Polarizing plate, optical device, and method for manufacturing polarizing plate

Abstract

The present invention provides a polarizing plate, an optical device and a method for manufacturing a polarizing plate. The purpose of the present invention is to provide a polarizing plate and an optical device with high transmittance on the transmission axis. The polarizing plate is a polarizing plate with a wire grid structure, comprising a transparent substrate, a first anti-reflection layer stacked on the first surface of the transparent substrate, a plurality of convex portions protruding from the first anti-reflection layer and a second anti-reflection layer stacked on the second surface opposite to the first surface, the plurality of convex portions are periodically arranged at a pitch shorter than the wavelength of light in a used frequency band, each convex portion extends in a first direction and has a reflective layer, a dielectric layer and an absorption layer in sequence starting from the first surface, the first anti-reflection layer and the second anti-reflection layer have high refractive index layers and low refractive index layers stacked alternately.

Description

Technical Field

[0001] The invention relates to a polarizing plate, an optical device and a method for manufacturing the polarizing plate. Background Art

[0002] Polarizing plates are used in liquid crystal displays, etc. In recent years, wire grid polarizing plates in which reflective layers are arranged at a period shorter than the wavelength of light in a used band have attracted attention.

[0003] For example, a polarizing plate having an antireflection layer and a wire grid in this order on a substrate is described in Patent Document 1. The antireflection layer in Patent Document 1 is formed of hollow particles and a binder.

[0004] For example, Patent Document 2 describes a wire grid polarizer in which an anti-reflection coating is applied to a surface of a substrate on which a wire grid is formed and a surface on the opposite side.

[0005] For example, Patent Document 3 describes a polarizing element having an antireflection layer on a surface of a substrate on which a wire grid is formed and on a surface on the opposite side.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2016-38537

[0009] Patent Document 2: Japanese Patent Application Publication No. 2005-242080

[0010] Patent Document 3: Japanese Patent Application Publication No. 2010-60587 Summary of the invention

[0011] Problems to be solved by the invention

[0012] In recent years, liquid crystal projectors and the like have been required to have higher brightness and higher definition, and polarizing plates having high transmittance characteristics have been required.

[0013] In view of the above problems, an object of the present invention is to provide a polarizing plate and an optical device having high transmission axis transmittance.

[0014] Solution to the problem

[0015] In order to solve the above-mentioned problems, the present invention provides the following means.

[0016] The polarizing plate involved in the first embodiment is a polarizing plate with a wire grid structure, comprising a transparent substrate, a first anti-reflection layer stacked on a first surface of the transparent substrate, a plurality of convex portions protruding from the first anti-reflection layer, and a second anti-reflection layer stacked on a second surface opposite to the first surface, wherein the plurality of convex portions are periodically arranged at a pitch shorter than the wavelength of light in a used frequency band, each convex portion extends in a first direction, and has a reflective layer, a dielectric layer and an absorption layer in sequence starting from the first surface, and the first anti-reflection layer and the second anti-reflection layer have high refractive index layers and low refractive index layers stacked alternately.

[0017] In the polarizing plate according to the above aspect, the number of layers of the first antireflection layer and the second antireflection layer may be 5 to 10.

[0018] In the polarizing plate involved in the above embodiment, the high refractive index layer may be TiO2 or Nb2O5, and the low refractive index layer may be SiO2.

[0019] In the polarizing plate according to the above aspect, a surface of a non-overlapping region of the first antireflection layer that does not overlap with the plurality of convex portions may be closer to the transparent substrate than a surface of an overlapping region overlapping with the plurality of convex portions.

[0020] In the polarizing plate according to the above aspect, a difference between a thickness of an overlapping region of the first antireflection layer overlapping with the plurality of convex portions and a thickness of a non-overlapping region not overlapping with the plurality of convex portions may be 9% or less of the thickness of the overlapping region.

[0021] In the polarizing plate according to the above aspect, a difference between a film thickness of an overlapping region of the first antireflection layer overlapping with the plurality of convex portions and a film thickness of a non-overlapping region not overlapping with the plurality of convex portions may be 30 nm or less.

[0022] An optical device according to a second aspect includes the polarizing plate according to the above aspect.

[0023] The third embodiment involves a method for manufacturing a polarizing plate having a wire grid structure, comprising the steps of alternately forming a high refractive index layer and a low refractive index layer on both surfaces of a transparent substrate and laminating a first anti-reflection layer and a second anti-reflection layer, a step of sequentially laminating a reflective layer, a dielectric layer and an absorption layer on the first anti-reflection layer to form a laminate, and a step of processing the laminate to form a plurality of convex portions periodically arranged at a pitch shorter than the wavelength of light in a used frequency band.

[0024] In the method for manufacturing a polarizing plate according to the above aspect, a non-overlapping region of the first antireflection layer that does not overlap with the plurality of convex portions may be etched via the plurality of convex portions.

[0025] Effects of the Invention

[0026] According to the polarizing plate and the optical device according to the above-described aspect, it is possible to increase the transmission axis transmittance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a perspective view of the polarizing plate according to the first embodiment.

