Optically anisotropic layer, laminate, light guide element, and head mounted display

Abstract

Provided are: an optically anisotropic layer capable of suppressing stray radiation from a light guide plate; a laminate; and a light guide element and a head mounted display which use the same. This optically anisotropic layer is formed using a composition containing a liquid crystal compound, and includes at least: a region A having a liquid crystal alignment pattern in which the direction of an optic axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in a plane; and a region C not having the liquid crystal alignment pattern, wherein the region A includes, in at least a portion of a side edge part in contact with the region C, a region Ad in which the liquid crystal alignment pattern changes, and the width Dd of the region Ad and the thickness T of the optically anisotropic layer have the relationship T<Dd<25×T.

Description

Optically anisotropic layer, laminate, light guide element, and head-mounted display

[0001] The present invention relates to an optically anisotropic layer that diffracts incident light, a laminate, a light guide element using the same, and a head-mounted display.

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

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

[0004] A known example of such a diffraction grating is a diffraction element using a liquid crystal. For example, Patent Document 1 describes an optical element including a plurality of stacked birefringent sublayers configured to change the direction of propagation of light passing therethrough in accordance with the Bragg condition, each stacked birefringent sublayer having a local optical axis that varies along the respective interface between adjacent stacked birefringent sublayers to define a respective grating period. The optical element described in Patent Document 1 is an optical element that diffracts transmitted light. 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 zone (exit pupil expansion). For example, Patent Document 4 describes an optical waveguide in which an input coupler (diffraction element) of an 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 portions, 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 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] When a liquid crystal diffraction element is used as the diffraction element of the light-guiding element used in AR glasses, if unintended stray light is emitted from the element, it can create an unnatural appearance and significantly reduce social acceptance of wearing the glasses.

[0011] The object of the present invention is to solve the problems of the conventional technology and to provide an optically anisotropic layer, a laminate, a light-guiding element, and a head-mounted display using them, which can suppress stray light radiation from a light-guiding plate.

[0012] [1] An optically anisotropic layer formed using a composition containing a liquid crystal compound, comprising at least a region A having 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, and a region C having no liquid crystal orientation pattern, wherein region A includes a region Ad in at least a part of a periphery adjacent to region C, where the liquid crystal orientation pattern changes, and wherein a width Dd of region Ad and a thickness T of the optically anisotropic layer satisfy the following formula (1): T < Dd < 25 × T (1) [2] A laminate comprising at least two or more optically anisotropic layers according to [1]. [3] A light guide element comprising, on a light guide plate, the optically anisotropic layer according to [1] or the laminate according to [2]. [4] A head-mounted display comprising the light guide element according to [3] and an image display element. [5] A method for manufacturing an optically anisotropic layer, wherein the optically anisotropic layer is formed using a composition containing a liquid crystal compound, and comprises at least a region A having a liquid crystal orientation pattern in which the direction of an optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and a region C having no liquid crystal orientation pattern, wherein region A includes a region Ad in at least a part of a peripheral portion adjacent to region C, where the liquid crystal orientation pattern changes, and a width Dd of region Ad and a thickness T of the optically anisotropic layer have a relationship represented by the following formula (1): T < Dd < 25 × T (1) 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 efficiency. [6] A method for producing a laminate, further comprising a step of laminating at least two or more optically anisotropic layers produced by the production method of [5]. [7] A method for producing a light-guiding element, further comprising a step of laminating, on a light-guiding plate, the optically anisotropic layer produced by the production method of [5] or a laminate produced by the production method of [6].[8] A method for manufacturing a head-mounted display, further comprising a step of optically coupling the light guide element manufactured by the manufacturing method of [7] with an image display element.

[0013] According to the present invention, it is possible to provide an optically anisotropic layer, a laminate, a light guide element that suppresses the emission of stray light from a light guide plate, and a head-mounted display that uses these and has excellent social acceptability.

[0014] FIG. 1 is a conceptual diagram of an example of the arrangement of regions A, B, and C in the optically anisotropic layer of the present invention. FIG. 2 is a top view of FIG. 1. FIG. 3 is a conceptual diagram of an example of region A in the optically anisotropic layer of the present invention. FIG. 4 is a top view of FIG. 3. FIG. 5 is a conceptual diagram of an example of region A, region Ad, and region C in the optically anisotropic layer of the present invention. FIG. 6 is a top view conceptually showing an example of the arrangement of regions A, B, C, and D in another example of the optically anisotropic layer of the present invention. FIG. 7 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 the optically anisotropic layer. FIG. 8 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 the optically anisotropic layer. FIG. 9 is an example of an exposure device for imparting the alignment restraining force of a liquid crystal alignment pattern to a photo-alignment film. FIG. 10 is a schematic diagram illustrating an example of a head-mounted display having the optically anisotropic layer of the present invention. Fig. 11 is a conceptual diagram showing an example of a laminate having a plurality of optically anisotropic layers of the present invention. Fig. 12 is a diagram showing the irradiation dose in Examples. Fig. 13 is a conceptual top view showing another example of the optically anisotropic layer of the present invention. Fig. 14 is a conceptual top view showing another example of the optically anisotropic layer of the present invention.

[0015] Hereinafter, the optically anisotropic layer, laminate, light guide element, and head-mounted display of the present invention will be described in detail based on 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 range 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 a range of error generally accepted in the technical field, for example, 99% or more, 95% or more, or 90% or more. Furthermore, with respect to angles, "perpendicular" and "parallel" mean 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 the half-value transmittance T1 / 2 (%), expressed by the following formula, where Tmin (%) is the minimum value of the transmittance of the target object (member). Formula for calculating half-value transmittance: T1 / 2 = 100 - (100 - Tmin) ÷ 2. Furthermore, the selective reflection central wavelengths of multiple layers being "equal" does not mean that they are strictly equal, and an error within a range that does not have an optical effect is allowed. Specifically, the selective reflection central wavelengths of multiple objects being "equal" means that the difference in the selective reflection central wavelengths between the respective objects is 20 nm or less, and this difference is preferably 15 nm or less, and more preferably 10 nm or less.

[0019] <Optically Anisotropic Layer> The optically anisotropic layer of the present invention is an optically anisotropic layer formed using a composition containing a liquid crystal compound, and the optically anisotropic layer has a region A having 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, and a region C having no liquid crystal orientation pattern. Furthermore, region A includes a region Ad in which the liquid crystal orientation pattern changes in at least a part of the edge portion adjacent to region C, and the width Dd of region Ad and the thickness T of the optically anisotropic layer have the following relationship (1): T < Dd < 25 × T (1) This region A is known to function as a liquid crystal diffraction element. Therefore, it can be said that the optically anisotropic layer of the present invention has a configuration in which a liquid crystal diffraction element and a liquid crystal layer having no diffraction effect are integrally formed.

[0020] Conventional liquid crystal diffraction elements are typically fabricated by cutting an optically anisotropic layer within a liquid crystal orientation pattern region within the optically anisotropic layer and laminating the resulting sheet-like optically anisotropic layer onto a predetermined substrate (e.g., a light guide plate, as described below). From the perspective of refractive index distribution, this cut surface represents a discontinuous change in refractive index, resulting in significant refracting of light rays crossing this area in unintended directions, resulting in stray light. For example, when a liquid crystal diffraction element is placed on a light guide plate and used in a head-mounted display, this stray light causes the edges of the liquid crystal diffraction element to appear shiny to non-head-mounted display wearers, negatively impacting social acceptance of wearing a head-mounted display. The inventors therefore discovered that stray light can be reduced by surrounding the liquid crystal diffraction element with a non-diffractive liquid crystal layer to reduce this discontinuous change in refractive index. However, they found that even with this configuration, the discontinuous change in refractive index is insufficiently reduced, resulting in insufficient reduction of stray light.

[0021] As a result of extensive research, the inventors have found that by having a configuration in which a liquid crystal diffraction element and a liquid crystal layer having no diffractive effect are integrally formed, and by providing a region in which the liquid crystal diffraction pattern gradually changes at the interface between the liquid crystal diffraction element and the region having no diffractive effect, light is diffused in various directions, thereby suppressing the generation of strong stray light in a specific direction and reducing the adverse effects on social acceptability of wearing a head-mounted display. The optically anisotropic layer will be described in detail below.

[0022] Fig. 1 is a conceptual diagram showing an example of the optically anisotropic layer of the present invention. Fig. 2 is a top view of Fig. 1. The optically anisotropic layer 1 shown in Figs. 1 and 2 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 A2a having a liquid crystal orientation pattern and a region C2c (hereinafter also referred to as a non-diffraction region) having no liquid crystal orientation pattern may be formed. Furthermore, a region B2b having a liquid crystal orientation pattern like region A but in which the details of the pattern may be different may also be formed. Region B is also shown in Figs. 1 and 2.

[0023] Region A2a and region B2b each have 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, and act as a liquid crystal diffraction element that diffracts incident light.

