Optical element and method for producing optical element

Abstract

To provide an optical element that has a high diffraction efficiency and can reduce haze, and a method for producing the optical element.SOLUTION: An optical element includes an alignment film and an optically anisotropic layer provided on the alignment film and containing anisotropic molecules. The alignment film includes first to N-th alignment treatment regions arranged in order from a central portion to an end portion of the alignment film in a plan view. The first to N-th alignment treatment regions respectively include first to N-th protrusions, which protrude toward the optically anisotropic layer and respectively extend in first to N-th directions. The first to (N-1)th directions are not parallel to one another. The N-th direction is parallel to the first direction. N is an integer of 3 or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to optical elements and methods for manufacturing optical elements. [Background technology]

[0002] In recent years, optical systems using optical elements such as Pancharatnam-Berry phase optical elements (PBOEs) have been proposed for display devices such as head-mounted displays. PBOEs include, for example, optically anisotropic layers formed using a liquid crystal composition containing liquid crystal molecules.

[0003] As a technology relating to optical elements, Patent Document 1 discloses a grating element in which a plurality of diffraction gratings are stacked on at least one resin sheet, and at least one of the stacked diffraction gratings is a polarizing diffraction grating made of uniaxial polymer liquid crystal, and at least one of the stacked diffraction gratings is a non-polarizing diffraction grating made of photocurable resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-112831 Summary of the Invention [Problem to be solved by the invention]

[0005] To achieve high diffraction efficiency, it is necessary to achieve an ideal molecular orientation in a PBOE. One method for fabricating a PBOE is mask exposure. When fabricating a PBOE using mask exposure, the alignment process is performed by exposing an alignment film on a support substrate multiple times using multiple masks. Misalignment of the masks can disrupt the molecular orientation, potentially resulting in a decrease in diffraction efficiency. Furthermore, orthogonal polarized ultraviolet (PUV) rays can be exposed to the same region of the alignment film, resulting in haze and reduced display quality.

[0006] The above-mentioned Patent Document 1 does not disclose an optical element that has high diffraction efficiency and can suppress haze.

[0007] The present invention has been made in consideration of the current situation, and aims to provide an optical element that has high diffraction efficiency and can suppress haze, and a method for manufacturing the optical element. [Means for solving the problem]

[0008] (1) One embodiment of the present invention is an optical element comprising an alignment film and an optically anisotropic layer provided on the alignment film and containing anisotropic molecules, wherein the alignment film has, in a planar view, a first alignment treatment region to an Nth alignment treatment region arranged in order from the center to the edge of the alignment film, and the first alignment treatment region to the Nth alignment treatment region each extend along a first direction to an Nth direction and have a plurality of first to Nth convex portions protruding toward the optically anisotropic layer, the first direction to the (N-1)th direction are not parallel to each other, and the Nth direction is parallel to the first direction, and N is an integer of 3 or greater.

[0009] (2) Furthermore, in addition to the configuration of (1), one embodiment of the present invention is an optical element in which, when viewed in a plane, when the same direction as the first direction is taken as a reference direction, the angle of the Nth direction with respect to the reference direction is within a range of 180°±3°, and the angles of the second direction to the (N-1)th direction with respect to the reference direction exceed the angle of the first direction with respect to the reference direction and gradually increase in this order within a range less than the angle of the Nth direction with respect to the reference direction.

[0010] (3) Furthermore, in addition to the configuration of (1) or (2), an embodiment of the present invention is an optical element in which, when viewed in a plane, the same direction as the first direction is taken as a reference direction, the angle of the ith direction with respect to the reference direction satisfies the following (Formula A):

[0011]

number

[0012] (4) Furthermore, in addition to the configuration of (1), (2), or (3), one embodiment of the present invention is an optical element that satisfies the following formula B1, where P is the sum of the lengths of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center of the alignment film to the edge, and Q=N-1 is the number of divisions.

[0013]

number

[0014] (5) Furthermore, in addition to the configuration of (1), (2), (3), or (4), an embodiment of the present invention is an optical element that satisfies the following formula B2, where P is the sum of the lengths of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center of the alignment film to the edge, and Q=N-1 is the number of divisions.

[0015]

number

[0016] (6) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), or (5), the height H of the first to Nth convex portions is less than the phase difference Δnd of the optically anisotropic layer.

[0017] (7) Furthermore, in addition to the configuration of (1), (2), (3), (4), (5) or (6), an embodiment of the present invention is an optical element in which, when the total length of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center to the edge of the alignment film is defined as pitch P and the number of divisions Q=N-1, convex pitch W, which is the pitch of the first convex portion to the Nth convex portion, satisfies the following formula C:

[0018]

number

[0019] (8) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6) or (7), the anisotropic molecules are elongated molecules, and in each of the first alignment treatment region to the Nth alignment treatment region, the anisotropic molecules are oriented so that the long axes of the anisotropic molecules are aligned along the first direction to the Nth direction.

[0020] (9) Furthermore, one embodiment of the present invention is an optical element having the configuration of (1), (2), (3), (4), (5), (6), (7), or (8), wherein N is 4 or greater.