[0028] Figure 2 It is a cross-sectional view of the polarizing plate according to the first embodiment.

[0029] Figure 3 This is a cross-sectional view of a characteristic portion of the polarizing plate according to the first embodiment.

[0030] Figure 4 It is a cross-sectional view of a polarizing plate according to a first modification.

[0031] Figure 5 The transmission axis transmittances of Examples 1 to 5 and Comparative Example 1 are shown.

[0032] Figure 6 This is a graph summarizing the transmission axis transmittance of Examples 1 to 5 and Comparative Example 1 according to wavelength.

[0033] Figure 7 The transmission axis transmittances of Examples 6 to 10 and Comparative Example 2 are shown.

[0034] Figure 8 This is a graph summarizing the transmission axis transmittance of Examples 6 to 10 and Comparative Example 2 according to wavelength.

[0035] Fig. 9 The transmittance of the substrate according to the reference example is shown.

[0036] Explanation of symbols

[0037] 10: transparent substrate, 10A: first surface, 10B: second surface, 20: first anti-reflection layer, 21, 31, 51: low refractive index layer, 21A: outermost layer, 22, 32, 52: high refractive index layer, 30: second anti-reflection layer, 40: convex portion, 42: reflective layer, 44: dielectric layer, 46: absorption layer, 100, 101: polarizing plate, R1: overlapping area, R2: non-overlapping area, R1a, R2a: surface. DETAILED DESCRIPTION

[0038] Hereinafter, the present embodiment will be described in detail with appropriate reference to the accompanying drawings. In the accompanying drawings used in the following description, in order to facilitate the understanding of the features, for the sake of convenience, there are cases where the features are enlarged and displayed, and the size ratios of the components may be different from the actual ones. The materials, dimensions, etc. illustrated in the following description are only examples, and the present invention is not limited thereto, and can be implemented with appropriate changes within the scope of achieving the effects of the present invention.

[0039] "Polarizing plate"

[0040] Figure 1 1 is a perspective view of a polarizing plate 100 according to a first embodiment. The polarizing plate 100 includes a transparent substrate 10, a first antireflection layer 20, a second antireflection layer 30, and a plurality of convex portions 40. The first antireflection layer 20 is laminated on a first surface 10A of the transparent substrate 10. The second antireflection layer 30 is laminated on a second surface 10B of the transparent substrate 10. The plurality of convex portions 40 protrude from the first antireflection layer 20. The second surface 10B is a surface of the transparent substrate 10 on the opposite side to the first surface 10A.

[0041] Here, directions are defined. The plane in which the transparent substrate 10 extends is the XY plane, and the direction in which the protrusion 40 extends is the Y direction. The direction perpendicular to the Y direction is the X direction. The direction perpendicular to the X direction and the Y direction is the Z direction. The Y direction is an example of a first direction.

[0042] The polarizing plate 100 attenuates polarized waves (TE waves (S waves)) having an electric field component parallel to the Y direction in which the convex portion 400 extends, and transmits polarized waves (TM waves (P waves)) having an electric field component perpendicular to the Y direction. The Y direction of the polarizing plate 100 is an absorption axis, and the X direction is a transmission axis. The polarizing plate 100 attenuates TE waves and transmits TM waves through four effects of selective light absorption of polarized waves due to transmission, reflection, interference, and optical anisotropy.

[0043] (Transparent substrate)

[0044] The transparent substrate 10 is transparent to light of wavelengths in the use band of the polarizing plate 100. "Having transparency" does not necessarily mean that 100% of the light of wavelengths in the use band is transmitted, as long as the function as a polarizing plate is maintained. The average thickness of the transparent substrate 10 is preferably 0.3 mm or more and 1 mm or less.

[0045] The refractive index of the transparent substrate 10 is, for example, 1.1 or more and 2.2 or less. The transparent substrate 10 is, for example, glass, crystal, sapphire, etc. The component composition of the glass material used for the transparent substrate 10 is not particularly limited.

[0046] For example, silicate glass is widely circulated as optical glass and is inexpensive. In addition, quartz glass (refractive index 1.46) and soda-lime glass (refractive index 1.51) are low in cost and excellent in transmittance. In contrast, crystal and sapphire have excellent thermal conductivity. The material of the transparent substrate 10 can be appropriately selected according to the performance required by the polarizing plate 100. For example, the polarizing plate used in the optical engine of the projector requires light resistance and heat dissipation because it is irradiated with strong light. The transparent substrate 10 for projector use preferably uses crystal or sapphire.

[0047] When the transparent substrate 10 is an optically active crystal such as crystal or sapphire, the optical properties are improved if the direction in which the protrusions 40 described later extend is parallel or perpendicular to the optical axis of the crystal. The optical axis is the direction along which the difference in refractive index between ordinary light and extraordinary light is minimized.

