Optical element

Abstract

In optical elements with microstructures, this prevents peeling of metal films and adhesion layers due to thermal changes. [Solution] An optical element comprising a resin substrate 11 having a base 12 and a microstructure 13, and a metal film 15 on the side surface of the microstructure 13, wherein a convex structure 14 is formed at the corner formed by the side surface of the microstructure 13 on which the metal film 15 is formed and the surface of the base 12, and the average volume of the convex structure is 14800 nm. 3 More than 83000nm 3 The following applies:

Description

[Technical Field]

[0001] This invention relates to an optical element having a microstructure. [Background technology]

[0002] It is known that functions such as anti-reflection and polarization control can be imparted to optical substrates by forming microstructures on their surfaces. The average period of the formed microstructure needs to be shorter than the wavelength of the target wavelength band in order to avoid diffraction phenomena in that band. For example, when targeting the visible light wavelength range, the average period needs to be shorter than 400 nm, which is the shortest wavelength in the visible range, and generally, microstructures with an average period of 250 nm or less are used. Methods for forming microstructures include pattern formation using electron beam lithography equipment, laser interference exposure equipment, semiconductor exposure equipment, and etching equipment, as well as transfer formation using molds with inverted microstructures. Furthermore, by forming a metal film on the microstructure obtained by the above means, it becomes possible to exhibit various optical functions. Specifically, it is known that reflective polarizing elements can be formed by forming an aluminum film on the line side surface of a line-and-space structure using methods such as oblique deposition. Reflective polarizing elements are optical elements used in folded optical systems that enable thinning and miniaturization, and their application to head-mounted displays and small camera products is progressing. Furthermore, in order to reduce manufacturing costs, reflective polarizing elements often use a resin substrate on which a line-and-space structure has been transferred. In this case, it is difficult to ensure sufficient adhesion at the interface between the aluminum film and the resin line-and-space structure, so a method of preventing peeling by using an adhesion layer has been proposed (Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-4491 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, because the coefficients of thermal expansion differ significantly between the inorganic materials that make up the metal film or adhesion layer and the resin materials that make up the line-and-space structure, there was a problem that they were prone to peeling due to, for example, heat cycling. The object of the present invention is to prevent peeling of metal films and adhesion layers due to thermal changes in optical elements having a microstructure. [Means for solving the problem]

[0005] The first aspect of the present invention is an optical element comprising a resin substrate having a base and a microstructure protruding from the base, and a metal film formed on at least a portion of the side surface of the microstructure, Multiple convex structures are provided on the side surface where the metal film is formed, and the average volume of the multiple convex structures is 14800 nm. 3 More than 83000nm 3 The following characteristics apply: The second aspect of the present invention is an optical element comprising a resin substrate having a base and a microstructure protruding from the base, an adhesion layer covering the surface of the resin substrate, and a metal film formed on at least a portion of the side surface of the microstructure via the adhesion layer, Multiple convex structures are provided on the surface of the base, and the average volume of the multiple convex structures is 14800 nm. 3 More than 83000nm 3 The following characteristics apply: [Effects of the Invention]

[0006] In the present invention, by providing a specific convex structure on the resin substrate, it is possible to suppress the peeling of the metal film or adhesive layer formed on the resin substrate and to provide an optical element that suppresses the deterioration of optical performance. [Brief explanation of the drawing]

[0007] [Figure 1]This figure shows the configuration of one embodiment of the optical element of the present invention, where (a) is a schematic plan view and (b) is a schematic cross-sectional view. [Figure 2] Figure 1 is a schematic cross-sectional view showing the manufacturing process of the optical element. [Figure 3] This figure schematically shows the configuration of another embodiment of the present invention, where (a) is a schematic plan view and (b) is a schematic cross-sectional view. [Figure 4] This figure schematically shows the configuration of another embodiment of the present invention, where (a) is a schematic plan view and (b) is a schematic cross-sectional view. [Figure 5] This diagram schematically shows the configuration of a conventional optical element, with (a) being a plan view and (b) being a cross-sectional view. [Modes for carrying out the invention]

[0008] The optical element of the present invention comprises a resin substrate having a base and a microstructure protruding from the base, and a metal film formed on at least a portion of the side surface of the microstructure, characterized in that the resin substrate has a convex structure of a specific size. Embodiments will be described in detail below.

