crystal compound is not cholesterically oriented and when the birefringence changes continuously in the thickness direction, it is difficult to measure the thickness of the region with high birefringence. In such cases, a portion of the optically anisotropic layer is etched, and the ratio of the birefringence Δn in the thickness direction can be determined from the difference in the oblique retardation Re(40) before and after etching. For example, the oblique retardation Re(40) is determined using an Axoscan (manufactured by Axometrics), and then the optically anisotropic layer is etched 100 nm from the surface. This process is repeated until the optically anisotropic layer is completely etched in the thickness direction. The magnitude of the oblique retardation Re(40) in the etched region is calculated from the difference in the oblique retardation Re(40) before and after 100 nm etching. Since the oblique retardation Re(40) is proportional to the birefringence index Δn, the thickness of the region having a high birefringence index of the liquid crystal compound in the thickness direction can be determined by determining the film thickness of the region having a large oblique retardation Re(40) in the thickness direction.

[0085] The configuration in which the diffraction efficiency of the optically anisotropic layer increases from one side to the other side along at least one direction in the plane of the optically anisotropic layer can be realized by gradually changing the ratio of the thickness of the region with high birefringence to the thickness of the optically anisotropic layer.As an example, by gradually increasing the ratio of the thickness of the region with high birefringence to the thickness of the optically anisotropic layer along at least one direction in the plane of the optically anisotropic layer, the diffraction efficiency of the optically anisotropic layer can be increased from one side to the other side.

[0086] In the optically anisotropic layer, in the structure that has a region with high birefringence and a region with low birefringence in thickness direction, since the region with different birefringence Δn in thickness direction has, when the diffraction efficiency in the plane of the optically anisotropic layer changes, the average value Δn of birefringence in thickness direction changes in plane.That is, when the diffraction efficiency of the optically anisotropic layer changes along at least one direction in the plane of the optically anisotropic layer from one side to the other, the average value Δn of birefringence in thickness direction changes gradually in plane.In this way, the structure that the birefringence Δn is different in thickness direction and the average value Δn of birefringence in thickness direction changes gradually in plane can be realized by, for example, in at least a part of the plane of the optically anisotropic layer, along at least one direction in the plane of the optically anisotropic layer, from one side to the other, the thickness of the optically isotropic region gradually decreases, and the thickness of the optically anisotropic region gradually increases. In the plane of the optically anisotropic layer, the maximum thickness of the high birefringence region is preferably 0.1 to 10 μm, more preferably 0.3 μm to 8 μm, and even more preferably 0.5 μm to 5 μm. In the plane of the optically anisotropic layer, the minimum thickness of the high birefringence region is preferably 0.0 to 5 μm, more preferably 0.0 μm to 3 μm, and even more preferably 0.0 μm to 1 μm. However, the maximum thickness and minimum thickness of the high birefringence region are preferably set appropriately depending on the performance required for the optically anisotropic layer and the light guide element, and are not limited to the above values.

[0087] Furthermore, among regions A, B, and C, it is preferable that the region used as the exit-side diffraction region and / or the region used as the intermediate diffraction region have diffraction efficiency that increases from one side to the other in one direction of the liquid crystal orientation pattern, as described above. With this structure, when light propagating within the light guide plate is diffracted by the liquid crystal diffraction element and emitted from the light guide plate, the brightness of the emitted light can be made uniform.

[0088] The change in diffraction efficiency may be such that the diffraction efficiency is higher in multiple directions in the plane. Figure 18 shows an example of the in-plane distribution of diffraction efficiency when viewed from a direction perpendicular to the main surface of the liquid crystal diffraction element. In Figure 18, the darker the black color, the higher the diffraction efficiency. However, various liquid crystal diffraction elements can be applied in accordance with the design of the light guide plate.

[0089] 22 and 23, the optically anisotropic layer has two regions having a liquid crystal orientation pattern, but this is not limiting. In the light guide element of the present invention, the optically anisotropic layer may further have a region C in the in-plane direction of the same optically anisotropic layer, which has a liquid crystal orientation 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.

[0090] Fig. 24 is a plan view conceptually illustrating another example of an optically anisotropic layer included in a light-guiding element of the present invention. The optically anisotropic layer 450 shown in Fig. 24 includes a region A 45a, a region B 45c, a region C 45d, and a non-diffraction region 45b. As shown in Fig. 24, the region A 45a and the region C 45d are spaced apart in the left-right direction in the figure, and the region C 45d and the region B 45c are spaced apart in the up-down direction in the figure. The non-diffraction region 45b is formed between the region A 45a and the region C 45d, and between the region C 45d and the region B 45c.

[0091] Region C45d, like regions A45a and B45c, 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. Like regions A45a and B45c, region C45d is a cholesteric liquid crystal layer. Furthermore, the liquid crystal orientation pattern in region C45d may be different from the liquid crystal orientation patterns in regions A45a and B45c.

[0092] Thus, the optically anisotropic layer 450 further including region C45d has three light-diffracting regions. Such an optically anisotropic layer 450 is used in combination with a light guide plate to form a light guide element. In this case, for example, region A45a acts as an incident diffraction element for directing light into the light guide plate, region B45c acts as an exit diffraction element for directing light out of the light guide plate, and region C45d acts as an intermediate diffraction element that diffracts light incident from region A45a toward region B45c. Region C45d, which acts as an intermediate diffraction element, can be configured to diffract a portion of light at multiple locations, thereby expanding the exit pupil. Furthermore, region C45d preferably has regions with different diffraction efficiencies in the in-plane direction, and it is preferable that the diffraction efficiency gradually change.

[0093] The optically anisotropic layer constituting the light guide element of the present invention may be a laminate of a plurality of optically anisotropic layers. Fig. 25 is a conceptual diagram showing an example in which a plurality of optically anisotropic layers are laminated.

[0094] 25 includes a first optically anisotropic layer 400a and a second optically anisotropic layer 400b. The first optically anisotropic layer 400a includes a region A 410a and a region B 410c having a liquid crystal alignment pattern, and a non-diffraction region 410b. The second optically anisotropic layer 400b includes a region A 420a and a region B 420c having a liquid crystal alignment pattern, 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 described above.

[0095] In Figure 25, region A410a of the first optically anisotropic layer 400a and region A420a of the second optically anisotropic layer 400b are arranged in an overlapping position, and non-diffraction region 410b having no liquid crystal orientation pattern of the first optically anisotropic layer 400a and non-diffraction region 420b having no liquid crystal orientation pattern of the second optically anisotropic layer 400b are arranged in an overlapping position, and region B410c of the first optically anisotropic layer 400a and region B420c of the second optically anisotropic layer 400b are arranged in an overlapping position.

[0096] 25, 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 layers are stacked so that the regions A of the optically anisotropic layers overlap, the regions B of the optically anisotropic layers overlap, and the non-diffraction regions of the optically anisotropic layers overlap.

[0097] 24 may be a laminate of two or more optically anisotropic layers each having a region C. In this case, it is preferable that the regions C of the optically anisotropic layers are laminated so as to overlap each other.

[0098] In a light guide element having the above-described laminate and a substrate (light guide plate), the optically anisotropic layer in contact with the substrate among the plurality of optically anisotropic layers constituting the laminate satisfies the above-described formula (1). For example, when the substrate (not shown) is in contact with the interface on the first optically anisotropic layer 400a side, the ordinary refractive index no and extraordinary refractive index ne of the liquid crystal compound used to form the first optically anisotropic layer and the average refractive index n of the substrate satisfy the following formula (1): ＢＡＳＥ The relationship satisfies the above formula (1).

[0099] In the laminate 500 shown in FIG. 25, the region A410a of the first optically anisotropic layer 400a and the region A420a 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 region A410a of the first optically anisotropic layer 400a and the length of the helical pitch of the cholesteric liquid crystal layer in the region A420a of the second optically anisotropic layer 400b are different from each other, or Alternatively, it is preferable that the region B410c of the first optically anisotropic layer 400a and the region B420c of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and that the length of the helical pitch of the cholesteric liquid crystal layer in the region B410c of the first optically anisotropic layer 400a and the length of the helical pitch of the cholesteric liquid crystal layer in the region B420c of the second optically anisotropic layer 400b are different from each other.

[0100] 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 different between the regions A and / or between the regions B of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b, the regions A and / or the regions B of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b will reflect 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 each wavelength of, for example, RGB. Therefore, it is preferable to use a laminated configuration of optically anisotropic layers having regions A and B (and further region C) that reflect and diffract light of these wavelengths. For example, the first optically anisotropic layer may be configured such that regions A and B are cholesteric liquid crystal layers having a selective reflection wavelength in the red wavelength range, and the second optically anisotropic layer is configured such that regions A and B are cholesteric liquid crystal layers having a selective reflection wavelength in the green wavelength range.

[0101] In the laminate 500 shown in FIG. 25, the region A410a of the first optically anisotropic layer 400a and the region A420a of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the direction of rotation of the helical spiral of the cholesteric liquid crystal layer in the region A410a of the first optically anisotropic layer 400a is different from the direction of rotation of the helical spiral of the cholesteric liquid crystal layer in the region A420a of the second optically anisotropic layer 400b. Alternatively, it is preferable that the region B410c of the first optically anisotropic layer 400a and the region B420c of the second optically anisotropic layer 400b are cholesteric liquid crystal layers, and the direction of spiral rotation of the cholesteric liquid crystal layer in the region B410c of the first optically anisotropic layer 400a and the direction of spiral rotation of the cholesteric liquid crystal layer in the region B420c of the second optically anisotropic layer 400b are different from each other.

[0102] As described above, the cholesteric liquid crystal layer has circular polarization selectivity depending on the direction of rotation of the helix in the helical structure. By making the directions of rotation of the helices in the regions A and / or B 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 region A 410a of the first optically anisotropic layer 400a reflects and diffracts right-handed circularly polarized light of a certain wavelength, the region A 420a of the second optically anisotropic layer 400b reflects and diffracts left-handed circularly polarized light of the same wavelength, and / or the region B 410c of the first optically anisotropic layer 400a reflects and diffracts right-handed circularly polarized light of a certain wavelength, and the region B 420c of the second optically anisotropic layer 400b reflects and diffracts left-handed circularly polarized light of the same wavelength.

[0103] Furthermore, in the laminate 500 as shown in Figure 25, it is preferable that the length of one period in which the orientation of the optical axis derived from the liquid crystal compound in region A410a of the first optically anisotropic layer 400a rotates 180° in the plane and the length of one period in region A420a of the second optically anisotropic layer 400b are different from each other, or the length of one period in which the orientation of the optical axis derived from the liquid crystal compound in region B410c of the first optically anisotropic layer 400a rotates 180° in the plane and the length of one period in region B420c of the second optically anisotropic layer 400b are different from each other.

[0104] As described above, the diffraction angles in region A and region B are determined according to the length of one period in the liquid crystal alignment 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 helical pitch lengths of region A and / or region B of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b are different, and the first optically anisotropic layer 400a and the second optically anisotropic layer 400b reflect and diffract light of different wavelengths, the diffraction angles will differ if the length of one period in the liquid crystal alignment pattern is the same, 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 regions A and / or the regions B of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b so that the diffraction angles of light in the regions A and / or the regions B of the first optically anisotropic layer 400a and the second optically anisotropic layer 400b are the same.

[0105] Furthermore, in the laminate 500 as shown in Figure 25, it is preferable that at least one of the following conditions is satisfied: one direction of the liquid crystal orientation pattern in region A410a of the first optically anisotropic layer 400a is different from one direction of the liquid crystal orientation pattern in region A420a of the second optically anisotropic layer 400b; or one direction of the liquid crystal orientation pattern in region B410c of the first optically anisotropic layer 400a is different from one direction of the liquid crystal orientation pattern in region B420c of the second optically anisotropic layer 400b.