[0021] (10) Another embodiment of the present invention provides a method for manufacturing an optical element, comprising: a transfer step of transferring the relief structure of a mold onto a resin layer to form an alignment film; and a liquid crystal layer formation step of arranging and hardening a polymerizable liquid crystal material on the surface of the alignment film on the side to which the shape of the mold has been transferred, wherein the mold has first to Nth regions arranged in order from a portion corresponding to the center of the alignment film toward a portion corresponding to an end thereof, and the first to Nth regions each have a plurality of first to Nth wall-shaped portions extending along a first to Nth direction, the first to (N-1)th directions are not parallel to each other, and the Nth direction is parallel to the first direction, and N is an integer of 3 or greater. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide an optical element that has high diffraction efficiency and can suppress haze, and a method for manufacturing the optical element. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a plan view schematically illustrating an optical element according to a first embodiment. [Figure 2] 2 is an enlarged perspective view schematically illustrating an alignment film included in the optical element of Embodiment 1. FIG. [Figure 3] 1A and 1B are cross-sectional views illustrating the fabrication of a PBOE by mask exposure. [Figure 4] 1A to 1C are schematic diagrams illustrating an example of a method for producing the optical element of the first embodiment. [Figure 5] FIG. 2 is a plan view schematically illustrating an example of a mold having projections and recesses used in producing the optical element of the first embodiment. [Figure 6] 6 is a scanning electron microscope photograph of a cross section taken along line V1-V2 in FIG. 5. [Figure 7] 2 is a polarizing microscope photograph showing an example of the optical element of the first embodiment. [Figure 8] 8 is a cross-sectional view of the optical element of the first embodiment taken along the line X1-X2 in FIG. 7. [Figure 9]2 is a polarizing microscope photograph showing an example of the optical element of the first embodiment. [Figure 10] 10 is a cross-sectional view of the optical element of the first embodiment taken along the line Y1-Y2 in FIG. 9. FIG. [Figure 11] 2 is a polarizing microscope photograph showing an example of the optical element of the first embodiment. [Figure 12] 2 is a perspective view schematically illustrating an example of the uneven shape of an alignment film included in the optical element of Embodiment 1. FIG. [Figure 13] 2 is a perspective view schematically illustrating an example of the uneven shape of an alignment film included in the optical element of Embodiment 1. FIG. [Figure 14] 10 is a scanning electron microscope photograph of a mold used in producing the optical element of Comparative Example 2. [Figure 15] 3 is a polarizing microscope photograph of the optical element of Example 1. [Figure 16] FIG. 3 is a diagram showing the evaluation results of the optical element of Example 1. [Figure 17] FIG. 10 is a diagram showing the evaluation results of the optical element of Example 2. [Figure 18] FIG. 10 is a diagram showing the evaluation results of the optical element of Example 3. [Figure 19] FIG. 10 is a diagram showing the evaluation results of the optical element of Example 4. [Figure 20] FIG. 10 is a diagram showing the molecular orientation used when calculating the diffraction efficiency of the optical element of Reference Example 1. [Figure 21] FIG. 1 is a schematic diagram showing a method for measuring diffraction efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments, and appropriate design changes can be made within the scope of the configuration of the present invention. In the following description, the same reference numerals will be used in different drawings as appropriate for the same parts or parts having similar functions, and repeated explanations will be omitted as appropriate. Each aspect of the present invention may be combined as appropriate within the scope of the gist of the present invention.

[0025] (Embodiment 1) Fig. 1 is a schematic plan view of an optical element of embodiment 1. Fig. 2 is an enlarged perspective schematic view of an alignment film included in the optical element of embodiment 1. The optical element 10 of this embodiment shown in Figs. 1 and 2 includes an alignment film 200 and an optically anisotropic layer 300 provided on the alignment film 200 and containing anisotropic molecules 310. The alignment film 200 includes a first alignment treatment region 200R1 to an Nth alignment treatment region 200R2, which are arranged in order from the center of the alignment film 200 toward the edge thereof in plan view. N The first alignment treatment region 200R1 to the Nth alignment treatment region 200R N are the first direction 200D1 to the Nth direction 200D N The first convex portion 200A1 to the Nth convex portion 200A1 are provided extending along the N The first direction 200D1 to the (N-1)th direction 200D N-1 are not parallel to each other and are in the Nth direction 200D N is parallel to the first direction 200D1, and N is an integer equal to or greater than 3. By adopting such an embodiment, an optical element (specifically, a Pancharatnam-Berry phase optical element (PBOE)) having high diffraction efficiency and capable of suppressing haze can be realized.

[0026] Here, PBOE is an optical element that functions based on a periodic in-plane molecular orientation pattern. To fabricate a practical optical element, the molecules must be rotated 180° at a period on the order of μm. Furthermore, to fabricate a PBOE with high diffraction efficiency, the molecular orientation must be ideally continuous. Therefore, when fabricating a PBOE using mask exposure to achieve discrete molecular orientation, as shown in Figure 3, increasing the number of masks is necessary to approach the ideal orientation. However, this method presents problems such as alignment disturbance due to mask alignment accuracy, degradation of display quality due to haze generation, and poor productivity due to the increased number of processes. Figure 3 is a cross-sectional schematic diagram illustrating the fabrication of a PBOE using mask exposure.

[0027] On the other hand, in this embodiment, molecular orientation patterning of the anisotropic molecules 310 is performed using the concave-convex pattern of the alignment film 200, thereby enabling highly reproducible manufacture of a PBOE without the need for highly accurate mask alignment. In this embodiment, as shown in Fig. 4, the anisotropic molecules 310 (e.g., reactive mesogens (RM)) are aligned using a concave-convex shape 200U provided on the surface of the alignment film 200 on the side of the optically anisotropic layer 300 by nanoimprinting or the like, to manufacture the optical element 10, which is a diffraction element. Fig. 4 is a schematic diagram illustrating an example of a method for manufacturing the optical element of embodiment 1.

