Wire grid type polarizing element and manufacturing method thereof

Abstract

Provided are: a wire grid type polarizing element having an excellent degree of polarization and having a high rate of polarized light transmittance in a perpendicular direction; and a manufacturing method thereof.　This wire grid type polarizing element includes: a base material formed such that a transparent sheet surface has a cross-section having a continuous wave shape; electroconductor protrusions that are continuous with tips of the wave shape, extending in a perpendicular direction that is perpendicular to an array direction, the electroconductor protrusions protruding in a direction in which the tips extend; and an electroconductor layer covering a surface section of said protrusions excluding the tips. The period (a) of the wave shape is 100-400 nm, the average depth (b) from convex tips of the wave shape to valleys of recesses of the wave shape is 200-600 nm, the average occupancy ([2d / a]×100) of the electroconductor layer, which is the ratio of the average width (d) in the array direction of two electroconductor layers present inside one cycle relative to the period (a), is 18-40%, and the average thickness (h) in the tip direction of the electroconductor protrusions is at least 1.5 times the average width (d) of the electroconductor layer.

Description

Wire grid polarizing element and method for manufacturing the same

[0001] The present invention relates to a wire-grid polarizing element that can be applied to the field of optical products such as displays, cameras, sunglasses, and optical measuring instruments that use electromagnetic waves such as visible light and near-infrared light, and a method for manufacturing the same.

[0002] Wire-grid polarizing elements have a substrate containing a layer of linear metal or other materials arranged in stripes at a specific period, and utilize this property to reflect or absorb light with an electric field component parallel to the linear materials, while transmitting light with an electric field component perpendicular to the linear materials, provided that the period is sufficiently smaller than the wavelength of the incident electromagnetic wave (light).Wire-grid polarizing elements are characterized by their excellent optical properties, which enable them to exhibit polarizing function over a wide wavelength range from visible light to near-infrared light, and their high durability.

[0003] Patent Document 1 listed below discloses a wire grid polarizer in which a base layer made of a metal oxide layer is formed on the tops of convex stripes of a transparent substrate having a textured structure and on all of the side surfaces thereof, and thin metal wires made of a metal layer are formed on at least the tops of the convex stripes and on 70% or more of the area of ​​the side surfaces of the convex stripes by an oblique vapor deposition method using a vacuum vapor deposition method, and a method for producing the same.

[0004] Patent Document 2 listed below discloses a wire grid polarizer with excellent polarization properties, which is obtained by making particles incident from an oblique direction onto the uneven surface of a grid structure layer on a transparent substrate having a one-dimensional lattice-like uneven structure, using a dry process such as sputtering or vacuum deposition, and forming an Al-Si alloy layer with a Si content of 0.05 to 1.5 wt % on the convex portions of the uneven structure, and a method for manufacturing the same.

[0005] Patent Document 3 listed below discloses an optical functional body having a filling layer formed on a substrate having a fine concave-convex pattern by electroless plating, with particles having a particle size smaller than the width of the concave portions of the concave-convex pattern, so as to fill the concave portions, and a method for manufacturing the same. It is generally known that in wire grid polarizing plates, the transmittance increases when the width of the conductive wires is made narrower relative to the period, and the light blocking performance of light with respect to the electric field component parallel to the wires is improved when the thickness of the conductive wires is made thicker (see Non-Patent Document 1). Therefore, Patent Document 3 shows that the concave-convex structure can be produced inexpensively by using a nanoimprint method to form the concave-convex structure.

[0006] Patent Document 4 discloses a polarization splitter element made of a triangular-wave metal thin film, which has periodicity in one of two orthogonal directions and is uniform in the other direction, and whose cross-sectional shape along the one direction is continuously repeated at a constant period equal to or less than the wavelength, and which satisfies the following conditions: Λ / λmin < 0.5, h > 1.5Λ d > 0.010 μm, where Λ is the period, h is the depth of the triangular-wave groove, d is the thickness of the metal thin film in the depth direction of the triangular-wave groove, and λmin is the minimum wavelength in the wavelength range used. That is, with regard to the shape of the metal thin film, the upper limit of the period Λ and the lower limits of the groove depth h and the thickness d of the metal thin film are disclosed.

[0007] Japanese Patent No. 5459210 Japanese Patent Publication No. 2009-204894 Japanese Patent No. 6042642 Japanese Patent No. 4650931

[0008] Low-reflective wire-grid polarizers with an absorptive layer formed by glancing angle deposition. Visual Information Media Magazine, Vol. 65, No. 10, pp. 1440-1445 (2011)

[0009] In the invention disclosed in Patent Document 1, when thin metal wires made of a metal layer are formed on the tops and side surfaces of the protrusions of a substrate by vapor deposition, the generation of minute metal particles due to crystallization of the metal material is suppressed, thereby reducing the transmittance of incident light through the polarizing element. A base layer made of a metal oxide layer is provided to prevent this. Furthermore, in order to form a metal layer on part of the side surfaces of the protrusions by oblique vapor deposition, there is a restriction that the height of the protrusions from the bottom of the concave portion of the uneven shape to the tip of the convex portion cannot be increased. For example, in Examples 1 to 11 corresponding to the working examples in the specification of Patent Document 1, the height of the protrusions is approximately 100 nm, and accordingly, the thickness of the metal layer formed on the tops of the convex shapes is also increased to improve the polarization degree. Therefore, there are restrictions on the uneven structure formed on the substrate.

[0010] The object of the invention disclosed in Patent Document 2 is to solve the problem that when pure aluminum (Al) is used as the metal constituting the wire grid, the pure Al particles formed on the convex portions of the substrate by a dry process are not refined, and therefore the designed polarization characteristics cannot be obtained. To solve this problem, an Al-Si alloy with a Si content of 0.05 to 1.5 wt % is used as the metal constituting the wire grid, thereby refining the particles formed on the convex portions and improving the polarization characteristics. However, the application of the invention disclosed in Patent Document 2 is limited to cases where an Al-based metal is formed on a substrate by a dry process as the metal constituting the wire grid.

[0011] The wire grid polarizer produced by the electroless plating method described in Patent Document 3 has a polarization degree of only about 90%. In order to increase the polarization degree while maintaining the transmittance, it is necessary to increase the aspect ratio (ratio of thickness to width) of the recesses filled with the conductor. However, in this case, there is a risk that the mold used to provide the uneven shape on the substrate may be destroyed and the uneven structure may collapse, so there are practical limitations to increasing the aspect ratio.

[0012] Patent Document 4 discloses that a polarization function is exhibited in a structure having a metal thin film with a triangular waveform cross section. However, the specification of the shape of the metal thin film only discloses an upper limit of the period for the wavelength range used, a lower limit of the height of the triangular waveform for the period, and a lower limit of the thickness of the metal thin film. Figures 1 and 3 in the examples of the document both disclose metal thin films with a period of 0.12 μm, a height (h) of 0.30 μm, and a depth direction thickness (d) of 0.03 μm. However, because the thickness perpendicular to the metal thin film surface is relatively thin and the width of the metal thin film in the periodic direction is also small, its polarization characteristics are approximately 70-75% for reflected S-polarized light and approximately 60-80% for transmitted P-polarized light in the wavelength range of 0.40-0.70 μm. Therefore, further study is needed to obtain a structure with a high degree of polarization. Also, as methods for producing a metal thin film, a method of laminating a metal thin film on a transparent substrate and a method of removing the transparent substrate from the metal thin film laminated on the transparent substrate and supporting the metal thin film on a rectangular frame or the like have been disclosed. However, it is not easy to produce a thin film with a large amplitude and a triangular waveform, and there is a risk that the tip of the thin film will be broken, and there is also a risk that it will be difficult in practice to remove the substrate from the metal thin film laminated on the substrate.

[0013] None of the above patent documents discloses a wire-grid polarizing element having a high transmittance and an excellent degree of polarization, in which a conductive layer made of various conductive materials is disposed on a substrate having a shape that can be stably manufactured, nor does it disclose a method for manufacturing such an element. The present invention has been made in view of this, and an object of the present invention is to provide a wire-grid polarizing element that exhibits a high degree of polarization and a high single transmittance (visible transmittance for light polarized perpendicular to the incident light), which can be manufactured inexpensively and stably, and a method for manufacturing such an element.