[0009] [First Embodiment] Figure 1 shows the configuration of a first embodiment of the optical element of the present invention. Figure 1(a) is a schematic plan view, and (b) is a schematic cross-sectional view of the A-A' region in (a). The dashed lines in Figure 1(a) show the side view and convex structure 14 of the microstructure 13 of the resin substrate 11 when the metal film 15 is removed.

[0010] The optical element of this embodiment comprises a resin substrate 11 and a metal film 15. The resin substrate 11 includes a base portion 12 and a microstructure 13 protruding from the surface of the base portion 12. The microstructure 13 is a line-and-space structure in which linear protrusions are arranged parallel to each other at a constant pitch. A convex structure 14 is formed on only one of a pair of sides parallel to the lines of the microstructure 13, and the metal film 15 is formed to cover the convex structure 14, the side having the convex structure 14, and the upper surface of the microstructure 13.

[0011] In this embodiment, the convex structure 14 is a rectangular parallelepiped and is formed at the corner formed by the side surface of the fine structure 13 and the surface of the base 12. Due to such a convex structure 14, the area of the interface between the metal film 15 and the resin base material 11 increases, so the adhesion strength between the metal film 15 and the resin base material 11 is enhanced, and peeling of the metal film 15 due to thermal changes is suppressed without impairing the optical characteristics.

[0012] The resin base material 11 and the metal film 15 have significantly different coefficients of thermal expansion. Specifically, the coefficient of thermal expansion of the resin material is on the order of 10×10 -5 / °C, and the coefficient of thermal expansion of the metal material is on the order of 10×10 -6 / °C. The resin material has a coefficient of thermal expansion about 10 times larger. Furthermore, while the dimensions of the fine structure 13 are on the order of nm, since the resin base material 11 is an optical element, it has a size of at least on the order of mm. Therefore, when the size of the resin base material 11 changes due to a temperature change in the usage environment, stress concentrates at the corner formed by the side surface of the fine structure 13 and the base 12. Furthermore, since the metal film 15 only deforms about 1 / 10 of the resin base material 11, it cannot follow the amount of deformation of the resin base material 11. As a result, the metal film 15 peels off starting from around the corner formed by the side surface of the fine structure 13 and the base 12.

[0013] Therefore, in the form for implementing the present invention, by providing the convex structure 14 at the corner formed by the side surface of the fine structure 13 and the base 12, the adhesion strength of the portion that becomes the starting point of peeling of the metal film 15 can be locally strengthened, and peeling of the entire film can be prevented.

[0014] On the other hand, by providing the convex structure 14, it may deviate from the original optical design value, so there is a possibility that the desired optical characteristics cannot be obtained. As a result of investigations by the present inventors, the correlation between the dimensions of the convex structure 14 and the change in optical characteristics was grasped, and the dimensional range of the convex structure 14 that can be used as an optical element was clarified.

[0015] Specifically, the average value of the volume of the convex structure 14 is 14800 nm 3 or more and 83000 nm 3If the following conditions are met, peeling of the metal film 15 can be suppressed without degrading the optical properties.

[0016] Moreover, in order to obtain the effect that the convex structure 14 suppresses peeling of the metal film 15 without degrading the optical properties, the preferable conditions are as follows.

[0017] The area of the interface where the resin substrate 11 contacts the metal film 15 is 160% or more and 680% or less of the area in the case where there is no convex structure 14.

[0018] The abundance ratio of the convex structure 14 is 1% or more and 35% or less. Here, the abundance ratio is the ratio of the upper surface area of the convex structure 14 formed in the region where the metal film 15 is formed within the evaluation area to the area of the evaluation area, as viewed in plan from the normal direction of the surface of the base 12 on which the fine structure 13 is formed. That is, in FIG. 1(a), it is the ratio of the sum of the upper surface areas of the plurality of convex structures 14 covered with the metal film 15 to the area of FIG. 1(a). Here, in the present embodiment, the abundance ratio is evaluated using an electron microscope observation image at 50,000 times as the evaluation area. The size of the evaluation area is approximately 2.5 μm in width and approximately 2.0 μm in length.

[0019] The surface area of one of the convex structures 14 is 2620 nm 2 or more and 9230 nm 2 or less.