[0028] Specifically, a mold 400 with a texture such as a wire grid shown in FIGS. 4 to 6 is pressed against a substrate (alignment film 200) to transfer the texture to the substrate, and a composition containing an RM is applied to the substrate. This allows the RM to be aligned according to the texture of the substrate. This method, in this embodiment, eliminates the deterioration of diffraction efficiency due to alignment accuracy, enabling stable production of optical elements 10 with high diffraction efficiency. Furthermore, since orthogonal polarized ultraviolet light is not applied to the same region of the alignment film, haze can be reduced. Furthermore, since multiple exposures using multiple masks are not required, productivity can be improved. FIG. 5 is a plan view schematic diagram showing an example of a mold with a texture used to fabricate the optical element of embodiment 1. FIG. 6 is a scanning electron microscope photograph of a cross section taken along line V1-V2 in FIG. 5.

[0029] In this way, in this embodiment, a concave-convex pattern of wavelength order is created on a substrate, and the RM is continuously aligned by the interaction between the groove structure and the RM to fabricate a PBOE. In this case, there is no risk of disturbing the molecular alignment, as occurs with mask exposure, and therefore it is possible to fabricate a PBOE that is easy to produce and has stable quality.

[0030] The above-mentioned Patent Document 1 discloses a technique for producing a diffraction grating by aligning a polymerizable liquid crystal with unevenness, but does not disclose that the diffraction efficiency can be improved by continuously aligning the polymerizable liquid crystal.

[0031] The optical element 10 of this embodiment and a method for manufacturing the same will now be described in detail.

[0032] 1, the optical element 10 of this embodiment includes, in order, a support substrate 100, an alignment film 200, and an optically anisotropic layer 300. The optical element 10 of this embodiment is a Pancharatnam Berry phase optical element. The Pancharatnam Berry phase optical element has the function of focusing and diverging circularly polarized light.

[0033] Examples of the support substrate 100 include glass substrates and plastic substrates. Examples of materials for glass substrates include float glass, soda glass, etc. Examples of materials for plastic substrates include plastics such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, and alicyclic polyolefin.

[0034] The alignment film 200 has a function of controlling the alignment of the anisotropic molecules 310 in the optically anisotropic layer 300. The alignment film 200 contains an alignment film polymer. The alignment film polymer may be a polymer (resin) commonly used in the field of liquid crystal panels, such as a polymer having polyimide in its main chain, a polymer having polyamic acid in its main chain, a polymer having poly(meth)acrylic acid in its main chain, a polymer having polyethylene in its main chain, a polymer having polystyrene in its main chain, a polymer having polyvinyl in its main chain, or a polymer having polysiloxane in its main chain.

[0035] The alignment film 200 is obtained, for example, by applying an alignment film material containing an alignment film polymer onto the support substrate 100 to form a resin layer, and then transferring the concave and convex shape of a mold onto the resin layer.

[0036] The alignment film 200 has, in plan view, a first alignment treatment region 200R1 to an N-th alignment treatment region 200R2, which are arranged in order from the center to the edge of the alignment film 200. NThe first alignment treatment region 200R1 to the Nth alignment treatment region 200R N are the first direction 200D1 to the Nth direction 200D N The first convex portion 200A1 to the Nth convex portion 200A1 are provided extending along the N That is, the i-th alignment treatment region 200R i is the i-th direction 200D i The i-th convex portion 200A extends along the i (where i is an integer between 1 and N). N-1 are not parallel to each other and are in the Nth direction 200D N is parallel to the first direction 200D1, and N is an integer equal to or greater than 3.

[0037] N is preferably an integer of 4 or greater, more preferably an integer of 8 or greater, and even more preferably an integer of 12 or greater. By adopting such an embodiment, higher diffraction efficiency can be achieved and haze can be further suppressed. N is, for example, preferably an integer of 90 or less, more preferably an integer of 45 or less, and even more preferably an integer of 30 or less. By adopting such an embodiment, productivity can be increased.

[0038] N is preferably an integer of 4 or more and 90 or less, more preferably an integer of 8 or more and 45 or less, and even more preferably an integer of 12 or more and 30 or less. By adopting such an embodiment, it is possible to improve productivity, realize higher diffraction efficiency, and further suppress haze.

[0039] As shown in FIG. 1, the first alignment treatment region 200R1 to the Nth alignment treatment region 200R N are preferably arranged concentrically from the center of the alignment film 200 to the edge.

[0040] 2, the alignment film 200 has a concave-convex shape 200U on the surface facing the optically anisotropic layer 300. The concave-convex shape 200U includes a plurality of i-th convex portions 200A. i (i represents an integer from 1 to N). That is, the concave-convex shape 200U is configured by a plurality of first convex portions 200A1 to a plurality of N-th convex portions 200A N The first protrusion 200A1 to the Nth protrusion 200A N is also simply referred to as the protrusion 200A.

[0041] First direction 200D1 to (N-1)th direction 200D N-1 are not parallel to each other and are in the Nth direction 200D N is parallel to the first direction 200D1. In this specification, two straight lines (including axes, directions, and orientations) being parallel means that the angle (absolute value) between them is within a range of 0±3°, preferably within a range of 0±1°, more preferably within a range of 0±0.5°, and particularly preferably 0° (completely parallel).