[0106] This allows, for example, light diffracted in region A 410a of the first optically anisotropic layer 400a to be selectively diffracted in region B 410c of the optically anisotropic layer 400a. Furthermore, light diffracted in region A 420a of the second optically anisotropic layer 400b to be selectively diffracted in region B 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 400c.

[0107] (Composition) The optically anisotropic layer included in the present invention is formed using a composition containing a liquid crystal compound having an ordinary refractive index no and an extraordinary refractive index ne, and at this time, the average refractive index n of the substrate BASE and n have the relationship of the following formula (1): no < n BASE <ne...(1)

[0108] Various known compositions can be used as the composition containing a liquid crystal compound. When a polymerizable liquid crystal compound is used as described below, the composition desirably further contains a polymerization initiator. Furthermore, the composition may contain a solvent, a surfactant, a chiral agent (optically active compound), a crosslinking agent, and other additives. The composition may also contain multiple types of liquid crystal compounds. These will be described in detail below.

[0109] --Liquid Crystal Compound-- Any known material can be used as the liquid crystal compound as long as it satisfies the above formula (1). Typical examples include those known as rod-shaped liquid crystal compounds. From the viewpoint of improving the physical strength, heat resistance, and durability of the optically anisotropic layer, the liquid crystal compound is preferably a polymerizable liquid crystal compound.

[0110] Examples of rod-shaped polymerizable liquid crystal compounds include rod-shaped nematic liquid crystal compounds. As rod-shaped nematic liquid crystal compounds, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. Not only low-molecular-weight liquid crystal compounds but also high-molecular-weight liquid crystal compounds can be used.

[0111] 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, an oxetanyl 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.

[0112] 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.

[0113] 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.

[0114] From the viewpoint of achieving superior effects of the present invention and obtaining diffracted light with high diffraction efficiency at large diffraction angles, the maximum value of the birefringence Δn of the liquid crystal compound within 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 selective reflection described above, the degree of orientation 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.

[0115] 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 ne 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 no 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.

[0116] 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.

[0117] 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:

[0118] 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.

[0119] Within the cholesteric liquid crystal layer, the minimum value of the birefringence index Δn of the liquid crystal compound is preferably 0.00 to 0.40, more preferably 0.00 to 0.30, and even more preferably 0.00 to 0.20. Specific examples of polymerizable liquid crystal compounds having large refractive index anisotropy include, 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 , JP 2005-015406 A, JP 2007-230968 A, JP 6761484 A, JP 6681992 A, WO 19 / 182129, CN01134217A, KR101069555B, KR101690767B, CN20120229730A, JP 4053782 A, JP 2009-249406 A, JP 4121075 A, JP 2005-528416 A, US 6514578 A, WO 06 / 006819 A, JP 2011 -184417, JP 2013-095685, JP 2013-103897, JP 2002-088008, JP 2002-226412, JP 2012-167214, JP 2012-167068, Japanese Patent Application No. 2018-084511, JP 2003-055317, JP 2001-329264, JP 2002-030016, JP 2003-055664, JP 2018-070889, CN10255789 No. 6, US2015369982, JP2020-105264A, JP2014-224237A, JP2012-051862A, JP2010-106274A, JP2005-179557A, JP2005-035985A, JP2002-012579A, JP2002-003845A, JP2001-233837A, JP2019-532167A, JP2016-509247A, JP2010-503733A,Examples of such compounds include those described in JP-A 2003-533557, WO 19 / 098115, WO 18 / 034216, WO 18 / 221236, WO 18 / 123396, WO 18 / 003482, WO 17 / 086143, WO 14 / 192655, WO 13 / 161669, and WO 09 / 104468.

[0120] In addition to the above, the polymerizable liquid crystal compound also includes the compounds shown below.

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] --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 or a twisted nematic liquid crystal phase. Examples of the surfactant include silicone surfactants and fluorine surfactants, with silicone surfactants being preferred.

[0131] 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.

[0132] 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.

[0133] --Chiral Agents (Optically Active Compounds)--Chiral agents (chiral agents) have the function of inducing a helical structure in a cholesteric liquid crystal phase or a twist in a twisted nematic 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. The chiral agent may also be a liquid crystal compound.

[0134] 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-2002-33855, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0135] -Photoreactive chiral agent- A photoreactive chiral agent is, for example, a compound represented by the following general formula (I). It can control the orientation structure of a liquid crystal compound and has the property of being able to change the helical pitch of the liquid crystal, i.e., the helical twisting power (HTP) of the helical structure, by irradiation with light. That is, it is a compound that induces a change in the helical twisting power of a helical structure induced in a liquid crystal compound, preferably a nematic liquid crystal compound, by irradiation with light (ultraviolet light to visible light to infrared light), and has, as necessary moieties (molecular structural units), a chiral moiety and a moiety that undergoes a structural change by irradiation with light. Moreover, the photoreactive chiral agent represented by the following general formula (I) can particularly significantly change the HTP of liquid crystal molecules.

[0136] The aforementioned HTP represents the twisting power of the helical structure of the liquid crystal, i.e., HTP = 1 / (pitch x chiral agent concentration [mass fraction]), and can be determined, for example, by measuring the helical pitch (one period of the helical structure; μm) of the liquid crystal molecules at a certain temperature and converting this value from the concentration of the chiral agent (chiral agent) [μm-1]. When a photoreactive chiral agent forms a selective reflection color depending on the illuminance of light, the aforementioned rate of change in HTP (= HTP before irradiation / HTP after irradiation) is preferably 1.5 or more, and more preferably 2.5 or more, if the HTP becomes smaller after irradiation, and is preferably 0.7 or less, and more preferably 0.4 or less, if the HTP becomes larger after irradiation.

[0137] Next, the compound represented by formula (I) will be described.

[0138] General formula (I)

[0139]

[0140] In the above formula, R represents a hydrogen atom, an alkoxy group having 1 to 15 carbon atoms, an acryloyloxyalkyloxy group having a total of 3 to 15 carbon atoms, or a methacryloyloxyalkyloxy group having a total of 4 to 15 carbon atoms. Examples of the alkoxy group having 1 to 15 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a hexyloxy group, and a dodecyloxy group. Among these, an alkoxy group having 1 to 12 carbon atoms is preferred, and an alkoxy group having 1 to 8 carbon atoms is particularly preferred.

[0141] Examples of the acryloyloxyalkyloxy group having a total of 3 to 15 carbon atoms include an acryloyloxyethyloxy group, an acryloyloxybutyloxy group, and an acryloyloxydecyloxy group. Among these, an acryloyloxyalkyloxy group having 5 to 13 carbon atoms is preferred, and an acryloyloxyalkyloxy group having 5 to 11 carbon atoms is particularly preferred.

[0142] Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbon atoms in total include a methacryloyloxyethyloxy group, a methacryloyloxybutyloxy group, and a methacryloyloxydecyloxy group. Among these, a methacryloyloxyalkyloxy group having 6 to 14 carbon atoms is preferred, and a methacryloyloxyalkyloxy group having 6 to 12 carbon atoms is particularly preferred.

[0143] The molecular weight of the photoreactive chiral agent represented by the general formula (I) is preferably at least 300. In addition, it is preferable that the photoreactive chiral agent has high solubility with the liquid crystal compound described below, and it is more preferable that the solubility parameter SP value thereof is close to that of the liquid crystal compound.

[0144] Specific examples of the compound represented by the general formula (I) (exemplary compounds (1) to (15)) are shown below, but the present invention is not limited to these.

[0145]

[0146]

[0147]

[0148] The photoreactive optically active compound may be, for example, a compound represented by the following general formula (II).

[0149] General formula (II)

[0150]

[0151] In the above formula, R represents a hydrogen atom, an alkoxy group having 1 to 15 carbon atoms, an acryloyloxyalkyloxy group having a total of 3 to 15 carbon atoms, or a methacryloyloxyalkyloxy group having a total of 4 to 15 carbon atoms. Examples of the alkoxy group having 1 to 15 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a hexyloxy group, an octyloxy group, and a dodecyloxy group. Among these, an alkoxy group having 1 to 10 carbon atoms is preferred, and an alkoxy group having 1 to 8 carbon atoms is particularly preferred.

[0152] Examples of the acryloyloxyalkyloxy group having a total of 3 to 15 carbon atoms include an acryloyloxy group, an acryloyloxyethyloxy group, an acryloyloxypropyloxy group, an acryloyloxyhexyloxy group, an acryloyloxybutyloxy group, and an acryloyloxydecyloxy group. Among these, an acryloyloxyalkyloxy group having 3 to 13 carbon atoms is preferred, and an acryloyloxyalkyloxy group having 3 to 11 carbon atoms is particularly preferred.

[0153] Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbon atoms in total include a methacryloyloxy group, a methacryloyloxyethyloxy group, and a methacryloyloxyhexyloxy group. Among these, a methacryloyloxyalkyloxy group having 4 to 14 carbon atoms is preferred, and a methacryloyloxyalkyloxy group having 4 to 12 carbon atoms is particularly preferred.

[0154] The molecular weight of the photoreactive optically active compound represented by the general formula (II) is preferably at least 300. In addition, the compound preferably has high solubility with the liquid crystal compound described below, and more preferably has a solubility parameter SP value similar to that of the liquid crystal compound.

[0155] Specific examples of the photoreactive optically active compound represented by the general formula (II) are shown below (exemplary compounds (21) to (32)), but the present invention is not limited to these.

[0156]

[0157]

[0158]

[0159] Furthermore, the photoreactive chiral agent can be used in combination with a non-photoreactive chiral agent, such as a chiral compound whose twisting power is highly temperature-dependent. Examples of the known non-photoreactive chiral agents include those described in JP-A No. 2000-44451, JP-T-10-509726, WO98 / 00428, JP-T-2000-506873, JP-T-9-506088, Liquid Crystals (1996, 21, 327), Liquid Crystals (1998, 24, 219), etc.

[0160] 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.

[0161] --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.

[0162] 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.

[0163] --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.

[0164] 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.

[0165] (Method of forming an optically anisotropic layer) 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, and then harden the liquid crystal compound. 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 to a desired state, and then harden the liquid crystal compound to form an optically anisotropic layer with the alignment state fixed. The liquid crystal composition can be applied by printing methods such as inkjet printing and scroll printing, as well as by any known method capable of uniformly applying a liquid to a sheet-like material, such as spin coating, bar coating, and spray coating.

[0166] 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.

[0167] 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.

[0168] There is no limitation on the thickness of the optically anisotropic layer, and the thickness may be appropriately set so as to obtain the required light reflectance depending on the use of the optically anisotropic layer, the light reflectance required for the optically anisotropic layer, and the material from which the optically anisotropic layer is formed.

[0169] The optically anisotropic layer may be formed on a substrate (light guide plate) using the substrate as a support, or may be formed on a support separate from the substrate. When the optically anisotropic layer is formed on a support separate from the substrate, the support may be a temporary support that is peeled off from the optically anisotropic layer and used to transfer the optically anisotropic layer to the substrate (light guide plate). Alternatively, the optically anisotropic layer may be used by being laminated on the substrate while still laminated on the support.

[0170] ((Support)) The support is a film-like material (sheet-like material, plate-like material) that supports the alignment film and the optically anisotropic layer. The support 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.

[0171] There is no limitation on the thickness of the support, and it may be set appropriately to a thickness that can support the alignment film and the optically anisotropic layer depending on the material forming the support, etc. The thickness of the support is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0172] The support may be a single layer or a multilayer. Specific examples of the material of the single layer support include glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin. Examples of the multilayer support include a substrate including any of the above-mentioned single layer supports, and another layer provided on the surface of this substrate.