[0014] In view of the above-mentioned prior art, the inventors have discovered that a wire-grid polarizing element having a transparent sheet surface with a continuous corrugated cross section along the arrangement direction of a concave-convex pattern, with the surface of a substrate having a specific range of period and a specific depth from the tips of the convex portions to the valleys of the concave portions in the concave-convex pattern, and a conductor layer covering the surface except for the tips of the convex portions of the concave-convex pattern, the conductor layer being formed so that the ratio of the width of the two conductor layers present in one period to the period in the arrangement direction, i.e., the conductor layer occupation rate, is within a specific range, and the average thickness of the conductor protrusions provided at the tips of the convex portions of the concave-convex pattern is at least a certain multiple of the width of the conductor layer in the arrangement direction, maintains an excellent degree of polarization and high light transmittance, and further that the wire-grid polarizing element can be relatively easily manufactured using a general-purpose conductor formation method without the need for a partial conductor removal process, thereby completing the present invention. That is, the gist of the present invention is as described in the following (1) to (8).

[0015] (1) A wire grid polarizing element comprising: a substrate on the surface of which a periodic uneven pattern is formed, the uneven pattern having a cross section along the arrangement direction of the uneven pattern being a continuous wave shape; and conductor protrusions formed on the surface of the substrate, the conductor protrusions being formed by further protruding in the direction of the tip from the tip of each convex portion formed extending in the longitudinal direction in the uneven pattern, and a conductor layer covering the surface except for the tips of the convex portions, wherein the period (a) of the uneven pattern on the surface of the substrate is 100 to 400 nm, the average depth (b) from the tip of the convex portion to the valley of the concave portion of the uneven pattern on the surface of the substrate is 200 to 600 nm, the average occupancy rate ([2d / a] x 100) of the conductor layer, expressed as the ratio of the average width (d) in the arrangement direction of two conductor layers present within each period to the period (a), is 18 to 40%, a wire grid polarization element characterized in that the average thickness (h) in the tip direction of the conductor protrusions provided at the tips of the convex portions of the uneven pattern is 1.5 times or more the average width (d) in the arrangement direction of the conductor layer.

[0016] (2) The wire-grid polarization element according to (1), wherein the average thickness (h) in the tip direction of the conductor protrusions provided at the tips of the convex portions of the concave-convex pattern on the surface of the substrate is 1.5 to 5 times the average width (d) in the arrangement direction of the conductor layers. (3) The wire-grid polarization element according to (1) or (2), wherein the average width (d) in the arrangement direction of the conductor layers arranged on the surface portion of the substrate excluding the tips of the convex portions of the concave-convex pattern on the surface of the substrate is 14 to 70 nm. (4) The wire-grid polarization element according to any one of (1) to (3), wherein the cross section of the wire-grid polarization element formed on the surface of the substrate along the arrangement direction has a triangular wave shape consisting of a continuous wave shape in the shape of an approximately isosceles triangle.

[0017] (5) The wire-grid polarization element according to any one of (1) to (4), wherein the cross-sectional shape in the arrangement direction of the conductor protrusions provided at the tips of the convex portions of the concave-convex pattern on the surface of the substrate and protruding toward the tips is a substantially rectangular, tapered, expanded at the tip, or substantially vertically elliptical. (6) The wire-grid polarization element according to any one of (1) to (5), wherein the conductor material forming the conductor protrusions and the conductor layer is one or more metals selected from aluminum, gold, silver, copper, platinum, molybdenum, nickel, chromium, titanium, tungsten, tantalum, zirconium, iron, niobium, hafnium, cobalt, palladium, bismuth, and neodymium, or an alloy of two or more of these metals.

[0018] (7) A method for manufacturing a wire grid polarizing element, comprising: forming, on the surface of a substrate having a periodic concave-convex pattern formed on the surface of a transparent sheet, the concave-convex pattern having a continuous wave-like cross section along the arrangement direction thereof, conductor protrusions formed at the tips of each convex portion formed extending in the longitudinal direction in the concave-convex pattern so as to further protrude in the direction of the tip; and forming a conductor layer covering the surface except for the tips of the convex portions, the period (a) of the concave-convex pattern on the surface of the substrate being 100 to 400 nm, and the average depth (b) from the tips of the convex portions to the valleys of the concave-convex pattern on the surface of the substrate being 200 to 600 nm, by a physical vapor deposition method in which a vapor deposition material is introduced from above in a direction perpendicular to the surface of the substrate, or by using tin ions (Sn２＋ ) and a liquid containing palladium ions (Pd ２＋ (8) A method for manufacturing a wire-grid polarizing element according to (7), wherein the physical vapor deposition is one of vacuum deposition, electron beam deposition, and sputtering, and the method comprises: forming a conductive layer having an average occupancy ([2d / a] x 100) of 18 to 40%, which is expressed as the ratio of the average width (d) of two conductive layers present in one period in the arrangement direction to the period (a), and conductive protrusions provided at the tips of the convex portions of the concave-convex pattern, the average thickness (h) in the tip direction of the conductive protrusions being 1.5 times or more the average width (d) of the conductive layers in the arrangement direction.

[0019] The wire-grid polarizing element of the present invention can improve the polarization degree by configuring the substrate so that the period (a) of the corrugated uneven pattern on its surface and the average depth (b) from the tips of the convex portions to the valleys of the concave portions are constant, and by configuring the conductor arranged on the surface of the substrate so that the ratio (2d / a) of the period (a) to the average width (d) of the conductor layer excluding the tips of the convex portions is within a certain range, and by configuring the ratio (h / d) of the thickness (h) of the conductor protrusions provided at the tips of the convex portions in the tip direction to the average width (d) of the conductor layer is constant, the polarization degree can be further improved and a required light transmittance can be maintained. Furthermore, compared to structures with a rectangular cross-sectional shape of the uneven structure, the polarizing element of the present invention using a corrugated uneven structure has a width that gradually changes in the thickness direction even for structures with the same depth (thickness), so that structural damage due to peeling of the conductor layer is less likely to occur. Furthermore, by selecting the material used for the substrate sheet, a wire-grid polarizing element with excellent environmental resistance, bendability, and stretchability can be easily obtained.

[0020] In the manufacturing method of the present invention for a wire-grid polarizing element having a corrugated cross section, molding methods such as film insert molding, cast molding, and injection molding can be used to mold the substrate, making it possible to produce three-dimensional curved molded products that can extract specific polarization components. Furthermore, when arranging a conductor on a substrate with a corrugated surface, general-purpose film-forming equipment can be used for common physical vapor deposition methods such as vacuum deposition, electron beam deposition, and sputtering, as well as electroless plating. Combining these processes makes commercial production relatively easy, and market expansion is expected, including applications to optical components. Furthermore, this manufacturing method is less likely to produce void-like defects even in post-processing steps such as hard coating.

[0021] 1A and 1B are explanatory conceptual diagrams showing an example of a wire-grid polarizing element of the present invention, where (1) is a perspective view, (2) is a cross-sectional view, and (3) is an enlarged view of part A in (2).

[0033] FIG. 1C is a conceptual diagram for explaining the conductor occupancy rate in three cross sections of a wire-grid polarizing element of the present invention.

[0034] FIG. 1D is a longitudinal cross-sectional view showing the positions of the three cross sections, where (2) is a cross-sectional view taken along line B-B, (3) is a cross-sectional view taken along line C-C, and (4) is a cross-sectional view taken along line D-D.

[0035] FIG. 1E is a conceptual diagram showing a cross section of another example of a wire-grid polarizing element of the present invention.

[0036] FIG. 1F is a conceptual diagram showing a cross section of an example of a wire-grid polarizing element of the present invention where an underlayer is provided.

[0037] FIG. 1G is a conceptual diagram showing a cross section of an example of a wire-grid polarizing element of the present invention where a coating layer is provided.