[0024] Moreover, the region A 2 a, the non-diffractive region (region C) 2 c, and the region B 2 b have approximately the same thickness, and both main surfaces of the optically anisotropic layer 400 are smooth, flat surfaces without an uneven structure.

[0025] There is no limitation on the thickness T of the optically anisotropic layer, and it may be set appropriately depending on the diffraction efficiency required for the optically anisotropic layer (region A), the material for forming the optically anisotropic layer, etc. The thickness T of the optically anisotropic layer is preferably 0.5 μm to 20 μm, more preferably 0.7 μm to 15 μm, and even more preferably 1.0 μm to 12 μm.

[0026] [Region A and Region B] Region A and Region B of the optically anisotropic layer of the present invention have a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0027] FIG. 3 is a side view conceptually illustrating the liquid crystal orientation pattern in region A (and region B). FIG. 3 conceptually illustrates the state of the optically anisotropic layer during its manufacture, and the liquid crystal film 10 has a structure in which a support 20, an alignment film 24, and an optically anisotropic layer 18 are laminated in this order. While the illustration shows the optical axis 30A derived from the liquid crystal compound 30 as varying in the thickness direction (cholesterically oriented), this does not limit the present invention; the optical axis 30A may also be configured to not vary in the thickness direction (not cholesterically oriented). When the liquid crystal compound 30 is cholesterically oriented, region A (and region B) acts as a reflective diffraction element that reflects and diffracts light. When the liquid crystal compound 30 is not cholesterically oriented, region A (and region B) acts as a transmissive diffraction element that transmits and diffracts light.

[0028] 4 is a top view conceptually illustrating the liquid crystal orientation pattern in region A. In the liquid crystal film 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 along one in-plane direction. In the present invention, one period (symbol Λ in FIG. 2 , also referred to as the "optical axis rotation period") is defined as the length of the rotation of the optical axis 30A by 180° in one direction in which the orientation of the optical axis 30A changes while continuously rotating in the liquid crystal orientation pattern. In the following description, "the orientation of the optical axis 30A rotates" may also be simply referred to as "the optical axis 30A rotates."

[0029] 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.

[0030] 3, even in the case of an orientation pattern in which the direction of the optical axis 30A changes in the thickness direction, for example, when the optical axis 30A is observed only on the surface formed by the surface in contact with the orientation film 24, the liquid crystal orientation pattern is as shown in Fig. 4. In other words, it should be noted that Fig. 4 is a conceptual diagram depicting the liquid crystal orientation pattern on a cross section in a plane parallel to the layer plane.

[0031] 4, 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 an arrow X and in a direction perpendicular to this direction (the direction of the arrow X) in accordance with the alignment pattern formed on the underlying alignment film 24. In the following description, the direction perpendicular to the direction of the arrow X will be referred to as the Y direction for convenience.

[0032] 3 and 5 described later, the Y direction is perpendicular to the paper surface. The liquid crystal compound 30 forming the optically anisotropic layer 18 has a liquid crystal orientation pattern in which the direction of the optic axis 30A changes while continuously rotating along the direction of the arrow X in the plane of the optically anisotropic layer 18. In the example shown in Figures 3 and 4, the liquid crystal compound 30 has a liquid crystal orientation pattern in which the optic axis 30A changes while continuously rotating clockwise along the direction of the arrow X.

[0033] The expression "the orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of the 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 the arrow X and the direction of the arrow X differs depending on the position in the direction of the arrow X, and that the angle formed between the optical axis 30A and the direction of the arrow X changes sequentially from θ to θ+180° or θ−180° along the direction of the arrow X.

[0034] 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.

[0035] 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.

[0036] 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. 4 , 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. 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.

[0037] An optically anisotropic layer having such a liquid crystal orientation pattern exhibits a diffractive effect for specific polarized light due to the distribution of refractive index derived from the optical axis 30A. The characteristics of the diffracted polarized light, its wavelength, output angle (diffraction angle), and diffraction efficiency are determined by the in-plane rotation period of the optical axis (one period Λ), the degree of change in the optical axis in the thickness direction, and the refractive index anisotropy Δn and wavelength dispersion of the liquid crystal compound. By appropriately setting these parameters, a liquid crystal diffraction element with desired diffraction characteristics can be obtained.

[0038] The region A includes a region Ad where the liquid crystal alignment pattern changes in at least a part of the edge portion that contacts the region C having no liquid crystal alignment pattern, which will be described later, and the relationship between the width Dd of the region Ad and the thickness T of the optically anisotropic layer is expressed by the following formula (1): T < Dd < 25 × T (1)

[0039] For example, in the case of the optically anisotropic layer 1 shown in Fig. 2, the regions A2a, B2b, and C2c are each rectangular, and include a region Ad where the liquid crystal orientation pattern changes in at least a part of the edge of one side of the region A2a where the region A2a and the region C2c meet, and / or in at least a part of the edge of one side of the region B2b where the region B2b and the region C2c meet. Hereinafter, the region Ad will be described with reference to Fig. 5.

[0040] 5 is a side view conceptually showing the regions A2a and C2c, and the changing region Ad2d. Region Ad has a liquid crystal orientation pattern and can be considered part of region A, but at least one of the following changes rapidly: the in-plane rotation period of the optical axis (one period Λ), the degree of change in the optical axis in the thickness direction, the degree of orientation order, its in-plane distribution, and the thickness of the region oriented with a predetermined liquid crystal orientation pattern. As described above, these parameters determine the characteristics of the diffraction element, and the rapid changes in these parameters in the in-plane direction significantly disrupt the phase of light passing through region Ad, thereby canceling out the diffraction phenomenon. By providing such region Ad, light rays crossing region Ad are diffused in various directions, and are therefore not emitted in an unexpected specific direction, which is thought to prevent stray light.

[0041] There are no particular limitations on the changes, and various parameters can be changed at various change rates. It is preferable that all change rates be continuous. The term "continuous change" used here means that when the change in the parameter of interest is expressed as a function of position, the differential function is algebraically continuous.

[0042] As an example of this change, an example will be given in which the rate of change of the orientation of the optical axis 30A changes in the in-plane and thickness directions. In the case where there is a liquid crystal alignment pattern in region A that changes with a certain in-plane period (one period) Λa and a thickness direction rotation pitch (helical pitch of cholesteric alignment) Pa, in region Ad, the in-plane period Λa continuously diverges to infinity and changes until the rotation can be considered to be zero, and the point at which the thickness direction rotation pitch Pa becomes zero changes continuously.

[0043] 5, when the region A2a has a liquid crystal orientation pattern that changes with a certain in-plane period (one period) Λa, the liquid crystal orientation pattern is formed throughout the thickness direction in the region A2a, i.e., the liquid crystal compound is oriented in a predetermined orientation state throughout the thickness direction, whereas the thickness of the region Ad2d where the liquid crystal orientation pattern is formed gradually decreases from the region A2a side toward the region C2c side. That is, the region Ad2d has a region where the liquid crystal compound is oriented in a predetermined orientation state and a region where the liquid crystal compound is not oriented in the thickness direction, and the thickness of the region where the liquid crystal compound is oriented in the predetermined orientation state gradually decreases from the region A2a side toward the region C2c side, while the thickness of the region where the liquid crystal compound is not oriented gradually increases.

[0044] As described above, the width Dd of the region Ad and the thickness T of the optically anisotropic layer satisfy the relationship of the following formula (1): T<Dd<25×T (1)

[0045] The method for measuring the width Dd of the region Ad may be selected as appropriate depending on the parameters that vary within the region Ad. That is, the boundary between the region A and the region Ad and the boundary between the region C and the region Ad can be determined using a measurement method that depends on the parameters that vary within the region Ad.

[0046] For example, when the parameter that changes within region Ad is the thickness of the region in which a liquid crystal orientation pattern is formed, as shown in Figure 5, cross-sectional SEM measurement of the optically anisotropic layer enables a distinction to be made between a region with high birefringence where bright and dark areas are visible in the thickness direction and an optically isotropic region in which bright and dark areas are not visible, and therefore the region with high birefringence can be regarded as the region in which a liquid crystal orientation pattern is formed and its thickness can be calculated for measurement.

[0047] The width Dd of the region Ad (the width in the direction perpendicular to the boundary line between the region A and the region C) is preferably 0.5 μm to 500 μm, more preferably 0.7 μm to 400 μm, and even more preferably 1.0 μm to 300 μm.

[0048] As will be described later, the region A may have a configuration in which the diffraction efficiency varies within the plane, and the parameters for varying the diffraction efficiency may be the same as the parameters that vary in the region Ad. However, unlike the changes in the region Ad, these changes are very gradual with respect to the wavelength of light, and therefore the diffraction phenomenon due to the distribution of optic axes formed in the optically anisotropic layer is not canceled out.