[0048] (First anti-reflection layer)

[0049] The first anti-reflection layer 20 is located on the first surface 10A of the transparent substrate 10. The first anti-reflection layer 20 is located between the transparent substrate 10 and the plurality of protrusions 40. Figure 2 It is a cross-sectional view of the polarizing plate 100 according to the first embodiment. Figure 3 It is a cross-sectional view of a characteristic portion of the polarizing plate 100 according to the first embodiment. Figure 3 1 is an enlarged cross-sectional view of the first anti-reflection layer 20 of the polarizing plate 100 .

[0050] The first anti-reflection layer 20 uses interference of light to prevent reflection. The first anti-reflection layer 20 is formed by alternately stacking low refractive index layers 21 and high refractive index layers 22. The low refractive index layer 21 has a lower refractive index than the adjacent layers. The high refractive index layer 22 has a higher refractive index than the adjacent layers. The refractive index of the low refractive index layer 21 is, for example, greater than 1.0 and lower than the refractive index of the transparent substrate 10. The refractive index of the high refractive index layer 22 is, for example, higher than the refractive index of the low refractive index layer 21.

[0051] The low refractive index layer 21 and the high refractive index layer 22 are dielectric layers. The low refractive index layer 21 and the high refractive index layer 22 are, for example, oxides such as Si oxide, Ti oxide, Zr oxide, Al oxide, Nb oxide, Ta oxide, Bi oxide, and Be oxide, magnesium fluoride, cryolite, germanium, silicon, and carbon. For example, the low refractive index layer 21 is SiO2, and the high refractive index layer 22 is TiO2 or NbO2.

[0052] The thickness of each of the low refractive index layer 21 and the high refractive index layer 22 is appropriately selected according to the wavelength range of the light of the use band, etc. The thickness of each layer of the low refractive index layer 21 and the high refractive index layer 22 is, for example, 1 nm or more and 500 nm or less. The thickness of each layer of the low refractive index layer 21 and the high refractive index layer 22 may be different.

[0053] The number of layers of the first antireflection layer 20 is not particularly limited, and is, for example, 5 to 10. If the number of layers is small, the antireflection function is reduced, and if the number of layers is large, the cost is increased.

[0054] The first anti-reflection layer 20 is composed of an overlapping region R1 overlapping with the convex portion 40 and a non-overlapping region R2 not overlapping with the convex portion 40. In the first anti-reflection layer 20, for example, the non-overlapping region R2 is dug toward the transparent substrate 10 side, and the non-overlapping region R2 is recessed toward the transparent substrate 10 side relative to the overlapping region R1. The surface R2a of the non-overlapping region R2 is closer to the transparent substrate 10 than the surface R1a of the overlapping region R1, for example.

[0055] The film thickness h1 of the overlapping region R1 is different from the film thickness h2 of the non-overlapping region R2, for example. The film thickness h1 of the overlapping region R1 corresponds to the total thickness of the first anti-reflection layer 20. The film thickness h1 of the overlapping region R1 is, for example, 200 nm or more and 700 nm or less. If the film thickness h1 is thin, the characteristics of the anti-reflection film will fluctuate. If the film thickness h1 is thick, the manufacturing cost will be increased, and the film will be easily peeled off and cracked.

[0056] The film thickness h2 of the non-overlapping region R2 is, for example, thinner than the film thickness h1 of the overlapping region R1. The film thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2 is, for example, greater than 0% and less than 10% of the film thickness h1 of the overlapping region R1, and is, for example, less than 9% of the film thickness h1 of the overlapping region R1. In addition, the film thickness difference h3 is, for example, greater than 0nm and less than 40nm, and is greater than 10nm and less than 30nm.

[0057] The layer of the first antireflection layer 20 that is farthest from the transparent substrate 10 is called the outermost layer 21A. The outermost layer 21A is, for example, a low refractive index layer. In the outermost layer 21A, the non-overlapping region R2 is recessed toward the transparent substrate 10 side compared with the overlapping region R1. The non-overlapping region R2 is, for example, recessed toward the transparent substrate 10 side in the outermost layer 21A compared with the overlapping region R1. The film thickness difference h3 of the overlapping region R1 relative to the film thickness h4 of the outermost layer 21A is, for example, 10% or more and 35% or less.

[0058] The first antireflection layer 20 can be formed by, for example, vapor deposition, sputtering, chemical vapor deposition (CVD), or atomic layer deposition (ALD).

[0059] (Second anti-reflection layer)

[0060] The second anti-reflection layer 30 is located on the second surface 10B of the transparent substrate 10. The second anti-reflection layer 30 uses interference of light to prevent reflection. The second anti-reflection layer 30 is formed by alternately stacking low refractive index layers 31 and high refractive index layers 32. The low refractive index layer 31 has a lower refractive index than the adjacent layer. The high refractive index layer 32 has a higher refractive index than the adjacent layer. The low refractive index layer 31 and the high refractive index layer 32 are the same as the low refractive index layer 21 and the high refractive index layer 22 of the first anti-reflection layer 20, except that the outermost layer 21A is not recessed.

