Method for manufacturing optical element, and apparatus for manufacturing optical element

Abstract

To provide a technique capable of reducing variation in retardation caused by bending processing of a phase difference plate.SOLUTION: A method for manufacturing an optical element comprises: preparing a first mold and a second mold; accommodating a three-dimensional structure in a first recess of the first mold with a curved surface of the three-dimensional structure facing the second mold; sandwiching a phase difference plate between the first mold and the second mold; heating the phase difference plate with the second mold; and bending a part of the phase difference plate heated by the second mold along the curved surface of the three-dimensional structure. In a planar view, the storage elastic modulus of the phase difference plate at room temperature varies in a 180° cycle. The second mold has a first heating region and a second heating region in a 180° cycle. The heating temperature (°C) of the first heating region is 80% to 97% of the heating temperature (°C) of the second heating region.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

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

[0003] Patent Document 2 discloses a photocurable composition for transferring the concave-convex pattern of a mold. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-534484 [Patent Document 2] Patent No. 5978761 Summary of the Invention [Problem to be solved by the invention]

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

[0006] A film-like retarder may include a liquid crystal layer. The liquid crystal layer contains liquid crystal molecules. The liquid crystal layer is difficult to stretch in the long axis direction of the liquid crystal molecules, but is easy to stretch in the short axis direction of the liquid crystal molecules. Therefore, bending the retarder can cause variations in thickness and retardation.

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

[0008] A method for manufacturing an optical element according to one embodiment of the present disclosure includes manufacturing an optical element including a retarder having a liquid crystal layer, an adhesive layer, and a three-dimensional structure having a curved surface facing the retarder via the adhesive layer. The method includes preparing a first mold having a first plane on which a first recess is formed and a second mold having a second plane facing the first plane of the first mold, placing the three-dimensional structure in the first recess of the first mold with the curved surface of the three-dimensional structure facing the second mold, sandwiching the retarder between the first mold and the second mold, heating the retarder with the second mold, and bending a portion of the retarder heated with the second mold along the curved surface of the three-dimensional structure. The storage modulus of the retarder at room temperature in a planar view changes in a 180° cycle. The second mold has, in a region overlapping with the first recess of the first mold in a plan view, a first heating region in contact with the portion of the retardation plate where the storage modulus is minimum and a second heating region in contact with the portion of the retardation plate where the storage modulus is maximum, arranged at a 180° interval. The heating temperature (°C) of the first heating region is 80% to 97% of the heating temperature (°C) of the second heating region. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, by bending the retardation plate heated to a desired temperature distribution in the second mold, it is possible to reduce variations in thickness of the retardation plate, and thus variations in retardation. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1(A) is a cross-sectional view showing a retardation plate, a three-dimensional structure, and an adhesive layer according to one embodiment, FIG. 1(B) is a cross-sectional view of an optical element according to one embodiment, and FIG. 1(C) is a plan view of the optical element shown in FIG. 1(B). [Figure 2]FIG. 2(A) is a perspective view showing an example of a transparent substrate and an alignment layer, and FIG. 2(B) is a perspective view showing an example of liquid crystal molecules aligned by the alignment layer shown in FIG. 2(A). [Figure 3] FIG. 3 is a cross-sectional view showing a modified example of the retardation plate. [Figure 4] FIG. 4 is a plan view showing an example of anisotropy of the storage elastic modulus of a retardation plate. [Figure 5] FIG. 5 is a plan view showing an example of the first mold. [Figure 6] FIG. 6 is a plan view showing an example of the second mold. [Figure 7] 7A and 7B are cross-sectional views taken along the θ4 and θ8 directions shown in FIGS. 5 and 6, respectively, where (A) is a cross-sectional view showing an example of the placement of a retardation plate, (B) is a cross-sectional view showing an example of the heating of a retardation plate, and (C) is a cross-sectional view showing an example of the bending process of a retardation plate. [Figure 8] 8A and 8B are cross-sectional views taken along the θ2 and θ6 directions shown in FIGS. 5 and 6, respectively, where (A) is a cross-sectional view showing an example of heating a retardation plate, (B) is a cross-sectional view showing an example of heating a retardation plate, and (C) is a cross-sectional view showing an example of bending a retardation plate. [Figure 9] FIG. 9 is a diagram showing the variation in retardation of the optical elements fabricated in Examples 1 to 3. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and their description may be omitted. In the specification, the symbol "to" indicating a range of values means that the values before and after it are included as the lower and upper limits. In the specification, the storage modulus is a value measured at room temperature.

[0012] In this specification, the term "half-wave plate" refers to not only known half-wave plates, but also plates that contain a chiral agent in the liquid crystal layer, have a region in which the direction of the optical axis rotates depending on the thickness direction, and have a thickness twice that of a quarter-wave plate.

[0013] In this specification, the quarter wave plate includes not only known quarter wave plates but also those having a region in which the direction of the optical axis rotates depending on the thickness direction, for example, by including a chiral agent in the liquid crystal layer.