[0042] In a plan view, when the same direction as the first direction 200D1 is taken as the reference direction, the Nth direction 200D N The angles of the second direction 200D2 to the (N-1)th direction 200D with respect to the reference direction are within a range of 180°±3°. N-1 The angle of the Nth direction 200D with respect to the reference direction exceeds the angle of the first direction 200D1 with respect to the reference direction. N It is preferable that the angle gradually increases in this order within a range less than the angle with respect to the reference direction. By adopting such an embodiment, higher diffraction efficiency can be achieved. Note that the angle in this specification means the angle when the optical element is viewed in a plan view, with a clockwise angle from the reference direction (angle 0°) being a positive angle and a counterclockwise angle from the reference direction (angle 0°) being a negative angle. Counterclockwise and clockwise both refer to the rotation direction when the optical element is viewed from the observation surface side (front).

[0043] When the same direction as the first direction 200D1 is taken as the reference direction in a plan view, it is preferable that the optical element 10 satisfies the following (Formula A): By adopting such an embodiment, high diffraction efficiency can be more effectively achieved.

[0044]

number

[0045] In this way, the first direction 200D1 to the Nth direction 200D N are arranged discretely so as to rotate 180° in the plane. That is, the longitudinal directions of the convex portions 200A of the concave-convex shape 200U are arranged discretely so as to rotate 180° in the plane.

[0046] Fig. 7 is a polarizing microscope photograph showing an example of the optical element of embodiment 1. Fig. 8 is a cross-sectional schematic diagram of the optical element of embodiment 1 taken along line X1-X2 in Fig. 7. Fig. 9 is a polarizing microscope photograph showing an example of the optical element of embodiment 1. Fig. 10 is a cross-sectional schematic diagram of the optical element of embodiment 1 taken along line Y1-Y2 in Fig. 9. Fig. 11 is a polarizing microscope photograph showing an example of the optical element of embodiment 1.

[0047] The alignment film 200 of the optical element 10 shown in FIGS. 7 to 10 includes a first alignment treatment region 200R1 to an N-th alignment treatment region 200R N(Specifically, N=9). While the second, fourth, sixth, and eighth alignment treatment regions are omitted in FIGS. 8 and 10, the optical element 10 shown in FIGS. 7 to 10 has a second alignment treatment region between the first alignment treatment region 200R1 and the third alignment treatment region 200R3, a fourth alignment treatment region between the third alignment treatment region 200R3 and the fifth alignment treatment region 200R5, a sixth alignment treatment region between the fifth alignment treatment region 200R5 and the seventh alignment treatment region 200R7, and an eighth alignment treatment region between the seventh alignment treatment region 200R7 and the ninth alignment treatment region 200R9. FIGS. 7 and 8 show a case where the pitch P is 500 μm. FIGS. 9 and 10 show a case where the pitch P is 40 μm. The pitch P is the distance between the first alignment treatment region 200R1 to the Nth alignment treatment region 200R on a straight line extending from the center of the alignment film 200 to the edge. N The pitch P is the sum of the lengths of the 310-axis and 311-axis directions of the anisotropic molecules. Specifically, the pitch P is the spatial period in which the molecular axis of the RM rotates in the plane.

[0048] When the pitch P is 500 μm, the regulating force of the alignment film 200 having the concave-convex shape 200U is discrete, as shown in FIGS. 7 and 8, and the molecular orientation of the anisotropic molecules 310 is also discrete. On the other hand, when the pitch P is 40 μm, the regulating force of the alignment film 200 having the concave-convex shape 200U is discrete, as shown in FIGS. 9 and 10, but the molecular orientation of the anisotropic molecules 310 is continuous, which can further improve the diffraction efficiency. Thus, even if the concave-convex shape 200U has a discrete distribution of the alignment regulating force, by setting the division number Q to a certain number or more, the RM may be continuously oriented. This makes it possible to achieve a continuous, almost ideal molecular orientation that cannot be achieved by conventional mask exposure, and further improves the diffraction efficiency.

[0049] Here, the division number Q is the number of boundaries of the alignment treatment regions of the alignment film 200 within the pitch P, as shown in FIG. 11. That is, the division number Q = N - 1. In other words, the division number Q is the number of types of alignment regulating force directions when the uneven shape 200U of the alignment film 200 is discretely rotated by 180° in the plane. For example, as shown in FIGS. 7 to 10, if the alignment film 200 has first to ninth alignment treatment regions, the number of boundaries of the alignment treatment regions in the region where the alignment direction of the anisotropic molecules 310 changes by 180° is eight, and therefore the division number Q is eight.

[0050] The optical element 10 preferably satisfies the following formula B1, and more preferably satisfies the following formula B2. By adopting such an embodiment, the anisotropic molecules 310 contained in the optically anisotropic layer 300 can be continuously aligned, thereby effectively improving the diffraction efficiency.

[0051]

number

[0052]

number

[0053] 12 and 13 are perspective schematic views showing an example of the concave-convex shape of the alignment film included in the optical element of Embodiment 1. As shown in FIGS. i are longitudinal wall-like portions, and the i-th protrusions 200A i The longitudinal direction of the i ) In this manner, the unevenness 200U is provided on the surface of the alignment film 200 facing the optically anisotropic layer 300. The longitudinal direction of the convex portions 200A constituting the unevenness 200U (i.e., the longitudinal direction of the wall-like portions) corresponds to the direction of the alignment regulating force.