[0061] (convex part)

[0062] The convex portion 40 protrudes from the transparent substrate 10 in the Z direction and extends in the Y direction. The convex portions 40 are periodically arranged in the X direction. The spacing P between adjacent convex portions 40 in the X direction is shorter than the wavelength of light in the use band of the polarizing plate 100. For example, the spacing P is greater than 100nm and less than 200nm. As long as the spacing P is within this range, the production of the convex portion 40 becomes easy, and the mechanical stability and optical property stability of the convex portion 40 are improved.

[0063] The pitch P between adjacent protrusions 40 can be measured as an average value using a scanning electron microscope or a transmission electron microscope. For example, the distances in the X direction between adjacent protrusions 40 are measured at any four positions, and the pitch P is calculated from the arithmetic average thereof. The measurement method of averaging the measured values ​​at any four positions of a plurality of protrusions 40 is called an electron microscopy method.

[0064] The convex portion 40 protrudes relative to the transparent substrate 10. The convex portion 40 protrudes, for example, in the Z direction as the main direction. The average width of the convex portion 40 in the X direction is, for example, not less than 20% and not more than 50% of the pitch P. The average width of the convex portion 40 refers to the average value of the width at each point when the convex portion 40 is divided into 10 parts in the Z direction. The height of the convex portion 40 is, for example, not less than 250nm and not more than 400nm. In addition, the aspect ratio obtained by dividing the height of the convex portion 40 by the average width is, for example, not less than 5 and not more than 13.3.

[0065] The convex portion 40 has a reflective layer 42, a dielectric layer 44, and an absorption layer 46 in order from the outermost layer 21A side of the first anti-reflection layer 20. When the light incident on the polarizing plate 100 from the first surface 10A side passes through the absorption layer 46 and the dielectric layer 44, a part is absorbed and attenuated. The TM (P wave) in the light passing through the absorption layer 46 and the dielectric layer 44 passes through the reflective layer 42. In contrast, the TE (S wave) in the light passing through the absorption layer 46 and the dielectric layer 44 is reflected by the reflective layer 42. When the reflected TE wave passes through the absorption layer 46 and the dielectric layer 44, a part is absorbed, and a part is reflected again and returns to the reflective layer 42. The TE wave reflected by the reflective layer 42 interferes and attenuates when passing through the absorption layer 46 and the dielectric layer 44. The polarizing plate 100 exhibits polarization characteristics by the selective attenuation of the TE wave as described above.

[0066] <Reflection layer>

[0067] The reflective layer 42 is located on the outermost layer 21A of the first anti-reflection layer 20. Other layers may be inserted between the outermost layer 21A of the first anti-reflection layer 20 and the reflective layer 42. The reflective layer 42 protrudes in the Z direction relative to the transparent substrate 10 and extends in the Y direction in a strip shape. The reflective layer 42 reflects TE waves (S waves) and transmits TM waves (P waves). The height of the reflective layer 42 is, for example, not less than 100 nm and not more than 300 nm.

[0068] The reflective layer 42 contains a material that is reflective with respect to light of a wavelength in the use frequency band. The reflective layer 42 contains, for example, a single metal such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, Ta, or an alloy thereof. The reflective layer 42 is formed, for example, of aluminum or an aluminum alloy. The reflective layer 42 is not limited to metals, and may also be an inorganic film or a resin film whose surface reflectivity is increased by coloring or the like.

[0069] The reflective layer 42 can be formed at a high density by, for example, vapor deposition or sputtering. The reflective layer 42 can also be formed of two or more layers having different constituent materials.

[0070] <Dielectric Layer>

[0071] The dielectric layer 44 is, for example, stacked on the reflective layer 42. The dielectric layer 44 is not necessarily in contact with the reflective layer 42, and another layer may be present between the dielectric layer 44 and the reflective layer 42. The dielectric layer 44 extends in the Y direction in a strip shape.

[0072] The film thickness of the dielectric layer 44 can be determined based on the polarized wave reflected by the absorption layer 46. The film thickness of the dielectric layer 44 is a thickness that makes the phase of the polarized wave reflected by the absorption layer 46 and the phase of the polarized wave reflected by the reflection layer 42 deviate by only half a wavelength. The film thickness of the dielectric layer 44 is, for example, not less than 1 nm and not more than 500 nm. As long as it is within this range, the phase relationship between the two reflected polarized waves can be adjusted, and the interference effect can be improved. The film thickness of the dielectric layer 44 can be obtained using the above-mentioned electron microscopy method.

[0073] The dielectric layer 44 contains, for example, metal oxide, magnesium fluoride (MgF2), cryolite, germanium, silicon, boron nitride, carbon, or a combination thereof. The metal oxide is, for example, Si oxide such as SiO2, Al2O3, beryllium oxide, bismuth oxide, boron oxide, tantalum oxide, etc. The dielectric layer 44 is, for example, Si oxide or Ti oxide.