[0020] The height of the convex structure 14 (in the vertical direction of the paper surface of FIG. 1(a)) is 12 nm or more and 68 nm or less.

[0021] The shape and area of the convex structure 14 according to the present embodiment can be obtained by selecting a predetermined region through electron microscope observation. Specifically, the horizontal size with respect to the base 12 is measured by observation from above. The direction perpendicular to the base 12 corresponding to the height of the convex structure 14 is measured by preparing a FIB cross-section sample. However, since it is difficult to evaluate the heights of all the convex structures 14 present in the evaluation area, in the present embodiment, the height measurement is performed on any five convex structures 14, and the average value thereof is used.

[0022] The resin substrate 11 can be any resin material with a transmittance of 90% or more at the wavelength of light used. In the visible light wavelength range, for example, polyester resin (PES), cycloolefin polymer resin (COP), polystyrene resin (PS), acrylic resin such as polymethyl methacrylate resin (PMMA), and polycarbonate resin (PC) can be used.

[0023] In this embodiment, the microstructure 13 is a line-and-space structure, but any structure that exhibits the desired optical function may be used. For example, a hole structure, a pillar structure, a moth-eye structure, or, in the case of a metamaterial, a ring-shaped structure or a partially missing ring-shaped structure may be used.

[0024] The metal film 15 can be any material that provides the desired optical properties; for example, in the visible light wavelength range, aluminum, silver, gold, copper, etc., can be used.

[0025] In the resin substrate 11, the base portion 12 and the microstructure 13 may be made of different resin materials or the same resin material, and preferably they are integrally molded from the same resin material. Similarly, the convex structure 14 may be made of a different resin material or the same resin material as the base portion 12 and the microstructure 13, and it is preferable that it be integrally molded with the base portion 12 and the microstructure 13.

[0026] Here, we will describe a method for manufacturing a resin substrate 11 in which the base 12, microstructure 13, and convex structure 14 are integrally molded. In this embodiment, we will show an example in which injection molding is performed using a mold in which the inverted structure of the microstructure 13 is formed. Figure 2 is a process diagram of the manufacturing method and is a schematic cross-sectional view of the same part as in Figure 1(b).

[0027] First, an injection molding die 21 is prepared as shown in Figure 2(a). The injection molding die 21 consists of a stainless steel base 21a and a nickel alloy mirror-finished part 21b. Next, as shown in Figure 2(b), a titanium film 22 and a silicon dioxide film 23 are deposited by sputtering. Next, as shown in Figure 2(c), a photoresist layer 24 is formed by a spin coating method. Next, as shown in Figure 2(d), a photoresist pattern 25 is obtained by exposure using the EB lithography method and then development. Next, as shown in Figure 2(e), the silicon dioxide film 23 exposed in the recesses of the photoresist pattern 25 is dry-etched using a dry etching method with CHF3 gas to obtain a silicon dioxide pattern 26. Next, as shown in Figure 2(f), the resist pattern 25 is removed by the oxygen ashing method. Next, as shown in Figure 2(g), a photoresist layer 27 is formed on the obtained silicon dioxide pattern 26 by spin coating.

[0028] Next, as shown in Figure 2(h), a photoresist pattern 28 is obtained by exposing the region corresponding to the convex structure using the EB lithography method and then developing it. Next, as shown in Figure 2(i), the silicon dioxide pattern 26 exposed in the recesses of the photoresist pattern 28 is dry-etched using a dry etching method with CHF3 gas to obtain recesses 29 on the upper surface of the silicon dioxide pattern 26. Next, as shown in Figure 2(j), the resist pattern 28 is removed by oxygen ashing. Then, a single-molecule release film (not shown) is formed on the surface of the silicon dioxide pattern 26 and the recesses 29 to obtain a microstructure mold 30. Next, as shown in Figure 2(k), the resin substrate 11 is molded and the microstructure 13 and convex structure 14 are transferred to the surface by injection molding using the microstructure mold 30 and mold 31. Next, as shown in Figure 2(l), a reflective polarizing element is obtained by depositing a metal film 15 on the upper and side surfaces of the microstructure 13 and the surface of the convex structure 14 by oblique deposition.