[0049] Specifically, for example, when the thickness of the region in which the liquid crystal orientation pattern is formed in region A is changed to change the diffraction efficiency, as described above, the thickness T of the entire optically anisotropic layer is several μm to several tens of μm, and therefore the change in thickness of the region in which the liquid crystal orientation pattern is formed is also several μm to several tens of μm, whereas as will be described later, the width of region A is about several mm to several cm, and therefore the ratio (change rate) of the change in the parameter for changing the diffraction efficiency to the width of region A is 1 / 50 or less, or 1 / 100 or less, or even 1 / 1000 or less. On the other hand, the change rate of the thickness of the region in region Ad in which the liquid crystal orientation pattern is formed is 1 / 25 to 1 from formula (1).

[0050] Therefore, it is possible to determine whether or not the area is in the Ad region from the rate of change of the parameter.

[0051] Examples of methods for providing such regions Ad include a method in which the orientation pattern of the orientation film 24 is changed in advance from the orientation pattern of region A, and then an optically anisotropic layer is formed, or a method in which, as will be described later, exposure conditions, heating conditions, or both are controlled when performing a process for forming regions A and C. Details will be described later.

[0052] The region B and the region D described later may also include a region Ad in which the liquid crystal alignment pattern changes in at least a part of the edge portion in contact with the region C.

[0053] 1, the optically anisotropic layer 1 of the present invention has a non-diffraction region (region C) 2c. The non-diffraction region 2c does not have the above-mentioned liquid crystal orientation pattern and does not have the function of diffracting incident light.

[0054] The non-diffraction region 2c 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 2c, the liquid crystal compound may be uniaxially oriented, twisted, or cholesterically oriented in the thickness direction, and uniaxial or twisted orientation is preferred. The non-diffraction region 2c 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 2c is a region in which the liquid crystal compound is oriented in one direction in the same plane, the non-diffraction region 2c preferably functions as a retardation region. The retardation region preferably imparts a retardation of λ / 8 to light from at least one incident direction. As a result, for example, circularly polarized light diffracted in the incident-side region A2a is converted into elliptically polarized light as it passes through the non-diffraction region 2c when guided through the light guide plate, undergoes total reflection at the interface between the non-diffraction region 2c and air, and is converted into linearly polarized light as it passes through the non-diffraction region 2c 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 make the light intensity of the output light in the output-side region B2b uniform.

[0055] Here, when the optically anisotropic layer of the present invention has Region B, the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal alignment pattern in Region A may be different from the direction of rotation of the optical axis derived from the liquid crystal compound along one direction in the liquid crystal alignment pattern in Region B. Also, the direction of the liquid crystal alignment pattern in Region A may be different from the direction of the liquid crystal alignment pattern in Region B. Furthermore, the length over which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in-plane in the liquid crystal alignment pattern in Region A (the length of one period Λ) may be different from the length over which the orientation of the optical axis derived from the liquid crystal compound rotates 180° in-plane in the liquid crystal alignment pattern in Region B (the length of one period Λ).

[0056] As will be described later, when the optically anisotropic layer is combined with a light guide plate and used in a light guide element, for example, region A acts as an incident diffraction element for making light incident on the light guide plate, and region B acts as an output diffraction element for making light exit from the light guide plate. Therefore, the diffraction performance required for region A and region B is different. Therefore, region A and region B may be set according to the required diffraction performance, respectively, in terms of the rotation direction, one period, one direction, etc. of the optical axis direction derived from the liquid crystal compound in the liquid crystal orientation pattern, and the liquid crystal orientation pattern in region A may be different from the liquid crystal orientation pattern in region B. Note that, in the light guide element described later, an example has been described in which region A acts as an incident diffraction element and region B acts as an output diffraction element, but region A may also act as an output diffraction element and region B as an incident diffraction element.

[0057] In the optically anisotropic layer of the present invention, region A and region B may each be a cholesteric liquid crystal layer that reflects and diffracts light, or region A and region B may each be a liquid crystal diffraction layer that transmits and diffracts light, or region A may be a cholesteric liquid crystal layer and region B may be a liquid crystal diffraction layer, or region A may be a liquid crystal diffraction layer and region B may be a cholesteric liquid crystal layer.

[0058] Furthermore, in the optically anisotropic layer of the present invention, when region A and region B are cholesteric liquid crystal layers, the helical pitch length of the cholesteric liquid crystal layer in region A and the helical pitch length of the cholesteric liquid crystal layer in region B may be different from each other. For example, when the optically anisotropic layer is combined with a light guide plate and region A is used as an incident diffraction element and region B as an output diffraction element, light is incident on region A from a substantially perpendicular direction, while light is incident on region B from an oblique direction. As described above, the cholesteric liquid crystal layer has wavelength-selective reflectivity, but when light is incident from an oblique direction, so-called blue shift occurs, in which the selectively reflected wavelength becomes shorter. Therefore, even if region A and region B diffract light of the same wavelength, it is preferable to set an appropriate helical pitch length for each region depending on the incident angle of light, etc.

[0059] Furthermore, the direction of rotation of the helix of the cholesteric alignment in region A may be different from the direction of rotation of the helix of the cholesteric alignment in region B. That is, the direction of rotation of the circularly polarized light reflected by region A may be different from the direction of rotation of the circularly polarized light reflected by region B. For example, when an optically anisotropic layer is combined with a light guide plate, and region A is used as an input diffraction element and region B is used as an output diffraction element, even if right-handed circularly polarized light is incident on the light guide plate from region A, when the light is depolarized and incident on region B while being totally reflected and guided within the light guide plate, the light may become unpolarized or light containing a left-handed circularly polarized component such as elliptically polarized light. Therefore, the circularly polarized light reflected and diffracted by region B may be different from the circularly polarized light reflected and diffracted by region A.

[0060] In the optically anisotropic layer of the present invention, when at least one of the regions A and B is a cholesteric liquid crystal layer, the region may have a region in which the helical pitch length of the cholesteric liquid crystal layer is different in the in-plane direction. This allows, for example, adjustments to make the in-plane color and brightness uniform when used as AR glass. Furthermore, by adjusting the desired color to be strongly reflected in the desired in-plane direction, AR glass with high light utilization efficiency can be obtained.

[0061] Furthermore, in the optically anisotropic layer of the present invention, when at least one of region A and region B is a cholesteric liquid crystal layer, this region may have a region in which the helical pitch length of the cholesteric liquid crystal layer varies in the thickness direction. As described above, a cholesteric liquid crystal layer reflects specific wavelengths depending on the helical pitch length. Therefore, by configuring the cholesteric liquid crystal layer so that the helical pitch length varies in the thickness direction, the band of wavelengths that are selectively reflected can be broadened.

[0062] In the optically anisotropic layer of the present invention, the diffraction efficiency of each of the regions A, B, and D described below may be constant in the plane, or the diffraction efficiency may vary depending on the position in the in-plane direction in at least one of the regions A, B, and D. When the diffraction efficiency varies depending on the position in the in-plane direction, it is preferable that the diffraction efficiency gradually increases along one direction in the plane. Specifically, it is preferable that the diffraction efficiency gradually increases along one direction in which the orientation of the optical axis of the liquid crystal compound in the liquid crystal orientation pattern changes while continuously rotating. The diffraction efficiency is the intensity ratio of the outgoing light (diffracted light) to the incident light.

[0063] As a result, when the optically anisotropic layer of the present invention is used in a light guide element for use in a head-mounted display such as AR (Augmented Reality) glasses, the brightness (amount of light) of light emitted from the light guide plate can be made uniform even when the exit pupil is enlarged. When the optically anisotropic layer is used in a light guide element for a head-mounted display, it is preferable that the diffraction efficiency gradually increases in the region that becomes the output diffraction element and the region that becomes the intermediate diffraction element.

[0064] The configuration in which the diffraction efficiency in any of Regions A, B, and D gradually increases along one direction can be realized by the optically anisotropic layer having either of the following configurations (i) and (ii): (i) a configuration in which the film thickness of the region having a liquid crystal alignment pattern increases from one side to the other in one direction in which the optical axis rotates; or (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.

[0065] In the optically anisotropic layer, the diffraction efficiency is high in the thick region and low in the thin region, so the diffraction efficiency can be changed by gradually increasing the thickness of the region having the liquid crystal orientation pattern along one in-plane direction.

[0066] As described above, in the optically anisotropic layer, the liquid crystal compounds are 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 compounds is not disordered, the thickness direction retardation Rth is high. On the other hand, in regions where the alignment of the liquid crystal compounds is disordered, light is not diffracted appropriately, resulting in low diffraction efficiency. Furthermore, in regions where the alignment of the liquid crystal compounds is disordered, the thickness direction retardation Rth is low. Therefore, the diffraction efficiency can be changed by gradually increasing the thickness direction retardation Rth along one in-plane direction.

[0067] Details of the configuration in which the diffraction efficiency of the optically anisotropic layer is gradually changed by the above methods (i) and (ii) are described in WO 2020 / 122119, etc. The manufacturing method will be described later.

