Wire grid type polarizing element and manufacturing method thereof

Abstract

The invention provides a wire grid type polarization element with required light transmittance under high polarization degree and a manufacturing method thereof. A wire grid-type polarizing element (11) is provided with: a base material (21) in which a plurality of recessed grooves (24) extending in parallel are periodically provided in one direction on a transparent sheet surface (22); and a conductor layer (31) formed in the recessed groove portion, in which the shape of the plurality of recessed groove portions provided in the base material is such that side wall surfaces (26) facing each other are parallel to each other, and the conductor layer formed in the recessed groove portion is formed with a substantially uniform thickness at least on both side wall surfaces (26) of the recessed groove portion in a state of facing each other across a gap (28).

Description

Technical Field

[0001] The present invention relates to a wire grid polarizing element mainly produced by plating means and a method for manufacturing the same, which can be expected to be applied to optical products such as displays, cameras, sunglasses, and optical measuring devices using electromagnetic waves such as visible light and near-infrared rays. Background Art

[0002] A wire grid polarizing element includes a layer in which linear objects made of a metal or the like are arranged in a stripe pattern at a specific period. If the period is sufficiently small compared to the wavelength of incident electromagnetic waves (light), light with an electric field component parallel to the linear objects can be reflected or absorbed, and light with an electric field component perpendicular to the linear objects can be transmitted. The advantages of such a polarizing element are excellent optical characteristics and high durability capable of exhibiting a polarization function from visible light to near-infrared rays.

[0003] As a method for inexpensively and efficiently forming an uneven shape on a substrate surface, a hot embossing method or a nanoimprint method is known. In addition, for a substrate having an uneven shape on its surface, a method of vapor-depositing a conductor on the side surface of the convex portion of the substrate using an inclined vapor deposition method is known. For example, Patent Document 1 below discloses a wire grid polarizing element with excellent polarization characteristics and a method for manufacturing the same. The wire grid polarizing element is obtained by causing particles to be incident from an inclined direction onto the uneven surface of a grid structure layer of a transparent substrate having a one-dimensional lattice-like uneven structure through a dry process such as sputtering or vacuum evaporation, and forming an Al—Si alloy layer having an Si content of 0.05 to 1.5 wt% on the convex portions of the uneven structure.

[0004] Patent Document 2 below discloses a wire grid polarizing sheet and a method for manufacturing the same. The wire grid polarizing sheet is formed with metal fine lines made of a metal layer existing on at least the top of the convex stripes and on more than 70% of the side surface area of the convex stripes on a base layer composed of the top of the convex stripes of a transparent substrate having an uneven structure and a metal oxide layer formed on the entire side surface thereof, by using an inclined vapor deposition method of a vacuum evaporation method.

[0005] In addition, as a method for manufacturing a wire grid polarizer more inexpensively and efficiently, a method is known in which a concavo-convex structure is formed and a conductive thin wire is formed by filling a conductive body in the concave portion by electroless plating. For example, Patent Document 3 below discloses an optical functional body formed by filling particles having a particle diameter smaller than the width of the concave portion on a substrate having a fine concavo-convex pattern by electroless plating. Generally, in a wire grid polarizer, the transmittance increases by making the width of the conductive wire thinner with respect to the period, and the light shielding performance for the light of the electric field component parallel to the wire improves by increasing the thickness of the conductive wire (Non-Patent Document 1). Therefore, it is important to balance the period, width, and thickness (aspect ratio) of the conductive wire in determining the performance of the wire grid polarizing element. Patent Document 3 also discloses that it can be manufactured inexpensively when a nanoimprint method is used in the formation of the concavo-convex structure. Prior Art Documents Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-204894 Patent Document 2: Japanese Patent No. 5459210 Patent Document 3: Japanese Patent No. 6042642 Non-Patent Documents

[0007] Non-Patent Document 1: Low-reflective wire-grid polarizers with an absorptive layer formed by glancing angle deposition, Journal of Imaging Science and Technology, Vol. 65, No. 10, pp. 1440-1445 (2011) Summary of the Invention Problems to be Solved by the Invention

[0008] However, the problem of the invention disclosed in Patent Document 1 above is to solve the following problem: When pure Al is used as the metal constituting the wire grid, since the pure Al particles formed on the convex portion of the substrate by a dry process are not refined, the polarization characteristics as designed cannot be obtained. In the invention disclosed in Patent Document 1, by using an Al-Si alloy having a Si content of 0.05 to 1.5 wt% as the metal constituting the wire grid, the particles formed on the convex portion are refined, and the improvement of the polarization characteristics is achieved. Therefore, the technology applicable to this invention is limited to the technology applicable when an Al-based metal is formed on a substrate by a dry process as the metal constituting the wire grid.

[0009] In the invention disclosed in the above-mentioned Patent Document 2, when forming a metal fine wire composed of a metal layer on the top and side surfaces of the ridges of a substrate by vapor deposition, crystallization of the metal material suppresses the generation of minute metal particles. Therefore, a base layer composed of a metal oxide layer is provided to prevent a reduction in the transmittance of incident light of a polarization element. In addition, in order to form a metal layer on a part of the side surface of the ridge by oblique vapor deposition, there is a limitation in that the height value of the ridge cannot be increased. For example, in Examples 1 to 11 corresponding to the embodiments in the specification of Patent Document 2, the height of the ridge is 100 nm in all cases. Therefore, there are limitations in the concavo-convex structure formed on the base material. In addition, when forming a metal layer on the side surface portion of the ridge by oblique vapor deposition, the thickness of the metal layer gradually decreases from the upper part to the lower part of the side surface. Therefore, it is difficult to make the thickness of the metal layer substantially uniform up to the lower part of the side surface.

[0010] In the above-mentioned Patent Document 3, an optical functional body is disclosed. When obtaining a structure in which a metal is filled in the recesses of a fine concavo-convex pattern with a high aspect ratio by electroless plating, in order to prevent fine particles from peeling off and falling off from the surface of the base material during the formation of the metal wire, particles having a diameter smaller than the width of the recess are filled in the recess by electroless plating to form a filling layer. However, the degree of polarization of the wire grid polarizer produced by the electroless plating method described in the above-mentioned Patent Document 3 does not reach 90%. In order to increase the degree of polarization while maintaining the transmittance of incident light, it is preferable to increase the aspect ratio of the conductor. Therefore, it is necessary to increase the aspect ratio (thickness to width ratio) of the recess of the base material filled with the conductor. However, in this case, there is a concern about damage to the mold and collapse of the convex portions of the formed concavo-convex structure body. Therefore, there are certain limitations in forming a base material with a high aspect ratio. In addition, in the above-mentioned Patent Document 3, a wire grid type polarization element in which the conductor layer is formed with a gap between the two side wall surfaces of the recess and a manufacturing method thereof are not disclosed.