[0173] ((Alignment Film)) An alignment film is formed on the surface of the support. The alignment film is used to orient the liquid crystal compound in a predetermined liquid crystal alignment pattern when forming an optically anisotropic layer. As described above, the optically anisotropic layer has a region A having a liquid crystal alignment pattern in which the direction of the optical axis 30A (see Figure 2) derived from the liquid crystal compound 30 changes while continuously rotating along one in-plane direction.

[0174] 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.

[0175] 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.

[0176] As the alignment film, a so-called photo-alignment film, which is formed by irradiating a photo-alignment material with polarized or non-polarized light, is preferably used. That is, as the alignment film, a photo-alignment film formed by applying a photo-alignment material onto a support is preferably used. Irradiation with polarized light can be performed from a vertical direction or an oblique direction to the photo-alignment film, and irradiation with non-polarized light can be performed from an oblique direction to the photo-alignment film.

[0177] 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-2007-160466. azo compounds described in JP-A-7-133184, JP-A-2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in JP-A-2002-229039, maleimides having photo-alignable units described in JP-A-2002-265541 and JP-A-2002-317013, and / or 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.

[0178] 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.

[0179] 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 a support, dried, and then exposed to laser light to form an alignment pattern.

[0180] Fig. 3 conceptually shows an example of an exposure device that exposes an alignment film to light to form an alignment pattern. 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 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 also has a λ / 2 plate that changes the polarization direction of the laser beam M emitted by the laser 62 and 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 P0. 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.

[0181] 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 having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 continuously rotates in one direction. Furthermore, 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.

[0182] In the present invention, 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.

[0183] A preferred embodiment of the method for producing an optically anisotropic layer included in the present invention is exemplified by a production method having steps 1 to 3. Step 1: forming a coating film using a composition containing a liquid crystal compound having a polymerizable group, and orienting 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 direction of the coating film; Step 3: subjecting the coating film obtained in step 2 to a heat treatment, and changing the degree of orientation depending on the polymerization rate in step 2, thereby forming regions with different diffraction efficiencies. Steps 1 to 3 above will be described in detail below.

[0184] (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 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 a 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 aligned. By carrying out this preferred embodiment, a laminate is formed, as shown in FIG. 14, which includes a support 320, an alignment film 322, and a coating film 324 (which will become an optically anisotropic layer in a later step).

[0185] 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.

[0186] 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.

[0187] (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 direction 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 the in-plane direction of the coating film in at least a part of the plane.

[0188] An example of how to achieve this will be described with reference to FIG. 14 . In a 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 327, the exposure energy is strong in region 316 of the coating film 324, depending on the transmittance of the photomask 329, and polymerization of the liquid crystal compound proceeds sufficiently. On the other hand, the exposure energy is weak in region 318 of the coating film 324, depending on the transmittance of the photomask 329, and polymerization of the liquid crystal compound does not proceed. By step 3, which will be described later, the degree of orientation of the liquid crystal in region 316 is high and the degree of orientation of the liquid crystal in region 318 is low. Therefore, an orientation gradient between the two is formed in the in-plane direction, and the diffraction efficiency gradually changes in the in-plane direction.

[0189] In step 2, the liquid crystal compound may be polymerized so as to form regions in which the polymerization rate distribution of the liquid crystal compound differs in the in-plane direction and the thickness direction. Examples of means for forming regions in which the degree of hardening of the liquid crystal compound differs in the thickness direction include a method of performing exposure or heat treatment in an atmosphere containing a component that inhibits polymerization, such as oxygen and moisture, 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.

[0190] An example of how to achieve this is described with reference to FIG. 15 . In the 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 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 the first region 326 gradually changes depending on the transmittance of the photomask 329. By process 3 described below, the degree of alignment of the liquid crystal in the first region 326 is high and the degree of alignment of the liquid crystal in the second region 328 is low. Therefore, a thickness gradient between the first region 326 and the second region 328 is formed in the in-plane direction, resulting in a gradual change in the diffraction efficiency in the in-plane direction. In particular, in step 3 described below, by making the second region 328 non-oriented, only the first region 326 with a high degree of orientation can function as a diffraction element. This increases the effective birefringence of the liquid crystal compound when light is diffracted, thereby improving diffraction efficiency. In addition, the effective refractive index of the liquid crystal compound increases when light is diffracted, allowing for a wider FOV when used for AR glasses, for example. Step 2 may also be performed by other methods.

[0191] Whether or not regions with different degrees of curing of the liquid crystal compound are formed in the in-plane direction of the coating film can be determined, for example, by analyzing the surface of the coating film using infrared absorption spectroscopy or the like and calculating the residual rate of polymerizable groups in the in-plane direction of the coating film.

[0192] 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 1 to 1000 mJ / cm. ２ is preferred, and 10 to 300 mJ / cm ２ is more preferred.

[0193] (Step 3) Step 3 is a step in which the coating film obtained in Step 2 is subjected to a heat treatment to form regions with different diffraction efficiencies in the in-plane direction. The coating film obtained in Step 2 includes regions with different polymerization rates of the liquid crystal compound in the in-plane direction of the coating film. When such a coating film is subjected to a heat treatment, the orientation state 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 orientation state of the liquid crystal compound cannot be maintained by the heat treatment, resulting in a decrease in the degree of orientation of the liquid crystal compound. This decrease in the degree of orientation of the liquid crystal compound reduces the diffraction efficiency in those regions. In other words, by performing this step, regions with a high polymerization rate of the liquid crystal compound become regions with high diffraction efficiency, and regions with a low polymerization rate of the liquid crystal compound become regions with low diffraction efficiency. In particular, in regions with a sufficiently low polymerization rate, the liquid crystal becomes non-oriented, thereby forming regions without a liquid crystal orientation pattern. The method for forming regions without a liquid crystal orientation pattern is not limited to this method, and examples include methods such as subjecting an alignment film to a non-patterned orientation treatment, such as uniaxial alignment.

[0194] 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 50 to 300°C, more preferably 100 to 200°C. The heating time at the heating temperature is preferably 0.5 to 30 minutes, more preferably 1 to 5 minutes. In this case, in a region with a low polymerization rate of the liquid crystal compound, if the heating temperature is sufficiently higher than the phase transition temperature of the liquid crystal phase to the isotropic phase (Iso) of the liquid crystal compound, an optically isotropic region without a liquid crystal orientation pattern is formed.

[0195] After step 3, step 4 may be carried out 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 ２The ultraviolet irradiation treatment is preferably carried out in an atmosphere with a low oxygen concentration, and more preferably in a nitrogen atmosphere.

[0196] In each of the above-described optically anisotropic layers, the optical axis 30A of the liquid crystal compound 30 in the liquid crystal orientation pattern in the diffraction region continuously rotates only along the direction of arrow X. However, the present invention is not limited to this, and various configurations can be used as long as the optical axis 30A of the liquid crystal compound 30 continuously rotates along one direction in the diffraction region. As described above, in the present invention, the optically anisotropic layer can also be a laminate formed by stacking multiple optically anisotropic layers. The lamination method includes a method of directly applying a liquid crystal composition onto a first optically anisotropic layer to form a second optically anisotropic layer, a method of applying an alignment film onto the first optically anisotropic layer and then performing an alignment treatment, and then applying a liquid crystal composition, and a method of laminating an optically anisotropic layer provided on another substrate, etc. The grating pitch (one period), grating angle, helical pitch, change in helical pitch in the thickness direction, tilt angle, change in tilt angle in the thickness direction, change in Δn in the thickness direction, size of the diffraction region, shape of the diffraction region, physical film thickness, optical thickness, and reflectance per wavelength of the diffraction region of each optically anisotropic layer can be arbitrarily adjusted. Furthermore, in one diffraction region, the grating pitch, grating angle, helical pitch, change in helical pitch in the thickness direction, change in Δn in the thickness direction, tilt angle, change in tilt angle in the thickness direction, physical thickness, optical thickness, and reflectance per wavelength can also be changed in the in-plane direction, and the direction and inclination of the change can also be arbitrarily adjusted. In addition, diffraction regions with adjusted parameters can be arbitrarily combined. In the present invention, the optically anisotropic layer preferably has regions in which the helical pitch length of the cholesteric liquid crystal layer varies within at least one of the aforementioned regions A and B, and more preferably, the helical pitch length varies continuously within the region. By varying the helical pitch length, the diffraction angle of the diffraction region for a certain wavelength can be controlled. Therefore, as shown in Figure 11 described below, by designing the helical pitch so that the appropriate diffraction angles are obtained at positions P1, P2, P3, and P4 of region B45c, the amount of light reaching the eye can be increased, thereby improving the brightness of the AR glasses.In the present invention, a plurality of units can be formed on a single substrate, each unit including at least a region A having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound is continuously rotated along at least one direction in the plane, a region B having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound is continuously rotated along at least one direction in the plane, and a region having no liquid crystal orientation pattern. Forming a plurality of units on a single substrate can improve productivity not only in the process of forming the optically anisotropic layer but also in downstream processes.

[0197] [Substrate] The light-guiding element of the present invention includes a substrate. The substrate is a light-guiding plate that guides light. Known substrates can be used, and examples thereof include glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin. From the viewpoint of optical isotropy, glass, polycarbonate, acrylic, and polyolefin are preferably used, and glass is more preferably used in terms of small dimensional changes due to temperature and humidity. Furthermore, when flexibility is required, acrylic, polyolefin, or polycarbonate is preferred.

[0198] Refractive index n of the substrate BASE From the viewpoint of expanding the FOV, is preferably 1.6 or more, more preferably 1.7 or more, and particularly preferably 1.8 or more.

[0199] The thickness of the substrate is not particularly limited, but is preferably 0.2 mm or more, more preferably 0.3 mm or more, from the viewpoints of physical strength and suppressing destructive interference to eliminate display unevenness, and is preferably 3.0 mm or less, more preferably 2.0 mm or less, from the viewpoints of weight reduction and appearance.

[0200] The substrate may be made of a single material, or may be a laminate of multiple layers made of different materials. BASE is the average refractive index of the layer closest to the optically anisotropic layer.

[0201] [Adhesive Layer (Pressure-Sensitive Adhesive Layer), Adhesive] The laminate and the light guide element may include an adhesive layer for adhering the optically anisotropic layers to each other and / or between the optically anisotropic layer and the light guide plate (substrate). In this specification, the term "adhesion" is used to include the concept of "sticking".

[0202] For example, water-soluble adhesives, ultraviolet-curable adhesives, emulsion-type adhesives, latex-type adhesives, mastic adhesives, multi-layer adhesives, paste-like adhesives, foam-type adhesives, supported film adhesives, thermoplastic adhesives, hot-melt adhesives, heat-setting adhesives, heat-activated adhesives, heat-seal adhesives, heat-curing adhesives, contact adhesives, pressure-sensitive adhesives (i.e., pressure-sensitive adhesives), polymerization-type adhesives, solvent-based adhesives, solvent-activated adhesives, ceramic adhesives, and the like. 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. Various adhesives can be used alone or in combination as needed.

[0203] In laminates and light guide elements, from the viewpoint of reducing interlayer reflection, it is preferable that the adhesive layer have a small difference in refractive index with adjacent layers. Specifically, the difference in refractive index between adjacent layers 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 particles, adjusting the resin refractive index, and the method described in JP-A-11-223712. Furthermore, when adjacent layers have in-plane refractive index anisotropy, the difference in refractive index between adjacent layers in all in-plane directions 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. When 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 providing 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 provide a refractive index distribution.

[0204] The refractive index of the adhesive layer n AD It is also preferable that n satisfies the relationship of the following formula (2): no < n AD < ne (2) When the adhesive layer satisfies the above formula (2), light reflection at the interface between the adhesive layer and the optically anisotropic layer or the interface between the adhesive layer and the substrate can be more suitably suppressed, thereby improving the light utilization efficiency.