[0014] An optical element 1 according to one embodiment will be described with reference to FIGS. 1 and 2. Depending on the application, it may be desirable for the optical element 1 to have a curved surface from the viewpoint of performance. For example, the optical element 1 includes a three-dimensional structure 40 having a curved surface 40a. Examples of the three-dimensional structure 40 include a lens, a prism, and a mirror. When the three-dimensional structure 40 is a lens, it may be a spherical lens or an aspherical lens. Furthermore, 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 of it. 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 a concave surface, as shown in Figures 1(A) and 1(B), for example. A concave surface is a curved surface in which the center of gravity P0 is recessed relative to the periphery. In both a cross section perpendicular to the X-axis direction and a cross section perpendicular to the Y-axis direction, the center of gravity P0 of the concave surface is recessed relative to the periphery of the concave surface. The X-axis, Y-axis, and Z-axis directions are perpendicular to each other. The Z-axis direction is the normal direction at the center of gravity P0 of the concave surface. The XY plane is parallel to the tangent plane at the center of gravity P0 of the concave surface.

[0017] In this embodiment, the curved surface 40a is a concave surface, but it may be a convex surface. A convex surface is a curved surface whose center of gravity P0 is more convex (protrudes) than the periphery. In both a cross section perpendicular to the X-axis direction and a cross section perpendicular to the Y-axis direction, the center of gravity P0 of the convex surface is more convex than the periphery of the convex surface.

[0018] The external shape of the three-dimensional structure 40 is not limited to the circle shown in FIG. 1(C), but may be, for example, an ellipse, a polygon (for example, a rectangle), or the like.

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

[0020] The optical element 1 includes a retardation plate 10. The retardation plate 10 is curved along the curved surface 40a of the three-dimensional structure 40. The retardation 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] 1(B), the retarder 10 includes, for example, a transparent substrate 11, an alignment layer 12, and a liquid crystal layer 13 in this order from the three-dimensional structure 40 side. Although not shown, the retarder 10 may also include, from the three-dimensional structure 40 side, the liquid crystal layer 13, an alignment layer 12, and a transparent substrate 11 in this order.

[0022] The transparent substrate 11 is made of, for example, a glass substrate or a resin substrate. The glass substrate or resin substrate may have a reflecting 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 have a single-layer structure made of a single substrate, or a multi-layer structure in which a layer that imparts a reflecting or absorbing function is laminated on the main substrate (glass substrate or resin substrate) to transmit light in a specific wavelength band. Furthermore, the transparent substrate 11 may be laminated with a layer that imparts a function such as antifouling in addition to the reflecting or absorbing function.

[0023] For example, the transparent substrate 11 may further include a resin layer or an inorganic layer in addition to a glass substrate or a resin substrate. The resin layer is a layer having functions such as a color correction filter, an underlayer such as 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 functions as a light interference layer (antireflection or wavelength selection filter). The inorganic layer is formed by, for example, sputtering, vapor deposition, or CVD.

[0024] From the viewpoint of bending processability, the transparent substrate 11 is preferably a resin substrate. Specific examples of the resin of the resin substrate include polymethyl methacrylate (PMMA), triacetyl cellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), and polycarbonate (PC).

[0025] The phase difference (retardation) of the transparent substrate 11 is, for example, 5 nm or less, and preferably 3 nm or less. From the viewpoint of reducing variations in color tone, the phase difference of the transparent substrate 11 is preferably as small as possible, and may even be zero. The phase difference of the transparent substrate 11 is measured, for example, by a 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 bending processability is good. The glass transition temperature of the transparent substrate 11 is measured, for example, by thermomechanical analysis (TMA).

[0027] The transparent substrate 11 has a thickness T1 (see FIG. 2) of, 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. When T1 is within the above range, both bending workability and handleability can be achieved.

[0028] The alignment layer 12 aligns the liquid crystal molecules in the liquid crystal layer 13. For example, a plurality of grooves 12b parallel to each other are formed on the surface 12a of the alignment layer 12 that contacts the liquid crystal layer 13. The plurality of grooves 12b are formed, for example, in a stripe pattern. When viewed in the Z-axis direction, the longitudinal direction of the grooves 12b is the X-axis direction, and the width direction of the grooves 12b is the Y-axis direction.

[0029] The parallelism of the grooves 12b is, for example, 0° to 5°, and preferably 0° to 1°. The parallelism of the grooves 12b is the maximum value of the angle formed by two adjacent grooves 12b when viewed in the Z-axis direction. The closer the angle formed by two adjacent grooves 12b is to 0°, the better the parallelism.

[0030] The depth D of the grooves 12b 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 alignment control force is strong and the liquid crystal molecules are easily aligned. On the other hand, if D is 500 nm or less, the transferability of the concave-convex pattern of the mold is good. Furthermore, if D is 500 nm or less, diffracted light is less likely to be generated.

[0031] The pitch p of the grooves 12b 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 alignment control force is strong and the liquid crystal molecules are easily aligned. If p is 300 nm or less, diffracted light is less likely to occur. On the other hand, if p is 10 nm or more, it is easy to form the concave-convex pattern of the mold.