[0011] In a method for manufacturing a low-reflection wire grid type polarization element based on vacuum film formation technology, for example, in the polarization element described in Non-Patent Document 1, the "Glancing angle deposition" technology for controlling the nano morphology of a thin film based on physical vapor deposition is used. However, since this technology requires high-precision film thickness control, it is not easy to increase the area of the polarization element, and the manufacturing process becomes complicated. Therefore, it is not easy to stably manufacture such a low-reflection wire grid type polarization element.

[0012] A wire grid polarizing element with excellent polarization degree and maintaining a required transmittance is required. In addition, a method for reliably manufacturing such a wire grid polarizing element by a simple process using various means and the like is also required. In recent years, wire grid polarizing plates that can be used in a wide wavelength band from visible light to near-infrared light are required not only in liquid crystal projectors, but also in LiDAR (a technology that irradiates a laser and measures the distance to an object, the shape of the object, etc. based on the information of the reflected light), in-vehicle cameras, industrial inspection cameras, measuring optical devices, polarized sunglasses, etc. The ripple effect brought about by the implementation is large. The present invention has been completed in view of this point, and its object is to provide a wire grid polarizing element that can maintain a required light transmittance at a high polarization degree and can be manufactured at low cost, and a manufacturing method thereof. Means for solving the problem

[0013] In view of the above prior art, the present inventors have found the following situation and thus completed the present invention: in a substrate in which a plurality of concave groove portions formed on opposite side wall surfaces parallel to each other are periodically arranged in one direction, by arranging a conductor layer in a state of being opposed to each other with a gap therebetween on both side wall surfaces of the concave groove portion in a manner that does not completely fill the concave groove portion, the ratio of the average depth (or thickness) in the back direction of the concave groove portion to the average thickness (or average width) in the direction perpendicular to the surface of the conductor layer formed on the side wall surface can be increased. As a result, a wire grid polarizing element that can maintain excellent polarization degree and required light transmittance can be obtained. That is, the gist of the present invention lies in the inventions described in the following (1) to (7).

[0014] (1) A wire grid polarizing element, comprising: a substrate having a plurality of concave groove portions extending in parallel and periodically arranged in one direction on the surface of a transparent sheet; and a conductor layer formed in the concave groove portion, wherein the wire grid polarizing element is characterized in that the shapes of the plurality of concave groove portions provided on the substrate are such that their respective opposite side wall surfaces are parallel to each other, the conductor layer formed in the concave groove portion is formed with a substantially uniform thickness at least on both side wall surfaces of the concave groove portion in a state of being opposed to each other with a gap therebetween. (2) The wire grid polarizing element according to (1) above, wherein the cross-sectional shape along the periodic direction of the concave groove portion provided on the substrate, whose opposite side wall surfaces are parallel to each other, is a substantially rectangular shape with the bottom side parallel to the substrate surface, a substantially pentagonal shape with the bottom side portion being an inverted triangular shape, or a U-shaped shape with the bottom side portion being substantially U-shaped. (3) The wire grid polarizing element according to (1) or (2) above, wherein the period (g) in one direction of the concave groove portion provided on the substrate is 50 nm to 400 nm, the average width (a) of the concave groove portion is 0.2 to 0.6 times the period (g), and the average depth (b) of the concave groove portion is 5 to 15 times the average width (a).

[0015] (4) The wire grid polarizing element according to any one of (1) to (3) above, wherein the average thickness (c) of each conductor layer formed on both side wall surfaces of the concave groove portion provided on the substrate is 0.15 to 0.30 times the average width (a) of the concave groove portion, and the average gap (f) between the conductor layers formed on both side wall surfaces of the concave groove portion is 0.40 to 0.70 times the average width (a) of the concave groove portion. (5) The wire grid polarizing element according to any one of (1) to (4) above, wherein the average width (a) of the concave groove portion provided on the substrate is 30 nm to 130 nm, and the average thickness (c) of each conductor layer formed on both side wall surfaces of the concave groove portion is 5 nm to 20 nm. (6) The wire grid polarizing element according to any one of (1) to (5) above, wherein conductor layers are formed on both side wall surfaces of the concave groove portion provided on the substrate, and further on the bottom and / or the convex portion surface between the concave groove portions.

[0016] (7) A method for manufacturing a wire grid polarizing element, which shapes the following substrate, that is, a plurality of concave groove portions extending in parallel are periodically provided on the surface of a transparent sheet in one direction, and the opposite side wall surfaces in the concave groove portions are respectively parallel to each other. Then, by electroless plating, conductor layers are formed to have a substantially uniform thickness in a state of being opposed to each other with a gap between at least both side wall surfaces of the concave groove portion provided on the substrate. The method for manufacturing the wire grid polarizing element is characterized in that, As a pretreatment of the substrate during the electroless plating, after cleaning the surface, etching and neutralization treatments are sequentially performed. Then, as a pretreatment for starting the electroless plating reaction, catalyst imparting and activation using a liquid containing tin ions (Sn 2+ ) and a liquid containing palladium ions (Pd 2+ ) are performed. After that, conductor layers having a substantially uniform thickness are formed on both side wall surfaces of the concave groove portion by electroless plating in a state of being opposed to each other with a gap. Advantages of the Invention

[0017] In the wire grid polarizing element of the present invention, in a substrate in which a plurality of concave groove portions extending in parallel are periodically provided in one direction on the surface of a transparent sheet material, two conductive layers formed on both side wall surfaces of one concave groove portion with a gap therebetween respectively perform a polarizing function. Therefore, two conductive layers are obtained for one concave groove portion in the structure, so that a conductor having an average period of 1 / 2 of the average period of the concave groove portion of the structure is obtained in appearance, and by forming a conductor along the surface of the substrate, the ratio (depth / thickness) of the average depth (or thickness) of the conductive layer from the sheet surface to the back side to the average thickness (or width) in the direction perpendicular to the surface of the conductive layer formed on the side wall surface can be increased, so that a high degree of polarization can be achieved. In addition, in a structure in which a conductive layer is formed not only on both side wall surfaces of the concave groove portion of the concavo-convex structure but also on the bottom of the concave groove portion, not only a high degree of polarization but also a required light transmittance can be obtained.

