Method for manufacturing optical elements

Abstract

To provide a technique that reduces variations in retardation caused by the bending processing of a retardation plate.SOLUTION: There is provided a method for manufacturing an optical element. The optical element includes a retardation plate having a liquid crystal layer, an adhesive layer, and a three-dimensional structure having a curved surface facing the retardation plate via the adhesive layer. The manufacturing method includes preparing a first mold that surrounds the three-dimensional structure, and holds the three-dimensional structure and the retardation plate at a distance from each other. The first mold has a flat surface in which an opening is formed and a protrusion protruding from the flat surface, with the protrusion being provided along a part of an edge of the opening. In plan view, the retardation plate has a storage modulus that changes in a period of 180°. A pair of the protrusions is provided at a position where the storage modulus is maximized. The manufacturing method includes bending processing of the retardation plate along a curved surface of the three-dimensional structure while supporting the retardation plate between the flat surface and the protrusion.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an optical element.

Background Art

[0002] The optical lens described in Patent Document 1 has a retardation body. The retardation body is a film or a coating. The coating material is, for example, a liquid crystal polymer. The film material is not disclosed. The retardation body is, for example, a quarter-wave plate.

[0003] Patent Document 2 discloses a photocurable composition for transferring the concavo-convex pattern of a mold.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] A film-like retardation plate is adhered to the curved surface of a three-dimensional structure via an adhesive layer. The retardation plate, the adhesive layer, and the three-dimensional structure portion constitute an optical element. The method for manufacturing the optical element includes a step of bending the retardation plate along the curved surface of the three-dimensional structure.

[0006] The film-like retardation plate may include a liquid crystal layer. The liquid crystal layer has liquid crystal molecules. The liquid crystal layer is difficult to stretch in the long axis direction of the liquid crystal molecules and is easy to stretch in the short axis direction of the liquid crystal molecules. Therefore, when the retardation plate is bent, the thickness may vary and the retardation may vary.

[0007] One aspect of this disclosure provides a technique for reducing retardation variations caused by bending of a phase difference plate. [Means for solving the problem]

[0008] A method for manufacturing an optical element according to one aspect of the present disclosure comprises a phase difference plate having a liquid crystal layer, an adhesive layer, and a three-dimensional structure having a curved surface facing the phase difference plate via the adhesive layer. The manufacturing method includes preparing a first mold that surrounds the three-dimensional structure and holds the three-dimensional structure and the phase difference plate at a distance from each other. The first mold has a plane in which an opening is formed and a protrusion projecting from the plane, the protrusion being provided along a part of the edge of the opening. In plan view, the storage modulus of the phase difference plate changes with a period of 180°. The protrusions are provided in pairs at the position where the storage modulus is maximum. The manufacturing method includes bending the phase difference plate along the curved surface of the three-dimensional structure while supporting the phase difference plate with the plane and the protrusion. [Effects of the Invention]

[0009] According to one aspect of this disclosure, by bending the phase difference plate while supporting it with a flat surface and a protrusion projecting from the flat surface, variations in the thickness of the phase difference plate can be reduced, and variations in retardation can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1(A) is a cross-sectional view showing a phase difference plate, a three-dimensional structure, and an adhesive layer according to one embodiment; Figure 1(B) is a cross-sectional view of an optical element according to one embodiment; and Figure 1(C) is a plan view of the optical element shown in Figure 1(B). [Figure 2] Figure 2(A) is a perspective view showing an example of a transparent substrate and an alignment layer, and Figure 2(B) is a perspective view showing an example of liquid crystal molecules aligned by the alignment layer shown in Figure 2(A). [Figure 3] Figure 3 is a cross-sectional view showing a modified example of a phase difference plate. [Figure 4]Figure 4 is a plan view showing an example of the anisotropy of the storage modulus of a phase difference plate. [Figure 5] Figure 5 is a plan view showing an example of the first type. [Figure 6] Figure 6 is a cross-sectional view showing an example of a method for manufacturing an optical element. [Figure 7] Figure 7 is a cross-sectional view showing an example of a method for manufacturing an optical element, following Figure 6. [Figure 8] Figure 8 is a cross-sectional view showing an example of a method for manufacturing an optical element, following Figure 7. [Figure 9] Figure 9 is a cross-sectional view showing an example of a method for manufacturing an optical element, following Figure 8. [Figure 10] Figure 10 shows the variation in retardation of the optical elements fabricated in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described below with reference to the drawings. In each drawing, identical or corresponding components are denoted by the same reference numeral, and their descriptions may be omitted. In the specification, the "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0012] In this specification, half-wave plates include, in addition to known half-wave plates, plates that contain a chiral agent in the liquid crystal layer, have a region in which the orientation of the optical axis rotates according to the thickness direction, and have twice the thickness of a quarter-wave plate.

[0013] In this specification, the term "quarter wave plate" includes not only known quarter wave plates but also, for example, those containing a chiral agent in the liquid crystal layer and having a region in which the orientation of the optical axis rotates according to the thickness direction.