[0029] In this embodiment, the convex structure 14 is shown as being formed at the corner formed by the side surface of the microstructure 13 and the surface of the base 12. However, it is sufficient to increase the contact area with the metal film 15, and it does not necessarily have to be at a corner. For example, as shown in Figure 4, it may be provided at a position away from the corner. However, considering stress concentration due to thermal expansion, it is preferable to place it at a corner. Figure 4(a) is a schematic plan view, and (b) is a schematic cross-sectional view of the A-A' section in (a). The dashed line in Figure 4(a) shows the side surface of the microstructure 13 and the convex structure 14 of the resin substrate 11 when the metal film 15 is removed.

[0030] [Second Embodiment] Figure 3 shows the configuration of a second embodiment of the optical element of the present invention. Figure 3(a) is a schematic plan view, and (b) is a schematic cross-sectional view of the A-A' region in (a). The dashed lines in Figure 3(a) show the side view and convex structure 14 of the microstructure 13 of the resin substrate 11 when the metal film 15 is removed.

[0031] In this embodiment, the structure is the same as the first embodiment except that a convex structure 14 is formed on the base portion 12 of the resin substrate 11 and an adhesive layer 41 is formed on the surface of the resin substrate 11. Only the differences from the first embodiment will be described, and the common points will be omitted from the explanation.

[0032] The adhesion layer 41 is preferably made of titanium, SiO, or chromium. The convex structure 14 is formed on the base 12 between adjacent microstructures 13.

[0033] In this embodiment, the proportion of the convex structure 14 is represented by the ratio of the sum of the upper surface areas of the convex structures 14 within the evaluation area to the area of ​​the evaluation area.

[0034] [Included components] This embodiment includes the following configuration. (Composition 1) An optical element comprising a resin substrate having a base and a microstructure protruding from the base, and a metal film formed on at least a portion of the side surface of the microstructure, Multiple convex structures are provided on the side surface where the metal film is formed, and the average volume of the multiple convex structures is 14800 nm. 3 More than 83000nm 3 An optical element characterized by the following: (Configuration 2) The optical element according to configuration 1, characterized in that the convex structure is formed at the corner formed by the side surface and the surface of the base. (Composition 3) The optical element according to configuration 1 or 2, characterized in that the area of ​​the interface in which the resin substrate contacts the metal film is 160% or more and 680% or less of the area of ​​the interface in the case where there is no convex structure. (Composition 4) The optical element according to any one of configurations 1 to 3, characterized in that, in a plan view taken from the normal direction of the surface of the base on which the microstructure is formed, the proportion of the convex structure, indicated by the ratio of the upper surface area of ​​the convex structure formed in the region where the metal film is formed within the evaluation area to the area of ​​the evaluation area, is 1% or more and 35% or less.

[0035] (Composition 5) An optical element comprising a resin substrate having a base and a microstructure protruding from the base, an adhesion layer covering the surface of the resin substrate, and a metal film formed on at least a portion of the side surface of the microstructure via the adhesion layer, Multiple convex structures are provided on the surface of the base, and the average volume of the multiple convex structures is 14800 nm. 3 More than 83000nm 3 An optical element characterized by the following: (Composition 6) The optical element according to configuration 5, characterized in that, in a plan view taken from the normal direction of the surface of the base on which the microstructure is formed, the proportion of the convex structure, indicated by the ratio of the upper surface area of ​​the convex structure to the area of ​​the evaluation area, is 1% or more and 35% or less. (Composition 7) The optical element according to configuration 5 or 6, characterized in that the area of ​​the interface in which the resin substrate contacts the adhesion layer is 160% or more and 680% or less of the area of ​​the interface in the case where there is no convex structure. (Composition 8) The optical element according to any one of configurations 1 to 7, characterized in that the microstructure is a line-and-space structure. (Composition 9) The optical element according to configuration 8, characterized in that the metal film is formed on one side surface and the top surface of each line of the microstructure. (Composition 10) The optical element according to configuration 9, characterized in that the metal film is an obliquely deposited film.