[0205] Refractive index n of adhesive layer AD can be measured by, for example, spectroscopic ellipsometry.

[0206] 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, and from the viewpoint of increasing the adhesive strength, post-treatments such as heat treatment and ultraviolet irradiation can be performed depending on the type of adhesive. The thickness of the adhesive layer can be adjusted as desired, but is preferably 0.1 μm or less, more preferably 0.05 μm or less, even more preferably 0.02 μm or less, and particularly preferably 0.01 μm or less. Methods for forming an adhesive layer of 0.1 μm or less include using silicon oxide (SiO ｘ One method is to vapor-deposit a ceramic adhesive such as a ceramic layer onto the bonding surface. The bonding surfaces of the bonding components can be subjected to surface modification treatments such as plasma treatment, corona treatment, and saponification 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. By making the thickness of the adhesive layer sufficiently smaller than the wavelength of the target light (the wavelength of visible light), interfacial reflection at the adhesive layer can be suppressed.

[0207] The adhesive layer may have a function of a so-called alignment film that has an alignment control force on the optically anisotropic layer.

[0208] In the light guide element, from the viewpoint of reducing interlayer reflection, it is also preferable that the substrate and the optically anisotropic layer are in direct contact with each other.

[0209] In the case where the substrate and the optically anisotropic layer are in direct contact with each other, there are no particular limitations on the method for fixing the substrate and the optically anisotropic layer. For example, the fixing may be a physical fixing method such as a method using a clip member that clamps the substrate and the optically anisotropic layer or a method using tape, or a chemical fixing method such as dehydration condensation.

[0210] [Light Guide Element and AR Display Device] An AR (Augmented Reality) display device of the present invention includes the light guide element described above and an image display device.

[0211] 11 conceptually shows an example of a first embodiment of an AR display device of the present invention having a light guide element of the present invention. The AR display device 50 shown in FIG. 11 has a display (image display device) 40 and a light guide element 45.

[0212] The light guide element 45 is a light guide element of the present invention and includes the optically anisotropic layer 400 and a light guide plate (substrate) 144. The light guide element of the present invention may also have a configuration including the above-described 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. As described above, the optically anisotropic layer 400 is a single optically anisotropic layer formed from three regions: region A 45a, non-diffraction region 45b, and region B 45c. The light guide plate 144 has a rectangular parallelepiped shape that is elongated in one direction and guides light therein. As shown in FIG. 11 , region A 45a of the optically anisotropic layer 400 is disposed on the surface (main surface) of one end of the light guide plate 144 in the longitudinal direction. Furthermore, region B 45c of the optically anisotropic layer 400 is disposed on the surface of the other end of the light guide plate 144. The position of region A45a of optically anisotropic layer 400 corresponds to the position of light incidence on light guide plate 144, and the position of region B45c of optically anisotropic layer 400 corresponds to the position of light emission on light guide plate 144. In addition, an optically isotropic non-diffractive region 45b is formed between region A45a and region B45c.

[0213] Region A45a of optically anisotropic layer 400 is an incident diffraction element region that diffracts light that is irradiated from display 40 and enters light guide plate 144 so as to be totally reflected within light guide plate 144. Region B45c of optically anisotropic layer 400 is an output diffraction element region that diffracts light that has been guided within light guide plate 144 so as to be output from light guide plate 144.

[0214] As shown in Figure 11, 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.

[0215] Since the optically anisotropic layer has polarization selectivity, a display that emits polarized light is preferably used. 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 a configuration in which an optically anisotropic layer having regions A and B that diffract the corresponding right-handed circularly polarized red light, an optically anisotropic layer having regions A and B that diffract left-handed green circularly polarized light, and an optically anisotropic layer having regions A and B that diffract right-handed blue circularly polarized light may be laminated on a light guide plate. This allows the polarization states of adjacent wavelengths of red and green, and green and blue to be different, thereby preventing 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 having regions A and B that diffract the corresponding right-handed circularly polarized light and an optically anisotropic layer having regions A and B that diffract 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.

[0216] Furthermore, the light guide element of the present invention is also suitable for use in a laser beam scanning display. A laser beam scanning display scans laser light using a MEMS mirror. In this case, if an optical system is designed so that the laser light is reflected by a polarizing mirror and then scanned by the MEMS mirror, glare can occur if the polarization selectivity of the polarizing mirror is insufficient. However, the optically anisotropic layer of the light guide element of the present invention itself has polarization selectivity, and can therefore compensate for the polarization selectivity of the polarizing mirror, thereby preventing glare.

[0217] 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 region A45a of the optically anisotropic layer 400. At this time, due to the diffraction effect of region A45a, the light is not specularly reflected (regularly reflected), but is reflected in a direction at an angle different from the direction of specular reflection. In the example shown in FIG. 11 , the light enters region A45a of the optically anisotropic layer 400 from a direction approximately perpendicular (Z direction) and is reflected in a direction inclined at a large angle from the perpendicular direction toward the longitudinal direction (X direction) of the light guide plate 144.

[0218] Because the light reflected by region A45a 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 non-diffraction 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 region B45c 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 effect of diffraction by region B45c of the optically anisotropic layer 400, the light is not specularly reflected, but is reflected in a direction at an angle different from the direction of specular reflection. In the example shown in Figure 11, light is incident on region B45c of the optically anisotropic layer 400 from an oblique direction and is reflected in a direction perpendicular to the surface of region B45c of the optically anisotropic layer 400.

[0219] The light reflected by region B45c 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 seen 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.

[0220] Here, the diffraction efficiency is adjusted in region B45c of the optically anisotropic layer 400, and when light propagating within the light guide plate 144 is diffracted in region B45c 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. 11, light I propagating through the light guide plate 144 reaches a position in region B45c of the optically anisotropic layer 400 while repeatedly reflecting off both surfaces (interfaces) of the light guide plate 144. The light I that has reached region B45c of the optically anisotropic layer 400 is partially diffracted at position P1 close to the incident side and emitted from the light guide plate 144 (emitted light R1). The undiffracted light I1 further propagates within the light guide plate 144, and a portion of the light R2 is diffracted again at a position P2 in the region B45c of the optically anisotropic layer 400, and is emitted from the light guide plate 144. The undiffracted light I2 further propagates within the light guide plate 144, and a portion of the light R3 is diffracted again at a position P3 in the region B45c of the optically anisotropic layer 400, and is emitted from the light guide plate 144. The undiffracted light I3 further propagates within the light guide plate 144, and a portion of the light R4 is diffracted again at a position P4 in the region B45c of the optically anisotropic layer 400, and is emitted from the light guide plate 144.

[0221] In this way, by configuring the light propagating within the light guide plate 144 to be diffracted at multiple locations by region B45c of the optically anisotropic layer 400 and emitted outside the light guide plate 144, the viewing area can be expanded (exit pupil expansion).

[0222] In the example shown in FIG. 11 , the optically anisotropic layer 400 of the light guide element 45 has a configuration including a region A 45 a, a region B 45 c, and a non-diffraction region 45 b, but this is not limited thereto. That is, in the example shown in FIG. 11 , the incident-side liquid crystal diffraction element and the exit-side liquid crystal diffraction element are integrally formed (as a single layer), but this is not limited thereto. FIG. 17 shows the configuration of an AR display device having another example of a light guide element. In the light guide element shown in FIG. 17 , the incident-side and exit-side liquid crystal diffraction elements are not formed from a single element (optically anisotropic layer). Instead, two liquid crystal diffraction elements, an incident-side liquid crystal diffraction element 46 and an exit-side liquid crystal diffraction element 47, are arranged spaced apart on the main surface of the light guide plate 144. The incident-side liquid crystal diffraction element 46 includes, for example, an optically anisotropic layer having only the region A having an alignment pattern, and / or the exit-side liquid crystal diffraction element 47 includes, for example, an optically anisotropic layer having only the region A having an alignment pattern.

[0223] In other words, the light-guiding element shown in Figure 17 can be said to include a substrate and two optically anisotropic layers provided on at least one of the main surfaces of the substrate and spaced apart in the planar direction of the main surfaces.

[0224] In this way, even when a liquid crystal diffraction element 46 on the incident side and a liquid crystal diffraction element 47 on the exit side are provided, at least one of the liquid crystal diffraction element 46 on the incident side and the liquid crystal diffraction element 47 on the exit side includes an optically anisotropic layer formed using a composition containing a liquid crystal compound having an ordinary refractive index no and an extraordinary refractive index ne, and the ordinary refractive index no and the extraordinary refractive index ne satisfy the relationship of the above-mentioned formula (1).

[0225] This prevents a situation in which, when a light guide plate with a high refractive index is used, a part of the light is reflected at the interface between the light guide plate and the liquid crystal diffraction element on the exit side due to the difference in refractive index between the light guide plate and the liquid crystal diffraction element, reducing the amount of light emitted along a predetermined optical path, thereby reducing the light utilization efficiency and narrowing the FOV. Also, in the liquid crystal diffraction element on the entrance side, a part of the light is reflected at the interface between the light guide plate and the liquid crystal diffraction element, reducing the amount of light entering the light guide plate, thereby reducing the light utilization efficiency.

[0226] In addition, when the light guide element has a diffraction element on the incident side and a diffraction element on the exit side, it is sufficient that either one of them is a liquid crystal diffraction element satisfying the above-mentioned configuration, and the other diffraction element may be a conventionally known diffraction element such as a surface relief type diffraction element or a volume hologram type diffraction element. However, from the viewpoint of improving the light utilization efficiency when light is incident on the light guide plate and when light is emitted from the light guide plate, it is preferable that both the diffraction element on the incident side and the diffraction element on the exit side are liquid crystal diffraction elements satisfying the above-mentioned configuration.

[0227] Furthermore, the light guide element may have an intermediate diffraction element in addition to the light guide plate 144, the incident-side liquid crystal diffraction element 46, and the exit-side liquid crystal diffraction element 47. That is, the light diffracted by the incident diffraction element and entering the light guide plate may be diffracted by the intermediate diffraction element to bend the direction of travel of the light within the light guide plate, and then diffracted by the exit-side diffraction element to emit the light outside the light guide plate. In this case, it is sufficient that at least one of the incident-side diffraction element, the intermediate diffraction element, and the exit-side diffraction element is a liquid crystal diffraction element that satisfies the above-described configuration.

[0228] Here, when the light-guiding element includes a substrate and two optically anisotropic layers provided on at least one of the main surfaces of the substrate and spaced apart in the planar direction of the main surfaces, it is preferable that the light-guiding element has a non-liquid crystal, optically isotropic isotropic layer disposed between the two optically anisotropic layers on the main surface of the substrate.

[0229] FIG. 27 is a schematic diagram illustrating another example of a light guide element of the present invention. The light guide element shown in FIG. 27 includes a substrate (light guide plate) 144, a liquid crystal diffraction element 46, a liquid crystal diffraction element 47, and an isotropic layer 54 arranged on one main surface of the substrate 144. The liquid crystal diffraction element 46 and the liquid crystal diffraction element 47 are spaced apart in the planar direction of one main surface of the substrate 144. The isotropic layer 54 is arranged (filled) over the entire area between the liquid crystal diffraction element 46 and the liquid crystal diffraction element 47 in the planar direction of one main surface of the substrate 144. The thickness of the isotropic layer 54 (height from the substrate 144) is thicker than the liquid crystal diffraction element 46 and the liquid crystal diffraction element 47, and covers the surfaces of the liquid crystal diffraction element 46 and the liquid crystal diffraction element 47 opposite the substrate 144. In other words, the isotropic layer 54 is arranged to embed the liquid crystal diffraction element 46 and the liquid crystal diffraction element 47.