[0014] Referring to FIGS. 1 and 2, an optical element 1 according to an embodiment will be described. Depending on the application, from the perspective of performance, it is desirable for the optical element 1 to have a curved surface. For example, the optical element 1 includes a three-dimensional structure 40 having a curved surface 40a. The three-dimensional structure 40 includes, for example, a lens, a prism, or a mirror. When the three-dimensional structure 40 is a lens, it may be a spherical lens or an aspherical lens. Further, when the three-dimensional structure 40 is a lens, it may be any of a biconcave lens, a plano-concave lens, a concave meniscus lens, a biconvex lens, a plano-convex lens, and a convex meniscus lens.

[0015] The three-dimensional structure 40 has a curved surface 40a. The curved surface 40a has a radius of curvature R of, for example, 10 mm to 100 mm over the entire surface or a part thereof. The radius of curvature R of the curved surface 40a is preferably 20 mm to 80 mm, more preferably 30 mm to 45 mm, and particularly preferably 35 mm to 40 mm.

[0016] The curved surface 40a is, for example, a concave curved surface as shown in FIGS. 1(A) and 1(B). A concave curved surface is a curved surface in which the centroid P0 is recessed from the periphery. In a cross-section perpendicular to the X-axis direction or in a cross-section perpendicular to the Y-axis direction, the centroid P0 of the concave curved surface is recessed from the periphery of the concave curved surface. The X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The Z-axis direction is the normal direction at the centroid P0 of the concave curved surface. The XY plane is parallel to the tangent plane at the centroid P0 of the concave curved surface.

[0017] Note that the curved surface 40a is a concave curved surface in the present embodiment, but it may be a convex curved surface. A convex curved surface is a curved surface in which the centroid P0 protrudes (projects) from the periphery. In a cross-section perpendicular to the X-axis direction or in a cross-section perpendicular to the Y-axis direction, the centroid P0 of the convex curved surface protrudes from the periphery of the convex curved surface.

[0018] The outer shape of the three-dimensional structure 40 is not limited to the circular shape shown in FIG. 1(C), and may be, for example, an elliptical shape or a polygon (for example, a quadrilateral).

[0019] The material of the three-dimensional structure 40 may be resin or glass. If the three-dimensional structure 40 is a resin lens, the resin of the resin lens may be, for example, polycarbonate, polyimide, polyacrylate, or cyclic olefin. If the three-dimensional structure 40 is a glass lens, the glass of the glass lens may be, for example, BK7 or synthetic quartz.

[0020] The optical element 1 includes a phase difference plate 10. The phase difference plate 10 is curved along the curved surface 40a of the three-dimensional structure 40. The phase difference plate 10 includes, for example, a transparent substrate 11, an alignment layer 12 formed on the transparent substrate 11, and a liquid crystal layer 13 formed on the alignment layer 12.

[0021] The phase difference plate 10 includes, for example, a transparent substrate 11, an alignment layer 12, and a liquid crystal layer 13 in this order from the side of the three-dimensional structure 40, as shown in Figure 1(B). Although not shown, the phase difference plate 10 may also include the liquid crystal layer 13, the alignment layer 12, and the transparent substrate 11 in this order from the side of the three-dimensional structure 40.

[0022] The transparent substrate 11 is composed of, for example, a glass substrate or a resin substrate. The glass substrate or resin substrate may have a reflective or absorbing function for one or more of infrared, visible light, and ultraviolet light, and may be configured to transmit light in a specific wavelength band. The transparent substrate 11 may be a single-layer structure of a single substrate, or it may be a multi-layer structure in which layers that impart reflective or absorbing functions to the main substrate (glass substrate or resin substrate) are laminated to transmit light in a specific wavelength band. In addition to reflective and absorbing functions, the transparent substrate 11 may also have layers that impart functions such as anti-fouling.

[0023] For example, the transparent substrate 11 may include a resin layer or an inorganic layer in addition to the glass substrate or resin substrate. The resin layer is a layer having a function such as a color correction filter, a base layer for a silane coupling agent, or an antifouling layer. The resin layer is formed by, for example, screen printing, vapor deposition, spray coating, or spin coating. The inorganic layer is, for example, a metal oxide layer having a function as an optical interference layer (anti-reflective or wavelength-selective filter). The inorganic layer is formed by, for example, sputtering, vapor deposition, or CVD.

[0024] The transparent substrate 11 is preferably a resin substrate from the viewpoint of bendability. Specific examples of resins for the resin substrate include polymethyl methacrylate (PMMA), triacetylcellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), or polycarbonate (PC).

[0025] The phase difference (retardation) of the transparent substrate 11 is, for example, 5 nm or less, preferably 3 nm or less. From the viewpoint of reducing color variation, the smaller the phase difference of the transparent substrate 11, the better, and it may even be zero. The phase difference of the transparent substrate 11 is measured, for example, by the parallel nicol rotation method.

[0026] The glass transition temperature Tg_f of the transparent substrate 11 is, for example, 80°C to 200°C, preferably 90°C to 180°C, and more preferably 100°C to 160°C. If Tg_f is within the above range, the bendability is good. The glass transition temperature of the transparent substrate 11 is measured, for example, by thermomechanical analysis (TMA).