[0068] In the example shown in FIGS. 1 and 2, the optically anisotropic layer has regions A and B, and a region C (non-diffraction region) between regions A and B, but the present invention is not limited to this.

[0069] FIG. 13 is a top view conceptually showing another example of the optically anisotropic layer of the present invention.

[0070] 13 is formed using a composition containing a liquid crystal compound, and has, in the in-plane direction, a region A2a having a liquid crystal orientation pattern and a region C (non-diffraction region) 2c having no liquid crystal orientation pattern. The configuration of region A2a and region C2c other than the arrangement is the same as in the example described above, and therefore a description thereof will be omitted.

[0071] 13, region A2a is rectangular and located approximately in the center in the in-plane direction. Region C2c is located so as to surround region A2a on all four sides, and region C2c is frame-shaped. Therefore, all four sides of region A2a are in contact with region C2c.

[0072] In the case of the optically anisotropic layer 3 shown in Figure 13, it is sufficient that at least some of the four edges of region A2a include a region Ad where the liquid crystal orientation pattern changes, and it is preferable that all four edges of region A2a include a region Ad where the liquid crystal orientation pattern changes.

[0073] FIG. 14 is a top view conceptually showing another example of the optically anisotropic layer of the present invention.

[0074] The optically anisotropic layer 4 shown in Figure 14 is formed using a composition containing a liquid crystal compound, and has, in the in-plane direction, a region A2a having a liquid crystal orientation pattern, a region B2b having a liquid crystal orientation pattern, and a region C (non-diffraction region) 2c not having a liquid crystal orientation pattern.

[0075] 14, regions A2a and B2b are each rectangular, and are spaced apart from each other in the left-right direction in the in-plane direction. Regions C2c are provided between regions A2a and B2b, around region A2a, and around region B2b. Therefore, four sides of region A2a are in contact with region C2c, and four sides of region B2b are in contact with region C2c.

[0076] 14, it is sufficient that the edge portion of at least one of the regions A2a and B2b includes a region Ad where the liquid crystal orientation pattern changes, that the edge portion of at least one of the four sides of the region A2a includes a region Ad where the liquid crystal orientation pattern changes, or that the edge portion of at least one of the four sides of the region B2b includes a region Ad where the liquid crystal orientation pattern changes. Preferably, the edge portions of all four sides of the region A2a include a region Ad where the liquid crystal orientation pattern changes, and / or the edge portions of all four sides of the region B2b include a region Ad where the liquid crystal orientation pattern changes.

[0077] 1 and 2, the optically anisotropic layer has two regions having a liquid crystal alignment pattern, but the present invention is not limited thereto. The optically anisotropic layer of the present invention may further have a region D in the in-plane direction of the same optically anisotropic layer, the region D having a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one in-plane direction.

[0078] Fig. 6 is a plan view conceptually showing another example of the optically anisotropic layer of the present invention. The optically anisotropic layer shown in Fig. 6 has a region A2a, a region B2b, a region D2e, and a non-diffraction region (region C) 2c. As shown in Fig. 6, the region A2a and the region D2e are spaced apart in the left-right direction in the figure, and the region D2e and the region B2b are spaced apart in the up-down direction in the figure. The non-diffraction region (region C) 2c is formed between the region A2a and the region D2e, and between the region D2e and the region B2b.

[0079] Region D2e, like regions A2a and B2b, 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 A2a and B2b, region D2e may be a cholesteric liquid crystal layer or a liquid crystal diffractive layer. Furthermore, the liquid crystal orientation pattern in region D2e may be different from the liquid crystal orientation patterns in regions A2a and B2b.

[0080] In the illustrated example, the vertical width of region D2e is approximately the same as the vertical width of region A2a, and regions A2a and D2e are located at different left-right positions with their vertical positions approximately coinciding in the figure. Also, the horizontal width of region D2e is approximately the same as the horizontal width of region B2b, and regions B2b and D2e are located at different vertical positions with their horizontal positions approximately coinciding in the figure.

[0081] 6, region A2a, region B2b, and region D2e are each rectangular, and region C2c is provided between region A2a and region B2b, between region B2b and region D2e, around region A2a, around region B2b, and around region D2e. Therefore, four sides of region A2a contact region C2c, four sides of region B2b contact region C2c, and four sides of region D2e contact region C2c.

[0082] 6, it is sufficient that at least one of the regions A2a, B2b, and D2e includes a region Ad where the liquid crystal orientation pattern changes, and at least a portion of the four edges of region A2a may include a region Ad where the liquid crystal orientation pattern changes, at least a portion of the four edges of region B2b may include a region Ad where the liquid crystal orientation pattern changes, and at least a portion of the four edges of region D2e may include a region Ad where the liquid crystal orientation pattern changes. Preferably, all four edges of region A2a include a region Ad where the liquid crystal orientation pattern changes, and / or all four edges of region B2b include a region Ad where the liquid crystal orientation pattern changes, and / or all four edges of region D2e include a region Ad where the liquid crystal orientation pattern changes.

[0083] Thus, the optically anisotropic layer 450 further including the region D2e has three regions that diffract light. Such an optically anisotropic layer 450 is used in combination with a light guide plate to form a light guide element. In this case, as described below, for example, the region A2a acts as an incident diffraction element for allowing light to enter the light guide plate, the region B2b acts as an exit diffraction element for allowing light to exit the light guide plate, and the region D2e acts as an intermediate diffraction element that diffracts light incident from the region A2a toward the region B2b. In this way, the region D2e acting as an intermediate diffraction element can be configured to diffract a portion of light at multiple locations, thereby achieving an exit pupil expansion. Furthermore, as described below, the region D2e preferably has regions with different diffraction efficiencies in the in-plane direction, and it is preferable that the diffraction efficiency gradually changes.

[0084] 2, 6, 13, and 14, the shapes of region A, region B, and region D in plan view are all substantially rectangular, but are not limited thereto and may be various shapes such as circular, elliptical, polygonal, or irregular. Furthermore, the shapes of region A and region B, or even region D, in plan view may be the same or different. Regardless of the shapes of region A, region B, and region D, it is sufficient that at least a portion of the periphery of each region includes a region Ad in which the liquid crystal orientation pattern changes, and it is preferable that the entire periphery of each region adjacent to region C includes a region Ad in which the liquid crystal orientation pattern changes.

[0085] The sizes of the regions A, B, and D in a planar view may be appropriately set depending on the application of the optically anisotropic layer, etc. For example, when the optically anisotropic layer is used in a head-mounted display described below, the sizes of the regions A, B, and D are preferably 3 mm to 1000 mm, more preferably 5 mm to 800 mm, and even more preferably 7 mm to 600 mm, in terms of circle-equivalent diameter.

[0086] In addition, when there are two regions having a liquid crystal alignment pattern, it is preferable that one of the regions includes a region Ad where the liquid crystal alignment pattern changes in the peripheral portion farthest from the other region.

[0087] Specifically, for example, in the optically anisotropic layer 4 shown in Figure 14, when region A2a is used as an incident diffraction element and region B2b is used as an exit diffraction element, it is preferable that region B2b, which becomes the exit diffraction element, includes region Ad, in which the liquid crystal orientation pattern changes, at the edge portion of side 9, of the four sides of region B2b, which is farthest from region A2a.

[0088] When two regions having a liquid crystal orientation pattern are used, and the other region is used as an incident diffraction element and one region is used as an exit diffraction element, light incident from the other region (incident diffraction element) proceeds toward one region (exit diffraction element), and while a portion of the light is emitted from the one region, it proceeds toward the side of the one region farthest from the other region. Therefore, light that is not emitted from one region may reach the side of the one region farthest from the other region and be significantly refracted in an unintended direction at the edge, resulting in stray light. In contrast, by including a region Ad in which the liquid crystal orientation pattern changes in the peripheral portion of one region farthest from the other region, the generation of stray light can be more effectively suppressed.

[0089] 6, when the optically anisotropic layer has three regions having liquid crystal orientation patterns, with region A2a being used as an incident diffraction element, region B2b being used as an exit diffraction element, and region D2e being used as an intermediate diffraction element, it is preferable that region B2b serving as the exit diffraction element includes a region Ad in which the liquid crystal orientation pattern changes, on the edge of one of its four sides that is farthest from region D2e.Furthermore, it is preferable that region D2e serving as the intermediate diffraction element includes a region Ad in which the liquid crystal orientation pattern changes, on the edge of one of its four sides that is farthest from region A2a.

[0090] Furthermore, in the case where the diffraction efficiency gradually increases along one direction in the plane in at least one of regions A, B, and D, it is preferable to include a region Ad in which the liquid crystal orientation pattern changes at the edge portion on the side where the diffraction efficiency is highest.