[0230] The isotropic layer 54 is a non-liquid crystal and optically isotropic layer. Specifically, the isotropic layer 54 can be formed from a transparent resin material such as polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), polysulfone (PSU), polyethersulfone (PES), and silicone resin.

[0231] In this way, by having the light-guiding element have the isotropic layer 54, it is possible to prevent a portion of the light guided within the light-guiding plate 144, which will be described later, from being scattered at the element end faces of the liquid crystal diffraction element 46 and the liquid crystal diffraction element 47, thereby preventing a decrease in the clarity of the image.

[0232] 27, in a preferred embodiment, the isotropic layer 54 covers the surfaces of the two optically anisotropic layers 46 and 47 opposite to the substrate 144. This allows the surface of the light-guiding element facing the isotropic layer 54 to be a smooth, flat surface without an uneven structure.

[0233] 28 , the isotropic layer 54 and the two optically anisotropic layers 46 and 47 may be configured so that their surfaces on the side opposite to the substrate 144 are flush with each other. That is, the thickness of the isotropic layer 54 may be approximately the same as that of the two optically anisotropic layers 46 and 47. This allows the surface of the light guide element on the isotropic layer 54 side to be a smooth, flat surface without an uneven structure.

[0234] Here, the refractive index of the isotropic layer n ISO It is preferable that n satisfies the relationship of the following formula (3): no < n ISO < ne (3) When the isotropic layer satisfies the above formula (3), it is possible to more effectively suppress light reflection at the interface (side surface) between the isotropic layer and the optically anisotropic layer or at the interface between the isotropic layer and the substrate, thereby improving the light utilization efficiency.

[0235] Refractive index n of the isotropic layer ISO can be measured by, for example, spectroscopic ellipsometry.

[0236] Here, in the case of the light-guiding element shown in Figure 17, it has been found that part of the light diffracted by the liquid crystal diffraction element 46 and guided through the light guide plate 144 is scattered by the element end face X of the liquid crystal diffraction element 46 and the element end face Y of the liquid crystal diffraction element 47, which may reduce the clarity of the image.

[0237] In contrast, in the case of the light-guiding element shown in Figure 11, the optically anisotropic layer is formed integrally with the diffractive regions A and B and the non-diffractive region, so that when combined with a light-guiding plate, the light guided through the light-guiding plate can be prevented from being scattered by the end faces of the diffractive element, and a highly clear image can be emitted from the light-guiding plate.

[0238] Furthermore, as described above, in cases where the liquid crystal diffraction element 46 on the incident side and the liquid crystal diffraction element 47 on the exit side are not integrated but are provided separately, as in the light-guiding element shown in Figure 17, by providing a non-liquid crystal, optically isotropic isotropic layer 54 between the liquid crystal diffraction element 46 on the incident side and the liquid crystal diffraction element 47 on the exit side, as in the examples shown in Figures 27 and 28, it is possible to prevent the light guided within the light-guiding plate from being scattered at the end faces of the diffraction elements, and to emit a highly clear image from the light-guiding plate.

[0239] Now, consider the case where the diffraction efficiency of the liquid crystal diffraction element 47 is constant within the plane. When the diffraction efficiency is constant, the light intensity (light amount) of the incident light I0 is large at position P1 close to the incident side, and therefore the intensity of the emitted 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 47, resulting in the emission of a portion of the light R2. However, because the light intensity of light I1 is smaller than that of light I0, the intensity of the light R2 is smaller than that of the light R1 reflected in the region close to the incident side, even though the light is diffracted with the same diffraction efficiency. 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 47, resulting in the emission of a portion of the light R3. However, because the light intensity of light I2 is smaller than that of light I1, the intensity of the light R3 is smaller than that of the light R2 reflected at position P2, even though the light is diffracted with the same diffraction efficiency. Furthermore, the light intensity of light R4 reflected at position P4 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 47 is constant within the plane, light with a high light intensity will be emitted from areas close to the incident side, and light with a low light intensity will be emitted from areas farther from the incident side, as shown by the dashed lines in Figure 12. This can result in a problem in which the intensity of the emitted light is non-uniform depending on the position.

[0240] In contrast, in the present invention, the region B45c of the optically anisotropic layer 400 on the exit side or the liquid crystal diffraction element 47 is configured so that the diffraction efficiency increases from one side to the other in one direction of rotation of the optical axis, and the region B45c of the optically anisotropic layer 400 or the liquid crystal diffraction element 47 is preferably arranged so that the diffraction efficiency increases in the direction of light propagation within the light guide plate 144. That is, in the example shown in Fig. 11, the region B45c of the optically anisotropic layer 400 is configured so that the diffraction efficiency increases from left to right in Fig. 11. Furthermore, in the example shown in Fig. 17, the liquid crystal diffraction element 47 is configured so that the diffraction efficiency increases from left to right in Fig. 17.

[0241] In this case, at position P1 close to the incident side, the light intensity (amount of light) 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 diffracted again at position P2 of region B45c of the optically anisotropic layer 400 (or the liquid crystal diffraction element 47), whereupon a portion of light R2 is 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 diffracted again at position P3 in region B45c of the optically anisotropic layer 400 (or the liquid crystal diffraction element 47), and a portion of the light R3 is emitted. Although the light intensity of light I2 is smaller 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 region B45c of the optically anisotropic layer 400 or the liquid crystal diffraction element 47 so that the diffraction efficiency increases from one side to the other in one direction of rotation of the optical axis, it is possible to emit light of a constant intensity at any position in the region B45c of the optically anisotropic layer 400 or the liquid crystal diffraction element 47. Therefore, as shown by the solid line in Fig. 12, it is possible to make the intensity of the emitted light approximately uniform regardless of the position.

[0242] In Figures 11 and 17, light is shown by arrows, but the light emitted from display 40 may be planar, and the planar light may be propagated within light guide plate 144 while maintaining its positional relationship, and may be diffracted by region B45c (liquid crystal diffraction element 47) of optically anisotropic layer 400.

[0243] Although the light-guiding element 45 in FIG. 11 has been described as having one optically anisotropic layer, as described above, the light-guiding element 45 may have multiple optically anisotropic layers 400. That is, the light-guiding element 45 may be configured using the above-described laminate. As described above, when the laminate has multiple optically anisotropic layers, it is preferable to have multiple optically anisotropic layers with different selective reflection wavelengths in region A and / or region B. For example, it may have optically anisotropic layers with region A and / or region B with selective reflection wavelengths of red light, green light, and blue light, respectively. This allows the optically anisotropic layer (and its laminate) to diffract red light, green light, and blue light, respectively, and the light-guiding element can appropriately guide light for a color display 40. In this case, it is preferable to appropriately change the length of one period of the liquid crystal orientation pattern depending on the selective reflection wavelength of each layer. Furthermore, when region A and / or region B is a cholesteric liquid crystal layer, it is preferable to appropriately change the helical pitch depending on the selective reflection wavelength of each layer. Alternatively, a configuration may be adopted in which two optically anisotropic layers have regions A and / or B that reflect circularly polarized light with the same selective reflection wavelength but opposite rotation directions. For example, a configuration may be adopted in which 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 are included. This allows the optically anisotropic layer (or a laminate thereof) to diffract right-handed and left-handed circularly polarized light, respectively, and the light guide element can guide right-handed and left-handed circularly polarized light, thereby improving light utilization efficiency. Alternatively, a configuration may be adopted in which two optically anisotropic layers have regions A and / or B that reflect circularly polarized light with the same selective reflection wavelength but opposite rotation directions but different helical pitches are included. This allows the optically anisotropic layer (or a laminate thereof) to diffract right-handed and left-handed circularly polarized light, respectively, and the light guide element can guide right-handed and left-handed circularly polarized light incident at different incident angles and emit the guided light at different angles, thereby increasing the FOV (Field of View).Similarly, in FIG. 17 , the light guide element is described assuming that the incident-side liquid crystal diffraction element 46 and the exit-side liquid crystal diffraction element 47 each have one optically anisotropic layer. However, each may have multiple optically anisotropic layers. In this case, it is preferable that the incident-side liquid crystal diffraction element 46 and the exit-side liquid crystal diffraction element 47 each have multiple optically anisotropic layers with different selective reflection wavelengths. Alternatively, the incident-side liquid crystal diffraction element 46 and the exit-side liquid crystal diffraction element 47 each may have two optically anisotropic layers that reflect circularly polarized light with the same selective reflection wavelength but opposite rotation directions. Note that, in the points described below, the incident-side diffraction region (region A) can be interpreted as the incident-side liquid crystal diffraction element, the exit-side diffraction region (region B) can be interpreted as the exit-side liquid crystal diffraction element, and the intermediate diffraction region (region C) can be interpreted as the intermediate liquid crystal diffraction element.

[0244] 11, the optically anisotropic layer 400 has an incident-side region A 45a, an exit-side region B 45c, and an isotropic non-diffraction region 45b, but is not limited thereto, and as described above, may have an intermediate diffraction region, i.e., region C. That is, light diffracted by the incident diffraction region (region A) and entering the light guide plate may be diffracted by the intermediate diffraction region (region C) to bend the traveling direction of the light within the light guide plate, and then diffracted by the exit-side diffraction region (region B) to emit the light outside the light guide plate. In this case, the incident-side diffraction region and the intermediate diffraction region can be formed in a single optically anisotropic layer (i.e., a configuration in which region A serves as the incident-side diffraction region and region B serves as the intermediate diffraction region), the intermediate diffraction region and the exit-side diffraction region can be formed in a single optically anisotropic layer (i.e., a configuration in which region A serves as the intermediate diffraction region and region B serves as the exit-side diffraction region), or all of the diffraction regions can be formed in a single optically anisotropic layer (i.e., a configuration having the aforementioned regions A, B, and C).However, from the perspective 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, in the case of a configuration having 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 make the light intensity of the exiting light uniform. In addition, in order to make the light intensity of the emitted light uniform, it is also preferable to use a configuration in which the in-plane distribution of diffraction efficiency in the intermediate diffraction region and the diffraction region on the output side differs from each other.

[0245] The light guide element 45 preferably includes a retardation plate laminated in addition to the light guide plate 144 and the optically anisotropic layer 400. This allows the non-diffraction region 45b of the optically anisotropic layer 400 to convert the light guided within the light guide plate into linearly polarized light, as in the case where the non-diffraction region 45b functions as a retardation region, thereby making it possible to uniform the light intensity of the emitted light in the emission-side region B45c. Furthermore, the linearly polarized light guided within the light guide plate may lose its polarization state in the emission-side region B45c. For this reason, the retardation plate is preferably a retardation plate patterned with different in-plane retardations so as to maintain the linear polarization state of the light guided within the light guide plate. Examples of such retardation plates include retardation plates made of a liquid crystal compound, which can be realized, for example, by patterning the alignment axis, twist angle, degree of orientation, etc. of the liquid crystal compound.

[0246] Furthermore, when the optically anisotropic layer has an intermediate diffraction region (region C), 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 propagation 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 use a configuration in which the helical pitch of the cholesteric liquid crystal layer in the intermediate diffraction region is larger than that of the incident-side diffraction region. This allows the intermediate diffraction region to efficiently bend the propagation direction of light within the light guide plate. Furthermore, it is preferable to use a configuration in which the direction of the liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in-plane is different from that of the incident-side diffraction region. This allows the intermediate diffraction region to be configured in such a way that it differs from that of the incident-side 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.