[0038] FIG. 1H is a cross-sectional view schematically showing examples of steps (1) to (4) for manufacturing a wire-grid polarizing element of the present invention.

[0039] FIG. 1I is an image (SEM image) of the cross section of the mold prepared in Example 1, observed with a scanning electron microscope (SEM). 1 is a SEM image of a cross section of a polarizing element test piece of the present invention prepared in Example 1-1. FIG. 2 is a SEM image of a cross section of a polarizing element test piece of the present invention prepared in Example 3. FIG. 3 is a SEM image of a cross section of a polarizing element test piece of the present invention prepared in Example 4-2. FIG. 4 is a cross section of a model of a polarizing element having a cross section of (1) rectangular, (2) trapezoidal, or (3) triangular wave, which was used in the numerical calculation of the optical properties in Reference Examples 1 and 2. FIG. 5 is a graph showing the results of numerical calculation of the optical properties of the polarizing element in Reference Example 1. FIG. 6 is a model diagram used in the numerical calculation of the optical properties of each of the triangular wave polarizing elements (1), (2), and (3) in Reference Example 3. FIG. 7 is a SEM image of a cross section of a mold prepared in Comparative Example 1. FIG. 8 is a SEM image of a cross section of a polarizing element test piece prepared in Comparative Example 1.

[0022] The present invention will be described below, divided into (1) a wire-grid polarizing element and (2) a method for manufacturing a wire-grid polarizing element. (1) Wire-grid polarizing element The elements and structure constituting the wire-grid polarizing element of the present invention will be described. Note that in the wire-grid polarizing element of the present invention, the shape of the conductor is not what is commonly called a "wire-like" shape, but the term "wire-grid polarizing element" is used in the relevant technical field even when the metal reflector is not wire-like, so the term wire-grid polarizing element will be used.

[0023]

[0023] Hereinafter, embodiments of the wire-grid polarizing element of the present invention will be described with reference to the drawings. Fig. 1(1) is a perspective view showing an example of a wire-grid polarizing element 11 of the present invention, in which a conductor layer 25 and conductor protrusions 26 are formed on the surface of a substrate 21. Fig. 1(2) is a cross-sectional view taken along the arrangement direction of the concave-convex pattern. Fig. 1(3) is a partially enlarged view of part A in Fig. 1(2). The notations shown in Figs. 1(2) and 1(3) for the period (a) of the concave-convex pattern on the substrate 21, the depth (b) from the tips 22 of the convex portions to the valleys of the concave portions 23, the average thickness (c) of the conductor layer 25 in the direction perpendicular to the surface of the wire-grid polarizing element 11, the average width (d) of the conductor layer 25 in the arrangement direction, the average width (e) of the conductor protrusions 26 provided at the tips 22 of the convex portions, and the average thickness (h) of the conductor protrusions 26 in the direction toward the tips are also used in other embodiments.

[0024] [Substrate] As shown in FIG. 1 , substrate 21 constituting the wire-grid polarizing element of the present invention is a transparent sheet whose surface is shaped so that a cross section along the arrangement direction of a periodic concave-convex pattern has a continuous wave shape, and the period (a) of the wave-shaped concave-convex pattern on the surface of substrate 21 is 100 to 400 nm, and the average depth (b) from tips 22 of convex portions to valleys of concave portions 23 of the concave-convex pattern is 200 to 600 nm.

[0025] As shown in Figures 1(1) and 1(2), the surface side of the substrate 21 is provided with protrusion tips 22 and recesses 23. In the case of such a corrugated shape, a slope is formed with respect to the direction in which light rays are incident from above, perpendicular to the substrate surface. Therefore, as described below, forming a conductive material layer on the surface of such a substrate can be expected to improve the degree of polarization. A specific example of the corrugated shape is a triangular corrugated shape, as shown in Figure 1(2), in which the corrugated portion of the substrate 21 is a continuous, approximately isosceles triangle. On the other hand, the effects of the present invention can also be achieved with a bullet shape or a sine wave shape, as shown by substrate 41 in Figure 3, or a shape in which the corrugated portion of the substrate has a portion parallel to the depth direction as part of the uneven structure, such as a countersunk screw shape without threads, as shown by substrate 42 in Figure 4. Furthermore, the cross-sectional shapes of the two sloped portions between the protrusions and recesses within one period do not have to be the same; one may be a triangular corrugated shape and the other a sine wave corrugated shape.

[0026] The average period (a) of the uneven pattern formed on the surface of the substrate generally needs to be equal to or less than the wavelength of the target incident electromagnetic wave, and therefore, when the target light range is primarily the visible light range, the average period (a) of the polarizing element of the present invention is selected from the range of 100 to 400 nm, preferably 100 to 200 nm. The depth (b) of the uneven pattern on the surface of the substrate, i.e., the depth (b) from the tip 22 of the convex portion to the valley of the concave portion 23 as shown in Figure 1 (2), depends on the physical properties of the conductive material, but from the perspective of ease of fabrication and durability of the substrate, it is sufficient to be 0.1 times or more the wavelength of the target electromagnetic wave, preferably about 0.5 to 1 time. However, in consideration of improving the degree of polarization, the depth (b) of the uneven pattern is selected from the range of 200 to 600 nm. In Reference Example 2 described later, the shape model of FIG. 12(1) was used as the target, and numerical calculations using rigorous coupled wave analysis were used to calculate changes in optical properties (degree of polarization and single transmittance (visible transmittance of polarized light perpendicular to the incident light)) when the depth (b) of the uneven structure increases in the range of 200 nm to 1000 nm. As a result, as shown in Table 4, the numerical calculations also confirmed that the degree of polarization improves as the depth (b) increases. In addition, from the viewpoints of moldability when producing the substrate and mechanical strength as a polarizing element, the depth (b) is preferably 600 nm or less.

[0027] The substrate 21 used in the wire-grid polarizing element of the present invention may be any material that is transparent to electromagnetic waves of the target wavelength, such as the visible light region or the infrared region, and examples thereof include amorphous thermoplastic resins such as polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cycloolefin polymer resin, cross-linked polyethylene resin, polyvinyl chloride resin, polyarylate resin, polyphenylene ether resin, modified polyphenylene ether resin, polyetherimide resin, polyethersulfone resin, polysulfone resin, and polyetherketone resin; crystalline thermoplastic resins such as polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polybutylene terephthalate resin, aromatic polyester resin, polyacetal resin, and polyamide resin; UV-curable resins and thermosetting resins such as acrylic, epoxy, and urethane; organic substrates such as triacetate resin; and inorganic substrates such as glass, silicon, quartz, and ceramic materials. Furthermore, such substrates are preferably single-layered in consideration of stretching processes such as bending, but may also be multi-layered.

[0028] [Wire-grid polarizing element] As shown in FIG. 1 , in a wire-grid polarizing element 11 of the present invention, conductor protrusions 26 formed on the surface of a substrate 21 having a corrugated cross section are formed so as to further protrude in the tip direction from tips 22 of each convex portion formed extending in the longitudinal direction of the uneven pattern, and conductor layers 25 covering the surface except for the tips of the convex portions, and the average occupancy rate ([2d / a] × 100) of the conductor layers 25, expressed as the ratio of the average width (d) in the arrangement direction of two conductor layers 25 present within one period to the period (a), is 18 to 40%, and the average thickness (h) in the tip direction of the conductor protrusions 26 provided on the tips 22 of the convex portions is 1.5 times or more the average width (d) in the periodic direction of the conductor layers.