[0074] The refractive index of the dielectric layer 44 is, for example, greater than 1.0 and less than 2.5. Since the optical properties of the reflective layer 42 are also affected by the refractive index of the surroundings (for example, the refractive index of the dielectric layer 44), the polarization properties can be controlled by adjusting the refractive index of the dielectric layer 44.

[0075] The dielectric layer 44 can be formed by, for example, vapor deposition, sputtering, chemical vapor deposition (CVD), or atomic layer deposition (ALD). The dielectric layer 44 may be formed of two or more layers.

[0076] <Absorbent layer>

[0077] The absorption layer 46 is, for example, stacked on the dielectric layer 44. The absorption layer 46 extends in a strip shape in the Y direction. The film thickness of the absorption layer 46 is, for example, 5 nm to 50 nm. The film thickness of the absorption layer 46 can be measured by the electron microscopy method described above.

[0078] The absorption layer 46 contains one or more substances having a light absorbing function with an optical constant attenuation constant not equal to zero. The absorption layer 46 contains, for example, a metal material or a semiconductor material. The material used in the absorption layer 46 can be appropriately selected according to the wavelength range of the light in the use band.

[0079] When a metal material is used in the absorption layer 46, the metal material is, for example, a single metal such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Sn, or an alloy containing one or more of these elements. In addition, when a semiconductor material is used in the absorption layer 46, the semiconductor material is, for example, Si, Ge, Te, ZnO, or a silicide material. Examples of silicide materials are β-FeSi2, MgSi2, NiSi2, BaSi2, CrSi2, TaSi, and the like. The polarizing plate 100 using these materials in the absorption layer 46 has a high extinction ratio in the visible light domain. In addition, the absorption layer 46 contains, for example, Fe or Ta and Si.

[0080] When the absorption layer 46 is a semiconductor material, the band gap energy of the semiconductor contributes to the absorption of light. The band gap energy of the semiconductor material is, for example, a value equal to or less than the value obtained by converting the wavelength of the use band into energy. For example, when the use band is the visible light region, a semiconductor material having a band gap energy of 3.1 eV or less corresponding to the absorption energy of a wavelength of 400 nm or more is used in the absorption layer 46.

[0081] The absorption layer 46 is not limited to one layer, and may be composed of two or more layers. When the absorption layer 46 is composed of two or more layers, the materials of each layer may be different. The absorption layer 46 may be formed by a method such as evaporation or sputtering.

[0082] (Protective layer, water-repellent layer)

[0083] In addition to the transparent substrate 10, the first anti-reflection layer 20, the second anti-reflection layer 30 and the convex portion 40, the polarizing plate 100 may also have other components. For example, the polarizing plate 100 may have a protective layer on the incident surface side of the light. The protective layer improves the reliability of the polarizing plate 100, such as heat resistance. In addition, for example, a water-repellent film may also be provided on the surface of the convex portion 40. The water-repellent film is formed, for example, by a fluorine-based silane compound such as perfluorodecyltriethoxysilane (FDTS). The water-repellent film can be formed, for example, by a CVD method or an ALD method. The water-repellent film improves the reliability of the polarizing plate 100, such as moisture resistance.

[0084] "Polarizing plate manufacturing method"

[0085] The method for manufacturing the polarizing plate 100 according to the present embodiment includes the steps of laminating the first antireflection layer 20 and the second antireflection layer 30 on the transparent substrate 10 , laminating a laminate serving as a basis for the convex portion 40 on the first antireflection layer 20 , and processing the laminate into the convex portion 40 .

[0086] First, low refractive index layers 21, 31 and high refractive index layers 22, 32 are alternately stacked on the first surface 10A and the second surface 10B of the transparent substrate 10, respectively. The low refractive index layers 21, 31 and the high refractive index layers 22, 32 are formed into films by, for example, evaporation, sputtering, CVD, or ALD. The number of layers of the low refractive index layers 21, 31 and the high refractive index layers 22, 32 can be appropriately changed. The film thickness of the low refractive index layers 21, 31 and the high refractive index layers 22, 32 can be appropriately selected according to the wavelength range of the light of the use frequency band, etc. By alternately stacking the low refractive index layers 21, 31 and the high refractive index layers 22, 32, the first anti-reflection layer 20 is formed on the first surface 10A and the second anti-reflection layer 30 is formed on the second surface 10B.

[0087] Next, a layer to be a reflective layer, a layer to be a dielectric layer, and a layer to be an absorption layer are sequentially stacked in a film forming step on the first antireflection layer 20 of the transparent substrate 10 to form a laminate. These layers are formed by, for example, sputtering or vapor deposition.

[0088] Next, the stack is processed. The stack is processed using, for example, photolithography, nanoimprinting, etc. For example, a one-dimensional lattice mask pattern is formed on one side of the stack by a resist. The convex portion 40 is formed by selectively etching the portion where the resist is not formed. The etching is performed, for example, by dry etching.