[0032] The opening width W of the groove 12b 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 12b (the width of the convex portion separating two grooves 12b).

[0033] The cross section of groove 12b perpendicular to the longitudinal direction (X-axis direction) is rectangular in Fig. 2, but it may also be triangular. The shallower the depth of groove 12b with a triangular cross section, the wider the width. In this case, it is easy to peel off the mold used in the imprinting method.

[0034] The alignment layer 12 is a copolymer of an energy-curable composition. The energy-curable composition is a photocurable composition or a thermosetting composition. Photocurable compositions are particularly preferred because of their excellent processability, heat resistance, and durability. The photocurable composition is, for example, a composition containing a monomer, a photopolymerization initiator, a solvent, and optional additives (for example, a surfactant, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, and an antifoaming agent). Examples of photocurable compositions that can be used include those described in paragraphs 0028 to 0060 of Patent Document 2.

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

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

[0037] The thickness T2 of the alignment layer 12 (see FIG. 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 alignment layer 12 is measured in the normal direction at each point on the surface 11a of the transparent substrate 11 on which the alignment layer 12 is formed. When the alignment layer 12 has grooves 12b, in this specification, the thickness T2 of the alignment layer 12 refers to the distance between the bottom of the grooves 12b and the surface 11a of the transparent substrate 11. If the thickness T2 of the alignment layer 12 is 20 μm or less, good processability is achieved.

[0038] The glass transition temperature Tg_al of the alignment 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 bending processability is good. The glass transition temperature of the alignment layer 12 is measured, for example, by TMA.

[0039] The alignment layer 12 is not limited to one having a fine parallel groove structure. The alignment layer 12 may be subjected to the following treatments. Examples of treatments that may be applied to the alignment layer 12 include rubbing of polyimide, photodecomposition of a silane coupling agent or polyimide by polarized UV irradiation, photodimerization or photoisomerization by polarized UV irradiation, flow alignment treatment by shear force, and alignment treatment by oblique deposition of an inorganic substance. A combination of these treatments may also be used.

[0040] The alignment layer 12 may have any configuration and may be omitted. In this case, the transparent substrate 11 may be subjected to a treatment for aligning the liquid crystal molecules of the liquid crystal layer 13. Such treatments include, for example, rubbing of polyimide, photolysis of a silane coupling agent or polyimide by irradiation with polarized UV light, photodimerization or photoisomerization by irradiation with polarized UV light, flow alignment treatment by shear force, or alignment treatment by oblique deposition of an inorganic material.

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

[0042] The liquid crystal layer 13 has a slow axis and a fast axis. When viewed in the Z-axis direction, the slow axis is in the X-axis direction and the fast axis is in the Y-axis direction. The slow axis is the direction with the largest refractive index, and the fast axis is the direction with 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 dimension d of the liquid crystal layer 13 in the Z-axis direction. In other words, Rd can be calculated using the formula Rd=Δn×d.

[0043] As shown in FIG. 2(B), the liquid crystal layer 13 contains a plurality of liquid crystal molecules 13a aligned parallel to one another by the alignment layer 12. As viewed in the Z-axis direction, the long axis direction of the liquid crystal molecules 13a is the X-axis direction, and the short axis direction of the liquid crystal molecules 13a is the Y-axis direction. In this embodiment, the liquid crystal molecules 13a are rod-shaped liquid crystals, but they may also be discotic liquid crystals. The liquid crystal molecules 13a may also be twisted.

[0044] The liquid crystal layer 13 is formed by applying and drying a liquid crystal composition. The liquid crystal composition contains a photocurable liquid crystal containing an acrylic group or a methacrylic group. The liquid crystal composition may contain a component that does not exhibit a liquid crystal phase by itself. It is sufficient that a liquid crystal phase is generated by polymerization. Examples of components that do not exhibit a liquid crystal phase include monofunctional (meth)acrylates, bifunctional (meth)acrylates, and trifunctional or higher functional (meth)acrylates. The liquid crystal composition may contain a photocurable monomer. The polymerizable liquid crystal composition may contain an additive. Examples of additives that can be used include polymerization initiators, surfactants, chiral agents, polymerization inhibitors, UV absorbers, antioxidants, light stabilizers, antifoaming agents, and dichroic dyes. Multiple types of additives may be used in combination.

[0045] The liquid crystal composition may be applied by a common method, such as 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 application.

[0046] The solvent for the liquid crystal composition is, for example, an organic solvent. The organic solvent is an alcohol (e.g., isopropyl alcohol), an amide (e.g., N,N-dimethylformamide), a sulfoxide (e.g., dimethyl sulfoxide), a hydrocarbon (e.g., benzene or hexane), an ester (e.g., methyl acetate, ethyl acetate, butyl acetate, or propylene glycol monoethyl ether acetate), a ketone (e.g., acetone or methyl ethyl ketone), or an ether (e.g., tetrahydrofuran or 1,2-dimethoxyethane). Two or more organic solvents may be used in combination. The liquid crystal layer 13 may be formed by a vapor deposition method or a vacuum injection method that does not use a solvent.