[0018] In the manufacturing method of the wire grid polarizing element of the present invention, for example, by hot embossing (or nanoimprinting) to form a substrate composed of a concavo-convex structure, and then using electroless plating, a conductive layer can be uniformly formed on the surface of the substrate of the concavo-convex structure. Therefore, the manufacturing method of the present invention is a simple and inexpensive process. In addition, in a structure in which a conductive layer is formed not only on both side wall surfaces of the concave groove portion of the concavo-convex structure but also on the bottom of the concave groove portion and / or the upper surface of the convex portion between the concave groove portions, that is, a structure in which the surface of a specific concavo-convex structure is covered with a conductive layer having a specific thickness, a required light transmittance and a high degree of polarization can be obtained. Therefore, after the conductor is formed, there is no need for a process of removing unnecessary portions of the conductor, so that it is not only environmentally friendly, but also the device cost and process cost during manufacturing can be reduced, and the productivity can be improved. The manufacturing method of the wire grid polarizing element of the present invention can utilize film insert molding, casting molding, etc. in the molding process, so that a three-dimensional curved surface molded product capable of extracting a specific polarization component can also be realized. In the manufacturing method of the present invention, by selecting the material used in the substrate sheet, a wire grid polarizing element having excellent environmental tolerance, flexibility, and stretchability can be easily obtained. In addition, since a conductive layer can be formed by using a general electroless plating method, by combining with a molding method such as injection molding, a molded product partially including a polarizing element can be realized, so that an expansion of the market such as the application to optical members that have been difficult to install in the past can be expected. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 (1) is a perspective view showing an example of the wire grid polarizing element of the present invention, Figure 1 (2) is a cross-sectional view thereof. Figure 2(1), (2), and (3) are cross-sectional views showing examples of the shapes of concave grooves provided on a substrate before a conductive layer is formed in the wire grid polarization element of the present invention. Figure 3 (1), (2), and (3) are cross-sectional views showing examples of the embodiment in which a conductive layer is formed on a substrate in the wire grid polarization element of the present invention. Figure 4 This is a cross-sectional view showing an example in which a base layer is provided in the wire grid polarization element of the present invention. Figure 5 (1) is a cross-sectional view showing an example in which a coating layer is provided on the wire grid polarization element of the present invention, including a concave groove portion. Figure 5 (2) is a cross-sectional view showing an example in which a coating layer is provided on the wire grid polarization element of the present invention in addition to the concave groove portion. Figure 6 (1) to (4) are cross-sectional views schematically showing an example of the production process of the wire grid polarization element of the present invention. Figure 7 This is an image (SEM image) of a cross section of the mold produced in Example 1 observed with a scanning electron microscope (SEM). Figure 8 (1) and (2) are SEM images of the cross section of the polarizing element test piece prepared in Example 1. Figure 9 (1) to (4) are the results of numerical calculations for Reference Example 1, in which the average thickness (c) of the conductor is divided into 5 nm, 10 nm, 15 nm, and 20 nm, respectively, and a graph is provided showing the relationship between the average width (a) of the concave groove portion and the polarization degree and single body transmittance (visual transmittance of polarized light in a direction perpendicular to the incident light). Figure 10 (1) to (4) are the results of numerical calculations for Reference Example 2, with the average width (a) of the concave groove being 30 nm, 60 nm, 90 nm, and 120 nm, respectively, and a graph showing the relationship between the average thickness (c) of the conductor layer and the polarization degree and single body transmittance. Figure 11 This is a SEM image of the polarizing element test piece produced in Comparative Example 2 observed from substantially the front. DETAILED DESCRIPTION

[0020] Hereinafter, the present invention will be divided into (1) a wire grid polarization element and (2) a method for manufacturing a wire grid polarization element, and will be described in detail with reference to the drawings. (1) Wire grid polarization element Each element and structure constituting the wire-grid polarization element of the present invention will be described. In addition, in the wire grid type polarizing element of the present invention, the shape of the conductor includes a shape such as a rectangular wave in cross section that is not a so-called "linear shape", but in the technical field, the term "wire grid polarizing element" is used even when the conductor is not linear. Therefore, the term "wire grid type polarizing element" is used. The wire grid type polarizing element of the present invention has: a substrate on the surface of a transparent sheet material, provided with a plurality of concave groove portions extending in parallel periodically in one direction; and a conductor layer formed in the concave groove portions. The wire grid type polarizing element is characterized in that the shapes of the plurality of concave groove portions provided on the substrate are such that the opposing side wall surfaces are parallel to each other, and the conductor layer formed in the concave groove portions is formed with a substantially uniform thickness in a state of being opposed to the two side wall surfaces of the concave groove portion with a gap therebetween.

[0021] [Substrate] The substrate 21 in the wire grid type polarizing element of the present invention is as Figure 1 , Figure 3 illustrated. On the surface 22 of the transparent sheet material, a plurality of concave groove portions 24 extending in parallel are provided periodically in one direction. The shapes of the plurality of concave groove portions are such that the opposing side wall surfaces 26 are parallel to each other. The conductor layer 31 formed in the concave groove portions is arranged with a substantially uniform thickness in a state of being opposed to the two side wall surfaces 26 of the concave groove portion 24 with a gap 28 therebetween. Figure 1 The display of the period (g), average width (a), average depth (b) of the concave groove portion 24 provided on the substrate, the average thickness (c) of each conductor layer 31 formed on the two side wall surfaces 26 of the concave groove portion 24 in the polarizing element, the average thickness (d) of the conductor layer 31 formed on the surface of the convex portion 25 between the concave groove portions, the average thickness (e) of the conductor layer 31 formed on the bottom 27, the width (f) of the gap 28 between the conductor layers 31 in the concave groove portion 24, the average period (h) of the conductor layer 31 on the side wall surface 26 of the concave groove portion 24, and the average period (i) of the conductor layer 31 on the side wall surface of the convex portion 25 shown in (2) is also used in common in other embodiments.

[0022] The substrate 21 used in the wire grid type polarization element of the present invention may be any substrate that is transparent to electromagnetic waves having wavelengths in the visible region, infrared region, etc. as the object. For example, amorphous thermoplastic resins such as polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cycloolefin polymer resin, crosslinked polyethylene resin, polyvinyl chloride resin, polyarylate resin, polyphenylene ether resin, modified polyphenylene ether resin, polyetherimide resin, polyethersulfone resin, polysulfone resin, polyetherketone resin; polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polybutylene terephthalate resin, aromatic polyester resin; crystalline thermoplastic resins such as polyacetal resin, polyamide resin; ultraviolet curable resins, thermosetting resins such as acrylic, epoxy, urethane; triacetate resin; inorganic substrates such as glass, silicon, quartz, ceramic materials. In addition, considering stretching processes such as bending processing, such a substrate is preferably a single layer, but may also be a multilayer.