[0091] In the edge portion on the side where the diffraction efficiency is high, the discontinuous change in refractive index becomes larger, and stray light is more likely to occur. Therefore, by providing the region Ad where the liquid crystal orientation pattern changes in the edge portion on the side where the diffraction efficiency is high, the occurrence of stray light can be more effectively suppressed.

[0092] 14, in a configuration in which region A2a is used as an incident diffraction element and region B2b is used as an exit diffraction element, and the exit pupil is expanded in region B2b, which serves as the exit diffraction element, region B2b has a configuration in which the diffraction efficiency gradually increases along the direction away from region A2a (from left to right in the figure). In such a configuration, region B2b preferably includes region Ad, where the liquid crystal orientation pattern changes, at the edge of side 9 farther from region A2a.

[0093] In addition, in at least one of regions A, B, and D, the diffraction efficiency gradually increases along one direction in the plane, and the edge portion on the side where the diffraction efficiency is highest includes a region Ad in which the liquid crystal orientation pattern changes, and if the parameter for changing the diffraction efficiency is the same as the parameter that changes in region Ad in which the liquid crystal orientation pattern changes, it can be said that the parameter gradually increases along one direction in the plane and then suddenly decreases.

[0094] For example, if this parameter is the thickness of the region in which the liquid crystal orientation pattern is formed, the thickness of the region in which the liquid crystal orientation pattern is formed gradually increases along one direction in the plane, and then suddenly decreases across the width Dd of the region Ad.

[0095] [Composition containing a liquid crystal compound] The optically anisotropic layer of the present invention is formed using a composition containing a liquid crystal compound. Known techniques can be applied to such compositions. A preferred composition is a composition containing a polymerizable liquid crystal compound and a polymerization initiator. If necessary, the composition may contain a chiral agent, a surfactant, and a crosslinking agent. It may also contain other components.

[0096] [Polymerizable Liquid Crystal Compound] The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a discotic liquid crystal compound. Examples of rod-shaped polymerizable liquid crystal compounds include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles. Not only low-molecular-weight liquid crystal compounds, but also polymeric liquid crystal compounds can be used. Polymerizable liquid crystal compounds containing a tolan structure (tolanes) are preferred because of their large refractive index anisotropy and the ease of achieving high diffraction efficiency at a thin thickness.

[0097] 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.

[0098] 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. Using two or more types of polymerizable liquid crystal compounds in combination is preferred because it can lower the alignment temperature and make it easier to form the domains Ad.

[0099] 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.

[0100] 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 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. The birefringence Δn of a liquid crystal compound can be measured by preparing a uniformly aligned liquid crystal material and using the principles of optical interference or refraction. More specifically, examples include a method in which the liquid crystal material is sealed in a wedge-shaped cell and measured using a fringe period determined by optical interference, a method using an Abbe refractometer, and a method using thin-film ellipsometry.

[0101] 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 is often 1.0 to 1.5. In the case of compounds with normal dispersion, the diffraction efficiency for each wavelength can be adjusted to a desired value by adjusting the selective reflection band exhibiting the selective reflection described above, the degree of orientation described below, the thickness, etc.

[0102] From the viewpoint of achieving superior effects of the present invention and enabling AR display with a wide viewing angle, the maximum extraordinary refractive index of the liquid crystal compound in the optically anisotropic layer is preferably 1.8 or more, more preferably 1.9 or more, and even more preferably 2.0 or more. The ordinary refractive index of the liquid crystal compound in the optically anisotropic layer is preferably 1.4 or more, more preferably 1.5 or more, and even more preferably 1.6 or more.

[0103] The birefringence Δn and refractive index preferably satisfy the above-mentioned ranges over the range of 380 to 780 nm, and more preferably over the range of 400 to 650 nm.

[0104] 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:

[0105] 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.

[0106] Within the optically anisotropic layer, the minimum value of the apparent birefringence Δna 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. The apparent birefringence Δna of the liquid crystal compound within the layer is determined by theoretically back-calculating the apparent birefringence Δna after measuring the optical properties of the optically anisotropic layer. For example, since the diffraction efficiency is correlated with Δna × T, Δna can be determined by back-calculating the correlation between the diffraction efficiency and the thickness T of the optically anisotropic layer.

[0107] As a compound that can satisfy the above-mentioned requirements, a polymerizable liquid crystal containing a tolan structure can be preferably used. More preferably, a polymerizable liquid crystal compound containing a tolan structure represented by the following general formula (2) is preferred: P1-R1-C≡C-R2-P2 (2) where R1 and R2 are divalent aromatic groups or cyclic alkyl groups that may have a substituent, such as phenylene, cyclohexylene, naphthylene, and biphenylene. R1 and R2 may be the same or different. Furthermore, P1 and P2 are functional groups having a polymerizable group, and P1 and R1, and P2 and R2 can be bonded together via any linking group.

[0108] Specific examples of such compounds include the compounds shown below.

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] [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. 60-105667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (described in U.S. Pat. No. 4,212,970). Oxime ester compounds and acylphosphine compounds are also suitable.

[0119] 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.

[0120] [Surfactant] The liquid crystal composition used in forming the optically anisotropic layer may contain a surfactant. The addition of a surfactant improves leveling properties and smoothness of the air interface of the layer, thereby improving diffraction efficiency, and when used as a light guide element, improving optical coupling efficiency and image quality. Furthermore, the surfactant is preferably a compound that can function as an alignment control agent that stably or quickly aligns liquid crystals. This function prevents the occurrence of alignment defects, allowing for the production of optically anisotropic layers, light guide elements, and head-mounted displays with excellent optical performance. Examples of surfactants include silicone-based surfactants and fluorine-based surfactants. Silicone-based surfactants are preferred because they provide sufficient smoothness even when added in small amounts.

[0121] 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.

[0122] 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.

[0123] [Chiral Agent (Optically Active Compound)] A chiral agent (chiral agent) has the function of inducing a helical structure in a liquid crystal phase. By inducing a helical structure (which can also be called a twisted structure when the helical period is small) in a liquid crystal phase by a chiral agent, an optically anisotropic layer can be formed without containing abnormalities such as alignment defects while maintaining the alignment order even in a complicated liquid crystal alignment pattern such as that shown in Figure 2. Therefore, it is preferable to add a chiral agent to the composition of the present invention.

[0124] The chiral agent can be selected according to the purpose, since the twist direction or helical pitch of the helix induced varies depending on the compound. The chiral agent is not particularly limited, 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 planar asymmetric compounds without an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound.In this embodiment, the polymerizable group of the polymerizable chiral agent is preferably the same type of group as the polymerizable group of the polymerizable liquid crystal compound.Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group.In addition, the chiral agent may be a liquid crystal compound.

[0125] When the chiral agent has a photoisomerizable group, it is possible to form a liquid crystal alignment pattern in which the change in the thickness direction of the rotation direction of the optical axis varies depending on the position in the plane by irradiating a photomask with actinic rays or the like after coating and alignment. The photoisomerizable group is preferably an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0126] As an example of such a photoisomerizable chiral compound, a compound represented by general formula (I) will be described.

[0127] General formula (I)

[0128]

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134]

[0135]

[0136]

[0137] The photoreactive optically active compound may be, for example, a compound represented by the following general formula (II).

[0138] General formula (II)

[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, 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145]

[0146]

[0147]

[0148] 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.

[0149] 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 contained.

[0150] [Crosslinking Agent] The liquid crystal composition may optionally contain a crosslinking agent to improve the film strength and durability after curing. As the crosslinking agent, those that are cured by ultraviolet light, heat, moisture, etc. can be suitably used. 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 can be easily obtained.

[0151] [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 deteriorate the optical performance, etc. From the viewpoint of reducing the difference in refractive index with the light guide plate and improving the optical coupling efficiency, high-refractive-index nanoparticles such as zirconia oxide nanoparticles and titanium oxide nanoparticles, or nanocomposites thereof, may be added.

[0152] 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.

[0153] <Method for producing optically anisotropic layer> The method for producing the optically anisotropic layer of the present invention preferably comprises the following steps: Step 1: 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; Step 2: 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; Step 3: a step of 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 efficiency. Each step will be described in detail below.

[0154] [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. 7, 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).

[0155] 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.

[0156] 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.

[0157] [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.

[0158] 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 use of the optically anisotropic layer, 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.

[0159] The support may be a single layer or a multilayer. In the case of a single layer, various materials used as support materials in optical elements can be used as the support. Specific examples of the support material include glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin. In the case of a multilayer, an example of the support includes one of the above-mentioned single-layer supports as a substrate, and another layer is provided on the surface of this substrate.

[0160] [Alignment Film] An alignment film is formed on the surface of the support. The alignment film is an alignment film for orienting the liquid crystal compound in region A (region B, region D) into a predetermined liquid crystal alignment pattern when forming an optically anisotropic layer. As described above, region A (region B, region D) of the optically anisotropic layer has a liquid crystal alignment pattern in which the orientation of the optical axis 30A (see FIG. 2) derived from the liquid crystal compound 30 changes while continuously rotating along one in-plane direction. In the present invention, the length of the rotation of the optical axis 30A by 180° in one direction in which the orientation of the optical axis 30A changes while continuously rotating in the liquid crystal alignment pattern is defined as one period (symbol Λ in FIG. 2, also referred to as the "optical axis rotation period").