[0247] In addition, multiple incident diffraction regions and intermediate diffraction regions may be arranged in the same plane. The multiple incident diffraction regions have different liquid crystal orientation patterns that rotate continuously in 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 intermediate diffraction regions arranged at different positions in the plane, bending the direction of travel of the light within the light guide plate, and then the guided light can be emitted at different angles by the diffraction region on the output side, thereby increasing the field of view (FOV). For example, as described in WO 2020 / 122128, the incident diffraction region and intermediate diffraction region can be configured to 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 that rotates continuously in one direction in the plane, and, if the diffraction region is 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. The multiple incident-side diffraction regions can be appropriately set to have a rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that continuously rotates in one direction in the plane, and the multiple incident-side diffraction regions can have different rotation directions of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern that continuously rotates in one direction in the plane. Furthermore, when the diffraction region is a cholesteric liquid crystal layer, the multiple incident-side diffraction regions can be appropriately set to have a helical twist rotation direction in the thickness direction (the rotation direction of the reflected circularly polarized light). Specifically, the multiple incident-side diffraction regions can be configured as a region in which the cholesteric liquid crystal layer has a right-handed helical cholesteric orientation and a region in which the cholesteric liquid crystal layer has a left-handed helical cholesteric orientation. 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 180° in the plane than the incident-side diffraction region. As described above, when the period of the intermediate diffraction region is shorter than that of the incident-side diffraction region, the helical pitch of the cholesteric liquid crystal layer in the intermediate diffraction region is preferably larger than that of the incident-side diffraction region. Furthermore, even in such a configuration, a configuration in which the in-plane distribution of the diffraction efficiency in the intermediate diffraction region and the diffraction region on the exit side is different can be preferably used in order to make the light intensity of the exiting light uniform.

[0248] Alternatively, different incident diffraction regions, intermediate diffraction regions, and output diffraction regions may be laminated. As described above, when multiple optically anisotropic layers are laminated, it is also preferable to laminate multiple optically anisotropic layers with different selective reflection wavelengths (helical pitches). This allows the optically anisotropic layers (their laminate) to diffract light of different colors (wavelengths), and the light-guiding element can appropriately guide light for a color display 40. In this case, it is preferable to appropriately set the length of one period of the liquid crystal orientation pattern in each diffraction region according to the selective reflection wavelength of each diffraction region in each layer. Alternatively, a configuration may be used in which two optically anisotropic layers are laminated, 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 red light and an optically anisotropic layer having a diffraction region that reflects left-handed circularly polarized red light are laminated. As a result, the optically anisotropic layer (or its laminate) can diffract right-handed circularly polarized light and left-handed circularly polarized light, respectively, and the light guide element can guide right-handed circularly polarized light and left-handed circularly polarized light, thereby increasing the light utilization efficiency. Alternatively, a configuration may be adopted in which two optically anisotropic layers are laminated, each having a diffraction region with a different helical pitch, which reflects circularly polarized light with the same selective reflection wavelength but opposite rotation directions. As a result, the optically anisotropic layer (or its laminate) can diffract right-handed circularly polarized light and left-handed circularly polarized light, respectively, and the light guide element can guide right-handed circularly polarized light and left-handed circularly polarized light incident at different incident angles and emit the guided light at different angles, thereby increasing the FOV.Furthermore, as described in, for example, WO2020 / 122128, WO2020 / 075738, WO2020 / 226078, WO2021 / 060528, etc., when multiple optically anisotropic layers are laminated, it is also preferable to laminate multiple optically anisotropic layers having diffraction regions (incident diffraction region, intermediate diffraction region, output diffraction region) of each optically anisotropic layer 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 laminate multiple optically anisotropic layers having diffraction regions 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 this can be set appropriately depending on the purpose. Furthermore, even when a plurality of optically anisotropic layers are laminated, a configuration in which the in-plane distribution of the diffraction efficiency in the intermediate diffraction region and the diffraction region on the output side is different can be preferably used in order to make the light intensity of the output light uniform. Furthermore, when a plurality of optically anisotropic layers are laminated, a configuration in which the in-plane distribution of the diffraction efficiency in the intermediate diffraction region and the diffraction region on the output side is different can be preferably used in each optically anisotropic layer. The arrangement of the diffraction regions is not limited, and they can be appropriately arranged in the in-plane or thickness direction (lamination) as necessary.

[0249] Alternatively, a diffraction region that also serves as both the intermediate diffraction region and the 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, the input diffraction region preferably 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 diffraction regions may be arranged at different positions within the plane or may be laminated. 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 direction of travel 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 is diffracted by the exit-side diffraction region, which functions as an intermediate diffraction region, bending the direction of travel of the light within the light guide plate, and the intermediate diffraction region functions as the exit-side diffraction region, allowing the guided light to exit at a different angle. This allows a light guide plate of compact size to have a larger FOV than when the intermediate diffraction region and the exit diffraction region are located at different positions within the plane. For example, as described in WO2021 / 201218, WO2021 / 256453, etc., 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, the 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 if 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 direction of rotation of the reflected circularly polarized light), and this can be set appropriately depending on the purpose.Furthermore, even in a configuration in which an intermediate diffraction region and a diffraction region that also serves as an output diffraction region are stacked, a configuration in which the in-plane distribution of the diffraction efficiency in each diffraction region is different can be preferably used in order to make the light intensity of the output light uniform. There are no limitations on the arrangement of the diffraction regions, and they can be appropriately arranged in the in-plane or thickness direction (stacking) as necessary.

[0250] 11, an optically anisotropic layer 400 having a reflective diffraction region is used, but the present invention is not limited to this, and an optically anisotropic layer having a transmissive diffraction region may also be used. In this case, the optically anisotropic layer (the diffraction region on the incident side) of the light guide element may be configured to be disposed on the surface of the light guide plate 144 on the display 40 side.

[0251] That is, in the example shown in FIG. 1 , the liquid crystal compound in region A and / or region B (or further region C) of the optically anisotropic layer is cholesterically oriented, but this is not limited thereto, and the liquid crystal compound may not be cholesterically oriented. FIG. 7 conceptually shows an example of a liquid crystal diffraction element including an optically anisotropic layer having the same alignment state as region A and / or region B (or further region C) of the optically anisotropic layer. The liquid crystal diffraction element 12 shown in FIG. 7 is a liquid crystal diffraction element that diffracts and transmits incident light. The liquid crystal diffraction element 12 shown in FIG. 7 has a configuration in which a support 20, an alignment film 24, and an optically anisotropic layer 16 are laminated in this order.

[0252] The optically anisotropic layer 16 is formed on the surface of the alignment film 24. The optically anisotropic layer 16 is a layer formed using a composition containing a liquid crystal compound, and has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound continuously rotates along at least one direction in the plane.

[0253] Fig. 8 shows a plan view of the liquid crystal diffraction element shown in Fig. 7. In Fig. 8, in order to clearly show the configuration of the liquid crystal diffraction element, only the liquid crystal compound 30 on the surface of the alignment film 24 is shown as the liquid crystal compound 30 in the optically anisotropic layer 16. However, the optically anisotropic layer 16 has a structure in which the liquid crystal compound 30 is stacked in the thickness direction, starting from the liquid crystal compound 30 on the surface of the alignment film 24, as shown in Fig. 7.

[0254] 8, the optically anisotropic layer 16 has a liquid crystal orientation pattern in which the direction of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction indicated by the arrow X within the plane of the optically anisotropic layer 16. That is, the optically anisotropic layer 16 has a liquid crystal orientation pattern within the plane similar to that of the optically anisotropic layer 18 shown in Figures 1 and 2. Therefore, a detailed description of the liquid crystal orientation pattern of the optically anisotropic layer 16 will be omitted.

[0255] In the optically anisotropic layer 16, the liquid crystal compounds aligned in the Y direction have the same angle between their optical axes 30A and the direction of arrow X (the direction in which the optical axes of the liquid crystal compounds 30 rotate). A region in which the liquid crystal compounds 30, with their optical axes 30A and the direction of arrow X forming the same angle, are arranged in the Y direction, is referred to as region R. In this case, the in-plane retardation (Re) value in each region R is preferably half the wavelength, i.e., λ / 2. These in-plane retardations are calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of region R and the thickness of the optically anisotropic layer 16. Here, the refractive index difference associated with the refractive index anisotropy of region R in the optically anisotropic layer 16 is a refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of region R and the refractive index in the direction perpendicular to the direction of the slow axis. That is, the refractive index difference Δn due to the refractive index anisotropy of region R is equal to the difference between the refractive index of liquid crystal compound 30 in the direction of optical axis 30A and the refractive index of liquid crystal compound 30 in the direction perpendicular to optical axis 30A in the plane of region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0256] When circularly polarized light enters such an optically anisotropic layer 16, the light is refracted and the direction of the circular polarization is converted. This effect is conceptually shown in FIG. 9 , using an example of the optically anisotropic layer 16. As shown in FIG. 9 , when left-handed circularly polarized incident light L1 enters the optically anisotropic layer 16, the incident light L1 is given a phase difference of 180° as it passes through the optically anisotropic layer 16, and the transmitted light L2 is converted to right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed in the optically anisotropic layer 16 is a periodic pattern in the direction of arrow X, the transmitted light L2 is refracted and travels in a direction different from the traveling direction of the incident light L1. In this way, the left-handed circularly polarized incident light L1 is converted to right-handed circularly polarized transmitted light L2, which is tilted at a certain angle in the direction of arrow X with respect to the incident direction.

[0257] 10, when right-handed circularly polarized incident light L4 enters the optically anisotropic layer 16, the incident light L4 is given a phase difference of 180° as it passes through the optically anisotropic layer 16 and is converted into left-handed circularly polarized transmitted light L5. Furthermore, because the liquid crystal orientation pattern formed in the optically anisotropic layer 16 is a periodic pattern in the direction of arrow X, the transmitted light L5 is refracted (diffracted) and travels in a direction different from the traveling direction of the incident light L4. In this way, the incident light L4 is converted into left-handed circularly polarized transmitted light L5 that is tilted at a certain angle in the azimuth direction opposite to the direction of arrow X with respect to the incident direction.

[0258] In the optically anisotropic layer 16, the in-plane retardation value of the plurality of regions R is preferably half the wavelength in order to obtain high diffraction efficiency. However, the in-plane retardation Re(550) of the plurality of regions R of the optically anisotropic layer 16 for incident light having a wavelength of 550 nm is preferably Δn 550 ×d is preferably within the range defined by the following formula (4): 550 is the refractive index difference associated with the refractive index anisotropy of the region R when the wavelength of incident light is 550 nm, and d is the thickness of the optically anisotropic layer 16. 550 ×d≦350 nm (4) That is, the in-plane retardation Re(550) of the plurality of regions R of the optically anisotropic layer 16=Δn 550When ×d satisfies the formula (4), a sufficient amount of the circularly polarized component of the light incident on the optically anisotropic layer 16 can be converted into circularly polarized light traveling in a direction inclined forward or backward with respect to the direction of the arrow X. In-plane retardation Re(550)=Δn 550 ×d is 225 nm≦Δn 550 ×d≦340 nm is more preferable, and 250 nm≦Δn 550 It is more preferable that ×d≦330 nm. The above formula (4) is a range for incident light having a wavelength of 550 nm, but the in-plane retardation Re(λ) of the plurality of regions R of the optically anisotropic layer 16 for incident light having a wavelength of λ nm is λ ×d is preferably within the range defined by the following formula (4-2), and can be set appropriately: 0.35×λnm≦Δn λ × d≦0.65 × λ nm (4-2)

[0259] In addition, the in-plane retardation values ​​of the regions R in the optically anisotropic layer 16 may be outside the range of the above formula (4). 550 ×d<200 nm or 350 nm<Δn 550 ×d, it is possible to separate light into light traveling in the same direction as the incident light and light traveling in a direction different from the incident light. 550 When ×d approaches 0 nm or 550 nm, the component of light traveling in the same direction as the incident light increases, and the component of light traveling in a direction different from the incident light decreases.