[0089] Furthermore, when forming the protrusion 40, etching is performed by adjusting the etching time, so that a portion that does not overlap with the protrusion 40 can be dug out in the outermost layer 21A of the first anti-reflection layer 20. By removing a portion of the outermost layer 21A, the surface R2a of the non-overlapping region R2 can be brought closer to the transparent substrate 10 than the surface R1a of the overlapping region R1.

[0090] The polarizing plate 100 according to the first embodiment is obtained through the above steps. A protective layer or a water-repellent layer may be further formed on the light irradiation surface of the polarizing plate 100 .

[0091] The polarizing plate 100 involved in the first embodiment has a high transmission axis transmittance because it has an anti-reflection layer on both sides of the transparent substrate 10. In addition, relative to the overlapping area R1, the non-overlapping area R2 of the first anti-reflection layer 20 that does not overlap with the convex portion 40 is dug out, thereby further improving the transmission axis transmittance. In addition, by adjusting the amount of digging out the non-overlapping area R2 relative to the overlapping area R1, the transmission axis transmittance can be improved in coordination with the wavelength range used.

[0092] Although the first embodiment has been described in detail above, the present invention is not limited to this configuration, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0093] For example, Figure 4 It is a cross-sectional view of a polarizing plate 101 according to a first modification. Figure 4 In the polarizing plate 101 shown in FIG. 1 , the first anti-reflection layer 50 is constructed differently from Figure 2 The polarizing plate 100 shown. Figure 2 The polarizing plate 100 shown is the same, and the same components are given the same reference numerals and their description is omitted.

[0094] The first anti-reflection layer 50 is formed by alternately stacking low refractive index layers 51 and high refractive index layers 52. The low refractive index layers 51 have a lower refractive index than the adjacent layers. The high refractive index layers 52 have a higher refractive index than the adjacent layers. The low refractive index layers 51 and the high refractive index layers 52 are the same as the low refractive index layers 21 and the high refractive index layers 22 of the first anti-reflection layer 20 except that the outermost layers are not recessed.

[0095] Since the polarizing plate 101 according to the first modification also has antireflection layers on both surfaces of the transparent substrate 10 , the transmission axis transmittance is high.

[0096] "Optical equipment"

[0097] The optical device involved in the second embodiment has the polarizing plates 100 and 101 involved in the above-mentioned first embodiment. Examples of the optical device include a liquid crystal projector, a head-up display, a digital camera, etc. The polarizing plates 100 and 101 involved in the first embodiment have excellent reliability and can be used for various purposes. In addition, the polarizing plates 100 and 101 are made of inorganic materials. Compared with organic polarizing plates, the polarizing plates 100 and 101 are particularly suitable for use in liquid crystal projectors, head-up displays, etc. that require heat resistance.

[0098] When the optical device has a plurality of polarizing plates, at least one of the plurality of polarizing plates is the polarizing plates 100, 101 involved in the first embodiment. For example, when the optical device is a liquid crystal projector, polarizing plates are arranged on the incident side and the exit side of the liquid crystal panel. One of the polarizing plates uses the polarizing plates 100, 101 involved in the first embodiment. In addition, the film thickness difference h3 can also be changed according to the wavelength of light incident on the polarizing plates 100, 101. For example, the film thickness difference h3 of the polarizing plates for incident light of the red wavelength band, the polarizing plates for incident light of the green wavelength band, and the polarizing plates for incident light of the blue wavelength band can be different.

[0099] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0100] Example

[0101] (Example 1)

[0102] Reproduction Figure 2 The polarizing plate 100 shown was used to obtain the transmission axis transmittance of the polarizing plate 100 by simulation. The simulation was performed by electromagnetic field simulation according to the RCWA (Rigorous Coupled Wave Analysis) method.

[0103] The structures of the first anti-reflection layer 20 and the second anti-reflection layer 30 in the polarizing plate 100 are summarized in Table 1. In Table 1, the first layer is the layer closest to the transparent substrate 10, and the layers are separated from the transparent substrate 10 in the order of the second layer, the third layer, the fourth layer, and the fifth layer. The structures of the layers of the first anti-reflection layer 20 and the second anti-reflection layer 30 are the same except that the outermost layer of the first anti-reflection layer 20 is dug down. The digging depth (the film thickness difference h3 between the film thickness h1 of the overlapping area R1 and the film thickness h2 of the non-overlapping area R2) of the outermost layer (the fifth layer in Table 1) of the first anti-reflection layer 20 is set to 10 nm. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 2.5%.

[0104] Table 1

[0105] Material Film thickness(nm) First floor <![CDATA[SiO2]]> 151.98 Second floor <![CDATA[Nb2O5]]> 11.64 Third floor <![CDATA[SiO2]]> 34.79 Fourth floor <![CDATA[Nb2O5]]> 112.29 Fifth floor <![CDATA[SiO2]]> 86.56 total 397.26

[0106] In addition, the structure of the convex part 40 is as follows:

[0107] Reflection layer 42: Al with a film thickness of 250 nm,

[0108] Dielectric layer 44: SiO2 with a thickness of 5 nm,

[0109] Absorption layer 46: FeSi with a film thickness of 25 nm,

[0110] Pitch of the protrusions 40: 141 nm.