[0054] The concave-convex shape 200U shown in Fig. 12 has a concave-convex structure with long sides, such as a wire grid. The concave-convex shape 200U shown in Fig. 12 is obtained by arranging grooves with lengths of several μm to several cm in a uniform direction, such as a wire grid.

[0055] The uneven shape 200U shown in Fig. 13 has an uneven structure realized by aligning nanorods. The uneven shape 200U shown in Fig. 13 can be obtained by arranging a plurality of grooves on the order of nm, for example.

[0056] First protrusion 200A1 to Nth protrusion 200A N The height H of the first convex portion 200A1 to the Nth convex portion 200A is preferably less than the phase difference (Δn×d) of the optically anisotropic layer 300. By adopting such an embodiment, higher diffraction efficiency can be achieved and haze can be further suppressed. Note that Δn and d represent the birefringence and thickness of the optically anisotropic layer 300, respectively. N The height H of the first protrusion 200A1 to the Nth protrusion 200A N The first protrusion 200A1 to the Nth protrusion 200A N The height H can be measured, for example, by a non-contact surface roughness measuring device conforming to ISO 25178.

[0057] First protrusion 200A1 to Nth protrusion 200A N The convex pitch W preferably satisfies the following formula C. By adopting such an embodiment, higher diffraction efficiency can be achieved and haze can be further suppressed.

[0058]

number

[0059] As shown in Figures 12 and 13, the convex pitch W is the distance between convex portions in a short direction perpendicular to the longitudinal direction of the convex portions when viewed in a plane, and refers to the distance from one end of a convex portion in the short direction to the end of a convex portion adjacent to the convex portion in the short direction.

[0060] For example, a cured polymerizable liquid crystal material (also called "reactive mesogen") is preferably used as the optically anisotropic layer 300. In this case, at least one of the polymerized and unpolymerized polymerizable liquid crystal material corresponds to the anisotropic molecules 310. The polymerizable liquid crystal material is preferably a photopolymerizable liquid crystal material that is cured by irradiation with light.

[0061] The optically anisotropic layer 300 is formed, for example, by applying and curing a polymerizable liquid crystal material (reactive mesogen). The polymerizable liquid crystal material may be a liquid crystal polymer having a photoreactive group. Examples of the polymerizable liquid crystal material include polymers having side chains with a structure containing a substituent (mesogen group) such as a biphenyl group, a terphenyl group, a naphthalene group, a phenylbenzoate group, an azobenzene group, or a derivative thereof, and a photoreactive group such as a cinnamoyl group, a chalcone group, a cinnamylidene group, a β-(2-phenyl)acryloyl group, a cinnamic acid group, or a derivative thereof, and a main chain structure such as acrylate, methacrylate, maleimide, N-phenylmaleimide, or siloxane. Such polymers may be homopolymers consisting of a single repeating unit, or copolymers consisting of two or more repeating units with different side chain structures. Examples of such copolymers include alternating, random, and Kraft copolymers. Furthermore, in such a copolymer, the side chain of at least one repeating unit may be a side chain having a structure containing both a mesogenic group and a photoreactive group as described above, and the side chains of the other repeating units may not contain such a mesogenic group or photoreactive group.

[0062] The polymerizable liquid crystal material may contain additives such as a photopolymerization initiator, etc. The photopolymerization initiator is not particularly limited, and any conventionally known initiator may be used.

[0063] Examples of solvents used for applying the polymerizable liquid crystal material include toluene, ethylbenzene, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol methyl ether, dibutyl ether, acetone, methyl ethyl ketone, ethanol, propanol, cyclohexane, cyclopentanone, methylcyclohexane, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, methoxybutyl acetate, N-methylpyrrolidone, dimethylacetamide, etc. These can be used alone or in combination of two or more.

[0064] As shown in FIG. 1, the optically anisotropic layer 300 includes a first alignment treatment region 200R1 to an Nth alignment treatment region 200R2. N In the above, the first direction 200D1 to the Nth direction 200D N It is preferable that the anisotropic molecules 310 have a molecular orientation along this line. By adopting such an embodiment, the anisotropic molecules 310 can be arranged in a more continuous and periodic pattern in the plane, thereby achieving higher diffraction efficiency. Note that the molecular orientation refers to the molecular orientation on the alignment film side of the optically anisotropic layer.

[0065] As shown in FIG. 1, the anisotropic molecules 310 are elongated molecules, and are arranged in the first alignment treatment region 200R1 to the Nth alignment treatment region 200R N In each of the above, the anisotropic molecules 310 are arranged such that the major axes of the anisotropic molecules 310 are aligned in the first direction 200D1 to the Nth direction 200D. N By adopting such an embodiment, the anisotropic molecules 310 can be arranged in a more continuous and periodic pattern within the plane, thereby achieving higher diffraction efficiency.

[0066] Next, a method for manufacturing the optical element 10 of this embodiment will be described.