[0029] In Reference Example 1 described below, numerical calculations were performed using rigorous coupled wave analysis to examine the changes in optical properties as the shape displacement (s) increased, with reference to the shape models of the polarizing element shown in Figures 12(1) to 12(3). When the cross section shown in Figure 12(1) is rectangular, the displacement (s) is 0 nm. As the displacement (s) is increased, the cross section shown in Figure 12(2) becomes trapezoidal. As the displacement (s) is further increased, the cross section shown in Figure 12(3) becomes triangular, with the displacement (s) reaching 70 nm. The numerical calculations confirmed that increasing the amount of displacement (s) improves the single-piece transmittance, as shown in Table 3. The conductive layer 25, which is provided to cover the surface of the substrate except for the tips 22 of the convex portions of the concave-convex pattern, is preferably formed to a substantially uniform thickness. However, the conductive layer 25 may be thicker on the tip 22 side of the convex portions than on the concave portion 23 side, or may be thinner on the tip 22 side of the convex portions than on the concave portion 23 side, and some deviation in film thickness is acceptable.

[0030] 1(3), the average width (d) of the conductor layers 25 in the arrangement direction or the average thickness (c) in the direction perpendicular to the surface can be selected from a range of about 0.005 to 0.4 times the period (a) for each layer in the direction of propagation of the electromagnetic wave, i.e., the direction from the tips 22 of the convex portions of the concave-convex structure to the concave portions 23. However, when the incident light is in the visible or near-infrared wavelength range, it is desirable to select the average width (d) of the conductor layers 25 in the arrangement direction from a range of 14 to 70 nm in consideration of improving the degree of polarization. The structure of the wire-grid polarizing element described above can also be used for electromagnetic waves in wavelength ranges other than the visible light range, such as the ultraviolet, near-infrared, infrared, terahertz, and microwave ranges, as long as the magnification range is the same.

[0031] In the wire-grid polarizing element of the present invention, two conductor layers are present in the region shown in Figure 2 (3) in one period of the corrugated uneven pattern, and the average occupancy of the conductor layers ([2d / a] x 100), which is expressed as the ratio of the average width (d) of the two conductor layers in the arrangement direction to the period (a) of the corrugated uneven pattern, is selected from the range of 18 to 40% in consideration of improving the degree of polarization. Furthermore, in Reference Example 1 described below, using the geometric model of Figure 12 (1), numerical calculations were performed using rigorous coupled wave analysis to calculate the changes in optical properties when the average thickness (c) of the conductor layer 25 in the direction perpendicular to the surface increases. It was confirmed that, as shown in Table 3, the degree of polarization tends to improve when the average thickness (c) increases from 5 nm to 10 nm and then to 15 nm.

[0032] The wire-grid polarizing element of the present invention is characterized in that a substrate is formed so as to have a continuous wave shape in a cross section along the arrangement direction of the uneven pattern, and is provided with a conductor layer 25 covering the substrate surface 24 except for the tips of the convex portions of the uneven pattern, and conductor protrusions 26 that protrude continuously from the tips 22 of the convex portions of the uneven pattern in a direction perpendicular to the arrangement direction toward the tips. The shape of such conductor protrusions 26 is not particularly limited, and examples of the cross-sectional shape in the arrangement direction include a substantially rectangular shape, a tapered shape, a thickened tip shape, and a substantially vertically elliptical shape. Of these, a substantially rectangular shape is preferred. Furthermore, in consideration of improving the degree of polarization, the average thickness (h) in the tip direction of the conductor protrusions 26 provided at the tips 22 of the convex portions of the uneven pattern on the substrate 21 is 1.5 times or more, and preferably 1.5 to 5.0 times, the average width (d) in the arrangement direction of the conductors 25. In Reference Example 3 described below, numerical calculations were performed using the rigorous coupled wave analysis method on the shape models shown in Figures 14(1) to 14(3) to examine the changes in optical properties when the average thickness (h) of the conductor protrusions 26 in the tip direction increases. As a result, as shown in Table 5, the numerical calculations confirmed that the degree of polarization tends to improve as the ratio (h / d) of the average thickness (h) of the conductor protrusions 26 in the tip direction to the average width (d) increases from 1 to 10. Furthermore, the average width (e) of the conductor protrusions 26 is preferably 0.005 to 0.4 times the period (a).

[0033] The conductor material used in the present invention can be any material that functions as a conductor in the wavelength range used. Specific examples include one or more metals selected from aluminum, gold, silver, copper, platinum, molybdenum, nickel, chromium, titanium, tungsten, tantalum, zirconium, iron, niobium, hafnium, cobalt, palladium, bismuth, and neodymium, or alloys of two or more of these metals. However, not only metals but also semiconductors can be used. Furthermore, when forming the conductor on the substrate 21, a base layer 27 made of a metal oxide such as silicon oxide, titanium oxide, hafnium oxide, or aluminum oxide can be formed in advance, as shown in FIG. 5. Furthermore, after forming the conductor layer 25 and the conductor protrusions 26 on the substrate 21, a coating layer 28 made of a transparent organic or inorganic material can be formed, as shown in FIG. 6. In this case, the recesses of the uneven pattern may or may not be filled with the coating layer 28.

[0034] The wire-grid polarizing element 11 of the present invention has a conductor layer 25 formed along the corrugated concave-convex pattern on the substrate surface 21, thereby achieving high adhesion to the substrate. As a result, the conductor is less likely to peel off due to expansion and contraction caused by temperature changes, and has excellent heat resistance and bending resistance. This makes it expected to be used not only in the optical systems of optical products such as various displays and cameras, and optical systems for optical measurement, but also in polarized sunglasses, smart glasses, and the like.

[0035] (2) Method for manufacturing a wire-grid polarizing element The method for manufacturing a wire-grid polarizing element of the present invention is a method for manufacturing a wire-grid polarizing element, which comprises forming, on the surface of a substrate which is a transparent sheet on which a periodic concave-convex pattern is formed, the concave-convex pattern having a cross section in the arrangement direction of the substrate in a continuous wave shape, conductor protrusions formed at the tips of each convex portion formed extending in the longitudinal direction of the concave-convex pattern so as to further protrude in the direction of the tip, and a conductor layer covering the surface except for the tips of the convex portions, and wherein the period (a) of the concave-convex pattern on the surface of the substrate is 100 to 400 nm and the average depth (b) from the tips of the convex portions to the valleys of the concave-convex pattern on the surface of the substrate is 200 to 600 nm, by a physical vapor deposition method in which a vapor deposition material is introduced from above in a direction perpendicular to the surface of the substrate, or by an electroless plating method in which a catalyst application treatment using stannous chloride and palladium chloride is performed as a pretreatment, The method is characterized by forming a conductor layer having an average conductor layer occupation rate ([2d / a] x 100) of 18 to 40%, which is expressed as the ratio of the average width (d) of two conductor layers present within one period in the arrangement direction to the period (a), and a conductor protrusion provided at the tip of the convex portion of the uneven pattern, the average thickness (h) in the tip direction of the conductor protrusion being 1.5 times or more the average width (d) of the conductor layer in the arrangement direction.

[0036] 7(1) to 7(4), an example of a method for manufacturing a wire-grid polarizing element of the present invention will be described, but the manufacturing method of the present invention is not limited to the following manufacturing example. One example of the manufacturing method includes a step of preparing a mold 31 having a corrugated cross section and having mold convex portions 32 and mold concave portions 33 to form a substrate 21 (first step: FIG. 7(1)), a step of performing thermal nanoimprinting (hot embossing) or photo-nanoimprinting on a transparent sheet using the mold 31 (second step: FIG. 7(2)), a step of forming the substrate 21 having a corrugated cross section including the convex portion tips 22 and the concave portions 23 (third step: FIG. 7(3)), and a step of forming a conductor layer 25 and conductor protrusions 26 on the surface of the substrate 21 having a corrugated cross section and having the convex portion tips 22 and the concave portions 23 (fourth step: FIG. 7(4)). In the manufacturing method of the present invention, the wire-grid polarizing element having a corrugated cross section of the present invention can basically be obtained in the above-mentioned steps 3 and 4, and there are no particular limitations on the means for forming the substrate 21 having a corrugated cross section in steps 1 and 2. Note that the indications of the period (a') and average depth (b') of the corrugated structure of the mold 31 in Figure 7 are also used in other embodiments.