[0111] (Example 2)

[0112] In Example 2, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the fifth layer in Table 1) of the first anti-reflection layer 20 is set to 20 nm, which is different from Example 1. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 5.0%.

[0113] (Example 3)

[0114] In Example 3, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the fifth layer in Table 1) of the first anti-reflection layer 20 is set to 30 nm, which is different from Example 1. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 7.6%.

[0115] (Example 4)

[0116] In Example 4, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the fifth layer in Table 1) of the first anti-reflection layer 20 is set to 40 nm, which is different from Example 1. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 10.0%.

[0117] (Example 5)

[0118] In Example 5, the only difference from Example 1 is that the outermost layer (the fifth layer in Table 1) of the first antireflection layer 20 is not dug down. Example 5 satisfies Figure 4 The structure of the polarizing plate 101 is shown.

[0119] (Comparative Example 1)

[0120] Comparative Example 1 is different from Example 5 in that the first antireflection layer 20 is not provided on the first surface 10A of the transparent substrate 10 , and the second antireflection layer 30 is provided on the second surface 10B.

[0121] Figure 5 The transmission axis transmittances of Examples 1 to 5 and Comparative Example 1 are shown. Figure 6This is a graph summarizing the transmission axis transmittance of Examples 1 to 5 and Comparative Example 1 according to wavelength. Examples 1 to 5 have improved transmission axis transmittance in the wavelength region of 520 nm to 630 nm with high visibility compared to Comparative Example 1. Compared with Comparative Example 1, the transmission axis transmittance of Example 5 is improved by an average of 1.8% to 2.7% in the entire visible light region. In addition, Examples 1 to 3, in which the outermost layer is dug to a depth of 30 nm or less, have improved transmission axis transmittance in a wider wavelength region than Example 5, which is not dug. Compared with Comparative Example 1, the transmission axis transmittance of Examples 1 and 2 is improved by an average of 0.3% to 3.1% in the entire visible light region. Compared with Comparative Example 1, the transmission axis transmittance of Examples 1 and 2 is improved by an average of 0.8% to 2.4% in the entire visible light region.

[0122] In addition, in the red wavelength region, the transmittance of Example 1 is the highest, and in the blue and green wavelength regions, the transmittance of Example 2 is the highest. Therefore, by designing the structure of the first anti-reflection layer 20 in accordance with the wavelength of the use band, a higher transmission axis transmittance can be achieved. For example, the polarizing plate of Example 2 can be used as the polarizing plate for blue and green in the projector, and the polarizing plate of Example 1 can be used as the polarizing plate for red.

[0123] (Example 6)

[0124] The first anti-reflection layer 20 and the second anti-reflection layer 30 in the polarizing plate 100 are different from Example 1. The structures of the first anti-reflection layer 20 and the second anti-reflection layer 30 in Example 6 are summarized in Table 2. In Table 2, the first layer is the layer closest to the transparent substrate 10, and the second layer, the third layer, the fourth layer, the fifth layer, the sixth layer, the seventh layer, the eighth layer, and the ninth layer are separated from the transparent substrate 10 in the order of the second layer, the third layer, the fourth layer, the fifth layer, the sixth layer, the seventh layer, the eighth layer, and the ninth layer. The structures of the first anti-reflection layer 20 and the second anti-reflection layer 30 are the same except that the outermost layer of the first anti-reflection layer 20 is dug down. The digging depth (the film thickness difference h3 between the film thickness h1 of the overlapping area R1 and the film thickness h2 of the non-overlapping area R2) of the outermost layer of the first anti-reflection layer 20 (the fifth layer in Table 2) is set to 10nm. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 1.6%.

[0125] Table 2

[0126] Material Film thickness(nm) First floor <![CDATA[SiO2]]> 170.99 Second floor <![CDATA[TiO2]]> 12.76 Third floor <![CDATA[SiO2]]> 33.72 Fourth floor <![CDATA[TiO2]]> 121.52 Fifth floor <![CDATA[SiO2]]> 36.77 Sixth floor <![CDATA[TiO2]]> 25.13 Seventh floor <![CDATA[SiO2]]> 39.09 Eighth Floor <![CDATA[TiO2]]> 114.39 Ninth Floor <![CDATA[SiO2]]> 86.78 total 641.15

[0127] (Example 7)

[0128] In Example 7, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the 9th layer in Table 2) of the first anti-reflection layer 20 is set to 20 nm, which is different from Example 6. The ratio of the digging depth to the total thickness of the first anti-reflection layer 20 is 3.1%.

[0129] (Example 8)

[0130] In Example 8, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the 9th layer in Table 2) of the first antireflection layer 20 is set to 30 nm, which is different from Example 6. The ratio of the digging depth to the total thickness of the first antireflection layer 20 is 4.7%.