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

[0048] The liquid crystal composition contains, as a polymerizable compound, for example, compounds represented by the following formulas (a-1) to (a-13).

[0049] [ka]

[0050] [ka]

[0051] [ka] In the above formulas (a-5) and (a-8), n is an integer of 3 to 6. In the above formulas (a-6) and (a-7), R is an alkyl group having 3 to 6 carbon atoms.

[0052] The thickness T3 (see FIG. 2) of the liquid crystal layer 13 is determined based on the wavelength of the light, the phase difference, and Δn (Δn=ne-no). For example, when the wavelength of the light is 543 nm and the phase difference is 1 / 4 wavelength, Rd is 136 nm. When Rd is 136 nm and Δn is 0.1, the thickness T3 of the liquid crystal layer 13 is 1360 nm.

[0053] The thickness T3 of the liquid crystal layer 13 is determined based on the wavelength of light, the retardation, 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 target retardation is easily obtained. Furthermore, if T3 is 30 μm or less, the liquid crystal molecules 13a are easily aligned.

[0054] The liquid crystal layer 13 is not limited to a quarter-wave plate, but may be a half-wave plate or the like. Furthermore, the liquid crystal layer 13 is not limited to a retardation layer that shifts the phase between two orthogonal linearly polarized light components, but may be a compensation layer. The compensation layer corrects, for example, the phase difference that occurs at different viewing angles of the liquid crystal display, thereby improving the contrast of the screen within a predetermined viewing angle.

[0055] The thickness T3 of the liquid crystal layer 13 is measured in the normal direction at each point on the surface 11a of the transparent substrate 11. When the alignment layer 12 has grooves 12b, the thickness T3 of the liquid crystal layer 13 in this specification refers to the distance between the bottom of the grooves 12b and the surface of the liquid crystal layer 13 opposite the alignment layer 12.

[0056] The glass transition temperature Tg_a of the liquid crystal layer 13 is, for example, 50° C. to 200° C., and preferably 80° C. to 180° C. If Tg_a is within the above range, the bending processability is good. The glass transition temperature Tg_a of the liquid crystal layer 13 is measured, for example, by TMA.

[0057] The thickness T4 of the retarder 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 retarder 10 is measured in the normal direction at each point on the surface 11a of the transparent substrate 11.

[0058] Although not shown, the retarder 10 may include a liquid crystal layer having a slow axis direction different from that of 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 retarder 10 may be a broadband retarder. The number of liquid crystal layers included in the retarder 10 may be two or more.

[0059] The retarder 10 is adhered to the three-dimensional structure 40 via an adhesive layer 20. The adhesive layer 20 is, for example, a transparent optical adhesive (OCA), a liquid adhesive (OSA), polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), a cycloolefin polymer (COP), or a thermoplastic polyurethane (TPU).

[0060] The adhesive layer 20 bonds the retardation film 10 and the three-dimensional structure 40. Before bonding the retardation film 10 and the three-dimensional structure 40, the adhesive layer 20 is laminated on the retardation film 10. The retardation film 10 and the adhesive layer 20 form a laminated plate 30. Note that the adhesive layer 20 may be laminated on the three-dimensional structure 40 before bonding the retardation film 10 and the three-dimensional structure 40.

[0061] The phase difference (retardation) of the adhesive layer 20 is, for example, 5 nm or less, and preferably 3 nm or less. From the viewpoint of reducing variations in color tone, the phase difference of the adhesive layer 20 is preferably as small as possible, and may even be zero. The phase difference of the adhesive layer 20 is measured, for example, by a parallel Nicol rotation method.

[0062] The glass transition point of the adhesive layer 20 is, for example, -60°C to 100°C, and preferably -40°C to 50°C. If the glass transition point of the adhesive layer 20 is within the above range, both bending workability and shape conformability can be achieved. The glass transition point of the adhesive layer 20 is measured, for example, by TMA.

[0063] The retarder 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 the range of (Tg_f-10)°C or higher and (Tg_f+30)°C or lower, for example. The retarder 10 and the three-dimensional structure 40 may be bonded together in a vacuum.

[0064] Next, a modified example of the retarder 10 will be described with reference to Fig. 3. The retarder 10 has 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 an example of the liquid crystal layer 13.

[0065] The retardation plate 10 has a half-wave plate 13C, a vertically aligned liquid crystal layer 13B, and a quarter-wave plate 13A in this order in the light transmission direction (the direction of the arrow in FIG. 3). The retardation plate 10 is used as a circular polarizer. The half-wave plate 13C is a linear polarizer.

[0066] The quarter-wave plate 13A and the half-wave plate 13C contain liquid crystal molecules fixed in a homogeneous or twisted alignment state. The vertically aligned liquid crystal layer 13B contains liquid crystal molecules fixed in a homeotropic alignment state. The homogeneous or twisted alignment is an alignment in which the long axes of the liquid crystal molecules are parallel to the plate surface of the retarder 10. The homeotropic alignment is an alignment in which the long axes of the liquid crystal molecules are perpendicular to the plate surface of the retarder 10.