[0027] The thickness T1 of the transparent substrate 11 (see Figure 2) is, for example, 0.01 mm to 0.3 mm, preferably 0.02 mm to 0.1 mm, and more preferably 0.03 mm to 0.09 mm. If T1 is within the above range, both bendability and handling properties can be achieved.

[0028] The alignment layer 12 aligns the liquid crystal molecules of the liquid crystal layer 13. On the surface 121 of the alignment layer 12 that is in contact with the liquid crystal layer 13, for example, a plurality of parallel grooves 122 are formed. These grooves 122 are formed, for example, in a stripe pattern. In a view along the Z-axis, the longitudinal direction of the grooves 122 is the X-axis direction, and the width direction of the grooves 122 is the Y-axis direction.

[0029] The parallelism of the grooves 122 is, for example, 0° to 5°, preferably 0° to 1°. The parallelism of the grooves 122 is the maximum value of the angle between two adjacent grooves 122 when viewed in the Z-axis direction. The closer the angle between two adjacent grooves 122 is to 0°, the better the parallelism.

[0030] The depth D of the groove 122 is, for example, 3 nm to 500 nm, preferably 5 nm to 300 nm, and more preferably 10 nm to 150 nm. If D is 3 nm or more, the orientation restricting force is large, and liquid crystal molecules are easily oriented. On the other hand, if D is 500 nm or less, the transferability of the mold's uneven pattern is good. Also, if D is 500 nm or less, diffracted light is less likely to be generated.

[0031] The pitch p of the groove 122 is, for example, 10 nm to 600 nm, preferably 50 nm to 300 nm, and more preferably 80 nm to 200 nm. If p is 600 nm or less, the orientation restricting force is large, and liquid crystal molecules are easily oriented. If p is 300 nm or less, diffraction light is less likely to occur. On the other hand, if p is 10 nm or more, the formation of the mold's uneven pattern is easy.

[0032] The opening width W of the groove 122 is, for example, 5 nm to 500 nm, preferably 20 nm to 200 nm, and more preferably 30 nm to 150 nm. The difference between the pitch p and the opening width W (pW: p > W) is the distance between the grooves 122 (the width of the protrusion separating the two grooves 122).

[0033] In Figure 2, the cross-section of the groove 122 perpendicular to its longitudinal direction (X-axis direction) is rectangular, but it may also be triangular. For a groove 122 with a triangular cross-section, the width increases as the depth decreases. In this case, the mold used in the imprint method is easily removed.

[0034] The orientation layer 12 is a copolymer of an energy-curable composition. The energy-curable composition is a photocurable composition or a thermosetting composition. A photocurable composition is particularly preferred in terms of its excellent processability, heat resistance, and durability. A photocurable composition is, for example, a composition comprising monomers, a photopolymerization initiator, a solvent, and additives as needed (e.g., surfactants, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, defoamers). As a photocurable composition, for example, those described in paragraphs 0028 to 0060 of Patent Document 2 can be used.

[0035] The orientation layer 12 is formed, for example, by an imprint method. In the imprint method, an energy-curable composition is sandwiched between the transparent substrate 11 and the mold, the uneven pattern of the mold is transferred to the energy-curable composition, and the energy-curable composition is cured. By using the imprint method, the dimensions and shape of the grooves 122 can be controlled with high precision, and the inclusion of foreign matter can be reduced.

[0036] The energy-curable composition may be applied to a transparent substrate 11 or to a mold. The application methods include spin coating, bar coating, dip coating, casting, spray coating, bead coating, wire bar coating, blade coating, roller coating, curtain coating, slit die coating, gravure coating, slit reverse coating, microgravure, or comma coating.

[0037] The thickness T2 of the orientation layer 12 (see Figure 2) is, for example, 1 nm to 20 μm, preferably 50 nm to 10 μm, and more preferably 100 nm to 5 μm. The thickness T2 of the orientation layer 12 is measured in the direction normal to each point on the surface 11a of the transparent substrate 11 on which the orientation layer 12 is formed. If the orientation layer 12 has grooves 122, in this specification, the thickness T2 of the orientation layer 12 is the distance between the bottom of the grooves 122 and the surface 11a of the transparent substrate 11. If the thickness T2 of the orientation layer 12 is 20 μm or less, the processability is good.

[0038] The glass transition temperature Tg_al of the orientation layer 12 is, for example, 40°C to 200°C, preferably 60°C to 180°C, and more preferably 80°C to 150°C. If Tg_al is within the above range, the bendability is good. The glass transition temperature of the orientation layer 12 is measured, for example, by TMA.

[0039] The orientation layer 12 is not limited to those containing a fine parallel groove structure. The orientation layer 12 may be subjected to the following treatments. Examples of treatments applied to the orientation layer 12 include polyimide rubbing, photodegradation of silane coupling agents or polyimides by polarized UV irradiation, photodimerization or photoisomerization by polarized UV irradiation, flow orientation treatment by shear force, or orientation treatment by oblique deposition of inorganic material. Multiple treatments may be used in combination.