[0037] In the first step, as shown in FIG. 7 (1), a mold 31 is fabricated having a mold recess 33 and a mold protrusion 32 corresponding to the protrusion tip 22 and the recess 23 of the substrate 21, respectively, with a period (a') and a depth (b') from the tip of the mold protrusion 32 to the valley of the mold recess 33. The means for fabricating the mold 31 preferably include exposure techniques such as electron beam lithography, focused ion beam, and interference exposure, self-organization techniques using nanoparticles, and dry etching or wet etching. It may also be fabricated by transfer from a master mold fabricated using these techniques. The mold 31 is not limited to those having a flat cross section with an uneven shape, but may also have a curved surface with a structure having a corrugated cross section. The material for the mold 31 is preferably silicon, but may also be glass such as quartz, ceramics such as alumina and silicon carbide, or metals such as nickel and stainless steel. It may also be a multilayer material with metals, semiconductors, and dielectrics deposited thereon. In addition, to improve the mold releasability during nanoimprinting or injection molding, it is preferable to form a fluorine-based mold release agent or a low-friction inorganic film on the surface of the mold 31, but silicone-based mold release agents can also be used depending on the mold material used and the resin material to be molded. The second step, shown in Figure 7 (2), is preferably transferred by thermal nanoimprinting (hot embossing) or photonanoimprinting, but molding methods such as injection molding and cast molding can also be used, and injection molding is more preferable in terms of operability, quality stability, and economy.

[0038] In the third step, a substrate 21 having a corrugated cross section including protrusion tips 22 and recesses 23 as shown in FIG. 7(3) is preferably fabricated through steps 1 and 2. However, the substrate 21 can also be fabricated using exposure techniques such as direct electron beam lithography, focused ion beam, and interference exposure, self-organization techniques using nanoparticles, and etching techniques. Furthermore, such a substrate 21 is not limited to a single layer, but may be multi-layered, and a different material from the substrate 21 can be used for the corrugated structure. In the fourth step, as shown in FIG. 7(4), a conductor can be formed on the substrate 21 using physical vapor deposition methods such as vacuum deposition, electron beam deposition, sputtering, chemical vapor deposition, atomic layer deposition, or a combination of these methods, or electroless plating. The preferred vapor deposition method is physical vapor deposition (front deposition), in which a deposition material is introduced from above the substrate surface in a direction perpendicular to the substrate surface. A specific example of the electroless plating method is (i) degreasing and cleaning using a surfactant and an alkaline aqueous solution to remove surface dirt, (ii) etching with an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, or hydrochloric acid to improve adhesion, followed by neutralization treatment in this order, and (iii) then, as a pretreatment for activating the chemical plating reaction, tin ions (Sn ２＋ ) and a liquid containing palladium ions (Pd ２＋ Specifically, the surface of the substrate to be chemically plated is preferably immersed in a solution containing tin ions (Sn ２＋ After immersion in a solution containing palladium ions (Pd ２＋ ) or tin ion (Sn ２＋ ) and palladium ions (Pd ２＋ (iv) Electroless plating is then performed using an electroless plating solution.

[0039] The surface of a substrate 21 is formed so as to have a continuous wave-like shape in cross section along the arrangement direction of the uneven pattern. A conductive layer 25 covers the surface 24 excluding the tip ends 22 of the convex portions of the uneven pattern, and conductive protrusions 26 protruding toward the tip (perpendicular to the arrangement direction) from the tip ends 22 of the convex portions of the uneven pattern. When these are formed, the average width (d) of the conductive layer in the arrangement direction and the thickness (h) of the conductive protrusions 26 toward the tip can be controlled by the irradiation time, voltage, degree of vacuum, distance between the target and the substrate surface, etc. in the above physical vapor deposition method, and by the plating processing time, temperature of the plating solution, concentration of the components of the plating solution, and agitation control of the plating solution, etc. in the electroless plating method.

[0040] Alternatively, after forming the conductor layer 25 and the conductor protrusions 26 on the substrate 21, the shape of the conductor can be controlled by dry etching or wet etching using an Ar ion beam or the like. When forming the conductor on the substrate 21, a base layer 27 made of a metal oxide such as silicon oxide, titanium oxide, hafnium oxide, or aluminum oxide can be formed in advance, as shown in FIG. 5 . Furthermore, after forming the conductor layer 25 and the conductor protrusions 26 on the substrate 21, a coating layer 28 can be formed as shown in FIG. 6 . In this case, the coating material is not limited to a colorless and transparent material, but a colored transparent material containing a pigment or the like can also be used. The recesses of the uneven pattern may or may not be filled with the coating layer 28.

[0041] In the step of forming the substrate, the explanation that "the period (a) of the corrugated uneven pattern is 100 to 400 nm, and the average depth (b) from the tips of the convex portions of the uneven pattern to the valleys of the concave portions is 200 to 600 nm" and in the step of forming a conductor on the substrate, "the average occupation rate of the conductor layers ([2d / a] × 100), which is expressed as the ratio of the average width (d) in the arrangement direction of two conductor layers present within one period to the period (a), is 18 to 40%, and the average thickness (h) in the tip direction of the conductor protrusions protruding toward the tip direction from the tips of the convex portions of the uneven pattern is 1.5 times or more the average width (d) in the arrangement direction of the conductor layers" are the same as those given in the explanation of the wire-grid polarizing element, and therefore will not be explained here.

[0042] The present invention will be specifically described in the following examples, comparative examples, and reference examples. It should be noted that the present invention is not limited to the following examples. The degree of polarization and light transmittance of the prepared test specimens were measured using the following equipment. A spectrophotometer (model: SolidSpec-3700) manufactured by Shimadzu Corporation was used. For the polarizing elements prepared in the examples and elsewhere, whose cross sections along the arrangement direction of the uneven pattern are wavy, the measurement targets were incident light of electric field components oscillating in directions parallel and perpendicular to the depth direction when viewed from the cross section. The polarization characteristics were evaluated based on the degree of polarization. If the luminous transmittance for light polarized parallel to the arrangement direction of the uneven pattern is Tp and the luminous transmittance (single transmittance) for light polarized perpendicular to the arrangement direction is Tv, the degree of polarization V is expressed by the following formula: V (%) = [(Tv - Tp) / (Tv + Tp)] １／２ ×100 The luminous transmittance for each polarization can be obtained from the transmittance (transmission spectrum) and luminosity curve for wavelengths of 380 to 780 nm (in 1 nm increments). Similarly, the degree of polarization V0 at a certain wavelength is given as follows, where Tp0 is the transmittance for parallel polarized light and Tv0 is the transmittance for perpendicular polarized light: V0 (%) = [(Tv0 - Tp0) / (Tv0 + Tp0)] １／２ ×100

[0043] (Example 1, Comparative Example 1) In Examples 1-1 and 1-2 and Comparative Example 1, a substrate was prepared by transferring a corrugated concave-convex pattern to the surface of a transparent sheet made of thermoplastic resin using a mold by thermal nanoimprinting. An aluminum layer was then formed on the substrate surface with the concave-convex pattern by vacuum deposition to prepare a polarizing element test piece. The polarization characteristics of the prepared test piece were evaluated. (1) Preparation of Substrate A polycarbonate sheet (manufactured by Mitsubishi Gas Chemical Company, Inc., product name: FE-2000, thickness: 300 μm) was used as the transparent sheet. The mold used was prepared by microfabrication of a 4-inch silicon wafer. The corrugated cross-sectional shape of the microstructure of the mold used had a wave period (a'), which is the wavelength of the wave, of 140 nm, an average wave depth (b') of 426 nm, and the corrugated portion had a triangular wave shape consisting of a series of approximately isosceles triangles. An image (SEM image) of an approximate cross section of the prepared mold taken with a scanning electron microscope (SEM) is shown in FIG. 8. Using the mold, a concave-convex structure having a wave-shaped cross section in the arrangement direction was transferred onto the surface of the sheet by thermal nanoimprinting to create a substrate.