[0067] The alignment layers 12A and 12C are an example of the alignment layer 12. The alignment layer 12A aligns the liquid crystal molecules that make up the quarter-wave plate 13A. The alignment layer 12C aligns the liquid crystal molecules that make up the half-wave plate 13C. Note that these alignment layers 12A and 12C may be omitted as long as the liquid crystal molecules are fixed in a state where they are aligned in a desired direction. The support layer 14 is a layer for transferring the vertically aligned liquid crystal layer 13B formed on a base sheet (not shown) from the base sheet.

[0068] Although the retardation plate 10 of this modification has the vertically aligned liquid crystal layer 13B between the quarter-wave plate 13A and the half-wave plate 13C, it is not necessary to have the vertically aligned liquid crystal layer 13B. The retardation plate 10 may have only the quarter-wave plate 13A and the half-wave plate 13C as the liquid crystal layer 13. Furthermore, the retardation plate 10 may have only the quarter-wave plate 13A or only the half-wave plate 13C as the liquid crystal layer 13.

[0069] Next, an example of the anisotropy of the storage modulus of the retarder 10 will be described, mainly with reference to FIG. 4. The liquid crystal layer 13 of the retarder 10 is difficult to stretch in the long axis direction of the liquid crystal molecules 13a (see FIG. 2(B)), but is easy to stretch in the short axis direction of the liquid crystal molecules 13a. The difficulty to stretch is expressed, for example, by the storage modulus. The storage modulus is measured in accordance with ISO 6721-4:1994. The difficulty to stretch is greatest in the direction in which the storage modulus is greatest.

[0070] If the liquid crystal molecules 13a are aligned in a planar view, the storage modulus of the liquid crystal layer 13 changes in a 180° cycle in a planar view. In this specification, a planar view means a view from a direction perpendicular to the plate surface of the retarder 10. In the vertically aligned liquid crystal layer 13B, the liquid crystal molecules are aligned vertically, and the storage modulus is uniform in a planar view.

[0071] In plan view, the storage modulus of the quarter-wave plate 13A and the half-wave plate 13C changes in a 180° cycle. The storage modulus of the quarter-wave plate 13A is maximum in the θ1 direction and the θ5 direction shown in FIG. 4. The storage modulus of the half-wave plate 13C is maximum in the θ3 direction and the θ7 direction shown in FIG. 4.

[0072] If the storage modulus of the liquid crystal layer 13 changes in a 180° cycle when viewed from above, the storage modulus of the retarder 10 also changes in a 180° cycle when viewed from above.

[0073] For example, when the retarder 10 has a quarter-wave plate 13A and a half-wave plate 13C, the storage modulus of the retarder 10 is greatest in the θ2 direction and the θ6 direction. The θ2 direction bisects the θ1 direction and the θ3 direction. The θ6 direction bisects the θ5 direction and the θ7 direction. The θ2 direction and the θ6 direction are 180° apart.

[0074] Furthermore, when the retarder 10 includes a quarter-wave plate 13A and a half-wave plate 13C, the storage modulus of the retarder 10 is smallest in the θ4 direction and the θ8 direction. The θ4 direction and the θ8 direction are perpendicular to the θ2 direction and the θ6 direction. The θ4 direction and the θ8 direction are 180° apart.

[0075] The retardation plate 10 does not necessarily have to have both the quarter-wave plate 13A and the half-wave plate 13C, but may have either one of them. In the latter case, the storage modulus of the retardation plate 10 also changes in a 180° cycle in plan view.

[0076] Next, an example of an apparatus 100 for manufacturing an optical element 1 will be described, mainly with reference to FIGS. 5 to 8. As shown in FIGS. 7 and 8, the apparatus 100 for manufacturing an optical element 1 includes a first mold 110 and a second mold 120. Note that the adhesive layer 20 is not shown in FIGS. 7 to 8. The first mold 110 has a first plane 111 on which a first recess 113 is formed. The second mold 120 has a second plane 121 that faces the first plane 111 of the first mold 110.

[0077] The first mold 110 and the second mold 120 are arranged with the retardation plate 10 sandwiched between them. For example, the first mold 110 is arranged below the retardation plate 10, and the second mold 120 is arranged above the retardation plate 10. In this case, the first mold 110 is the lower mold, and the second mold 120 is the upper mold. A first flat surface 111 of the first mold 110 is the upper surface of the lower mold, and a second flat surface 121 of the second mold 120 is the lower surface of the upper mold.

[0078] Before the first mold 110 and the second mold 120 sandwich the retarder 10, the first recess 113 of the first mold 110 accommodates the three-dimensional structure 40 with the curved surface 40a of the three-dimensional structure 40 facing the second mold 120. The first recess 113 is formed, for example, in the upper surface of the lower mold, and accommodates the three-dimensional structure 40 with the curved surface 40a of the three-dimensional structure 40 facing upward.