[0040] The orientation layer 12 can have any configuration and may be omitted. In that case, the transparent substrate 11 may be subjected to a treatment to orient the liquid crystal molecules of the liquid crystal layer 13. Examples of such treatments include polyimide rubbing, photodegradation of a silane coupling agent or polyimide by polarized UV irradiation, use of photodimerization or photoisomerization by polarized UV irradiation, flow orientation treatment by shear force, or orientation treatment by oblique deposition of inorganic material.

[0041] The liquid crystal layer 13 is, for example, a quarter-wave plate. A quarter-wave plate and a linear polarizer (not shown) may be used in combination. The absorption axis of the linear polarizer and the slow axis of the quarter-wave plate are offset by 45°. A circular polarizer is formed by the linear polarizer and the quarter-wave plate.

[0042] The liquid crystal layer 13 has a slow axis and a fast axis. Viewed along the Z axis, the slow axis is along the X axis and the fast axis is along the Y axis. The slow axis is in the direction of the largest refractive index, and the fast axis is in the direction of the smallest refractive index. The retardation Rd is the product of the difference Δn (Δn = ne - no) between the refractive index ne of the slow axis and the refractive index no of the fast axis, and the Z axis dimension d of the liquid crystal layer 13. In other words, Rd can be calculated from the formula Rd = Δn × d.

[0043] As shown in Figure 2(B), the liquid crystal layer 13 contains a plurality of liquid crystal molecules 131 oriented parallel to each other by the alignment layer 12. In a view along the Z-axis, the long axis of the liquid crystal molecules 131 is the X-axis, and the short axis of the liquid crystal molecules 131 is the Y-axis. In this embodiment, the liquid crystal molecules 131 are rod-shaped liquid crystals, but they may also be discotic liquid crystals. The liquid crystal molecules 131 may also be twisted.

[0044] The liquid crystal layer 13 is formed by coating and drying a liquid crystal composition. The liquid crystal composition includes a photocurable liquid crystal containing an acrylic group or a methacrylic group. The liquid crystal composition may also contain components that do not exhibit a liquid crystal phase on their own. It is sufficient that a liquid crystal phase is formed by polymerization. Examples of components that do not exhibit a liquid crystal phase include monofunctional (meth)acrylates, bifunctional (meth)acrylates, and trifunctional or more (meth)acrylates. The liquid crystal composition may also contain a photocurable monomer. The polymerizable liquid crystal composition may contain additives. Examples of additives include polymerization initiators, surfactants, chiral agents, polymerization inhibitors, ultraviolet absorbers, antioxidants, light stabilizers, defoamers, or dichroic dyes. Multiple types of additives may be used in combination.

[0045] The coating method for the liquid crystal composition may be a general one. Examples of coating methods for the liquid crystal composition include spin coating, bar coating, extrusion coating, direct gravure coating, reverse gravure coating, or die coating. The solvent in the liquid crystal composition is removed by heating after coating.

[0046] The solvent in the liquid crystal composition is, for example, an organic solvent. Organic solvents include alcohols (e.g., isopropyl alcohol), amides (e.g., N,N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), hydrocarbons (e.g., benzene or hexane), esters (e.g., methyl acetate, ethyl acetate, butyl acetate, or propylene glycol monoethyl ether acetate), ketones (e.g., acetone or methyl ethyl ketone), or ethers (e.g., tetrahydrofuran or 1,2-dimethoxyethane). Two or more organic solvents may be used in combination. The liquid crystal layer 13 may also be formed by a solvent-free deposition method or vacuum injection method.

[0047] The liquid crystal composition used may have a positive or negative wavelength dispersion of Δn after curing.

[0048] The liquid crystal composition includes polymerizable compounds, such as those shown in the following formulas (a-1) to (a-13).

[0049] [ka] [ka] [ka] In formulas (a-5) and (a-8) above, n is an integer between 3 and 6. In formulas (a-6) and (a-7) above, R is an alkyl group having 3 to 6 carbon atoms.

[0050] The thickness T3 of the liquid crystal layer 13 (see Figure 2) is determined based on the wavelength of light, the phase difference, and Δn (Δn = ne - no). For example, if the wavelength of light is 543 nm and the phase difference is 1 / 4 wavelength, then Rd is 136 nm. If Rd is 136 nm and Δn is 0.1, then the thickness T3 of the liquid crystal layer 13 is 1360 nm.

[0051] The thickness T3 of the liquid crystal layer 13 is determined based on the wavelength of light, the phase difference, and Δn, as described above, and is not particularly limited, but is for example 0.3 μm to 30 μm, preferably 0.5 μm to 20 μm, and more preferably 0.8 μm to 10 μm. If T3 is 0.3 μm or more, the desired phase difference is easily obtained. Also, if T3 is 30 μm or less, the liquid crystal molecules 131 are easily oriented.