[0036] (Composition 11) The optical element according to any one of configurations 1 to 10, characterized in that the microstructure is made of a resin material. (Composition 12) The optical element according to any one of configurations 1 to 11, characterized in that the base is made of a resin material. (Composition 13) The optical element according to configuration 12, characterized in that the microstructure and the base are integrally molded. (Composition 14) The optical element according to any one of configurations 1 to 13, characterized in that the metal film is made of aluminum. (Composition 15) One of the surface areas of the aforementioned convex structure is 2620 nm 2 More than 9230nm 2 An optical element according to any one of configurations 1 to 14, characterized in that it is as follows. (Composition 16) The optical element according to any one of configurations 1 to 15, characterized in that the height of the convex structure is 12 nm or more and 68 nm or less. [Examples]

[0037] (Example 1) The optical element was fabricated using the manufacturing method shown in Figure 2. A polyester resin (refractive index: 1.65) was used as the resin substrate 11. The microstructure 13 was a line-and-space structure with a pitch of 150 nm, a line width of 50 nm, and a line height of 200 nm. The convex structure 14 was defined as having an average value of multiple structures, with a width of 40 nm in the line direction, a width of 30 nm in the pitch direction, and a height of 20 nm, and its proportion of existence was set to 1%. The material of the metal film 15 was aluminum, and the film thickness on the top surface of the microstructure 13 was set to 50 nm, while the film thickness on the sides was set to 20 nm.

[0038] The injection mold 21 for forming the resin substrate 11 consists of a stainless steel base 21a and a nickel alloy mirror-finish portion 21b. A titanium film 22 and a silicon dioxide film 23 were deposited on the mirror-finish portion 21b by sputtering. The thickness of the titanium film 22 was approximately 50 nm, and the thickness of the silicon dioxide film 23 was approximately 250 nm.

[0039] Next, a photoresist layer 24 was formed by spin coating. The spin coating conditions were 3000 rpm / 20 seconds, and the thickness of the photoresist layer 24 was approximately 150 nm. Next, after exposure using the EB lithography method and subsequent development, a photoresist pattern 25 with a pitch of 150 nm, a line width of 50 nm, and a height of approximately 150 nm, which is equivalent to the thickness of the photoresist layer 24, was obtained. Next, the silicon dioxide film 23 exposed in the recesses of the photoresist pattern 25 was dry-etched using a dry etching method with CHF3 gas to obtain a silicon dioxide pattern 26. In this example, the etching time was adjusted so that the height of the silicon dioxide pattern 26 was approximately 200 nm. Next, the resist pattern 25 was removed by the oxygen ashing method.

[0040] Next, a photoresist layer 27 was formed on the obtained silicon dioxide pattern 26 by spin coating. In this example, the spin coating conditions were 3000 rpm / 20 seconds, and the film thickness from the surface of the silicon dioxide pattern 26 to the surface of the photoresist layer 27 was approximately 50 nm. Next, a photoresist pattern 28 was obtained by exposing the region corresponding to the convex structure 14 using the EB lithography method and then developing the material. In this example, a pattern with a width of 40 nm in the line direction and a width of 30 nm in the pitch direction was formed. The height was approximately 50 nm, which is equivalent to the film thickness of the photoresist layer 27.

[0041] Next, the silicon dioxide pattern 26 exposed in the recesses of the photoresist pattern 28 was dry-etched using a dry etching method with CHF3 gas to obtain recesses 29 on the upper surface of the silicon dioxide pattern 26. In this example, the etching time was adjusted so that the depth of the recesses 29 was approximately 20 nm. Next, the resist pattern 27 was removed by oxygen ashing. Subsequently, a single-molecule release film (not shown) was formed on the surface of the silicon dioxide pattern 26 and the recesses 29 to obtain a microstructured mold 30.

[0042] Next, by injection molding using the microstructure mold 30, the resin substrate 11 was molded and the microstructure 13 and convex structure 14 were transferred to its surface simultaneously. When the shapes of the microstructure 13 and convex structure 14 were evaluated using an electron microscope, it was found that an almost inverted structure of the microstructure mold 30 had been obtained. Next, aluminum was deposited on the upper and side surfaces of the microstructure 13 and on the surface of the convex structure 14 by oblique vapor deposition to form a metal film 15, thereby obtaining a reflective polarizing element.

[0043] When the surfaces of the microstructured mold 30 and the resin substrate 11 were observed with an electron microscope, it was found that the silicon dioxide pattern 26 and recesses 29 formed on the microstructured mold 30 were also formed on the surface of the resin substrate 11.