[0161] In the following description, "the orientation of the optical axis 30A rotates" may also be simply referred to as "the optical axis 30A rotates."

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] (Method of Exposing Photo-Alignment Film) Fig. 9 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. 9 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 light M emitted by the light source 64 into two light beams MA and MB, mirrors 70A and 70B arranged on the optical paths of the two split light 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 light 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 (light 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.

[0169] 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, as described above. 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.

[0170] 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 by a method of rubbing the support or a method of processing the support 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 derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0171] [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.

[0172] An example of how to achieve this is described with reference to FIG. 7 . 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 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 orientation of the liquid crystal in region 316 is maintained, while the orientation of the liquid crystal in region 318 is disturbed. This change has a gradient, and the diffraction efficiency gradually changes in the in-plane direction. Note that, unlike the change in region Ad described above, these changes are very gradual with respect to the wavelength of light, and therefore do not cancel out the diffraction phenomenon due to the distribution of optic axes formed in the optically anisotropic layer. The measure of gradual or sudden change varies depending on the wavelength of light used, but in this specification, the change is considered to be "gradual" when the line segment length (the width of the area in the direction of change) of the changing areas A, B, and D is 50 times or more the thickness T of the optically anisotropic layer.

[0173] 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.

[0174] An example of how to achieve this is described with reference to FIG. 8 . 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.

[0175] 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.

[0176] 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.

[0177] [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 is in a non-oriented state, 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.

[0178] 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.

[0179] 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 ２ The ultraviolet irradiation treatment is preferably carried out in an atmosphere with a low oxygen concentration, and more preferably in a nitrogen atmosphere.

[0180] Here, examples of methods for forming the region Ad where the liquid crystal orientation pattern changes include, as described above, a method in which the orientation pattern of the orientation film formed before step 1 is changed in advance from the orientation pattern of region A at a position corresponding to region Ad, and then an optically anisotropic layer is formed, or a method in which, in step 2, when exposing a coating film of the liquid crystal composition through a photomask, the exposure conditions, heating conditions, or both are controlled.

[0181] More specifically, for example, in step 2, when exposing the coating film of the liquid crystal composition through a photomask, the boundary between the area exposed by the photomask and the area shielded by the photomask can be blurred by increasing the distance between the photomask and the coating film, or by using non-parallel light for exposure, thereby forming region Ad.

[0182] Alternatively, for example, the region Ad can be formed by shifting the region where the alignment pattern of the alignment film is formed from the region exposed by the photomask.

[0183] Alternatively, for example, during exposure, one of the surfaces of the coating film or the substrate can be brought into contact with a contact-type temperature control device such as a cooling stage or a hot stage to control the temperature distribution of the coating film, thereby generating two regions with different orientation states, and then forming region Ad as a transition region between them. That is, region Ad can be formed by providing a region where a temperature gradient occurs in the film during exposure.

[0184] [Other steps] As mentioned above, the optically anisotropic layer of the present invention can also be formed into a laminate by laminating a plurality of optically anisotropic layers.Lamination methods include a method of directly coating a liquid crystal composition on a first optically anisotropic layer to form a second optically anisotropic layer, a method of coating an alignment film on the first optically anisotropic layer and then performing alignment treatment, and then coating and forming a liquid crystal composition, and a method of laminating an optically anisotropic layer provided on another substrate, etc., and the grating pitch (rotation period), grating angle, helical pitch, helical pitch change in thickness direction, tilt angle, tilt angle change in thickness direction, Δn change in thickness direction, size of the diffraction region, shape of the diffraction region, physical film thickness, optical thickness, and reflectance for each wavelength of the diffraction region of each optically anisotropic layer can be arbitrarily adjusted. In addition, in one diffraction region, it is possible to change 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 for each wavelength, and the direction and inclination of the change can also be adjusted as desired. Furthermore, diffraction regions with the above parameters adjusted can be combined as desired.

[0185] In the optically anisotropic layer of the present invention, preferably, in the aforementioned region A, or if region A and region B are present, the helical pitch length of the cholesteric liquid crystal layer varies within at least one of the aforementioned regions A and B. It is more preferable that 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 FIG. 10, by designing the helical pitch so that 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. Furthermore, in the present invention, multiple units can be formed within a single substrate, with 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 continuously rotates along at least one direction in the plane, and a region without a liquid crystal orientation pattern. Forming multiple units within a single substrate can improve productivity not only in the process of forming the optically anisotropic layer of the present invention, but also in downstream processes.

[0186] <Laminate> The laminate of the present invention is a laminate comprising two or more of the optically anisotropic layers described above. FIG. 11 is a conceptual diagram illustrating an example of the laminate of the present invention. The laminate 500 shown in FIG. 11 has a first optically anisotropic layer 400a and a second optically anisotropic layer 400b. The first optically anisotropic layer 400a has 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 has 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 described above.

[0187] In Figure 11, 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 not having a liquid crystal orientation pattern of the first optically anisotropic layer 400a and non-diffraction region 420b not having a 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.

[0188] 11, the laminate is configured to have two optically anisotropic layers stacked, but is not limited to this and may have a configuration of 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 in positions where the regions A of each optically anisotropic layer overlap, the regions B of each optically anisotropic layer overlap, and the non-diffraction regions of each optically anisotropic layer overlap.

[0189] 6 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.

[0190] As will be described later, when a light guide element in which the laminate 500 is combined with a light guide plate is used in a head-mounted display or the like, if the head-mounted display displays color images, the light guide element needs to guide light of each wavelength, for example, RGB. Therefore, it is preferable to use a configuration in which optically anisotropic layers having regions A and B (and further region C) that reflect and diffract light of these wavelengths are laminated. For example, a configuration can be used in which regions A and B of the first optically anisotropic layer are liquid crystal diffraction elements having a selective diffraction wavelength in the red wavelength range, and regions A and B of the second optically anisotropic layer are liquid crystal diffraction elements having a selective diffraction wavelength in the green wavelength range.

[0191] [Adhesive Layer (Pressure-Sensitive Adhesive Layer), Adhesive] The laminate and the light guide element may include an adhesive layer for bonding the optically anisotropic layers together and / or the optically anisotropic layer to the light guide plate. In this specification, the term "adhesion" is used to include the concept of "sticking." Examples of such adhesives include water-soluble adhesives, UV-curable adhesives, emulsion adhesives, latex adhesives, mastic adhesives, multilayer adhesives, paste-like adhesives, foam adhesives, supported film adhesives, thermoplastic adhesives, hot-melt adhesives, heat-setting adhesives, heat-activated adhesives, heat-seal adhesives, heat-curable adhesives, contact adhesives, pressure-sensitive adhesives (i.e., pressure-sensitive adhesives), polymerization adhesives, solvent-based adhesives, solvent-activated adhesives, and ceramic adhesives. Specific examples include an aqueous solution of a boron compound, a curable adhesive of an epoxy compound that does not contain an aromatic ring in the molecule, as disclosed in JP 2004-245925 A, an active energy ray-curable adhesive described in JP 2008-174667 A, which contains as essential components a photopolymerization initiator having a molar absorption coefficient of 400 or more at a wavelength of 360 to 450 nm and an ultraviolet-curable compound, and an active energy ray-curable adhesive described in JP 2008-174667 A, which contains, per 100 parts by mass of the total amount of (meth)acrylic compounds, (a) a (meth)acrylic compound having two or more (meth)acryloyl groups in the molecule, (b) a (meth)acrylic compound having a hydroxyl group in the molecule and only one polymerizable double bond, and (c) a phenol ethylene oxide-modified acrylate or nonylphenol ethylene oxide-modified acrylate. Various adhesives can be used alone or in combination as needed.

[0192] In laminates and light guide elements, from the viewpoint of reducing unnecessary reflection, it is preferable that the difference in refractive index between the adhesive layer and adjacent layers be small. 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 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 can be used. Furthermore, when adjacent layers have in-plane refractive index anisotropy, the difference in refractive index between the 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 imparting a refractive index distribution in the thickness direction include providing multiple adhesive layers, mixing the interfaces between multiple adhesive layers, and controlling the uneven distribution of materials within the adhesive layers to impart a refractive index distribution.

[0193] The adhesive layer can be provided on one or both of the members to be bonded by any method such as coating, vapor deposition, or transfer. From the viewpoint of increasing the adhesive strength, post-treatment 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 20 μm or less, more preferably 0.1 μm or less, and even more preferably 0.01 μm or less. Methods for forming an adhesive layer of 0.1 μm or less include silicon oxide (SiO x One method is to vapor-deposit a ceramic adhesive such as a ceramic adhesive layer onto the bonding surface. The bonding surfaces of the bonding members 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.