[0067] As shown in FIG. 4, the method for manufacturing the optical element 10 of this embodiment includes a transfer step of transferring the relief structure of a mold 400 onto a resin layer to form an alignment film 200, and a liquid crystal layer formation step of disposing and curing a polymerizable liquid crystal material on the surface of the alignment film 200 on the side where the shape of the mold 400 has been transferred. As shown in FIG. 5, the mold 400 has a first region 400R1 to an Nth region 400R2 that are arranged in order from a portion corresponding to the center of the alignment film 200 toward a portion corresponding to an end of the alignment film 200. N The first region 400R1 to the Nth region 400R N are the first direction 200D1 to the Nth direction 200D N The first wall-shaped portion 400A1 to the Nth wall-shaped portion 400A are provided extending along the N The first direction 200D1 to the (N-1)th direction 200D N-1 are not parallel to each other and are in the Nth direction 200D N is parallel to the first direction 200D1. N is an integer equal to or greater than 3. Note that the portion corresponding to the center of the alignment film 200 does not necessarily have to be the center of the mold 400. Also, the portion corresponding to the edge of the alignment film 200 does not necessarily have to be the edge of the mold 400.

[0068] The mold 400 has a first region 400R1 to an Nth region 400R N respectively represent the first alignment treatment region 200R1 to the Nth alignment treatment region 200R of the alignment film 200. N That is, the first region 400R1 to the Nth region 400R of the mold 400 N The uneven structures are respectively located in the first alignment treatment region 200R1 to the Nth alignment treatment region 200R of the alignment film 200. N For example, the relief structure of the first region 400R1 of the mold 400 is transferred to the first alignment treatment region 200R1 of the alignment film 200.

[0069] The method for manufacturing the optical element 10 of this embodiment may include a resin layer formation step, prior to the transfer step, in which an alignment film material containing an alignment film polymer is applied to the support substrate 100 to form a resin layer. In the resin layer formation step, a coating device such as a slit coater or spin coater can be suitably used to apply the alignment film material. After the alignment film material has been applied to a uniform thickness, it may be pre-baked, for example, at a temperature of about 70 to 100°C for 1 to 10 minutes.

[0070] The liquid crystal layer forming step is a step of disposing and curing a polymerizable liquid crystal material on the surface of the alignment film 200 on the side to which the shape of the mold 400 has been transferred. In the liquid crystal layer forming step, the polymerizable liquid crystal material is disposed on the alignment film 200 by, for example, coating. A coating device such as a slit coater or a spin coater can be suitably used for coating. The polymerizable liquid crystal material is cured using, for example, an exposure device that irradiates light (ultraviolet light) with a wavelength of 313 to 365 nm. [Example]

[0071] The effects of the present invention will be explained below with reference to examples, comparative examples and reference examples, but the present invention is not limited to these examples.

[0072] (Comparative Examples 1 and 2) The optical element of Comparative Example 1 was fabricated as follows: First, a photo-alignment film was applied to a glass substrate, and polarized ultraviolet light (polarized UV) was applied to the photo-alignment film at 75 mJ / cm 2 . 2 After the polarized UV irradiation, the film was left at 160°C for 20 minutes, and then RM was applied to the photo-alignment film at 1000 rpm. After the RM was applied, the film was left at 60°C for 60 seconds, and then 200 mJ / cm 2 The optical element of Comparative Example 1 was obtained by irradiating the film with unpolarized UV light.

[0073] Fig. 14 is a scanning electron microscope photograph of the mold used in producing the optical element of Comparative Example 2. The optical element of Comparative Example 2 was produced as follows. First, a mold (wire grid) having the concave-convex structure shown in Fig. 14 was transferred to a resin layer provided on a glass substrate to form an alignment film. RM was applied at 1000 rpm to the surface of the alignment film on the side where the concave-convex structure was transferred. After applying the RM, the element was left at 60°C for 60 seconds, and then 200 mJ / cm 2 The optical element of Comparative Example 2 was obtained by irradiating the film with unpolarized UV light.

[0074] The optical elements of Comparative Examples 1 and 2 were evaluated for retardation (Δnd) and haze. Retardation was measured using an AxoScan manufactured by Optoscience. Haze was measured using an NDH 2000 manufactured by Nippon Denshoku Industries. The results are shown in Table 1 below. For the production of PBOE, it is preferable that the optical elements have a retardation of 260 nm or more with respect to light of 550 nm and a haze of 0.20 or less.

[0075] [Table 1]

[0076] As can be seen from Table 1 above, in Comparative Examples 1 and 2, sufficient results were obtained in terms of both retardation and haze for producing a PBOE. Both the optical elements of Comparative Examples 1 and 2 functioned as half-wave plates, making it possible to produce a PB lens. It was also found that the uneven alignment film used in Comparative Example 2 had the same alignment control power as a photo-alignment film. Since the optical elements of Comparative Examples 1 and 2 had a uniform patterning direction, no diffraction occurred, and the diffraction efficiency could not be measured.

[0077] Example 1 An optical element of Example 1 corresponding to the optical element of Embodiment 1 was fabricated. First, an alignment film material containing an alignment film polymer was applied to a glass substrate to form a resin layer. A mold having a concave-convex structure previously fabricated using aluminum wire was transferred to the resin layer to obtain an alignment film. The concave-convex structure was patterned as shown in FIGS. 5 and 6 so that the optical element (PBOE) of Embodiment 1 could be fabricated. In this example, a PBOE was fabricated in which the alignment control force was divided into eight directions. Specifically, the first direction was set to 0°, the second direction to 22.5°, the third direction to 45°, the fourth direction to 67.5°, the fifth direction to 90°, the sixth direction to 112.5°, the seventh direction to 135°, the eighth direction to 157.5°, and the ninth direction to 180° (i.e., parallel to the first direction).