[0023] On the substrate 21 constituting the wire grid type polarization element of the present invention, as Figure 1 illustrated in (1) and (2) of Figure 2 , it has a surface 22 side and a back surface 23 side. On the surface 22 side, a plurality of concave groove portions 24 with opposite side wall surfaces 26 parallel to each other extend in parallel and are periodically formed in one direction. The outer shape of the substrate 21 is not particularly limited as long as it can form the period (g), average width (a), and average depth (b) of the concave groove portions 24 that maintain the required transmittance and exhibit a high degree of polarization. As the cross-sectional shape perpendicular to the period direction, examples include Figure 2 the shape shown in (1) of

[0024] where the bottom side is parallel to the substrate surface and the overall shape is substantially rectangular, the shape shown in (2) where the bottom side portion is an inverted triangular shape and the overall shape is substantially pentagonal, the shape shown in (3) where the bottom side portion is substantially U-shaped and the overall shape is U-shaped. In addition, the surface of the convex portion 25 may also be uneven. In Figure 1Regarding (2), the period (g) of the concave groove portion 24 of the base material 21 only needs to be equal to or less than the wavelength of the electromagnetic wave to be targeted. That is, as a polarization element for the visible light region, it is preferably 50 nm to 400 nm, more preferably 50 nm to 200 nm. The smaller the average width (a) of the concave groove portion 24 is with respect to the period, the higher the transmittance. However, in order to obtain the required transmittance while maintaining a high degree of polarization, it is preferably in the range of 0.2 to 0.6 times the period. When the electromagnetic wave to be targeted is in the visible light and near-infrared regions, it is preferably 30 nm to 130 nm. There is a tendency that the higher the average depth (b) of the concave groove portion 24 is, the higher the degree of polarization. Therefore, it is preferably 5 times or more the average width (a). However, considering the mechanical strength for preventing breakage, damage, etc. and the formability using a mold, etc., it is preferably in the range of 5 times to 15 times the average width (a). The average depth (b) depends on the material of the conductor even in the visible light region, but is preferably 400 nm or more. It should be noted that when the cross-sectional shape of the base material is Figure 2 as shown in (2) and (3) of, and the bottom portion is not parallel to the surface of the base material, the average value of the depth in this cross-sectional shape is taken as the average depth (b).

[0025] [Wire grid polarizing element] The wire grid polarizing element of the present invention is manufactured by forming a conductor layer 31 on the concave groove portion 24 etc. on the surface 22 side of the above-mentioned base material 21. The conductor layer 31 needs to be provided on the two side wall surfaces 26 of the concave groove portion 24 with a gap 28 therebetween at least as Figure 3 shown in (1) of, but can also be provided on the two side wall surfaces 26 and the bottom portion 27 of the concave groove portion 24 as Figure 3 shown in (2) of, or can be provided on the two side wall surfaces 26, the bottom portion 27 of the concave groove portion 24 and the surface of the convex portion 25 between the concave groove portions 24 as Figure 3 shown in (3) of.

[0026] The material of the conductor layer 31 used in the present invention only needs to be a material that functions as a conductor in the wavelength region to be utilized. Examples include aluminum, gold, silver, copper, platinum, molybdenum, nickel, chromium, titanium, tungsten, tantalum, zirconium, iron, niobium, hafnium, cobalt, etc. Not only metals can be cited, but also semiconductors, their alloys, compounds, etc. As Figure 4 shown, when forming the conductor layer 31 in the concave groove portion 24, a base layer 32 composed of a dielectric such as silicon oxide, titanium oxide, hafnium oxide, etc. can also be formed in advance. In addition, as Figure 5 shown, after forming the conductor layer 31 on the two side wall surfaces 26 of the concave groove portion 24, a coating 33 composed of a transparent body of an organic material or an inorganic material can be formed. When forming the coating 33, as Figure 5As shown in (1) of, the gap in the concave groove portion 24 can be filled with the coating 33, but it can also be a cavity as shown in Figure 5 of (2).

[0027] Referring to Figure 1 of (2) and Figure 3 of (1), the average thickness (c) of each of the two conductor layers 31 formed on the respective side wall surfaces 26 of the concave groove portion 24 formed therein, that is, the average thickness of the portion corresponding to the average width of the conductor of the wire grid type polarizing element, is preferably 0.15 to 0.30 times the average width (a) of the concave groove portion 24 formed in the substrate. When the incident light is in the visible light region and the near-infrared region, the average thickness (c) is preferably 5 nm to 20 nm. When forming the conductor layer 31 in the concave groove portion 24, it is necessary to form it such that the concave groove portion 24 is not completely filled with the conductor, that is, the conductor layers 31 are formed on the two side wall surfaces 26 in the concave groove portion 24 with a gap 28 therebetween. In this case, the average width (f) of the gap 28 is preferably in the range of 0.40 to 0.70 times the average width (a) of the concave groove portion 24 formed in the substrate. In addition, there is a relationship represented by the following formula among the average width (a) of the above-mentioned concave groove portion, the average thickness (c) of the conductor layer on a single side wall surface, and the average width (f) of the gap. Average width (a) of the concave groove portion = 2 × [Average thickness (c) of the conductor layer] + [Average width (f) of the gap]

[0028] By making the shape of the conductor layer 31 as described above, compared with the ratio (b / a) of the average depth (b) to the average width (a) of the concave groove portion 24 in the substrate, the ratio of the average depth in the back direction of the conductor layer 31 formed on the side wall surface 26 of the concave groove portion 24 in the polarizing element to the average thickness (or average width) of the conductor layer (depth / thickness (c)) becomes larger. In addition, the period (h) of the conductor layer 31 formed on the side wall surface 26 of the concave groove portion 24 can be made about 0.5 times the period of the concave groove portion 24, which helps to shorten the target wavelength that the wire grid type polarizing element can use. In addition, the average depth in the back direction of the above-mentioned conductor layer 31 is as Figure 3 shown in (1) to (3) of, and the depth is slightly different depending on whether a conductor layer 31 is formed on the convex portion 25 between the bottom 27 of the concave groove portion 24 and the concave groove portion 24. In addition, the period (h) of the conductor layer 31 in the side wall of the concave groove portion 24 can be represented by a - c, and the period (i) of the conductor layer 31 in the side wall of the convex portion 25 can be represented by (g - a) + c.

[0029] The conductor layer 31 formed in the concave groove portion 24 of the wire grid type polarizing element of the present invention can be formed not only on the side wall surface 26 of the concave groove portion 24, but also asFigure 3 On the surface of the convex portions 25 formed between the concave groove portions 24 and / or on the bottom 27 of the concave groove portions 24 as shown in (2) and (3). The average thickness (c) of the conductor layer 31 on the side wall surface 26 of the concave groove portion 24 is preferably formed to be thicker on average than the average thickness (d) of the surface of the convex portion 25 between the concave groove portions 24 or the average thickness (e) of the bottom 27, but the ratio of each of the thicknesses (c), (d), and (e) in the direction perpendicular to each surface of the conductor layer 31 is not particularly limited. That is, the conductor layer 31 with substantially the same average thickness can be formed uniformly on the side wall surface 26, the convex portion 25, and the bottom 27 of the concave groove portion 24, or the average thicknesses ((d) and (e)) of the conductor layer 31 on the surface of the convex portion 25 and the bottom 27 between the concave groove portions 24 can be formed to be thicker than the average thickness (c) of the conductor layer 31 on the side wall surface 26 of the concave groove portion 24.