[0052] Furthermore, the liquid crystal layer 13 is not limited to a quarter-wave plate, but may be a half-wave plate or the like. Also, the liquid crystal layer 13 is not limited to a phase difference layer that shifts the phase between two orthogonal linear polarization components, but may be a compensation layer. The compensation layer, for example, corrects the phase difference that occurs at different viewing angles of the liquid crystal display and improves the contrast of the screen within a predetermined viewing angle.

[0053] The thickness T3 of the liquid crystal layer 13 is measured in the direction normal to each point on the surface 11a of the transparent substrate 11. If the alignment layer 12 has grooves 122, in this specification, the thickness T3 of the liquid crystal layer 13 is the distance between the bottom of the grooves 122 and the surface of the liquid crystal layer 13 opposite to the alignment layer 12.

[0054] The glass transition temperature Tg_a of the liquid crystal layer 13 is, for example, 50°C to 200°C, preferably 80°C to 180°C. If Tg_a is within the above range, the bendability is good. The glass transition temperature Tg_a of the liquid crystal layer 13 is measured, for example, by TMA.

[0055] The thickness T4 of the phase difference plate 10 is not particularly limited, but is, for example, 0.011 mm to 0.301 mm, preferably 0.021 mm to 0.101 mm, and more preferably 0.031 mm to 0.091 mm. The thickness T4 of the phase difference plate 10 is measured in the direction normal to each point on the surface 11a of the transparent substrate 11.

[0056] Although not shown in the figures, the phase difference plate 10 may include a liquid crystal layer with a different phase-lagging axis direction from the liquid crystal layer 13, and may further include an alignment layer that aligns the liquid crystal molecules of the liquid crystal layer. In other words, the phase difference plate 10 may be a broadband phase difference plate. The number of liquid crystal layers included in the phase difference plate 10 may be two or more.

[0057] The phase difference plate 10 is bonded to the three-dimensional structure 40 via an adhesive layer 20. The adhesive layer 20 is, for example, a transparent optical adhesive (OCA), liquid adhesive (OSA), polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), cycloolefin polymer (COP), or thermoplastic polyurethane (TPU).

[0058] The adhesive layer 20 adheres the phase difference plate 10 and the three-dimensional structure 40. Before bonding the phase difference plate 10 and the three-dimensional structure 40, the adhesive layer 20 is laminated with the phase difference plate 10. The phase difference plate 10 and the adhesive layer 20 constitute the laminated plate 30. Alternatively, the adhesive layer 20 may be laminated with the three-dimensional structure 40 before bonding the phase difference plate 10 and the three-dimensional structure 40.

[0059] The phase difference (retardation) of the adhesive layer 20 is, for example, 5 nm or less, preferably 3 nm or less. From the viewpoint of reducing color variation, the smaller the phase difference of the adhesive layer 20, the better, and it may even be zero. The phase difference of the adhesive layer 20 is measured, for example, by the parallel nicol rotation method.

[0060] The glass transition temperature of the adhesive layer 20 is, for example, -60°C to 100°C, preferably -40°C to 50°C. If the glass transition temperature of the adhesive layer 20 is within this range, both bendability and shape conformability can be achieved. The glass transition temperature of the adhesive layer 20 is measured, for example, by TMA.

[0061] The phase difference plate 10 and the three-dimensional structure 40 are bonded together while being heated. The heating temperature (°C) is set based on the glass transition temperature Tg_f of the transparent substrate 11, and is set within a range of, for example, (Tg_f-10)°C or higher and (Tg_f+30)°C or lower. The bonding of the phase difference plate 10 and the three-dimensional structure 40 may be carried out in a vacuum.

[0062] Next, a modified example of the phase difference plate 10 will be described with reference to Figure 3. The phase difference plate 10 includes a transparent substrate 11, an alignment layer 12A, a quarter-wave plate 13A, a support layer 14, a vertically aligned liquid crystal layer 13B, an alignment layer 12C, and a half-wave plate 13C. The quarter-wave plate 13A, the vertically aligned liquid crystal layer 13B, and the half-wave plate 13C are examples of liquid crystal layers 13.

[0063] The phase difference plate 10 has, in the direction of light transmission (arrow direction in Figure 3), a half-wave plate 13C, a vertically aligned liquid crystal layer 13B, and a quarter-wave plate 13A in this order. The phase difference plate 10 is used as a circular polarizer. The half-wave plate 13C is a linear polarizer.

[0064] The quarter-wave plate 13A and the half-wave plate 13C contain liquid crystal molecules fixed in a homogeneous or twisted orientation. The vertically oriented liquid crystal layer 13B contains liquid crystal molecules fixed in a homeotropic orientation. Homogeneous or twisted orientation is an orientation in which the long axis of the liquid crystal molecules is parallel to the surface of the phase difference plate 10. Homeotropic orientation is an orientation in which the long axis of the liquid crystal molecules is perpendicular to the surface of the phase difference plate 10.