[0079] The first mold 110 has first gas holes 114 in the first plane 111. A plurality of first gas holes 114 are formed at intervals along the periphery of the first recess 113 so as to surround the first recess 113. The first gas holes 114 are formed, for example, outside the periphery of the first recess 113 and inside the periphery of a second recess 123, which will be described later.

[0080] The manufacturing apparatus 100 for the optical element 1 includes a first gas supply unit 131 and a first gas suction unit 132. The first gas supply unit 131 injects gas (e.g., compressed air) from the first gas holes 114. The first gas suction unit 132 sucks gas (e.g., air) from the first gas holes 114. The gas hole for suction and the gas hole for injection may be provided separately.

[0081] The second mold 120 has a heater 122 that heats the retarder 10. The heater 122 includes, for example, an electric heater. After the retarder 10 is heated and softened, the retarder 10 can be bent.

[0082] The second mold 120 may have a second recess 123 on the second plane 121. The periphery of the second recess 123 is formed so as to surround the periphery of the first recess 113 in a plan view, as shown in FIG. 6. In the description of the manufacturing apparatus 100, a plan view means a view from a direction perpendicular to the first plane 111 or the second plane 121.

[0083] The second mold 120 has second gas holes 124 in a wall surface (e.g., a ceiling surface) of the second recess 123. A plurality of second gas holes 124 are formed at intervals along the periphery of the second recess 123. The second gas holes 124 are formed, for example, inside the periphery of the second recess 123 and outside the periphery of the first recess 113.

[0084] The manufacturing apparatus 100 for the optical element 1 includes a second gas supply unit 141 and a second gas suction unit 142. The second gas supply unit 141 injects gas (e.g., compressed air) from the second gas holes 124. The second gas suction unit 142 injects gas (e.g., air) from the second gas holes 124. The gas holes for suction and the gas holes for injection may be provided separately.

[0085] The manufacturing apparatus 100 for the optical element 1 includes a stress application unit 150. The stress application unit 150 applies stress to the retarder 10, which has been heated by the second mold 120, in order to bend a portion of the retarder 10 along the curved surface 40a of the three-dimensional structure 40. The stress application unit 150 includes, for example, a first gas supply unit 131, a first gas suction unit 132, a second gas supply unit 141, and a second gas suction unit 142. It is sufficient that the stress application unit 150 includes at least one of the first gas suction unit 132 and the second gas supply unit 141.

[0086] 5 to 8 again, an example of a method for manufacturing the optical element 1 will be described. The method for manufacturing the optical element 1 includes preparing a first mold 110 and a second mold 120. The method for manufacturing the optical element also includes accommodating the three-dimensional structure 40 in the first recess 113 of the first mold 110 with the curved surface 40a of the three-dimensional structure 40 facing the second mold 120.

[0087] 7(A) and 8(A), the method for manufacturing the optical element 1 includes sandwiching the retarder 10 between a first mold 110 and a second mold 120. The retarder 10 is placed on the first plane 111 so that the periphery of the retarder 10 coincides with the periphery of the first plane 111 of the first mold 110. This allows the alignment direction of the liquid crystal molecules to be adjusted to a desired direction.

[0088] In plan view, it is preferable that both the first mold 110 and the retarder 10 are rectangular with long and short sides. In plan view, the optical characteristics of the retarder 10 change in a 180° cycle. By overlapping the first mold 110 and the retarder 10 so that their long sides coincide with each other, the alignment direction of the liquid crystal molecules can be adjusted to a desired direction.

[0089] In addition, both the first mold 110 and the retarder 10 may be square in plan view. In this case, it is preferable that an alignment mark indicating the alignment direction of the liquid crystal molecules is formed on the retarder 10. Based on the alignment mark, the alignment direction of the liquid crystal molecules can be adjusted to a desired direction.

[0090] 7(B) and 8(B), the manufacturing method of the optical element 1 includes heating the retarder 10 with the second mold 120. At this time, the second gas suction unit 142 sucks gas from the second recess 123 through the second gas holes 124, thereby adsorbing the retarder 10 to the wall surface (e.g., ceiling surface) of the second recess 123. The retarder 10 is in close contact with the second mold 120, and heat from the second mold 120 is efficiently transferred to the retarder 10. At this time, the first gas supply unit 131 may inject gas into the second recess 123 through the first gas holes 114.

[0091] 7(C) and 8(C), the manufacturing method of the optical element 1 includes bending a part of the retarder 10 heated by the second mold 120 along the curved surface 40a of the three-dimensional structure 40. The stress application unit 150 injects gas from the second gas holes 124 and sucks gas from the first gas holes 114 to apply stress to the retarder 10. As a result, the retarder 10 is pressed against the three-dimensional structure 40.

[0092] Although not shown, the retarder 10 first contacts the center of the curved surface 40a of the three-dimensional structure 40, and then gradually contacts it from the center toward the periphery. This allows air to escape from the center toward the periphery, preventing air from getting trapped. The retarder 10 contacts the entire curved surface 40a of the three-dimensional structure 40. Any portion of the retarder 10 that extends beyond the curved surface 40a is cut away. This results in the optical element 1.