[0030] In addition, since the wire grid type polarization element 11 of the present invention is formed with the conductor layer 31 along the concavo-convex structure on the surface of the substrate 21, a relatively high adhesion to the substrate 21 can be obtained. Therefore, for the expansion and contraction caused by temperature changes, etc., the conductor is not easily peeled off, and it has excellent heat resistance and excellent bending resistance. Thus, it can be applied not only to the optical systems of various optical products such as displays and cameras, and optical systems for optical measurement, but also to polarized sunglasses, smart glasses, etc.

[0031] (2) Manufacturing method of wire grid type polarization element The manufacturing method of the wire grid type polarization element of the present invention is characterized in that a substrate is formed, that is, on the surface of a transparent sheet, a plurality of concave groove portions extending in parallel are periodically provided in one direction, and the opposite side wall surfaces in the concave groove portions are parallel to each other. Then, by electroless plating, a conductor layer is formed with a substantially uniform thickness on at least two side wall surfaces of the concave groove portions provided on the substrate in a state of being opposed to each other with a gap therebetween. As the pretreatment of the substrate when performing this electroless plating, after cleaning the surface, etching and neutralization treatment are sequentially performed. Then, as the pretreatment for starting the electroless plating reaction, catalyst imparting and activation using a liquid containing tin ions (Sn 2+ ) and a liquid containing palladium ions (Pd 2+ ) are performed, and then, by electroless plating, a conductor layer with a substantially uniform thickness is formed on the two side wall surfaces of the concave groove portion in a state of being opposed to each other with a gap therebetween.

[0032] Using Figure 6 The schematic cross-sectional view shown illustrates an example of the manufacturing method of the wire grid type polarization element of the present invention. That is, as an example of the manufacturing method, as shown in Figure 6As shown, there may be processes including the following processes: a process of preparing a mold 41 for providing a concave groove portion 24 on the surface 22 side of a substrate 21 (the first process: Figure 6 of (1)); a process of performing thermal nanoimprinting (hot embossing) or photonic nanoimprinting (the second process: Figure 6 of (2)); a process of preparing a substrate 21 provided with a concave groove portion 24 (the third process: Figure 6 of (3)); and a process of forming a conductor layer 31 on at least the side wall surface 26 of the concave groove portion 24 (the fourth process: Figure 6 of (4)). However, essentially, the wire grid type polarization element of the present invention can be obtained only through the third process and the fourth process, and the method of providing the concave groove portion 24 on the substrate 21 prepared in the third process is not particularly limited.

[0033] In the first process, the method of manufacturing the mold 41 having a convex portion 42 corresponding to the shape of the concave groove portion 24 preferably uses exposure techniques such as electron beam lithography, focused ion beam, interference exposure, self-assembly techniques using nanoparticles, etc., as well as dry etching or wet etching, etc. In addition, it can also be manufactured by transfer from a master mold made using them. The material of the mold 41 is preferably silicon, but it can also be glass such as quartz, ceramics such as alumina and silicon carbide, metals such as nickel and stainless steel, or a multilayer material formed by stacking a metal, semiconductor, or dielectric on them. In addition, in order to improve the demolding property in nanoimprinting and injection molding, it is preferable to coat a fluorine-based release agent or form a low-friction inorganic film on the surface of the mold 41, but depending on the mold material used and the resin material to be molded, a silicon-based release agent can also be coated.

[0034] The second process preferably uses a thermal nanoimprinting (hot embossing) method or a photonic nanoimprinting method for transfer, but other molding methods such as injection molding and casting molding can also be used. When using such a forming means, the form of the mold that can be used is not limited to a flat shape, and can also be a roll shape. In the third process, as the method of manufacturing the substrate 21 provided with the concave groove portion 24, it is preferably manufactured through the first process and the second process, but the substrate 21 can also be manufactured using exposure techniques such as electron beam lithography, focused ion beam, interference exposure, self-assembly techniques using nanoparticles, etching techniques, etc. In addition, such a substrate 21 is not limited to a single layer, and can also be a multilayer, and the layer forming the surface of the concave groove portion can also be formed of a different material such as an ultraviolet curable resin.

[0035] In the fourth process, in view of mass productivity, the electroless plating method is preferably used, but in the case of manufacturing the wire grid type polarization element of the present invention, in addition to physical vapor deposition methods such as vacuum evaporation and sputtering, chemical vapor deposition methods and atomic layer deposition methods can also be used. In addition, means combining them can also be used. As a specific example in the case of using the electroless plating method, it is preferable that (i) degreasing and cleaning using a surfactant and an alkaline aqueous solution are performed to remove surface dirt, (ii) after etching with an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, or hydrochloric acid to improve adhesion, a neutralization treatment is performed in sequence, and (iii) then, as an activation treatment for the electroless plating reaction, it is immersed in a liquid containing tin ions (Sn 2+ ) and a liquid containing palladium ions (Pd 2+ ). Specifically, examples include: the sensitizer-activator process in which the surface of the substrate to be electroless plated is immersed in a liquid containing tin ions (Sn 2+ ) and then immersed in a liquid containing palladium ions (Pd 2+ ) once or twice; or the catalyser-accelerator process in which a palladium colloid solution is prepared by mixing a liquid containing tin ions (Sn 2+ ) and palladium ions (Pd 2+ ), the surface of the substrate is immersed therein, and then immersed in a hydrochloric acid solution to promote the electroless plating reaction. (iv) After that, it is preferable to form a conductor layer in a state of being opposed to each other with a gap therebetween on both side wall surfaces of the concave groove portion by the electroless plating method. In the above treatment, considering the adhesion to the wall surface, the activation treatment of imparting a palladium catalyst to the wall surface of the electroless plating using a liquid containing tin ions (Sn 2+ ) and a liquid containing palladium ions (Pd 2+ ) is the most important.

[0036] As the surface for forming the conductor layer on the substrate, at least the two side wall surfaces of the concave groove portion can be cited. As an arbitrary portion, the bottom of the concave groove portion and the surface of the convex portion between the concave groove portions can be cited. As a method for forming the conductor layer at each arbitrary position, masking, etching, etc. can be used. In addition, as a means for controlling the thickness of the conductor layer formed on the substrate surface, the plating treatment time, the temperature of the plating solution, the component concentration of the plating solution, the control of the diffusion layer which is a layer having a concentration gradient of the plating solution during plating, etc. can be cited. In addition, as Figure 4 shown, when forming the conductor layer 31 in the concave groove portion 24, a base layer 32 made of a dielectric such as silicon oxide, titanium oxide, or hafnium oxide can also be formed in advance. In order to improve environmental tolerance, after forming the conductor layer 31, a coating 33 of an organic or inorganic substance can be provided on its surface as shown in Figure 5 (1) and (2). The coating is not limited to a transparent material, and can also be a transparent material having a color tone containing a pigment such as a pigment. In addition, the shape of the conductor can also be controlled by dry etching such as Ar ion beam after forming the conductor layer 31.