[0065] Alignment layers 12A and 12C are examples of alignment layer 12. Alignment layer 12A aligns the liquid crystal molecules constituting the quarter-wave plate 13A. Alignment layer 12C aligns the liquid crystal molecules constituting the half-wave plate 13C. Note that these alignment layers 12A and 12C are not necessary, as long as the liquid crystal molecules are fixed in a state where they are oriented in the desired direction. Support layer 14 is a layer for transferring the vertically aligned liquid crystal layer 13B, which is formed on a substrate sheet (not shown), from the substrate sheet.

[0066] In this modified example, the phase difference plate 10 has a vertically aligned liquid crystal layer 13B between the quarter-wave plate 13A and the half-wave plate 13C, but it does not have to have a vertically aligned liquid crystal layer 13B. The phase difference plate 10 may have only the quarter-wave plate 13A and the half-wave plate 13C as the liquid crystal layer 13. Alternatively, the phase difference plate 10 may have only the quarter-wave plate 13A or only the half-wave plate 13C as the liquid crystal layer 13.

[0067] Next, an example of the anisotropy of the storage modulus of the phase difference plate 10 will be explained, mainly with reference to Figure 4. The liquid crystal layer 13 of the phase difference plate 10 is difficult to stretch in the direction of the long axis of the liquid crystal molecules 131 (see Figure 2(B)) and easy to stretch in the direction of the short axis of the liquid crystal molecules 131. The difficulty of stretching is expressed, for example, by the storage modulus. The storage modulus E is measured in accordance with ISO 6721-4:1994. The difficulty of stretching is maximized in the direction in which the storage modulus is maximized.

[0068] If the liquid crystal molecules 131 are oriented in a plan view, the storage modulus of the liquid crystal layer 13 changes with a 180° period in a plan view. In this specification, a plan view means a view from a direction perpendicular to the surface of the phase difference plate 10. In a vertically oriented liquid crystal layer 13B, the liquid crystal molecules are oriented vertically, and the storage modulus is uniform in a plan view.

[0069] In a plan view, the storage modulus of the quarter-wave plate 13A and the half-wave plate 13C changes with a period of 180°. The storage modulus of the quarter-wave plate 13A is maximum in the θ1 and θ5 directions shown in Figure 4. Similarly, the storage modulus of the half-wave plate 13C is maximum in the θ3 and θ7 directions shown in Figure 4.

[0070] If the storage modulus of the liquid crystal layer 13 changes with a 180° period in a planar view, then the storage modulus of the phase difference plate 10 also changes with a 180° period in a planar view.

[0071] For example, if the phase difference plate 10 has a quarter-wave plate 13A and a half-wave plate 13C, the storage modulus of the phase difference plate 10 is maximized in the θ2 direction and the θ6 direction. The θ2 direction is the direction that bisects the θ1 direction and the θ3 direction. The θ6 direction is the direction that bisects the θ5 direction and the θ7 direction. The θ2 direction and the θ6 direction are 180° apart.

[0072] Furthermore, when the phase difference plate 10 has a quarter-wave plate 13A and a half-wave plate 13C, the storage modulus of the phase difference plate 10 is minimized in the θ4 and θ8 directions. The θ4 and θ8 directions are perpendicular to the θ2 and θ6 directions. The θ4 and θ8 directions are 180° apart.

[0073] Furthermore, the phase difference plate 10 does not necessarily have to have both the quarter-wave plate 13A and the half-wave plate 13C; it may have only one of them. In the latter case as well, the storage modulus of the phase difference plate 10 changes with a period of 180° when viewed from above.

[0074] Next, an example of a method for manufacturing the optical element 1 will be described, mainly with reference to Figures 5 to 9. The method for manufacturing the optical element 1 includes a step of preparing a first mold 50. The first mold 50 surrounds the three-dimensional structure 40 and holds the three-dimensional structure 40 and the phase difference plate 10 with a gap between them. Note that the adhesive layer 20 is not shown in the illustration.

[0075] The first type 50 includes, for example, an outer frame 51 that holds the periphery of the phase difference plate 10, and an inner frame 52 positioned inside the outer frame 51. The inner frame 52 is divided into a plurality of blocks (not shown). Therefore, the inner frame 52 can change the distance between the three-dimensional structure 40 and the phase difference plate 10. The inner frame 52 can also be evacuated using a vacuum pump or the like.

[0076] The first type 50 preferably has the same external dimensions as the phase difference plate 10. That is, the periphery of the first type 50 preferably has the same size as the periphery of the phase difference plate 10. The phase difference plate 10 is installed so that its periphery coincides with the periphery of the outer frame 51. This allows the orientation direction of the liquid crystal molecules to be adjusted to a desired direction.

[0077] In a plan view, it is preferable that both the first type 50 and the phase difference plate 10 are rectangles having a long side and a short side. The optical properties of the phase difference plate 10 change with a period of 180°. By superimposing the first type 50 and the phase difference plate 10 so that their long sides coincide, the orientation direction of the liquid crystal molecules can be adjusted to a desired direction.

[0078] In addition, both the Type 1 50 and the phase difference plate 10 may be square in plan view. In this case, it is preferable that alignment marks representing the orientation direction of the liquid crystal molecules are formed on the phase difference plate 10. Based on the alignment marks, the orientation direction of the liquid crystal molecules can be adjusted to a desired direction.