[0131] (Example 9)

[0132] In Example 9, only the digging depth (thickness difference h3 between the film thickness h1 of the overlapping region R1 and the film thickness h2 of the non-overlapping region R2) of the outermost layer (the ninth layer in Table 2) of the first antireflection layer 20 is set to 40 nm, which is different from Example 6. The ratio of the digging depth to the total thickness of the first antireflection layer 20 is 6.2%.

[0133] (Example 10)

[0134] In Example 10, the only difference from Example 6 is that the outermost layer (the ninth layer in Table 2) of the first antireflection layer 20 is not dug. Example 10 satisfies Figure 4 The structure of the polarizing plate 101 is shown.

[0135] (Comparative Example 2)

[0136] Comparative Example 2 is different from Example 10 in that the first antireflection layer 20 is not provided on the first surface 10A of the transparent substrate 10 , and the second antireflection layer 30 is provided on the second surface 10B.

[0137] Figure 7 The transmission axis transmittances of Examples 6 to 10 and Comparative Example 2 are shown. Figure 8 This is a graph summarizing the transmission axis transmittances of Examples 6 to 10 and Comparative Example 2 according to wavelength. Examples 6 to 10 all have improved transmission axis transmittances compared to Comparative Example 2 in the wavelength region of 520 nm to 600 nm with high visibility.

[0138] (Reference example)

[0139] In the reference example, an antireflection layer is formed on both surfaces of the transparent substrate. The reference example has no convex portion and does not exhibit polarization characteristics.

[0140] The configuration of the antireflection layers on both surfaces in Reference Example 1 is the same as that of the second antireflection layer 30 in Example 1.

[0141] Reference Example 2 is different from Reference Example 1 in that the film thickness of the outermost layer is increased by 20 nm.

[0142] Reference Example 3 is different from Reference Example 1 in that the film thickness of the outermost layer is increased by 40 nm.

[0143] Reference Example 4 is different from Reference Example 1 in that the film thickness of the outermost layer is reduced by 20 nm.

[0144] Reference Example 5 is different from Reference Example 1 in that the film thickness of the outermost layer is reduced by 40 nm.

[0145] Fig. 9 The transmittance of the substrate involved in the reference example is shown. Fig. 9 As shown in the figure, for the anti-reflection layer that uses light interference to prevent reflection, the design of the film thickness of each layer is important. If the film thickness is changed, the transmittance will be greatly reduced. On the other hand, the above-mentioned Examples 1 to 4 and 6 to 9 have the following unexpected results, that is, by digging down the outermost layer, the transmittance is improved regardless of whether the designed layer thickness of the anti-reflection layer is changed.

Claims

1. A polarizing plate having a wire grid structure, A transparent substrate, a first antireflection layer laminated on a first surface of the transparent substrate, a plurality of convex portions protruding from the first antireflection layer, and a second antireflection layer laminated on a second surface opposite to the first surface, The plurality of convex portions are periodically arranged at a pitch shorter than the wavelength of light in the used frequency band, Each convex portion extends in a first direction and has a reflective layer, a dielectric layer and an absorption layer in sequence starting from the first surface. The first anti-reflection layer and the second anti-reflection layer include high refractive index layers and low refractive index layers stacked alternately. The difference between the thickness of the first antireflection layer in the overlapping region overlapping with the plurality of convex portions and the thickness of the first antireflection layer in the non-overlapping region not overlapping with the plurality of convex portions is 10 nm to 30 nm.

2. The polarizing plate according to claim 1, The number of layers of the first anti-reflection layer and the second anti-reflection layer is 5 to 10.

3. The polarizing plate according to claim 1 or 2, The high refractive index layer is TiO2 or Nb2O5, and the low refractive index layer is SiO2.

4. The polarizing plate according to claim 1 or 2, A surface of a non-overlapping region of the first anti-reflection layer that does not overlap with the plurality of convex portions is closer to the transparent substrate than a surface of an overlapping region that overlaps with the plurality of convex portions.

5. The polarizing plate according to claim 1 or 2, The difference between the thickness of the first antireflection layer in an overlapping region overlapping with the plurality of convex portions and the thickness of the first antireflection layer in a non-overlapping region not overlapping with the plurality of convex portions is 9% or less of the thickness of the overlapping region. 6 . An optical device comprising the polarizing plate according to claim 1 .

7. A method for manufacturing a polarizing plate according to any one of claims 1 to 5, which is a method for manufacturing a polarizing plate having a wire grid structure, comprising: The process of alternately forming high refractive index layers and low refractive index layers on both sides of a transparent substrate and laminating a first antireflection layer and a second antireflection layer, a step of laminating a reflective layer, a dielectric layer and an absorption layer in sequence on the first anti-reflection layer to form a laminate, and The step of processing the laminate to form a plurality of convex portions periodically arranged at a pitch shorter than the wavelength of light in a used frequency band.

8. The method for manufacturing a polarizing plate according to claim 7, The non-overlapping region of the first anti-reflection layer that does not overlap with the plurality of convex portions is etched via the plurality of convex portions.

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