[0037] By the manufacturing method of the wire grid type polarization element of the present invention, a substrate having concave groove portions in which opposing side wall surfaces are parallel to each other and are periodically arranged in one direction is formed on the surface of a transparent sheet material. Then, on at least both side wall surfaces of the concave groove portions of the substrate, a conductor layer is formed with a substantially uniform thickness in a state of being opposed to each other with a gap therebetween. Thus, a wire grid type polarization element having the following preferred modes can be manufactured. As a preferred mode of the shape of the concave groove portions provided in the substrate, as the cross-sectional shape along the periodic direction of the concave groove portions, a substantially rectangular shape, a substantially pentagonal shape with an inverted triangular shape as the bottom side, a U-shaped shape, etc. can be cited. In addition, the period (g) in one direction of the concave groove portions is 50 nm to 400 nm, the average width (a) of the concave groove portions is 0.2 to 0.6 times the period (g) or 30 nm to 130 nm, and the average depth (b) of the concave groove portions is 5 to 15 times the average width (a), etc. As a preferred mode of the conductor layer formed on the surface of the substrate, it can be cited that the average thickness (c) of each of the conductor layers formed on both side wall surfaces of the concave groove portions of the substrate is 0.15 to 0.30 times the average width (a) of the concave groove portions or 5 nm to 20 nm, and the average gap (f) between the conductor layers formed on both side wall surfaces of the concave groove portions is 0.40 to 0.70 times the average width (a) of the concave groove portions, etc. Examples

[0038] Next, the present invention will be specifically described by the following examples and comparative examples. In addition, the present invention is not limited to the following examples. The measurement of the degree of polarization and the light transmittance of the produced test pieces was carried out using the following device. A spectrophotometer (model: SolidSpec-3700) manufactured by Shimadzu Corporation was used. For the conductor layer (concave groove portion) of the produced wire grid type polarization element, incident light with electric field components vibrating in the parallel direction and the vertical direction was used. Regarding the polarization characteristics, evaluation based on the degree of polarization was carried out. If the visual transmittance when the polarized light is in the parallel direction with respect to the conductor layer (concave groove portion) is set as Tp, and the visual transmittance when the polarized light is in the vertical direction is set as Tv, then the degree of polarization V is V = [(Tv - Tp) / (Tv + Tp)] 1 / 2 . The visual transmittance of each polarized light can be obtained from the respective transmittances (transmission spectra) at wavelengths of 380 nm to 780 nm (1 nm scale) and the visual sensitivity curve. Similarly, regarding the degree of polarization at a certain wavelength, if the transmittance of polarized light in the direction parallel to the conductor (concave groove portion) is set as Tp0 and the transmittance of polarized light in the perpendicular direction is set as Tv0, then the degree of polarization V0 at a certain wavelength is obtained by the following formula. Degree of polarization V0 = [(Tv0 - Tp0) / (Tv0 + Tp0)] 1 / 2

[0039] (Example 1) On the surface of a thermoplastic resin sheet, a substrate having a fine concave groove portion structure is formed by thermal nanoimprinting using a mold. Then, a nickel layer is formed on the surface including the concave groove portion by electroless plating in such a way that the concave groove portion is not completely filled with a conductor, and a Figure 3 polarization element test piece as shown in (3) is fabricated. (1) Fabrication of the substrate As the sheet, a polycarbonate sheet (manufactured by Mitsubishi Gas Chemical Company, Inc., trade name: FE - 2000, thickness: 300 μm) is used. The mold used is a 4 - inch silicon wafer micro - machined. Regarding the fine structure of the mold used, the convex portion shape for forming the concave groove portion on the substrate surface has an average width (a') of 54 nm, an average length (b') of 586 nm, and a bullet - shaped tip portion that gradually tapers towards the tip, and the arrangement period (g') is 140 nm. Using this mold, the mold temperature is adjusted to 175 °C, and a fine concave structure is transferred onto the sheet surface by thermal nanoimprinting to fabricate the substrate. The scanning electron microscope (SEM) image (SEM image) of the approximate cross - section of the mold used in Example 1 is shown in Figure 7 .

[0040] (2) Formation of the conductor based on electroless nickel plating Electroless plating is performed on both side wall surfaces of the fine concave groove portion structure using an electroless nickel - boron plating solution (trade name: TopChemialloy66 - LF) manufactured by Okuno Pharmaceutical Co., Ltd. As a pretreatment, the surface of the substrate to be electroless - plated is first 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. Then, as an activation pretreatment for the electroless plating reaction, a treatment (sensitizer - activator method) using a liquid containing tin ions (Sn 2+ ) and a liquid containing palladium ions (Pd 2+ ) (both manufactured by Okuno Pharmaceutical Co., Ltd.) to promote the electroless plating reaction is performed. The above electroless nickel-boron plating solution at room temperature (23 °C) was used for treatment for a predetermined time, followed by washing with water and drying, thereby producing a polarization element test piece having a conductive layer formed on both side walls of the concave groove portion, the surface of the convex portion between the concave groove portions, and the bottom of the concave groove portion.

[0041] (3) Evaluation results The optical properties of the results of treatment at plating times of 60 seconds, 90 seconds, 105 seconds, and 120 seconds are shown in Table 1. While maintaining a good monomer transmittance, the degree of polarization reached 97.3% at a plating time of 90 seconds, and a degree of polarization of 99.8% was obtained at a plating time of 120 seconds. Figure 8 (1) is an SEM image of the wire grid type polarization element produced at a plating time of 120 seconds in Example 1 observed from a substantially cross section, Figure 8 (2) of Figure 8 is an enlarged image of (1) of. The average width of the concave groove portion of the wire grid type polarization element produced at the plating time of 120 seconds is 58 nm, the average width of the conductive layer formed on both side walls of the concave groove portion is 17 nm, and the average gap between the conductive layers formed on both side walls of the concave groove portion is 24 nm. Therefore, the conductive layer can be formed along the surface of the substrate in such a manner that the concave groove portion of the above substrate is not completely filled with the conductor, that is, in such a manner that two conductor lines exist in one concave groove portion with the conductive layers formed on both side walls of the concave groove portion separated by a gap. When focusing on the conductive portion formed along the side wall surface of the concave groove portion that exhibits the polarization function, the aspect ratio reaches about 20, confirming that a structure including a conductor that is thin and has a thickness when observed from the optical axis direction can be formed, and a high degree of polarization can be obtained while maintaining the required transmittance.