[0079] The first type 50 has a plane 54 on which an opening 53 is formed, and a protrusion 55 that projects from the plane 54. The protrusion 55 is provided along a part of the edge of the opening 53. The protrusion 55 is preferably set away from the edge of the opening 53, as shown in Figures 5 to 9, but it may be in contact with the edge of the opening 53.

[0080] As shown in Figure 5, a pair of protrusions 55 are provided at positions where the storage modulus of the phase difference plate 10 is maximized. For example, if the phase difference plate 10 has a quarter-wave plate 13A and a half-wave plate 13C, the storage modulus of the phase difference plate 10 is maximized in the θ2 direction and the θ6 direction. Therefore, protrusions 55 are provided in the θ2 direction and the θ6 direction.

[0081] As shown in Figures 6 to 9, the manufacturing method of the optical element 1 includes a step of bending the phase difference plate 10 along the curved surface 40a of the three-dimensional structure 40 while supporting the phase difference plate 10 with a flat surface 54 and a protrusion 55. The protrusion 55 allows for a larger height difference between the phase difference plate 10 and the three-dimensional structure 40 compared to the flat surface 54.

[0082] The greater the height difference between the phase difference plate 10 and the three-dimensional structure 40, the easier it is to stretch the phase difference plate 10. By providing a protrusion 55 at the position where the storage modulus of the phase difference plate 10 is maximized, the phase difference plate 10 can be stretched uniformly. Therefore, variations in the thickness of the phase difference plate 10 can be reduced, and variations in the retardation Rd of the phase difference plate 10 can be reduced.

[0083] As shown in Figure 7, the manufacturing method of the optical element 1 may include a step of arranging the second mold 60 on the opposite side (for example, above) of the first mold 50 with respect to the phase difference plate 10. The first mold 50 is the lower mold, and the second mold 60 is the upper mold. The second mold 60 includes, for example, a base plate 61 that contacts the phase difference plate 10, and a heating plate 62 that heats the phase difference plate 10 via the base plate 61.

[0084] The base plate 61 has a recess 63 on the surface facing the phase difference plate 10. A protrusion 55 is inserted into the recess 63. Multiple gas holes (not shown) are formed on the wall surface of the recess 63. The gas holes draw in gas (e.g., air) from the recess 63. The gas holes also inject gas (e.g., compressed air) into the recess 63. The gas holes for drawing in gas and the gas holes for injecting gas may be provided separately.

[0085] As shown in Figure 7, the gas holes in the base plate 61 draw in gas from the recess 63, causing the phase difference plate 10 to adhere to the wall surface of the recess 63. In this state, the heater of the heating plate 62 heats the phase difference plate 10 via the base plate 61, softening the phase difference plate 10. Because the phase difference plate 10 is in close contact with the base plate 61, the heat from the heating plate 62 is easily transferred to the phase difference plate 10.

[0086] Subsequently, as shown in Figure 8, the gas holes in the base plate 61 inject gas into the recess 63, and at the same time the first type 50 is depressurized by a vacuum pump, the phase difference plate 10 is pressed against the three-dimensional structure 40. The phase difference plate 10 first contacts the center of the curved surface 40a of the three-dimensional structure 40, and then gradually makes contact from the center towards the periphery. This allows air to escape from the center towards the periphery, suppressing air trapping.

[0087] As shown in Figure 9, the phase difference plate 10 contacts the entire curved surface 40a of the three-dimensional structure 40. The portion of the phase difference plate 10 that extends beyond the curved surface 40a is cut off. This results in the optical element 1. [Examples]

[0088] The experimental data is described below. In Example 1 and Comparative Example 1, the optical element 1 was fabricated under the same conditions except for the presence or absence of the protrusion 55. In Example 1, the first type 50 with the protrusion 55 was used, while in Comparative Example 1, the first type 50 without the protrusion 55 was used. In Comparative Example 1, the protrusion 55 was removed, and the phase difference plate 10 was bent along the curved surface 40a of the three-dimensional structure 40 while the phase difference plate 10 was supported only by the flat surface 54.