[0194] <Method for Producing Laminate> The method for producing the laminate of the present invention can be carried out by further carrying out a step of laminating at least two or more optically anisotropic layers produced by the above-mentioned method for producing an optically anisotropic layer.

[0195] The lamination step may involve bonding the two layers via the adhesive layer or pressure-sensitive adhesive layer described above, or may involve subjecting the surface of the resulting optically anisotropic layer to an adhesion treatment, followed by heating, pressurizing, irradiating with electromagnetic waves, irradiating with light, or the like, while the two layers are in direct contact with each other. For example, when laminating via an adhesive layer or pressure-sensitive adhesive layer, it is preferable to carry out a step of providing an adhesive or pressure-sensitive adhesive, or a precursor thereof, on one or both of the two layers, and a step of laminating the other layer and then heating, pressurizing, irradiating with electromagnetic waves, or irradiating with light to develop the adhesive strength of the adhesive or pressure-sensitive adhesive layer. These steps can be carried out using known methods.

[0196] When two optically anisotropic layers are provided on a support via an alignment film, or when the layers are supported on a temporary support, a step of peeling and removing at least one of the supports or temporary supports from the laminate may be added after the step of developing the adhesive strength of the adhesive layer or pressure-sensitive adhesive layer. In this case, in order to suppress the application of stress to the optically anisotropic layer or laminate due to peeling, the peel strength of the support or temporary support to be peeled from the laminate is preferably 10 to 1,000 mN / 10 mm. This range prevents poor adhesion during the manufacturing process of the optically anisotropic layer and suppresses changes in the optical properties of the optically anisotropic layer or laminate due to peel stress. Furthermore, the peel angle during peeling is preferably in the range of 45° to 90°. The peel speed is preferably in the range of 10 mm to 300 mm / min. By applying at least one of these conditions, changes in the optical properties of the optically anisotropic layer or laminate due to peel stress can be suppressed.

[0197] (Other Treatments) A step of providing a mark of any shape may be added as necessary for the purpose of accurately installing the optically anisotropic layer (or laminate) on various devices (e.g., a light guide plate), improving the accuracy of the axis and cutting position during cutting, etc. The type and shape of the mark can be selected as desired, and methods that can be selected include physically providing the mark using a laser or inkjet method, partially changing the alignment state of the liquid crystal, and providing a partially bleached or dyed region.

[0198] Furthermore, to protect the optically anisotropic layer, a protective layer (such as a gas barrier layer, a moisture-blocking layer, an ultraviolet absorbing layer, a scratch-resistant layer, or a transparent colored layer) can be provided as needed. The protective layer can be formed directly on the optically anisotropic layer, or it can be provided via another optical film such as a pressure-sensitive adhesive layer. An antireflection layer (such as a low-reflection (LR) layer, an anti-reflection (AR) layer, or a moth-eye layer) can be provided to reduce the surface reflectance. Various protective layers can be appropriately selected from known materials. When a gas barrier layer is provided, polyvinyl alcohol, glass, or the like is preferred. Polyvinyl alcohol can also function as a polarizer. The ultraviolet absorbing layer is a layer containing an ultraviolet absorber. The ultraviolet absorber preferably has excellent absorption ability for ultraviolet light with a wavelength of 370 nm or less and, from the viewpoint of good display performance, has little absorption of visible light with a wavelength of 400 nm or more. Only one ultraviolet absorber can be used, or two or more ultraviolet absorbers can be used in combination. Examples of such ultraviolet absorbers include those described in Japanese Patent Application Laid-Open No. 2001-072782 and Japanese Patent Application Laid-Open No. 2002-543265. Specific examples of ultraviolet absorbers include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylic acid ester-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, and nickel complex salt-based compounds. The transparent colored layer is a layer that absorbs or reflects at least a portion of visible light. By combining a transparent colored layer with an optically anisotropic layer, the external color of an optical element including an optically anisotropic layer can be adjusted. For example, if the optically anisotropic layer is colored, the color can be adjusted to a neutral color by combining a transparent colored layer.

[0199] These other layers may be provided inside the laminate, or may be provided on the outer surface of the laminate after the laminate is formed.

[0200] <Light Guide Element> A light guide element using the optically anisotropic layer of the present invention has either the optically anisotropic layer or the laminate described above, and a light guide plate.

[0201] The light guide plate referred to here refers to a component that guides light propagating within a layer by total internal reflection on the surface. Known materials can be used, such as glass and resin. Generally, the higher the refractive index of the light guide plate, the higher the internal total reflectance and the wider the internal total reflection angle, which has the advantage of enabling a large FOV when used in head-mounted displays such as AR glasses or sensor elements. Therefore, it is particularly preferable to use quartz glass, alkali-free glass, or high refractive index glass.

[0202] The thickness of the light guide plate is not particularly limited, but since it is thin from the viewpoint of weight and a certain thickness or more is required in order to limit the light guide mode, it is preferably 30 to 5000 μm, more preferably 50 to 3000 μm, and even more preferably 100 to 2000 μm. The refractive index of the light guide plate is preferably in the range of 1.7 to 2.5, and more preferably in the range of 1.8 to 2.2.

[0203] <Method for Manufacturing Light-Guiding Element> The method for manufacturing a light-guiding element of the present invention can be achieved by further performing a step of laminating the optically anisotropic layer (or laminate) obtained by the above-mentioned method on a light-guiding plate. The laminating step may involve adhering the optically anisotropic layer (or laminate) to the light-guiding plate via the above-mentioned adhesive layer or pressure-sensitive adhesive layer. Alternatively, the laminating step may involve subjecting the surfaces of either or both of the optically anisotropic layer (or laminate) and the light-guiding plate to an adhesion treatment, followed by heating, pressurizing, irradiating with electromagnetic waves, irradiating with light, or the like while they are in direct contact with each other. For example, when laminating via an adhesive layer or pressure-sensitive adhesive layer, it is preferable to perform a step of providing an adhesive, pressure-sensitive adhesive, or a precursor thereof on one or both of these layers, and a step of laminating the other layer and then developing the adhesive strength of the adhesive layer or pressure-sensitive adhesive layer by heating, pressurizing, irradiating with electromagnetic waves, or irradiating with light. These steps can be performed using known methods.

[0204] In another preferred embodiment, the above-mentioned method for producing an optically anisotropic layer (or laminate) may be carried out using a light guide plate as a support when producing the optically anisotropic layer (or laminate). In this case, the optically anisotropic layer and the light guide plate can be bonded without an adhesive layer or pressure-sensitive adhesive layer, which is preferable in that the process can be simplified and an optically excellent light guide plate can be produced.

[0205] In one preferred embodiment, a light guide element can be obtained by laminating an optically anisotropic layer (or laminate) on a light guide plate that has been cut or shaped in advance to a shape suitable for installation in a device, and, if necessary, adjusting the shape of the optically anisotropic layer (or laminate) to match the light guide plate before or after the lamination step. In this case, the optically anisotropic layer and the light guide plate can be laminated while being precisely aligned with each other using alignment means such as marking.

[0206] In another preferred embodiment, a light guide plate can be obtained by, in this order, preparing an original light guide plate before cutting it into a shape suitable for installation in a device, laminating an original sheet of optically anisotropic layer (or laminate) manufactured by the above-described manufacturing method on this original light guide plate, and cutting the resulting laminate of the original light guide plate and original sheet of optically anisotropic layer (or laminate) all at once into a shape suitable for installation in a device. This embodiment is particularly preferred in that it does not require alignment of the optically anisotropic layer (or laminate) with the shape of the light guide plate, and cutting can be performed in the cutting step according to alignment means such as markings applied to the optically anisotropic layer (or laminate), thereby producing a light guide plate with high positional accuracy of the optically anisotropic layer (region A, etc.).

[0207] (Cutting of Light Guide Plate) There are no limitations on the method for cutting the light guide plate, and various known methods can be used, such as a method of physically cutting using a blade such as a Thomson blade, or a method of cutting by irradiating a laser. When using a light guide plate made of an inorganic material such as glass, laser cutting is preferred. When using a laser, it is preferable to select the pulse width (nanoseconds, picoseconds, femtoseconds) and wavelength taking into consideration the cutting ability, damage to the material, etc. Furthermore, after cutting, the end faces may be polished. From the viewpoint of improving the processability during cutting and suppressing dust generation, cutting can also be performed with a peelable protective film attached.

[0208] Furthermore, when cutting the light guide plate after laminating the original sheet of the optically anisotropic layer (or laminate) and the original light guide plate, a cutting line may be set using a positioning means such as marking, or the cutting position may be arbitrarily determined by cutting while observing the liquid crystal orientation pattern, for example, as disclosed in JP-A-2004-141889. In this case, the liquid crystal orientation pattern may be easily observed through a polarizing plate, a retardation film, or the like.