[0044] (2) Preparation of Polarizing Element Test Pieces by Vacuum Vapor Deposition Next, using an electron beam vacuum deposition apparatus, the substrate was fixed to a stage so that the surface faced the deposition source (this is not an oblique deposition method, but a fixing method commonly used in deposition methods). While rotating the stage, an aluminum layer was vapor-deposited on the surface except for the tips of the convex portions of the uneven pattern. At the tips of the convex portions, aluminum was vapor-deposited so that the average thickness (h) in the direction toward the tip of the conductor protrusion was 41 nm, 80 nm, and 24 nm in Example 1-1, Example 1-2, and Comparative Example 1, respectively, to prepare three types of polarizing element test pieces. The shapes of the substrates and polarizing element test pieces prepared are summarized in Table 1. An SEM image of the cross section of the polarizing element test piece prepared in Example 1-1 is shown in FIG. 9.

[0045] (3) Evaluation Results The degree of polarization and single transmittance were measured for the obtained polarizing element test pieces. These results are summarized in Table 1. In Examples 1-1 and 1-2, excellent results were obtained for both the degree of polarization and the single transmittance. In Example 1-2, the average width (d) of the aluminum layer in the arrangement direction was 26 nm, and the average thickness (h) of the conductor protrusions in the tip direction was 80 nm. The ratio (h / d) of the average thickness (h) to the average width (d) of the protrusions was approximately 3.1. Furthermore, the average occupancy rate (2d / a) of the conductor layer was 37.1% for a period of 140 nm. In Example 1-2, the optical characteristics were a degree of polarization of 99% and a single transmittance of 37%. In Comparative Example 1, the average width (d) of the conductor layer in the arrangement direction was 10 nm, so the average occupancy rate (2d / a) of the conductor layer was 14.3%, and the degree of polarization was a low value of 45%.

[0046] Example 2 In Example 2, a substrate was prepared in the same manner as in Example 1, and then a chrome layer was formed on the substrate surface having a concave-convex pattern by vacuum deposition to prepare a polarizing element test piece, and the polarization characteristics were evaluated. (1) Preparation of Polarizing Element Test Piece Using the same sheet and mold as those used in Example 1, a concave-convex pattern having a wavy cross section in the arrangement direction was transferred to the sheet surface by thermal nanoimprinting to prepare a substrate. Then, using an electron beam vacuum deposition apparatus as in Example 1, a chrome layer was formed on the substrate surface by the same method as described in Example 1 to prepare a polarizing element test piece. The shapes of the prepared substrates and polarizing element test pieces are summarized in Table 1.

[0047] (2) Evaluation Results The average width (d) of the chromium layer formed on the surface of the substrate in the arrangement direction was 25 nm, and the average thickness (h) of the conductor protrusions in the tip direction was 61 nm. From these values, the ratio (h / d) of the average thickness (h) of the protrusions to the average width (d) was 2.44, and the average occupation ratio (2d / a) of the conductor layer was 35.7%. The polarization degree and single transmittance of the obtained polarizing element test piece were measured, and the polarization degree was 99% and the single transmittance was 33%, respectively, indicating good results for both the polarization degree and the single transmittance.

[0048] (Example 3) In Example 3, a substrate was prepared in the same manner as in Example 1, and then a nickel layer was formed by electroless plating on the substrate surface having the concave-convex pattern to prepare a polarizing element test piece, and the polarization characteristics were evaluated. (1) Preparation of substrate Using the same sheet and mold as those used in Example 1, a concave-convex pattern having a wavy cross section in the arrangement direction was transferred to the sheet surface by thermal nanoimprinting to prepare a substrate.

[0049] (2) Formation of a conductor by electroless nickel plating method Electroless plating was performed on the surface of the substrate using an electroless nickel-boron plating solution (trade name: Top Chemialloy 66-LF) manufactured by Okuno Chemical Industries Co., Ltd. As a pretreatment, the surface of the substrate to be electroless plated was degreased and cleaned using a surfactant and an alkaline aqueous solution, then etched with an aqueous solution of inorganic acid, followed by a neutralization treatment. After that, as a pretreatment for activating the chemical plating reaction, tin ions (Sn ２＋ ) and a liquid containing palladium ions (Pd ２＋ A treatment (sensitizer-activator method) to accelerate the chemical plating reaction was carried out using a solution containing 1,2-dichloro-2,4-trimethylsilyl-1 ...

[0050] (3) Evaluation Results The optical properties of the obtained test piece were a polarization degree of 99% and a single-piece transmittance of 20%. Figure 10 shows an SEM image of the polarizing element with a corrugated cross section produced in Example 3, observed from approximately the cross section. From this figure, it can be seen that a conductor of approximately uniform thickness was formed on the surface portion of the triangular wave-shaped cross section. The depth from the tip of the triangular wave-shaped convex portion to the valley of the concave portion was approximately 387 nm, and the average width (d) in the arrangement direction of the conductor layer was 14 nm. The average thickness (h) of the conductor protrusion was 21 nm, and the ratio (h / d) of the thickness (h) to the average width (d) of the conductor layer was approximately 1.5. In this case, the conductor occupancy rate in each layer from the tip of the triangular wave-shaped convex portion to the valley of the concave portion was approximately 20% on average, and the conductor occupancy rate in both the top and bottom layers was 30% or less. This confirmed that the polarizing element having a corrugated cross section produced by electroless plating has a high degree of polarization and the required light transmittance.

[0051]

[0052] (Example 4, Comparative Examples 2 and 3) In Example 4, a substrate was prepared in the same manner as in Example 1, and then an aluminum layer and a silicon oxide and aluminum layer were formed on the surface of the substrate by sputtering, to prepare a polarizing element test piece. (1) Preparation of Polarizing Element Test Piece Using the same sheet and mold as those used in Example 1, a concavo-convex pattern having a wavy cross section in the alignment direction was transferred to the sheet surface by thermal nanoimprinting, to prepare a substrate.

[0053] Thereafter, in Comparative Example 2 and Examples 4-1 and 4-2, a sputtering apparatus was used to fix the substrate to a stage so that the substrate surface faced the aluminum target, and while rotating the stage, an aluminum layer was formed on the substrate surface so that the average width (d) in the arrangement direction had the thickness shown in Table 2, thereby producing three types of polarizing element test pieces. Furthermore, in Comparative Example 3 and Examples 4-3 and 4-4, a sputtering apparatus was used in the same manner as in Examples 4-1 and 4-2, and a substrate was fixed to a stage so that the substrate surface faced the aluminum target, and while rotating the stage, an aluminum layer was formed on the substrate surface so that the average width (d) in the arrangement direction had the thickness shown in Table 2, thereby producing three types of polarizing element test pieces. ２Three types of polarizing element test pieces were prepared by forming a silicon oxide layer on the surface to an average thickness (f) of 10 nm in the direction perpendicular to the surface, and then forming an aluminum layer on the surface of the silicon oxide layer so that the average width (d) in the alignment direction was the width shown in Table 2. The shapes of the substrates and polarizing element test pieces prepared are summarized in Table 2.

[0054] (2) Evaluation Results The degree of polarization and single transmittance were measured for the polarizing element test pieces obtained in Examples 4-1 to 4 and Comparative Examples 2 and 3. The measurement results are summarized in Table 2. Good results were obtained for both the degree of polarization and single transmittance for all of the polarizing element test pieces produced in Examples 4-1 to 4. In the polarizing element test piece produced in Example 4-2, the average thickness (h) of the conductor protrusions was approximately 72 nm, the average width (d) of the conductor layer in the arrangement direction was approximately 21 nm, and the ratio (h / d) of the average thickness (h) of the conductor protrusions to the average width (d) of the conductor layer in the arrangement direction was approximately 3.4. An SEM image of the cross section of the polarizing element test piece produced in Example 4-2 is shown in Figure 11. In both Comparative Examples 2 and 3, the average width (d) of the conductor layer in the arrangement direction was 11 nm, resulting in an average conductor occupancy of 15.7%, and as a result, the degree of polarization was a low value of 89%.