[0260] Furthermore, the in-plane retardation Re(450) of each region R of the optically anisotropic layer 16 for incident light having a wavelength of 450 nm is expressed as Re(450)=Δn 450 ×d and the in-plane retardation Re(550)=Δn of the region R of the optically anisotropic layer 16 for incident light having a wavelength of 550 nm. 550 ×d preferably satisfies the following formula (5): 450 is the refractive index difference associated with the refractive index anisotropy of the region R when the wavelength of the incident light is 450 nm. (Δn 450 × d) / (Δn 550×d)<1.0 (5) Formula (5) indicates that the liquid crystal compound 30 contained in the optically anisotropic layer 16 has reverse dispersion. That is, when formula (5) is satisfied, the optically anisotropic layer 16 can accommodate incident light of a wide wavelength band.

[0261] Here, the refraction angles of the transmitted light beams L2 and L5 can be adjusted by changing the period Λ of the liquid crystal orientation pattern formed in the optically anisotropic layer 16. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the light beams passing through adjacent liquid crystal compounds 30, resulting in greater refraction (diffraction) of the transmitted light beams L2 and L5. Furthermore, the refraction angles of the transmitted light beams L2 and L5 relative to the incident light beams L1 and L4 vary depending on the wavelengths of the incident light beams L1 and L4 (transmitted light beams L2 and L5). Specifically, the longer the wavelength of the incident light, the greater the refraction (diffraction) of the transmitted light beams. That is, when the incident light beams are red, green, and blue, the red light beam is refracted (diffracted) the most, and the blue light beam is refracted (diffracted) the least. Furthermore, the direction of refraction (diffraction) of the transmitted light beams can be reversed by reversing the rotation direction of the optical axis 30A of the liquid crystal compound 30, which rotates along the direction of arrow X.

[0262] The optically anisotropic layer 16 is composed of a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound or a discotic liquid crystal compound, and has a liquid crystal orientation pattern in which the optical axis of the rod-shaped liquid crystal compound or the optical axis of the discotic liquid crystal compound is aligned as described above. The optically anisotropic layer 16 composed of a cured layer of the liquid crystal composition can be obtained by forming an alignment film 24 on the support 20, and then applying and curing a liquid crystal composition on the alignment film 24. The application and curing methods of the liquid crystal composition are the same as those for the optically anisotropic layer (cholesteric liquid crystal layer) described above. While it is the optically anisotropic layer 16 that functions as the optically anisotropic region, the present invention also includes an embodiment in which a laminate integrally comprising the support 20 and the alignment film 24 functions as the optically anisotropic region.

[0263] The liquid crystal composition for forming the optically anisotropic layer 16 contains a rod-shaped liquid crystal compound or a discotic liquid crystal compound, and may further contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, a crosslinking agent, and an alignment aid. The liquid crystal composition may also contain a solvent. The rod-shaped liquid crystal compound, discotic liquid crystal compound, etc. contained in the liquid crystal composition for forming the optically anisotropic layer 16 may be the same as the rod-shaped liquid crystal compound, discotic liquid crystal compound, etc. contained in the liquid crystal composition for forming the optically anisotropic layer 18 (cholesteric liquid crystal layer) described above. That is, the liquid crystal composition for forming the optically anisotropic layer 16 is the same as the liquid crystal composition for forming the optically anisotropic layer 18 described above, except that it does not contain a chiral agent. The optically anisotropic layer 16 may also have a so-called twisted structure, in which the orientation of the liquid crystal compound changes continuously from one interface side to the other interface side in the thickness direction. The twisted structure is a structure in which the liquid crystal compound is twisted and rotated in the thickness direction to such an extent that it does not form a cholesteric liquid crystal phase and does not substantially exhibit selective reflectivity. Specifically, the twisted structure is a structure in which the twist of the optical axis in the entire thickness direction is less than one turn, i.e., the twist angle is less than 360°. The twisted structure can be formed by appropriately adding a chiral agent to the liquid crystal composition.

[0264] The light guide element of the present invention can also be used in combination with other components, such as a structure sandwiched between two sheets of glass, a low-reflection layer, an ultraviolet absorbing layer, a polarizing plate, or a lens component.

[0265] The light-guiding element and the AR display device of the present invention have been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made within the scope of the present invention.

[0266] 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 appropriately changed 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.

[0267] 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.

[0268] 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 --------------------------------------------------

[0269] -Material for photo alignment-

[0270]

[0271] (Exposure of Alignment Film) Using the exposure device shown in Figure 3, exposure was performed on each of region 1 and region 2 of the alignment film 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 Λ (the length of 180° rotation of the optical axis) of the orientation pattern formed by the interference of the two laser beams was controlled to be 0.44 μm by changing the crossing angle (crossing angle α) of the two beams.

[0272] (Formation of Optically Anisotropic Layer) The following composition LC-1 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0273] Composition LC-1 ----------------------------------- Rod-shaped liquid crystal compound L-1 90.00 parts by mass Rod-shaped liquid crystal compound L-2 10.00 parts by mass Polymerization initiator (Omnirad (registered trademark) 819, manufactured by BASF) 3.00 parts by mass Chiral agent Ch-1 5.20 parts by mass Leveling agent T-1 0.10 parts by mass Methyl ethyl ketone 126.7 parts by mass Cyclopentanone 126.7 parts by mass

[0274] Rod-shaped liquid crystal compound L-1

[0275]

[0276] The ordinary refractive index no of compound L-1 was 1.59, and the extraordinary refractive index ne was 1.83.

[0277] Rod-shaped liquid crystal compound L-2

[0278]

[0279] The ordinary refractive index no of compound L-2 was 1.56, and the extraordinary refractive index ne was 1.70.

[0280] Chiral agent Ch-1

[0281]

[0282] Leveling agent T-1

[0283]

[0284] The prepared composition LC-1 was applied onto the alignment film P-1 to form a composition layer. The application was performed using a spin coater at 1500 rpm. The support having the composition layer was heated on a hot plate at 120°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 20 mJ / cm using a 365 nm LED UV exposure device at 40°C under a nitrogen atmosphere through the mask MK-1. 2The composition layer was exposed to an exposure dose of 300 mJ / cm using a 365 nm LED UV exposure device at 200°C under a nitrogen atmosphere. The positional relationship between the exposure dose of ultraviolet light irradiated onto the composition layer through mask MK-1 and each region of the alignment film is as shown in FIG. 16. Subsequently, the composition layer was heat-treated at 200°C (above the liquid crystal phase-isotropic phase (Iso) of the liquid crystal composition) for 1 minute, and then exposed to ultraviolet light with a wavelength of 365 nm at 300 mJ / cm using a 365 nm LED UV exposure device at 200°C under a nitrogen atmosphere. 2 The coating film was irradiated with a dose of 0 mJ / cm 2 to fix the alignment of the liquid crystal compound, thereby forming an optically anisotropic layer. The optically anisotropic layer was prepared to have a thickness of 2 μm. In the optically anisotropic layer, the dose of 0 mJ / cm 2 shown in FIG. 2 A non-diffractive region is formed at the position of 2 Region A (diffraction region) is formed at a position exceeding 0 mJ / cm. 2 Region B (diffraction region) is formed at the position above.

[0285] (Measurement of refractive index) In the exposure of the alignment film, a polarized ultraviolet light exposure device was used to expose the alignment film to linearly polarized ultraviolet light (illuminance 4.5 mW, irradiation amount 500 mJ / cm 2 An alignment film P-2 was obtained in the same manner as in the alignment film P-1, except that the irradiated light was irradiated with 1000 nm of fluorine.

[0286] Composition LC-1a was prepared by omitting the chiral agent Ch-1 from composition LC-1. The prepared composition LC-1a was applied onto 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 120°C for 1 minute. Subsequently, ultraviolet light having a wavelength of 365 nm was applied at 20 mJ / cm using a 365 nm LED UV exposure device under a nitrogen atmosphere at 40°C. 2 The composition layer was exposed to light at an exposure dose of 1000 nm to obtain an optically anisotropic layer for refractive index measurement.

[0287] Using an ellipsometer, the complex reflectance of the optically anisotropic layer for refractive index measurement was measured at an incident angle of 50 to 70°. Analysis using an optical model that takes into account the anisotropy of the refractive index revealed that the extraordinary refractive index n e at a wavelength of 550 nm was 1.81 and the ordinary refractive index n o was 1.58.

[0288] (Preparation of Light Guide Element) The optically anisotropic layer prepared above was disposed on a glass substrate having a refractive index of 1.8 to obtain a light guide element 1. This light guide element 1 satisfies the above formula (1).

[0289] [Evaluation] (Evaluation of Diffraction Efficiency) As shown in Figure 13, a Dove prism 110 was placed on the surface of the light guide element 1 fabricated above facing the light guide plate, and the optically anisotropic layer was evaluated. In Figure 13, a glass Dove prism was used as the Dove prism 110, and its refractive index was selected to be the same as that of the light guide plate. The optically anisotropic layer was peeled off from the support before use. There was optical contact between the optically anisotropic layer and the light guide plate, and between the light guide plate and the Dove prism.

[0290] 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 and the Dove prism 110 .

[0291] When light is emitted from a laser, it passes through linear polarizer 112 and λ / 4 plate 114, becomes right-handed circularly polarized light, and enters Dove prism 110. It then propagates through Dove prism 110 and enters the optically anisotropic layer. The diffracted light reflected and diffracted by the optically anisotropic layer propagates through Dove prism 110 in the direction opposite to the surface on which the optically anisotropic layer is disposed. The light propagated through Dove prism 110 reaches the lower surface of Dove prism 110 and is emitted.

[0292] The incident angle θ of the light guide element 1 was gradually increased from 45° while the emitted light was directed onto a screen and visually observed. When θ exceeded a certain angle, the intensity of the emitted light suddenly decreased, and the emitted light could no longer be observed on the screen. The value of θc at that time was recorded. The extraction angle of the emitted light just before it became unobservable was defined as θd. For the light guide element 1 fabricated by the above method, the value of θc was 74° and the value of θd was 29°.

[0293] Comparative Example 1 A light guide element 2 was prepared and evaluated in the same manner as in Example 1, except that the following composition LC-2 was used as the liquid crystal composition for forming the optically anisotropic layer.

[0294] Composition LC-2 ----------------------------------- Rod-like liquid crystal compound L-2 100.00 parts by mass Polymerization initiator (Omnirad (registered trademark) 819, manufactured by BASF) 3.00 parts by mass Chiral agent Ch-1 5.20 parts by mass Leveling agent T-1 0.10 parts by mass Methyl ethyl ketone 126.7 parts by mass Cyclopentanone 126.7 parts by mass

[0295] (Measurement of refractive index) Composition LC-2a was prepared by omitting the chiral agent Ch-1 from composition LC-2. Except for using composition LC-2a, an optically anisotropic layer for refractive index measurement of Comparative Example 1 was obtained in the same manner as the optically anisotropic layer for refractive index measurement of Example 1, and the refractive index was measured in the same manner as in Example 1. The extraordinary refractive index ne at a wavelength of 550 nm was 1.70, and the ordinary refractive index no was 1.56. Therefore, the light guide element 1 of Comparative Example 1 does not satisfy the above formula (1).

[0296] The optically anisotropic layer prepared by the above method had a θc value of 67° and a θd value of 24°.

[0297] Example 2 A light guide element 3 was prepared and evaluated in the same manner as in the light guide element 1, except that the following composition LC-3 was used as the liquid crystal composition for forming the optically anisotropic layer, and exposure of the composition through a mask MK-1 was carried out at 80°C.