[0209] To prevent light leakage from the edge of the light guide plate, the edge may be blackened or provided with a light-absorbing layer. In addition, to prevent cuts at the edge of the light guide plate and ensure the safety of users, it is preferable that the corners of the light guide plate are chamfered.

[0210] <Head-Mounted Display> Fig. 10 conceptually shows an example of a first embodiment of a head-mounted display of the present invention having a light-guiding element of the present invention. A head-mounted display 50 shown in Fig. 10 has a display (image display device) 40 and a light-guiding element 45.

[0211] The light guide element 45 is the light guide element of the present invention described above, and includes the optically anisotropic layer 400 of the present invention and a light guide plate 144. As described above, the light guide element of the present invention may be configured to include a laminate of the present invention having multiple optically anisotropic layers and a light guide plate. In other words, the light guide element of the present invention may include multiple optically anisotropic layers. In the example shown in FIG. 10 , 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. 10 , region A 45a of the optically anisotropic layer 400 is disposed on the surface (main surface) of one end side 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 side 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.

[0212] 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.

[0213] In the example of FIG. 10 , the display 40 is disposed facing one end of the light guide plate 144, facing the surface opposite to the surface on which the optically anisotropic layer 400 is disposed. The surface of one end of the light guide plate 144 opposite to the surface on which the optically anisotropic layer 400 is disposed is the observation position for the user U. 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. There are no limitations on the display 40, and various known displays used in head-mounted displays 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.

[0214] In the head-mounted display 50 configured as described above, light displayed by the display 40 enters the light guide plate 144 from one end of the light guide plate 144, on the surface opposite to the surface on which the optically anisotropic layer 400 is disposed, as indicated by the arrow. The light that enters the light guide plate 144 is reflected by the region A45a of the optically anisotropic layer 400. At this time, due to the diffraction effect of the 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. 10, the light enters the 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.

[0215] 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, and therefore the angle of the light's traveling direction with respect to the surface of the light guide plate 144 is small. As a result, 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 diffraction effect of 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 specular reflection direction. In the example shown in FIG. 10 , 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.

[0216] 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 head-mounted display 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.

[0217] 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 widening the viewing zone (exit pupil expansion). Specifically, in Fig. 10, light I propagating through the light guide plate 144 is repeatedly reflected on both surfaces (interfaces) of the light guide plate 144 before reaching a position in region B45c of the optically anisotropic layer 400. 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.

[0218] 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).

[0219] 10, 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 other words, the optically anisotropic layer (its diffraction region on the incident side) may be configured to be disposed on the surface of the light guide plate 144 on the display 40 side.

[0220] The optically anisotropic layer of the present invention can be used for various applications that reflect (diffract) or transmit (diffract) light at angles other than specular reflection, such as an optical path changing element in an optical device, a light concentrating element, a light diffusing element in a predetermined direction, a diffraction element, etc.

[0221] In the above examples, the optically anisotropic layer (diffraction region) of the present invention is used as an optically anisotropic layer that reflects or transmits visible light, but the present invention is not limited thereto, and various configurations can be used. For example, the optically anisotropic layer (diffraction region) of the present invention may be configured to reflect or transmit infrared or ultraviolet light, or may be configured to reflect or transmit only light other than visible light. In addition, the optically anisotropic layer of the present invention can be used in combination with other components. For example, it can be sandwiched between two sheets of glass, or it can be used in combination with a low-reflection layer, an ultraviolet-absorbing layer, a polarizing plate, a lens component, etc.

[0222] The optically anisotropic layer, laminate, light-guiding element, and head-mounted display 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.

[0223] 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.

[0224] 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.

[0225] 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 --------------------------------------------------

[0226] -Material for photo alignment-

[0227]

[0228] (Exposure of Alignment Film) Using the exposure device shown in Figure 9, 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.

[0229] (Formation of Optically Anisotropic Layer) The following composition LC-1 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0230] 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

[0231] Rod-shaped liquid crystal compound L-1

[0232]

[0233] Rod-shaped liquid crystal compound L-2

[0234]

[0235] Chiral agent Ch-1

[0236]

[0237] Leveling agent T-1

[0238]

[0239] 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 1 cm above the composition layer, and ultraviolet light having a wavelength of 365 nm was irradiated at 20 mJ / cm from a 365 nm LED UV exposure device through the mask MK-1 at 40°C under a nitrogen atmosphere. 2 The composition layer was exposed to light at an exposure dose of 300 mJ / cm using a 365 nm LED UV exposure machine at 200°C under a nitrogen atmosphere. The exposure dose of ultraviolet light irradiated onto the composition layer through the mask MK-1 and the positional relationship of each region of the alignment film were as shown in Figure 12. Subsequently, after a heat treatment at 200°C for 1 minute, the composition layer was exposed to ultraviolet light at a wavelength of 365 nm at 300 mJ / cm using a 365 nm LED UV exposure machine at 200°C under a nitrogen atmosphere. 2 The coating film was irradiated with light at an irradiation dose of 1000 .mu.m to fix the alignment of the liquid crystal compound, thereby forming an optically anisotropic layer having a thickness of 2 .mu.m.

[0240] In the optically anisotropic layer, the irradiation amount 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 12, the width of the region A was 5 mm, and the width of the region B was 30 mm.

[0241] The optically anisotropic layer was cut at the position where the irradiation dose changed, and the cross section was observed under SEM. A striped pattern corresponding to the distribution of the optical axes of the liquid crystal material was confirmed, revealing a region Ad where the pattern changed rapidly at the contact point between region A and region B and region C. The width Dd of region Ad and the thickness T (2 μm) of the optically anisotropic layer satisfied the relationship shown in formula (1). The width of region Ad was approximately 5 μm at all positions.

[0242] The fabricated optically anisotropic layer was placed on a light guide plate to fabricate a light guide element. The light guide plate was made of commercially available optical-grade high-refractive index glass (refractive index 1.8, optically polished) cut to fit the shape of the smart glasses to be mounted.

[0243] [Evaluation] (Visibility of stray light) Smart glasses (Vuzix Blade 2) from Vuzix were disassembled, and the light guide element of the present invention was installed in place of the light guide plate of the product. The light emission brightness of the display element was set to maximum, and stray light from the light guide plate was visually confirmed with the naked eye from the side opposite to the wearer while the glasses were being worn. No stray light was observed, and the wearer's facial expression could be seen without any problems.

[0244] Comparative Example 1 An optically anisotropic layer and a light guide element of Comparative Example 1 were produced in the same manner as in Example 1, except that, when exposing the composition layer, a prism and a microlens sheet were attached to the light exit section of the UV exposure machine used in Example 1 to make the emitted light parallel, and the distance between the mask MK-1 and the coating film was set to 1 mm.

[0245] When the cross section was observed with an SEM in the same manner as in Example 1, no region where the stripe pattern corresponding to the distribution of the optical axes of the liquid crystal material changed at the contact points of region A and region B with region C could be confirmed, i.e., Dd<T. Similarly, when the light-guiding element of Comparative Example 1 was incorporated into smart glasses and the visibility of stray light was evaluated, stray light was visible in some peripheral parts of region A and region B, which interfered with the visibility of the wearer's facial expression.

[0246] 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.

[0247] 1, 3 to 4 Optically anisotropic layer 2a Region A 2b Region B 2c Non-diffraction region (region C) 2d Region Ad 2e Region D 10 Liquid crystal film 18 Optically anisotropic layer 20 Support 24 Alignment film 30 Liquid crystal compound 30A Optical axis 40 Display (image display device) 45 Light guide element 45a Region A 45b Non-diffraction region 45c Region B 50 Head-mounted display 60 Exposure device 62 Laser 64 Light source 68 Beam splitter 70A, 70B Mirror 72A, 72B 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 Optically anisotropic layer 400a First optically anisotropic layer 400b Second optically anisotropic layer 410a, 420a Region A 410b, 420b Non-diffractive region 410c, 420c Region B 500 Laminate M Laser light MA, MB Light ray P O Linear polarized light P R Right circular polarization P L Left circularly polarized light α Crossing angle I0 to I3 Light propagating within the light guide plate P1 to P4 Position R1 to R4 Light

Claims

1. An optically anisotropic layer formed using a composition containing a liquid crystal compound, comprising at least a region A having 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, and a region C having no liquid crystal orientation pattern, wherein the region A includes a region Ad in which the liquid crystal orientation pattern changes in at least a part of the edge portion adjacent to the region C, and wherein the width Dd of the region Ad and the thickness T of the optically anisotropic layer have the relationship of the following formula (1): T < Dd < 25 × T (1) 2. A laminate comprising at least two optically anisotropic layers according to claim 1.

3. A light guide element comprising the optically anisotropic layer of claim 1 or the laminate of claim 2 on a light guide plate.

4. A head-mounted display comprising the light guide element of claim 3 and an image display element.

Images