[0093] 6, the second mold 120 has first heated regions 125 and second heated regions 126 at 180° intervals in an area that overlaps with the first recess 113 of the first mold 110 in a plan view. The first heated region 125 contacts the portion of the retarder 10 where the storage elastic modulus is minimum. The second heated region 126 contacts the portion of the retarder 10 where the storage elastic modulus is maximum. The heating temperature (°C) of the first heated region 125 is 80% to 97% of the heating temperature (°C) of the second heated region 126.

[0094] The smaller the storage modulus of the retarder 10, the greater the elongation of the retarder 10. Furthermore, the lower the temperature of the retarder 10, the smaller the elongation of the retarder 10. In this embodiment, the heating temperature (°C) of the first heating region 125 is 80% to 97% of the heating temperature (°C) of the second heating region 126, so that the retarder 10 can be uniformly elongated. This reduces variations in the thickness of the retarder 10, and also reduces variations in the retardation Rd of the retarder 10.

[0095] The heating temperature (°C) of the first heating area 125 may be 80% to 97% of the heating temperature (°C) of the second heating area 126, preferably 82% to 90%, and more preferably 84% to 88%.

[0096] The heater 122 of the second mold 120 may heat both the first heating region 125 and the second heating region 126. In this case, the second mold 120 has a heat insulating layer 127 that creates a temperature difference between the first heating region 125 and the second heating region 126. The heat insulating layer is, for example, a silicone rubber sheet. The heat insulating layer 127 is attached to, for example, a metal plate. In this case, the heat insulating layer 127 forms the first heating region 125, and the metal plate forms the second heating region 126.

[0097] The heat insulating layer 127 forms a step between the first heating region 125 and the second heating region 126. The thicker the heat insulating layer 127, the greater the temperature difference between the first heating region 125 and the second heating region 126. The thickness of the heat insulating layer 127 is adjusted so that the heating temperature (°C) of the first heating region 125 is 80% to 97% of the heating temperature (°C) of the second heating region 126.

[0098] Although not shown, the second mold 120 may have a heater for heating the first heating region 125 and a heater for heating the second heating region 126 separately. In this case, by independently setting the outputs of the multiple heaters, a temperature difference can be created between the first heating region 125 and the second heating region 126. In this case, the second mold 120 can have the first heating region 125 and the second heating region 126 on the same plane. [Example]

[0099] Experimental data will be described below. In Example 1, Comparative Example 1, and Comparative Example 2, optical elements 1 were fabricated under the same conditions except for the presence or absence of the heat insulating layer 127 and the thickness of the heat insulating layer 127. In Example 1, a 3.0 mm thick silicone rubber sheet was used as the heat insulating layer 127, thereby reducing the temperature of the first heated region 125 (103°C) to 86% of the temperature of the second heated region 126 (120°C). In Comparative Example 1, the heat insulating layer 127 was not used, thereby making the temperature of the first heated region 125 (120°C) the same as the temperature of the second heated region 126 (120°C). In Comparative Example 2, a 5.0 mm thick silicone rubber sheet was used as the heat insulating layer 127, thereby reducing the temperature of the first heated region 125 (95°C) to 79% of the temperature of the second heated region 126 (120°C).

[0100] In Example 1, Comparative Example 1, and Comparative Example 2, a retarder 10 was prepared, which included 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, as shown in FIG. 3 . A TAC film was prepared as the transparent substrate 11. The alignment layer 12A was formed by a transfer method using NK Ester ADCP manufactured by Shin-Nakamura Chemical Co., Ltd., forming a stripe pattern grating (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 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 transferring a stripe pattern grating (pitch p: 90 nm, groove depth D: 30 nm, thickness T2: 5.1 μm) using NK Ester ADCP (manufactured by Shin-Nakamura Chemical Co., Ltd.) by a transfer method. The half-wave plate 13C was formed by spin-coating LC242 (manufactured by BASF) onto the alignment layer 12A, drying it by heating, and curing it by UV exposure. The thickness T3 of the half-wave plate 13C was 2.3 μm.

[0101] Next, the adhesive layer 20 was attached to the retardation film 10 (specifically, the transparent substrate 11) to produce the laminate 30. The adhesive layer 20 was attached using a hand roller.

[0102] 7(A) and 8(A), the three-dimensional structure 40 was placed in the first recess 113 of the first mold 110, and the retardation plate 10 was placed on the first flat surface 111 of the first mold 110. Thereafter, the second mold 120 was placed on top of the retardation plate 10.

[0103] 7(B) and 8(B), the second mold 120 adsorbed the retarder 10 onto the wall surface of the second recess 123. In this state, the second mold 120 heated the retarder 10, and the retarder 10 was softened.

[0104] Next, as shown in Figures 7(C) and 8(C), the second gas supply unit 141 injected gas at 0.9 MPa from the second gas holes 124, and the first gas suction unit 132 sucked gas from the first gas holes 114, thereby pressing the retarder 10 against the three-dimensional structure 40. The retarder 10 first contacted the center of the curved surface 40a of the three-dimensional structure 40, and then gradually contacted the three-dimensional structure 40 from the center toward the periphery. After that, the portion of the retarder 10 that protruded from the curved surface 40a was cut off. In this way, the optical element 1 was produced.