[0089] In Example 1 and Comparative Example 1, the phase difference plate 10 was prepared as shown in Figure 3, comprising a transparent substrate 11, an alignment layer 12A, a quarter-wave plate 13A, a support layer 14, a vertically aligned liquid crystal layer 13B, an alignment layer 12C, and a half-wave plate 13C, in this order. The transparent substrate 11 was a TAC film. The alignment layer 12A was formed by a transfer method using NK ester ADCP manufactured by Shin Nakamura Chemical Industry Co., Ltd. to create a stripe pattern grid (pitch p: 90 nm, groove depth D: 30 nm, thickness T2: 1.8 μm). The quarter-wave plate 13A was formed by spin coating LC242 manufactured by BASF onto the alignment layer 12A, drying by heating, and curing by UV exposure. The thickness T3 of the quarter-wave plate 13A was 1.2 μm. The support layer 14 was formed by transferring NK ester A-200 manufactured by Shin Nakamura Chemical Industry Co., Ltd. onto the quarter-wave plate 13A and curing it by UV exposure. The thickness of the support layer 14 was 1.3 μm. The vertically aligned liquid crystal layer 13B was formed by transferring NV FILM manufactured by ENEOS Liquid Crystal Corporation onto the support layer 14. The thickness T3 of the vertically aligned liquid crystal layer 13B was 0.8 μm. The alignment layer 12C was formed by using NK ester ADCP manufactured by Shin Nakamura Chemical Industry Co., Ltd. to create a stripe pattern grid (pitch p: 90 nm, groove depth D: 30 nm, thickness T2: 5.1 μm) by transfer method. The half-wave plate 13C was formed by applying LC242 manufactured by BASF Corporation onto the alignment layer 12A by spin coating, drying it by heating, and curing it by UV exposure. The thickness T3 of the half-wave plate 13C was 2.3 μm.

[0090] Next, a laminated board 30 was fabricated by bonding an adhesive layer 20 to the phase difference plate 10 (specifically, the transparent substrate 11). A hand roller was used to bond the adhesive layer 20.

[0091] Next, as shown in Figure 6, the three-dimensional structure 40 was housed in the opening 53 of the first type 50, and the phase difference plate 10 was placed on the plane 54 of the first type 50. After that, the second type 60 was installed on top of the phase difference plate 10.

[0092] Next, as shown in Figure 7, the second type 60 adsorbed the phase difference plate 10 onto the wall surface of the recess 63. In this state, the second type 60 heated the phase difference plate 10, softening it. The heating temperature of the phase difference plate 10 was 150°C.

[0093] Next, as shown in Figure 8, the second type 60 injected gas at 0.9 MPa while the first type 50 was depressurized by a vacuum pump, pressing the phase difference plate 10 against the three-dimensional structure 40. The phase difference plate 10 first made contact with the center of the curved surface 40a of the three-dimensional structure 40, and then gradually made contact from the center towards the periphery.

[0094] As shown in Figure 9, the phase difference plate 10 was bonded to the entire curved surface 40a of the three-dimensional structure 40, and then the portion of the phase difference plate 10 that extended beyond the curved surface 40a was cut off. This created the optical element 1.

[0095] The retardation Rd of the optical elements fabricated in Example 1 and Comparative Example 1 was measured using a WPA-200-L from Photonic Lattice Co., Ltd. Measurement points were placed at equal intervals on a circle 15 mm from the centroid P0 of the curved surface 40a, and were spaced at 22.5° intervals from the 0° direction to the 180° direction. Note that the +y direction in Figure 4 is the 0° direction, the -x direction in Figure 4 is the 90° direction, and the -y direction in Figure 4 is the 180° direction. The measurement results are shown in Figure 10.

[0096] In Figure 10, the solid line represents the retardation Rd of the optical element fabricated in Example 1, and the dashed line represents the retardation Rd of the optical element fabricated in Comparative Example 1. As is clear from Figure 10, the presence of the protrusion 55 reduces the variation in the retardation Rd of the optical element compared to the case without the protrusion 55.

[0097] The above describes a method for manufacturing an optical element related to this disclosure, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope described in the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of Symbols]

[0098] 1 Optical element 10 Retardation plate 13. Liquid crystal layer 20 Adhesive layer 40 3D structures 40a curved surface 50 Type 1 53 Opening 54 plane 55 Convex part

Claims

1. A method for manufacturing an optical element comprising a phase difference plate having a liquid crystal layer, an adhesive layer, and a three-dimensional structure having a curved surface facing the phase difference plate via the adhesive layer, The method includes preparing a first mold that surrounds the three-dimensional structure and holds the three-dimensional structure and the phase difference plate at a distance from each other, The first type has a plane in which an opening is formed and a protrusion projecting from the plane, the protrusion being provided along a part of the edge of the opening, In a plan view, the phase difference plate changes its storage modulus with a period of 180°. The aforementioned protrusions are provided in pairs at the position where the storage modulus is maximized. The manufacturing method for an optical element comprises bending the phase difference plate along the curved surface of a three-dimensional structure while supporting the phase difference plate with the plane and the protrusion.

2. The method for manufacturing an optical element according to claim 1, wherein the phase difference plate has a half-wave plate and a quarter-wave plate as the liquid crystal layer.

3. The method for manufacturing an optical element according to claim 2, wherein the phase difference plate has a vertically aligned liquid crystal layer between the half-wave plate and the quarter-wave plate.

4. The second type is positioned on the opposite side from the first type, with respect to the aforementioned phase difference plate. With the protrusion inserted into the recess on the surface of the second type facing the first type, the second type adsorbs the phase difference plate to the recess, The second type heats the phase difference plate while the second type is adsorbing the phase difference plate, As the second type injects gas onto the phase difference plate, the first type is depressurized, thereby bending the phase difference plate along the curved surface of the three-dimensional structure. A method for manufacturing an optical element according to any one of claims 1 to 3, comprising having

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