[0042] (Example 2) In Example 2, in the same manner as in Example 1, a substrate having a fine concave groove portion structure was formed by the thermal nanoimprint method using a mold, and then, by electroless plating, a nickel layer was formed on the surface including the side wall surface of the concave groove portion in such a manner that the concave groove portion was not completely filled with the conductor, thereby producing a polarization element test piece. (1) Production of polarization element test piece The same sheet and the same mold as those used in Example 1 were used. The mold temperature was adjusted to 175 °C, and a fine concave structure was transferred onto the sheet surface by the thermal nanoimprint method to produce a substrate. Then, the same pretreatment process as in Example 1 was carried out. Using the same electroless plating solution as in Example 1, the temperature of the plating solution was set to 16.5°C, 17.8°C, 18.8°C, 20.0°C, 21.0°C, and the plating time was set to 150 seconds respectively for electroless plating. A nickel layer was formed on the side wall surface, the convex portion surface, and the bottom of the concave groove portion to produce a polarization element test piece. (2) Evaluation results For the obtained polarization element test piece, the degree of polarization and the monomer transmittance were measured. These results are summarized in Table 1. Good results were obtained for both the degree of polarization and the monomer transmittance.

[0043] (Comparative Example 1) Similar to Example 1, a substrate having a fine concave groove portion structure on the surface was fabricated by thermal nanoimprinting using a mold. Then, nickel was formed on the surface including the concave groove portion by electroless plating to produce a polarization element test piece. (1) Fabrication of polarization element test piece The same sheet material and the same mold as those used in Example 1 were used. A fine concave structure was transferred onto the sheet surface by thermal nanoimprinting to fabricate a substrate. Then, the same pretreatment process as in Example 1 was carried out. Using the same electroless plating solution at room temperature (23°C) as in Example 1, a conductor was formed on the substrate surface by electroless plating with the plating time set to 15 minutes to produce a polarization element test piece.

[0044] (2) Evaluation results For the obtained polarization element test piece, the degree of polarization and the monomer transmittance were measured. Since the concave groove portion of the substrate was completely filled with the conductor and the conductor was also formed relatively thickly on the convex portion surface, the monomer transmittance was 0%, and the required transmittance could not be obtained. From the above, it was confirmed that when forming a conductor layer on the substrate surface, the formation amount of the conductor is important. If the concave groove portion of the substrate is completely filled with the conductor, the formation amount of the conductor on the convex portion surface also becomes large, and the monomer transmittance decreases significantly.

[0045] (Comparative Example 2) Similar to Comparative Example 1, a substrate having a fine concave groove portion structure on the sheet surface was fabricated by thermal nanoimprinting using a mold. Then, similar to Comparative Example 1, a nickel layer was formed on the surface including the concave groove portion by electroless plating to produce a test piece. Then, the obtained test piece was further etched from the upper surface of the test piece using an argon ion beam to produce a polarization element test piece. (1) Fabrication of polarization element test piece The same sheet material and the same mold as those used in Comparative Example 1 were used. A fine concave structure was transferred onto the sheet surface by thermal nanoimprinting to fabricate a substrate. Then, through the same pretreatment process and electroless plating process as in Comparative Example 1, a polarization element with nickel filled in the concave groove portion on the surface of the substrate was formed. Subsequently, an argon ion beam etching process was further performed to fabricate a polarization element test piece.

[0046] (2) Evaluation results For the obtained polarization element test piece, the degree of polarization and the monomer transmittance were measured. In the electroless plating process, for a sample in which the concave groove portion was completely filled with a conductor and a conductor was also formed thickly on the convex portion, argon ion beam etching was performed to remove the excessively formed nickel layer, and the Figure 11 polarization element test piece shown in the figure was obtained. The optical properties of the obtained polarization element test piece were a degree of polarization of 99.1% and a monomer transmittance of 14.3%, and good degree of polarization and monomer transmittance were obtained. However, from the viewpoints of productivity and optical properties, when Example 1 and Comparative Example 2 were compared, in Example 1, the processing was completed before the electroless plating process. In contrast, in the process of Comparative Example 2, after the electroless plating process, an additional process for removing the excessively formed nickel layer in the argon ion beam etching process etc. was required, and the productivity was significantly reduced. In addition, when comparing the optical properties, a high degree of polarization of 99% or more was achieved while maintaining the required transmittance in both cases, so substantially the same effects were obtained. However, from the viewpoint of productivity, the superiority of the wire grid type polarization element of the present invention was confirmed.

[0047] [Table 1]

[0048] (Reference Example 1) In the same manner as described in Example 1, using the same mold, a fine concave groove portion structure was formed on the surface of a transparent sheet by thermal nanoimprinting. Subsequently, by electroless plating, a nickel layer was formed on the surface including both side walls of the concave groove portion in such a way that the concave groove portion was not completely filled with a conductor, thereby fabricating a polarization element test piece. In a shape model assuming the above situation, numerical calculations based on the rigorous coupled wave analysis method were performed. (1) Numerical calculation of optical properties with respect to the average width (a) of the concave groove portion when the average thickness (c, d, e) of the conductor layer was used as a parameter The numerical calculations were performed using DiffractMOD of Synopsys K.K. (former RSoft) in Japan, based on Figure 1The shape model is calculated. The substrate is assumed to be polycarbonate, and the refractive index is defined as 1.58. The conductor is assumed to be nickel, and the refractive index uses the value from A.D. Rakic et al., "Optical properties of metallic films for vertical-cavity optoelectronic devices," Appl. Opt. 37, 5271 (1998). Here, the average thickness (c) of the conductor layer formed on the side wall surface in the concave groove portion, the average thickness (d) of the conductor layer on the convex portion surface, and the average thickness (e) of the conductor layer at the bottom are set to the same thickness (c = d = e), and the degree of polarization and monomer transmittance corresponding to the average width (a) of the concave groove portion are calculated when the thicknesses are 5 nm, 10 nm, 15 nm, and 20 nm, respectively.

[0049] (2) Calculation results The calculation results are shown in Table 2 and Figure 9 as follows. When the thickness (c) of the conductor layer is 5 nm, a degree of polarization of 90% or more and a monomer transmittance of 24% or more are obtained when the average width (a) of the concave groove portion is 30 nm to 130 nm. When the thickness (c) of the conductor layer is 10 nm, a degree of polarization of 98% or more is obtained when the average width (a) of the concave groove portion is 20 nm to 130 nm, and a degree of polarization of 99% or more is obtained when the average width (a) of the concave groove portion is 40 nm or more, and the minimum monomer transmittance is 12%. When the average thickness (c) of the conductor layer is 15 nm, a degree of polarization of 99% or more is obtained when the average width (a) of the concave groove portion is 30 nm to 130 nm, and the minimum monomer transmittance is 6%. When the average thickness (c) of the conductor layer is 20 nm, a degree of polarization of 99% or more is obtained when the average width (a) of the concave groove portion is 40 nm to 130 nm, and the monomer transmittance is less than 5%, around 3% to 5%.