[0078] Next, RM was applied using a spin coater to the surface of the alignment film on the side where the relief structure was transferred. The film thickness of the RM was set so that the phase difference for 532 nm light was λ / 2. After application, the RM was cured with UV light to obtain the optical element of Example 1. The optical element of Example 1 was observed with a polarizing microscope, and the results are shown in Figure 15. Figure 15 is a polarizing microscope photograph of the optical element of Example 1.

[0079] The optical element of Example 1 is not manufactured using mask exposure, so there is no deterioration in diffraction efficiency due to alignment accuracy, and high diffraction efficiency (for example, diffraction efficiency of 90% or more) can be achieved. Furthermore, because orthogonal polarized ultraviolet light is not exposed to the same region of the alignment film, low haze (for example, haze of 0.30 or less) can be achieved.

[0080] The orientation direction of the molecules contained in the optically anisotropic layer of the optical element of Example 1 was evaluated as follows. The PBOE (optical element) was observed with a polarizing microscope, and the change in brightness per pitch (180° rotation of the molecule) was measured. If there was a flat region, the molecular orientation was evaluated as discrete, and if a continuous change in brightness was observed, the molecular orientation was evaluated as continuous (continuous orientation).

[0081] The evaluation results of the optical element of Example 1 are shown in Figure 16. Figure 16 is a diagram showing the evaluation results of the optical element of Example 1. As shown in Figure 16, the pitch (180° rotation of molecules) of the optical element of Example 1 was 560 µm. In addition, the alignment control force was divided into eight (first direction: 0°, second direction: 22.5°, third direction: 45°, fourth direction: 67.5°, fifth direction: 90°, sixth direction: 112.5°, seventh direction: 135°, and eighth direction: 157.5°).

[0082] The orientation direction of the anisotropic molecules 310 is shown on the polarizing microscope photograph in Figure 16. When the one-dimensional brightness distribution along the dashed line in the polarizing microscope photograph was graphed by image processing, a region of constant brightness was observed on the graph. This indicates that the anisotropic molecules 310 (RM) are aligned discretely because they are aligned according to the orientation regulating force of the substrate.

[0083] (Examples 2 to 4) The pitch P (molecular 180° rotation) of the optical element (PBOE) of Example 1 was designed to decrease with increasing distance from the center of the optical element in plan view. Therefore, using the optical element of Example 1, molecular orientation in regions with different pitches P was investigated. In Examples 2 to 4, the molecular orientation was investigated in regions where the pitch P was 180 μm, 80 μm, and 40 μm, respectively. The results are shown in FIGS. 17 to 19. FIG. 17 is a diagram showing the evaluation results of the optical element of Example 2. FIG. 18 is a diagram showing the evaluation results of the optical element of Example 3. FIG. 19 is a diagram showing the evaluation results of the optical element of Example 4.

[0084] As shown in Figures 17 to 19, the division number Q relative to the pitch P ((pitch P) / (division number Q)) in Examples 2 to 4 was 22.5 μm, 10 μm, and 5 μm, respectively, which was smaller than 70 μm in Example 1. When (pitch P) / (division number Q) was 22.5 μm, the molecular orientation was almost continuous, but there were still some discrete regions. When (pitch P) / (division number Q) was 10 μm and 5 μm, the molecular orientation was completely continuous. From the above, it was found that when (pitch P) / (division number Q)<22.5 μm, the RMs were aligned continuously despite the underlying alignment layer 200 having a discrete alignment control force. Therefore, it was found that higher diffraction efficiency was obtained when (pitch P) / (division number Q)<22.5 μm.

[0085] Note that (pitch P) / (number of divisions Q) is a parameter introduced to generalize this discussion, and the same consideration can be applied even if the pitch P or number of divisions Q changes.

[0086] (Diffraction efficiency (calculated value) of the optical element of Reference Example 1) The diffraction efficiency of the optical element of Reference Example 1 was determined by simulation. Fig. 20 is a diagram showing molecular orientations used when calculating the diffraction efficiency of the optical element of Reference Example 1. The optical element of Reference Example 1 has eight types of molecular orientations and can be modeled as shown in Fig. 20. Therefore, the diffraction efficiency of the optical element of Reference Example 1 was determined by simulation based on the molecular orientations shown in Fig. 20. As shown in Fig. 20, the optical element of Reference Example 1 was a one-dimensional diffraction grating having eight types of molecular orientations: 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, and 157.5°.

[0087] Once the molecular orientation is determined, the diffraction efficiency of the optical element (PBOE) can be calculated using Fraunhofer diffraction. The calculation formula for the diffraction efficiency η is given by the following (Equation D1). In the following (Equation D1), Λ represents the period on the x-axis, and Φ(x) represents the molecular orientation in Figure 20. Here, the PBOE optical element has a periodic molecular orientation in the x-axis direction. This period is defined as Λ [m]. Λ affects the diffraction angle but not the diffraction efficiency, so it was set to an appropriate value in the calculations in this example.

[0088]

number

[0089] The diffraction efficiency (calculated value) of the optical element of Reference Example 1 obtained by the above (Equation D1) was 95%.