[0055] Comparative Example 4: A polarizing element test piece was produced by forming a bullet-shaped micro-recessed structure with a nearly continuous concave and convex shape on the surface of a thermoplastic resin sheet using a mold by thermal nanoimprinting. A nickel layer was then formed on the surface, including the recesses, by electroless plating. (1) Formation of a Micro-recessed Structure on the Sheet Surface: The same sheet as used in Example 1 was used. The mold used was a 4-inch silicon wafer that had been microfabricated. The convex shapes forming the recesses on the substrate surface had a bullet-shaped tip with an average width of 54 nm, an average spatial width of 86 nm (period: 140 nm), an average depth of 586 nm, and a gradually tapering tip. The bottom of the recess was flat. Using this mold, a micro-recessed structure was transferred to the sheet surface by thermal nanoimprinting. Figure 15 shows an SEM image of the cross section of the mold used in Comparative Example 4, observed from approximately the front. (2) Formation of a Conductor by Electroless Nickel Plating: Electroless plating was performed on the sheet with the micro-recessed structure using the same plating solution as used in Example 3. The pretreatment was the same as that used in Example 3, and the specimen was treated for 120 seconds in a plating solution at room temperature (23°C), followed by rinsing with water and drying to prepare a polarizing element test piece. The prepared substrate and the shape of the polarizing element test piece are summarized in Table 2. An SEM image of the cross section of the prepared polarizing element test piece is shown in Figure 16.

[0056] (3) Evaluation Results The optical properties of the prepared polarizing element test specimen were a polarization degree of 99% and a unit transmittance of 9.1%, as shown in Table 2. In FIG. 16 , a nickel plating film approximately 17 nm thick was uniformly formed on the surface of the substrate, but the conductor occupancy rate in each layer of the concave-convex structure was approximately 84% in the top layer of the convex portion, approximately 24% in the middle layer, and 12% to 24% in the bottom layer of the concave-convex portion. Comparing the results of Comparative Example 4 with the test specimen prepared in Example 3, it can be seen that while both achieved a polarization degree of 99%, the unit transmittance of the test specimen prepared in Comparative Example 4 was reduced to less than half. Therefore, it was confirmed that the wire-grid polarizing element of the present invention, whose cross section in the arrangement direction is corrugated, has improved unit transmittance.

[0057]

[0058] Reference Example 1 (1) Overview As in Example 1, a polarizing element with a shape model shown in Figures 12(1) to 12(3) was obtained by using a mold to form a corrugated cross-section in the alignment direction on the surface of a sheet using thermal nanoimprinting, and then uniformly forming a nickel layer on the surface, including the corrugated portion, using electroless plating. The optical properties were evaluated by numerical calculations using rigorous coupled wave analysis. Using the displacement (s) of the conductor shape as a parameter, when the cross-section is rectangular as shown in Figure 12(1), the displacement (s) is 0 nm. Increasing the displacement (s) from this point results in a trapezoidal cross-section as shown in Figure 12(2). Further increasing the displacement (s) results in a triangular cross-section as shown in Figure 12(3), with a displacement (s) of 70 nm. Using the shape models shown in Figures 12(1) to 12(3) as reference, numerical calculations using rigorous coupled wave analysis confirmed that increasing the displacement (s) improves the unit transmittance, as shown below.

[0059] (2) Numerical calculation of optical properties versus displacement (s) when the average thickness (c) of the conductive layer is used as a parameter. Numerical calculations were performed using DiffractMOD from Nihon Synopsys, LLC (formerly RSoft) based on the geometric models shown in Figures 12(1) to 12(3). The substrates 43, 44, and 45 shown in Figures 12(1) to 12(3) were assumed to be polycarbonate, and the refractive index was defined as 1.58. The conductive layer 25 was assumed to be nickel, and the refractive index was determined from the value disclosed in A.D. Rakic ​​et al., "Optical properties of metallic films for vertical-cavity optoelectronic devices," Appl. Opt. 37, 5271 (1998). The period (a) of the uneven shape was set to 140 nm, the width (w) of the recess when the displacement (s) was 0 nm was set to 70 nm, and the depth (b) was set to 400 nm. The average thickness (c) of the conductive layer was set to 5 nm, 10 nm, and 15 nm. The polarization degree and single transmittance were calculated for the displacement (s). The rigorous coupled wave analysis method calculates by assigning a refractive index distribution to each layer of the calculation model. However, in the case of a tilted structure such as that shown in Figure 12(2) or Figure 12(3), the layers that provide the refractive index distribution were approximately divided by a certain interval. In this calculation, the interval was set to 1 / 10 of the depth (b) of the corrugated uneven structure.

[0060] (3) Calculation Results (i) When the Average Thickness (c) of the Conductor Layer is 10 nm The transmission spectra plotting the calculated results of the parallel polarized light transmittance (Tp) and the perpendicular polarized light transmittance (Tv) at each wavelength are shown in Figures 13(1) and 13(2), respectively. When the displacement (s) is 0 nm, i.e., when the conductor is uniformly formed on a rectangular concave-convex shape, as the displacement (s) increases, the transmission spectrum of the parallel polarized light transmittance (Tp) shows almost no change, but the transmission spectrum of the perpendicular polarized light transmittance (single transmittance, Tv) shows a tendency for the transmittance to gradually increase. As shown in Table 3, when the displacement (s) is 0 nm, the polarization degree is 99% and the single transmittance is 12%, whereas when the displacement is 70 nm, the polarization degree improves to 99% and the single transmittance improves to 28%.

[0061] (ii) When the average thickness (c) of the conductor layer was 5 nm, the degree of polarization was 96% and the single-piece transmittance was 24% when the displacement (s) was 0 nm, whereas the degree of polarization improved to 97% and the single-piece transmittance improved to 39% when the displacement was 70 nm. (iii) When the average thickness (c) of the conductor layer was 15 nm, the degree of polarization was 99% and the single-piece transmittance was 6% when the displacement (s) was 0 nm, whereas the degree of polarization improved to 99% and the single-piece transmittance improved to 19% when the displacement was 70 nm. Therefore, numerical calculations assuming the shape models shown in Figures 12(1) to 12(3) showed that increasing the change (s) from a rectangular cross-sectional shape to a wavy cross-sectional shape improved the single-piece transmittance. This proves that the wire-grid polarizing element of the present invention, having a wavy cross-section, contributes to a greater improvement in the single-piece transmittance than conventional wire-grid polarizing elements having a rectangular cross-section.

[0062]

[0063] (Reference Example 2) Using the same geometric model shown in FIG. 12 as used in Reference Example 1, numerical calculations were performed using the rigorous coupled wave analysis method to examine the relationship between the optical properties and the depth (b) from the tip of the convex portion of the concave portion to the valley of the concave portion. (1) Numerical calculation of optical properties when the depth (b) from the tip of the convex portion of the concave portion to the valley of the concave portion is used as a parameter. Numerical calculations were performed based on the geometric model shown in FIG. 12(1) using the same software as used in Reference Example 1. The substrate 43 was assumed to be polycarbonate, and the refractive index was defined as 1.58. The conductive layer 25 was assumed to be nickel, and the refractive index was determined using the value described in the literature, A.D. Rakic ​​et al., "Optical properties of metallic films for vertical-cavity optoelectronic devices," Appl. Opt. 37, 5271 (1998). The polarization degree and single transmittance were calculated when the period (a) of the uneven structure was 140 nm, the width (w) of the recess when the displacement (s) was 0 nm was 70 nm, the average thickness (c) perpendicular to the surface of the conductive layer 25 was 10 nm, and the depth (b) was 200 nm, 300 nm, 400 nm, 600 nm, and 1000 nm.

[0064] (2) Calculation Results The degree of polarization and single transmittance were calculated from the calculated values. These results are summarized in Table 4. When the depth (b) was 200 nm, the degree of polarization was 96.6%, and when the depth (b) was 300 nm, the degree of polarization reached 99.4%, and the single transmittance at this time was a high value of 28%. These results prove that a higher degree of polarization can be obtained by numerical calculation as the depth (b) from the tip of the convex portion to the valley of the concave portion of the uneven shape increases.