[0298] Composition LC-3 ----------------------------------- Rod-like liquid crystal compound L-3 100.00 parts by mass Polymerization initiator (Omnirad (registered trademark) 819, manufactured by BASF) 3.00 parts by mass Chiral agent Ch-1 5.20 parts by mass Leveling agent T-1 0.10 parts by mass Methyl ethyl ketone 210.5 parts by mass Cyclopentanone 126.7 parts by mass ---------------------------------------------------

[0299] Rod-shaped liquid crystal compound L-3

[0300]

[0301] (Measurement of refractive index) Composition LC-3a was prepared by omitting the chiral agent Ch-1 from composition LC-3, and composition LC-3a was used. Except for exposing the composition at 80°C, an optically anisotropic layer for refractive index measurement of Example 2 was produced in the same manner as the optically anisotropic layer for refractive index measurement of Example 1, and the refractive index was determined. The extraordinary refractive index ne was 1.95, and the ordinary refractive index no was 1.6. Therefore, the light-guiding element 3 of Example 2 satisfies the above formula (1).

[0302] Furthermore, the light guide element 3 fabricated by the above method had a θc value of 80° and a θd value of 31°.

[0303] Example 3 A light guide element 4 was produced and evaluated in the same manner as in the light guide element 1, except that the following composition LC-4 was used as the liquid crystal composition for forming the optically anisotropic layer, the support having the composition layer was heated on a hot plate at 140°C for 1 minute, and then the composition was exposed to light through a mask MK-1 at 120°C.

[0304] Composition LC-4 ----------------------------------- Rod-like liquid crystal compound L-4 100.00 parts by mass Polymerization initiator (Omnirad (registered trademark) 819, manufactured by BASF) 3.00 parts by mass Chiral agent Ch-1 5.20 parts by mass Leveling agent T-1 0.10 parts by mass Methyl ethyl ketone 210.5 parts by mass Cyclopentanone 210.5 parts by mass

[0305] Rod-shaped liquid crystal compound L-4

[0306]

[0307] (Measurement of refractive index) Composition LC-4a was prepared by omitting the chiral agent Ch-1 from composition LC-4, and the refractive index of Example 3 was determined in the same manner as for the optically anisotropic layer for refractive index measurement in Example 1, except that composition LC-4a was used. The extraordinary refractive index ne was 2.01, and the ordinary refractive index no was 1.63. Therefore, the light-guiding element 4 of Example 3 satisfies the above formula (1).

[0308] Furthermore, the light guide element 4 fabricated by the above method had a θc value of 85° and a θd value of 33°.

[0309] Example 4 A light guide element 5 was fabricated and evaluated in the same manner as the light guide element 3, except that a glass substrate with a refractive index of 1.9 was used as the base material. Therefore, the light guide element 5 of Example 4 satisfies the above formula (1). Furthermore, the value of θc of the light guide element 5 was 70°, and the value of θd was 32°.

[0310] Example 5 A light guide element 6 was fabricated and evaluated in the same manner as the light guide element 4, except that a glass substrate with a refractive index of 2.0 was used as the base material. Therefore, the light guide element 6 of Example 5 satisfies the above formula (1). Furthermore, the value of θc of the light guide element 6 was 71°, and the value of θd was 39°.

[0311] Example 6 A light guide element 7 was fabricated and evaluated in the same manner as light guide element 1, except that an optically anisotropic layer was disposed on a glass substrate with a refractive index of 1.8 via an adhesive layer. The refractive index of the adhesive layer was 1.65, and the thickness was 1.0 μm. The light guide element 7 of Example 6 satisfied the above formula (1). The θc value of light guide element 7 was 70°, and the θd value was 26°.

[0312] Example 7 A light guide element 8 was fabricated and evaluated in the same manner as the light guide element 7, except that the thickness of the adhesive layer was changed to 0.1 μm. The light guide element 8 of Example 7 satisfied the above formula (1). The light guide element 8 had a θc value of 74° and a θd value of 29°.

[0313] Example 8 A light guide element 9 was fabricated and evaluated in the same manner as the light guide element 7, except that the refractive index of the adhesive layer was changed to 1.7. The light guide element 9 of Example 8 satisfied the above formula (1). The value of θc of the light guide element 9 was 74°, and the value of θd was 29°.

[0314] [Example 9] An optically anisotropic layer 1 was prepared in the same manner as in Example 1, and region A and region B were cut out. The optically anisotropic layer of region A and the optically anisotropic layer of region B were placed at positions spaced apart in the in-plane direction on a glass substrate with a refractive index of 1.8. The positional relationship between region A and region B was the same as in Example 1.

[0315] Next, an isotropic layer composition having the following formulation was applied onto the glass substrate thus obtained, on which the regions A and B were arranged. Under a nitrogen atmosphere, ultraviolet light having a wavelength of 365 nm was applied at 1000 mJ / cm using a 365 nm LED UV exposure device. 2 An isotropic layer was formed by exposing the composition layer to an irradiation amount of 1000 nm. The isotropic layer was flush with the optically anisotropic layers in region A and region B. In this manner, a light guide element 10 was obtained. The light guide element 10 of Example 9 satisfies the above formula (1).

[0316] Composition for isotropic layer ----------------------------------- SP327 (manufactured by Osaka Organic Chemical Industry Ltd.) 100.00 parts by mass Polymerization initiator (manufactured by BASF, Omnirad (registered trademark) 819) 3.00 parts by mass Methyl ethyl ketone 200.00 parts by mass Cyclopentanone 200.00 parts by mass

[0317] The resulting isotropic layer had a refractive index of 1.48.

[0318] Furthermore, when evaluated in the same manner as in Example 1, the value of θc of the light guide element 10 was 74°.

[0319] Example 10 A light guide element 11 was produced and evaluated in the same manner as the light guide element 10, except that the composition forming the isotropic layer was changed to the following isotropic layer composition 2. The light guide element 11 of Example 10 satisfies the above formula (1).

[0320] Isotropic layer composition 2 ----------------------------------- Fluorene acrylate (Oxol EA-0200, manufactured by Osaka Gas Chemicals Co., Ltd.) 100.00 parts by mass Polymerization initiator (Omnirad (registered trademark) 819, manufactured by BASF) 3.00 parts by mass Methyl ethyl ketone 200.00 parts by mass Cyclopentanone 200.00 parts by mass -----------------------------------

[0321] The resulting isotropic layer had a refractive index of 1.59.

[0322] The value of θc of the light guide element 11 was 74°.

[0323] From the evaluation results of the Examples and Comparative Examples, it was found that the optically anisotropic layer has an ordinary refractive index no and an extraordinary refractive index ne, and an average refractive index n of the substrate. BASEIt has been shown that the relationship of the following formula (1) between θc and θd is large, that is, the diffractive effect of the optically anisotropic layer is effective for light with a high angle, and the light with a high angle is emitted. Therefore, the light guide element of the present invention can improve the light utilization efficiency compared to the comparative example.

[0324] [Evaluation] (Evaluation of brightness uniformity and image clarity) Vuzix smart glasses (Vuzix Blade 2) were disassembled, and the light guide element of the present invention was installed in place of the light guide plate of the product. The brightness uniformity of the displayed image and the clarity of the image were then evaluated. The brightness of the displayed image was uniform, and the image was clear. Furthermore, compared to light guide element 10, light guide elements 1 to 9 and 11 displayed clearer boundaries when displaying a checkerboard pattern.

[0325] 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.

[0326] 10, 12 Liquid crystal diffraction element 16 Optically anisotropic layer 18 Optically anisotropic layer (cholesteric liquid crystal layer) 20 Support 24 Alignment film 30 Liquid crystal compound 30A Optical axis 40 Display (image display device) 42 Light area 44 Dark area 45 Light guide element 45a Region A 45b Non-diffraction area 45c Region B 45d Region C 46, 47 Liquid crystal diffraction element 50 AR display device 54 Isotropic layer 60 Exposure device 62 Laser 64 Light source 68 Beam splitter 70A, 70B Mirror 72A, 72B λ / 4 plate 110 Dove prism 112 Linear polarizer 114 λ / 4 plate 144 Light guide plate 316, 318 Region 320 Support 322 Alignment film 324 Coating film 326 First region 328 Second region 329 Photomask 400, 450 Optically anisotropic layer 400a First optically anisotropic layer 400b Second optically anisotropic layer 410a, 420a Region A 410b, 420b Non-diffraction region 410c, 420c Region B 500 Laminate M Laser light MA, MB Light ray P O Linear polarized light P R Right circular polarization PL 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. A substrate and an optically anisotropic layer provided on at least one main surface of the substrate, wherein the optically anisotropic layer is formed using a composition containing a liquid crystal compound having an ordinary refractive index no and an extraordinary refractive index ne, and includes a region A having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and wherein the ordinary refractive index no and the extraordinary refractive index ne and the average refractive index n of the substrate are BASE and a light guide element having the relationship of the following formula (1): no < n BASE <ne...(1) 2. The light guide element according to claim 1, wherein the extraordinary refractive index ne is 1.8 or more.

3. The light guide element according to claim 1, wherein the ordinary light refractive index no is 1.4 or more.

4. The average refractive index n of the substrate BASE The light guide element according to claim 1 , wherein the σ is 1.7 or more.

5. The light guide element according to claim 1, wherein the diffraction efficiency in the region A varies in the in-plane direction.

6. The light guide element according to claim 5, wherein the region A has a region in which the diffraction efficiency gradually increases in an in-plane direction.

7. A light-guiding element according to claim 1, wherein the optically anisotropic layer further has a region B having an orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while rotating continuously along at least one direction in the plane, and the rotation direction of the optical axis of the liquid crystal compound in region A along one direction in the orientation pattern and the rotation direction of the optical axis of the liquid crystal compound in region B along one direction in the orientation pattern are different from each other.

8. The light guide element according to claim 7, wherein one direction of the alignment pattern in the region A and one direction of the alignment pattern in the region B are different from each other.

9. A light-guiding element according to claim 7, wherein the length over which the orientation of the optical axis derived from the liquid crystal compound in the orientation pattern of region A rotates 180° in the plane is different from the length over which the orientation of the optical axis derived from the liquid crystal compound in the orientation pattern of region B rotates 180° in the plane.

10. The light guide element according to claim 7, wherein at least one of the region A and the region B is a cholesteric liquid crystal layer in which the liquid crystal compound is cholesterically aligned.

11. The light guide element according to claim 7, wherein the optically anisotropic layer further includes a non-orientation pattern region having no orientation pattern, and at least a portion of the plane of the non-orientation pattern region is optically isotropic.

12. The light guide element according to claim 11, wherein the optically anisotropic layer is smooth and does not have an uneven structure.

13. An adhesive layer is provided between the substrate and the optically anisotropic layer, and the refractive index of the adhesive layer is n AD The light guide element according to claim 1, wherein n satisfies the following formula (2): AD <ne...(2) 14. The light guide element according to claim 1, further comprising an adhesive layer between the substrate and the optically anisotropic layer, the adhesive layer having a thickness of 0.1 μm or less.

15. The light guide element according to claim 1, wherein the substrate and the optically anisotropic layer are in direct contact with each other.

16. A light guide element according to claim 1, comprising two optically anisotropic layers arranged on a main surface of the substrate and spaced apart in the plane direction of the main surface, and a non-liquid crystal, optically isotropic isotropic layer arranged on the main surface of the substrate between the two optically anisotropic layers.

17. The light guide element according to claim 16, wherein the isotropic layer covers the surface of each of the two optically anisotropic layers opposite to the substrate.

18. The light guide element according to claim 16, wherein the surfaces of the isotropic layer and the two optically anisotropic layers opposite to the substrate are flush with each other.

19. Refractive index n of the isotropic layer ISO The light guide element according to claim 16, wherein n satisfies the following formula (3): ISO <ne...(3) 20. An AR display device comprising a light guide element according to any one of claims 1 to 19 and an image display device.

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