[0090] (Diffraction efficiency (measured value) of the optical element of Example 4) FIG. 21 is a schematic diagram showing a method for measuring diffraction efficiency. The diffraction efficiency was measured for the optical element of Example 4. The diffraction efficiency was measured using the configuration shown in FIG. 21, and a laser light source with a wavelength of 532 nm was used. Here, in measuring the diffraction efficiency, light emitted from the laser light source first passes through a circular polarizer to become circularly polarized light and is emitted to the optical element 10. Of the light that passes through the outer periphery of the optical element 10, the main light moves toward the focal point. On the other hand, unnecessary light such as zero-order light is diffracted in a direction different from the main light. The diffraction efficiency is defined by the following (Equation D2).

[0091]

number

[0092] Therefore, the light intensity was measured at the first and second measurement points shown in Figure 21, the light intensity at the first measurement point was defined as the total transmitted light intensity, and the light intensity at the second measurement point was defined as the main light intensity, and the diffraction efficiency was calculated from the measured values ​​using the above (Equation D2). As a result, the diffraction efficiency (measured value) of the optical element of Example 4 was 98%. The calculated value of the diffraction efficiency of the optical element of Reference Example 1 and the measured value of the diffraction efficiency of the optical element of Example 4 are shown in Table 2 below.

[0093] [Table 2]

[0094] The closer to 100% the diffraction efficiency is, the more preferable it is. From the results shown in Table 2 above, it was found that the optical element of Example 4 can achieve a diffraction efficiency higher than the calculated value. This is thought to be because in Examples 2 to 4, as shown in Figures 17 to 19, the molecular orientation of the optically anisotropic layer 300 is continuous despite the alignment regulating force of the alignment film 200 being discrete. Note that the calculated value is the diffraction efficiency obtained assuming that the molecular orientation of the optically anisotropic layer 300 is discrete. [Explanation of symbols]

[0095] 10: Optical elements 100: Support substrate 200: Alignment film 200A, 200A i (i = integer between 1 and N): convex part 200D i (i = integer between 1 and N): direction 200R i (i=an integer between 1 and N): Alignment treatment area 200U: Uneven shape 300: Optically anisotropic layer 310: Anisotropic molecules 400: Mold 400A i (i = integer between 1 and N): wall-shaped part 400R i (i = integer between 1 and N): Area H: Height P: Pitch Q: Number of divisions W: Convex pitch

Claims

1. An alignment film; an optically anisotropic layer provided on the alignment film and containing anisotropic molecules; the alignment film has first to Nth alignment treatment regions arranged in order from a center portion of the alignment film toward an end portion thereof in a plan view, the first to Nth alignment treatment regions extend along first to Nth directions, respectively, and each of the first to Nth alignment treatment regions has a plurality of first to Nth convex portions protruding toward the optically anisotropic layer; The first direction to the (N-1)th direction are not parallel to each other, the Nth direction is parallel to the first direction, An optical element, wherein N is an integer of 3 or more.

2. When the same direction as the first direction is taken as a reference direction in a plan view, the angle of the Nth direction with respect to the reference direction is within a range of 180°±3°, The optical element of claim 1, characterized in that the angles of the second direction to the (N-1)th direction with respect to the reference direction gradually increase in this order within a range that exceeds the angle of the first direction with respect to the reference direction and is less than the angle of the Nth direction with respect to the reference direction.

3. The optical element according to claim 1, characterized in that, when viewed in a plane, the same direction as the first direction is taken as a reference direction, the angle of the i-th direction with respect to the reference direction satisfies the following (Formula A): [Equation 1] (wherein i in formula A represents an integer of 2 or more and N or less.)

4. The optical element described in claim 1, characterized in that when the total length of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center to the end of the alignment film is defined as pitch P and the number of divisions Q = N-1, the following (Equation B1) is satisfied. [Equation 2]

5. The optical element described in claim 1, characterized in that when the total length of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center to the end of the alignment film is defined as pitch P and the number of divisions Q = N-1, the following (Equation B2) is satisfied. [Equation 3]

6. 2. The optical element according to claim 1, wherein the height H of the first to Nth convex portions is less than the retardation Δnd of the optically anisotropic layer.

7. When the total length of the first alignment treatment region to the Nth alignment treatment region on a straight line from the center of the alignment film to the edge thereof is defined as a pitch P, and the number of divisions Q is defined as N-1, 2. The optical element according to claim 1, wherein a convex pitch W, which is a pitch between the first convex portion to the Nth convex portion, satisfies the following formula C: [Equation 4]

8. the anisotropic molecules are elongated molecules, The optical element described in claim 1, characterized in that in each of the first alignment treatment region to the Nth alignment treatment region, the anisotropic molecules are oriented so that the long axes of the anisotropic molecules are aligned along the first direction to the Nth direction.

9. 9. The optical element according to claim 1, wherein N is 4 or more.

10. a transfer step of transferring the relief structure of the mold onto the resin layer to form an alignment film; a liquid crystal layer forming step of disposing and curing a polymerizable liquid crystal material on the surface of the alignment film on which the shape of the mold is transferred, the mold has first to N-th regions arranged in order from a portion corresponding to a center of the alignment film toward a portion corresponding to an end of the alignment film, The first to Nth regions each include a plurality of first to Nth wall portions extending along a first to Nth direction, The first direction to the (N-1)th direction are not parallel to each other, the Nth direction is parallel to the first direction, A method for manufacturing an optical element, wherein N is an integer of 3 or more.

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