[0105] The retardation Rd of the optical elements fabricated in Example 1, Comparative Example 1, and Comparative Example 2 was measured by converting a laser (manufactured by Thorlabs, model LP520-SF15A, wavelength 520 nm) into linearly polarized light at a desired angle through a polarizer, then converting it into circularly polarized light perpendicular to the optical element. The converted circularly polarized light was then incident on a polarimeter to determine the Stokes parameter, which was then converted into Rd. Measurement points were arranged at equal intervals on a 15 mm circumference from the center of gravity P0 of the curved surface 40a, from the 0° direction to the 360° direction, at 5° intervals. Note that the -x direction in FIG. 4 corresponds to the 0° direction and the 360° direction, the +y direction in FIG. 4 corresponds to the 90° direction, the +x direction in FIG. 4 corresponds to the 180° direction, and the -y direction in FIG. 4 corresponds to the 270° direction. The measurement results for retardation Rd are shown in FIG. 9 together with the measurement results for storage modulus G'. In FIG. 9, the values of the retardation Rd and the storage modulus G' are relative values.

[0106] 9, it can be seen that Example 1 can reduce the variation in retardation Rd of the optical element compared to Comparative Examples 1 and 2. The variation in retardation Rd in Example 1 was 1.8 nm, the variation in retardation Rd in Comparative Example 1 was 5.0 nm, and the variation in retardation Rd in Comparative Example 2 was 4.0 nm.

[0107] The optical element manufacturing method and optical element manufacturing apparatus according to the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0108] 1 Optical elements 10 Retardation plate 13 Liquid crystal layer 20 Adhesive layer 40 3D structures 40a curved surface 100 Manufacturing equipment 110 Type 1 111 1st plane 113 First recess 120 Type 2 121 2nd plane 125 1st heating area 126 2nd heating area

Claims

1. A method for manufacturing an optical element, comprising: manufacturing an optical element including 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, preparing a first mold having a first plane in which a first recess is formed, and a second mold having a second plane opposite to the first plane of the first mold; placing the three-dimensional structure in the first recess of the first mold with the curved surface of the three-dimensional structure facing the second mold; sandwiching the retardation plate between the first mold and the second mold; Heating the retarder with the second mold; bending a part of the retardation plate heated in the second mold along the curved surface of the three-dimensional structure; and The storage modulus of the retardation plate at room temperature in a plan view changes in a 180° cycle, the second mold has, in a region overlapping with the first recess of the first mold in a plan view, a first heated region in contact with a portion of the retardation plate where the storage elastic modulus is minimum and a second heated region in contact with a portion of the retardation plate where the storage elastic modulus is maximum, arranged at a 180° interval; A method for manufacturing an optical element, wherein the heating temperature (°C) of the first heating region is 80% to 97% of the heating temperature (°C) of the second heating region.

2. 2. The method for manufacturing an optical element according to claim 1, wherein the second mold has separate heaters for heating the first heating region and heaters for heating the second heating region, and the first heating region is on the same plane as the second heating region.

3. The method for manufacturing an optical element described in claim 1, wherein the second mold has a heater that heats both the first heating area and the second heating area, and a heat insulating layer that creates a temperature difference between the first heating area and the second heating area.

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

5. The method for manufacturing an optical element according to claim 4 , wherein the retardation plate has a vertically aligned liquid crystal layer between the half-wave plate and the quarter-wave plate.

6. An optical element manufacturing apparatus for manufacturing an optical element including 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, a first mold having a first plane in which a first recess is formed, and a second mold having a second plane opposite to the first plane of the first mold, the first recess accommodates the three-dimensional structure with the curved surface of the three-dimensional structure facing the second mold; the first type and the second type are disposed with the retardation plate therebetween, the second mold has a heater that heats the retardation plate, the manufacturing apparatus includes a stress applying unit that applies stress to the retardation plate so as to bend a portion of the retardation plate heated by the second mold along the curved surface of the three-dimensional structure; The storage modulus of the retardation plate at room temperature in a plan view changes in a 180° cycle, the second mold has, in a region overlapping with the first recess of the first mold in a plan view, a first heated region in contact with a portion of the retardation plate where the storage elastic modulus is minimum and a second heated region in contact with a portion of the retardation plate where the storage elastic modulus is maximum, arranged at a 180° interval; An optical element manufacturing apparatus, wherein the heating temperature (°C) of the first heating region is 80% to 97% of the heating temperature (°C) of the second heating region.

7. 7. The optical element manufacturing apparatus of claim 6, wherein the second mold has separate heaters for heating the first heating region and heaters for heating the second heating region, and the first heating region is on the same plane as the second heating region.

8. The optical element manufacturing apparatus of claim 6, wherein the second mold has a heater that heats both the first heating area and the second heating area, and a heat insulating layer that creates a temperature difference between the first heating area and the second heating area.

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