[0050] (Reference Example 2) In the same shape model as in Reference Example 1, numerical calculations based on the rigorous coupled-wave analysis method are performed. (1) Numerical calculation of the optical properties with respect to the formation amount of the conductor when the width of the concave groove portion is used as a parameter Using the same software as in Reference Example 1, based on Figure 1Numerical calculations were performed on the shape model. The substrate was assumed to be polycarbonate, and the refractive index was defined as 1.58. The conductor layer was assumed to be nickel, and the refractive index was taken from the literature A.D. Rakic et al., “Optical properties of metallic films for vertical-cavity optoelectronic devices,” Appl. Opt. 37, 5271 (1998). Here, similar to Reference Example 1, the average thickness (c) of the conductor layer formed on the side wall surface in the concave groove portion, the average thickness (d) of the conductor layer on the convex portion surface, and the average thickness (e) of the conductor layer at the bottom were set to the same thickness (c = d = e). The degree of polarization and the monomer transmittance with respect to the thickness (c) of each conductor layer were calculated when the average width (a) of the concave groove portion was set to 30 nm, 60 nm, 90 nm, and 120 nm.

[0051] (2) Calculation results The calculation results are shown in Table 2 and Figure 10 as follows. When the average width (a) of the concave groove portion is 30 nm, a degree of polarization of 99% or more and a monomer transmittance of 6% are obtained when the thickness (c) of the conductor layer is 15 nm. When the average width (a) of the concave groove portion is 60 nm, a degree of polarization of 99% or more and a monomer transmittance of 8% are obtained when the thickness (c) of the conductor layer is 15 nm, a degree of polarization of 99% or more and a monomer transmittance of 5% are obtained when the thickness (c) of the conductor layer is 20 nm, and a degree of polarization of 99% or more and a monomer transmittance of 1% are obtained when the thickness (c) of the conductor layer is 30 nm. When the average width (a) of the concave groove portion is 90 nm, a degree of polarization of 99% or more and a monomer transmittance of 6% are obtained when the thickness (c) of the conductor layer is 15 nm, a degree of polarization of 99% or more and a monomer transmittance of 3% are obtained when the thickness (c) of the conductor layer is 20 nm, and the monomer transmittance is 0% when the thickness (c) of the conductor layer is 40 nm. When the average width (a) of the concave groove portion is 120 nm, a degree of polarization of 99% or more and a monomer transmittance of 8% are obtained when the thickness (c) of the conductor layer is 15 nm, a degree of polarization of 99% or more and a monomer transmittance of 4% are obtained when the thickness (c) of the conductor layer is 20 nm, and the monomer transmittance is 0% when the thickness (c) of the conductor layer is 60 nm. From the above results, it can be confirmed that in the wire grid polarizing element of the present invention, in order to obtain a high degree of polarization while maintaining the required transmittance, it is important not to fill the concave groove portion of the substrate with a conductor, and to dispose the conductor layers on both side wall surfaces of the concave groove portion in a state of being opposed to each other with a gap therebetween, and to appropriately control the thickness (c) of the conductor layer.

[0052] [Table 2] Industrial application fields

[0053] The wire grid polarizing element of the present invention can be inexpensively manufactured while maintaining the required light transmittance at a high degree of polarization, and thus can be expected to be applied to optical products such as liquid crystal projectors, LiDARs, in-vehicle cameras, industrial inspection cameras, measuring optical devices, and polarized sunglasses. In addition, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2022-135198 filed on August 26, 2022 are hereby incorporated by reference as the disclosure of the present invention. Explanation of reference numerals

[0054] 11: Wire grid polarizing element; 21: Substrate; 22: Surface; 23: Back surface; 24: Concave groove portion; 25: Protrusion; 26: Side wall surface; 27: Bottom; 28: Gap; 31: Conductor layer; 32: Base layer; 33: Coating; 41: Mold; 42: Mold protrusion.

Claims

1. A wire grid polarizing element having: a substrate in which a plurality of recessed groove portions extending in parallel are periodically provided in one direction on the surface of a transparent sheet; and a conductor layer formed in the recessed groove portions, wherein the wire grid polarizing element is characterized in that the shapes of the plurality of recessed groove portions provided in the substrate are such that the opposing side wall surfaces thereof are parallel to each other, the conductor layer formed in the recessed groove portions is formed with a substantially uniform thickness in a state of being opposed to each other with a gap therebetween at least on both side wall surfaces of the recessed groove portions.

2. The wire grid polarizing element according to claim 1, wherein the cross-sectional shape along the periodic direction of the recessed groove portions provided in the substrate, in which the opposing side wall surfaces are parallel to each other, is a substantially rectangular shape with the bottom side parallel to the substrate surface, a substantially pentagonal shape with the bottom side portion being an inverted triangular shape, or a U-shaped shape with the bottom side portion being a substantially U-shaped shape.

3. The wire grid polarizing element according to claim 1, wherein the period (g) in one direction of the recessed groove portions provided in the substrate is 50 nm to 400 nm, the average width (a) of the recessed groove portions is 0.2 to 0.6 times the period (g), the average depth (b) of the recessed groove portions is 5 to 15 times the average width (a).

4. The wire grid polarizing element according to claim 1, wherein the average thickness (c) of each conductor layer formed on both side wall surfaces of the recessed groove portions in the substrate is 0.15 to 0.30 times the average width (a) of the recessed groove portions, and the average gap (f) between the conductor layers formed on both side wall surfaces of the recessed groove portions is 0.40 to 0.70 times the average width (a) of the recessed groove portions.

5. The wire grid polarizing element according to claim 1, wherein the average width (a) of the recessed groove portions provided in the substrate is 30 nm to 130 nm, the average thickness (c) of each conductor layer formed on both side wall surfaces of the recessed groove portions is 5 nm to 20 nm.

6. The wire grid polarizing element according to claim 1, wherein conductor layers are formed on both side wall surfaces of the recessed groove portions provided in the substrate, and further on the bottom surface and / or the surface of the convex portions between the recessed groove portions.

7. A method for manufacturing a wire grid polarizing element, which shapes a substrate in which a plurality of recessed groove portions extending in parallel are periodically provided in one direction on the surface of a transparent sheet, and the opposing side wall surfaces in the recessed groove portions are respectively parallel to each other, and then, by electroless plating, a conductor layer is formed with a substantially uniform thickness in a state of being opposed to each other with a gap therebetween at least on both side wall surfaces of the recessed groove portions provided in the substrate, wherein the method for manufacturing the wire grid polarizing element is characterized in that As a pretreatment of the substrate for the chemical plating, the surface is cleaned and then etched and neutralized in sequence. Then, as a pretreatment to start the chemical plating reaction, a substrate containing tin ions (Sn 2+ ) and liquid containing palladium ions (Pd 2+ ) is imparted with a catalyst of a liquid and activated, and then a conductor layer of approximately uniform thickness is formed by chemical plating on both side walls of the concave groove portion in a state where the two side walls are opposed to each other with a gap therebetween.

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