[0065]

[0066] Reference Example 3 As in Example 1, a polarizing element was assumed in which a corrugated pattern was formed on the surface of a sheet by thermal nanoimprinting using a mold, and then the resulting polarizing element was obtained by vapor deposition or sputtering. In the shape model shown in Figures 14(1) to 14(3), numerical calculations were performed using rigorous coupled wave analysis, with the average width (d) of the conductor layer 25 in the arrangement direction being 5 or 10 nm, and the average thickness (h) of the conductor protrusions 26 being expressed as the ratio (h / d) of the average width (d) in the arrangement direction of the conductor layer 25. The ratio (h / d) of the average thickness (h) of the conductor protrusions toward the tip to the average width (d) in the arrangement direction of the conductor layer was used as a parameter, and calculations were performed using the cross-sectional shape shown in Figure 14(1) when h / d was 1, the cross-sectional shape shown in Figure 14(2) when h / d was 3, and the cross-sectional shape shown in Figure 14(3) when h / d was 5.

[0067] (1) Numerical calculation of optical properties when the ratio (h / d) of the average thickness (h) to the average width (d) in the arrangement direction of the conductor layer is used as a parameter. Numerical calculations were performed using DiffractMOD by Nihon Synopsys, LLC (formerly RSoft) based on the geometric models shown in Figures 14(1) to 14(3). The substrate 21 was assumed to be polycarbonate, and the refractive index was defined as 1.58. The conductor layer 25 was assumed to be nickel or aluminum, and the refractive indexes used were those described in A.D. Rakic ​​et al., "Optical properties of metallic films for vertical-cavity optoelectronic devices," Appl. Opt. 37, 5271 (1998). The period (a) of the corrugated unevenness was set to 140 nm, and the depth (b) of the unevenness was set to 400 nm. The polarization degree and single transmittance were calculated for nickel when the average width (d) of the conductive layer was 5 nm and 10 nm, and for aluminum when the average width (d) of the conductive layer was 5 nm. While the rigorous coupled wave analysis method calculates by providing a refractive index distribution for each layer of the calculation model, in the case of a tilted structure such as those shown in Figures 14(1) to 14(3), the layers that provide the approximate refractive index distribution were divided at a certain interval. In this calculation, the interval was set to 1 / 10 of the depth (b) of the corrugated unevenness structure.

[0068] (2) Calculation Results The calculation results are summarized in Table 5. Reference Example 3-1 shows the degree of polarization and the single transmittance when the average width (d) of the nickel conductor layer 25 is 5 nm, Reference Example 3-2 shows the degree of polarization and the single transmittance when the average width (d) of the nickel conductor layer 25 is 10 nm, and Reference Example 3-3 shows the degree of polarization and the single transmittance when the average width (d) of the aluminum conductor layer 25 is 5 nm. Table 5 confirms that, compared to when the ratio (h / d) of the average thickness (h) toward the tip of the conductor protrusion to the average width (d) in the arrangement direction of the conductor layer is 1, as h / d increases to 2, 3, 5, and 10, the degree of polarization improves while maintaining a high single transmittance. For example, when the average width (d) of the nickel conductor layer is 10 nm, the degree of polarization is 99.6% when h / d is 1, whereas the degree of polarization reaches 99.9% when h / d is 10. Numerical calculations have demonstrated that the use of the high polarization structure of the present invention makes it possible to improve the degree of polarization while maintaining high transmittance.

[0069] Industrial application fields

[0070] The wire-grid polarizing element of the present invention can be applied to optical products that use electromagnetic waves such as visible light and near-infrared light, such as displays, cameras, sunglasses, and optical measuring instruments. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2022-135199, filed on August 26, 2022, are incorporated herein by reference as part of the disclosure of the present invention.

[0071] REFERENCE SIGNS LIST 11 Wire grid polarizing element 21 Substrate 22 Tip of convex portion 23 Concave portion 24 Substrate surface 25 Conductive layer 26 Conductive protrusion 27 Underlayer 28 Coating layer 31 Mold 32 Convex portion of mold 33 Concave portion of mold 41 Substrate 42 Substrate 43 Substrate 44 Substrate 45 Substrate

Claims

1. A wire grid polarizing element comprising: a substrate on the surface of which a periodic uneven pattern is formed, the uneven pattern having a cross section in the arrangement direction of the uneven pattern being a continuous wave shape; and, disposed on the surface of the substrate, conductor protrusions formed by protruding further in the direction of the tip from the tip of each convex portion formed extending in the longitudinal direction of the uneven pattern, and a conductor layer covering the surface except for the tips of the convex portions, wherein the period (a) of the uneven pattern on the surface of the substrate is 100 to 400 nm, the average depth (b) from the tip of the convex portion to the valley of the concave portion of the uneven pattern on the surface of the substrate is 200 to 600 nm, and the average occupancy rate ([2d / a] x 100) of the conductor layer, expressed as the ratio of the average width (d) in the arrangement direction of the two conductor layers present within each period to the period (a), is 18 to 40%, a wire grid polarization element characterized in that the average thickness (h) in the tip direction of the conductor protrusions provided at the tips of the convex portions of the uneven pattern is 1.5 times or more the average width (d) in the arrangement direction of the conductor layer.

2. The wire grid polarization element according to claim 1, wherein the average thickness (h) in the tip direction of the conductor protrusions provided at the tips of the convex portions of the uneven pattern on the surface of the substrate is 1.5 to 5 times the average width (d) in the arrangement direction of the conductor layer.

3. The wire grid polarization element according to claim 1, wherein the average width (d) in the arrangement direction of the conductive layer disposed on the surface portion of the substrate surface excluding the tips of the convex portions of the concave-convex pattern is 14 to 70 nm.

4. The wire grid polarization element according to claim 1, wherein the cross-sectional shape of the continuous wave pattern formed on the surface of the substrate along the arrangement direction is a triangular wave pattern consisting of a continuous approximately isosceles triangle shape.

5. The wire grid polarization element according to claim 1, wherein the cross-sectional shape in the arrangement direction of the conductor protrusions protruding toward the tip end at the tip end of the convex portion of the uneven pattern on the surface of the substrate is substantially rectangular, tapered, widened at the tip end, or substantially vertically elliptical.

6. The wire-grid polarizing element according to claim 1, wherein the conductive material forming the conductive protrusions and conductive layer is one or more metals selected from aluminum, gold, silver, copper, platinum, molybdenum, nickel, chromium, titanium, tungsten, tantalum, zirconium, iron, niobium, hafnium, cobalt, palladium, bismuth, and neodymium, or an alloy of two or more of these metals.

7. A method for manufacturing a wire grid polarizing element, comprising: forming, on the surface of a substrate, a periodic concave-convex pattern formed on the surface of a transparent sheet, the concave-convex pattern having a continuous wave-like cross section along the arrangement direction thereof; forming conductor protrusions formed at the tips of each convex portion formed extending in the longitudinal direction of the concave-convex pattern so as to further protrude in the direction of the tip; and forming a conductor layer covering the surface except for the tips of the convex portions; wherein the period (a) of the concave-convex pattern on the surface of the substrate is 100 to 400 nm, and the average depth (b) from the tips of the convex portions to the valleys of the concave-convex pattern on the surface of the substrate is 200 to 600 nm; and the method comprises introducing a vapor deposition material from above in a direction perpendicular to the surface of the substrate, or by using tin ions (Sn ２＋ ) and a liquid containing palladium ions (Pd ２＋ a conductive layer having an average occupancy ([2d / a] x 100) of 18 to 40%, which is expressed as the ratio of the average width (d) of two conductive layers present in one period in the arrangement direction to the period (a), and conductive protrusions provided at the tips of the convex portions of the concave-convex pattern, and each of the conductive protrusions has an average thickness (h) in the tip direction that is 1.5 times or more the average width (d) of the conductive layers in the arrangement direction, by an electroless plating method that applies a catalyst and activates the conductive layer using a solution containing 8. The method for producing a wire grid polarizing element according to claim 7, wherein the physical vapor deposition method is any one of vacuum deposition, electron beam deposition, and sputtering.

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