[0044] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no peeling of the metal film 15 was observed. The heat cycle conditions were a minimum temperature of -30°C and a maximum temperature of 70°C, and 50 cycles were performed. Furthermore, as a result of evaluating the optical properties, the P-polarization transmittance was worsened by approximately 0.2% compared to the case without the convex structure 14 (Comparative Example 1 described later), but this was within a range that did not affect the product performance. The P-polarization transmittance was evaluated by incidenting polarized light vibrating perpendicular to the line direction of the microstructure 13 onto the reflective polarizing element and measuring the amount of light transmitted. The configuration and characteristics are shown in Table 1. In Table 1, "Optical Degradation" indicates the percentage decrease in the above-mentioned P-polarization transmittance.

[0045] (Example 2) COP resin (refractive index: 1.53) was used as the resin substrate 11, and the microstructure 13 was a line-and-space structure with a pitch of 150 nm, a line width of 50 nm, and a line height of 250 nm. The convex structure 14 had a width of 30 nm in the line direction, a width of 30 nm in the pitch direction, and a height of 68 nm, with the proportion of the convex structure 14%. The material of the metal film 15 was silver, with a film thickness of 60 nm on the top surface of the microstructure 13 and a film thickness of 20 nm on the sides. The reflective polarizing element was fabricated in the same manner as in Example 1 for other configurations and manufacturing methods.

[0046] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no peeling of the metal film 15 was observed. Furthermore, evaluation of the optical properties showed that the P-polarization transmittance was approximately 9.9% worse compared to the case without the convex structure 14. Although this was a significant decrease in transmittance compared to Example 1, it remained within a range that was acceptable for product performance. On the other hand, since the surface area increase due to the convex structure 14 was greater, it is expected that the environmental durability will be further improved. The configuration and characteristics are shown in Table 1.

[0047] (Example 3) PC resin (refractive index: 1.59) was used as the resin substrate 11, and the microstructure 13 was a line-and-space structure with a pitch of 120 nm, a line width of 40 nm, and a line height of 100 nm. The convex structure 14 had a width of 35 nm in the line direction, a width of 38 nm in the pitch direction, and a height of 12 nm, and the proportion of the convex structure 14 was set to 30%. The metal film 15 was made of aluminum, with a film thickness of 50 nm on the top surface and 40 nm on the side surface of the microstructure 13. The reflective polarizing element was fabricated in the same manner as in Example 1 for other configurations and manufacturing methods.

[0048] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no peeling of the metal film 15 was observed. Furthermore, evaluation of the optical properties showed that the P-polarization transmittance was approximately 3.8% worse compared to the case without the convex structure 14, but this was within a range that was acceptable for product performance. The configuration and characteristics are shown in Table 1.

[0049] (Example 4) As shown in Figure 3, an optical element was fabricated having an adhesion layer 41 and a convex structure 14 formed on the surface of a base 12. The resin substrate 11 was made of PMMA resin (refractive index: 1.49), and the microstructure 13 was a line-and-space structure with a pitch of 250 nm, a line width of 70 nm, and a line height of 100 nm. The convex structure 14 had a width of 30 nm in the line direction, a width of 25 nm in the pitch direction, and a height of 20 nm, and the proportion of the convex structure 14 was set to 5%.

[0050] Titanium was used as the adhesion layer 41 and was formed with a thickness of approximately 20 nm by conventional vapor deposition to cover the base 12, microstructure 13, and convex structure 14. The metal film 15 was made of aluminum, with a top film thickness of 50 nm and a side film thickness of 30 nm for the microstructure 13. The reflective polarizing element was fabricated in the same manner as in Example 1 for other configurations and manufacturing methods.

[0051] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no delamination of the adhesion layer 41 and the metal film 15 was observed. Furthermore, when the optical properties were evaluated, the P-polarization transmittance was worsened by approximately 1.0% compared to the case without the convex structure 14, but this was within a range that did not affect product performance. The configuration and characteristics are shown in Table 1.

[0052] (Example 5) The resin substrate 11 was made of PS resin (refractive index: 1.59), and the microstructure 13 was a line-and-space structure with a pitch of 150 nm, a line width of 50 nm, and a line height of 100 nm. The convex structure 14 had a width of 45 nm in the line direction, a width of 45 nm in the pitch direction, and a height of 40 nm, with the proportion of the convex structure 14 being 20%. The adhesion layer 41 was made of SiO and was formed with a thickness of approximately 10 nm to cover the base 12, microstructure 13, and convex structure 14. Furthermore, the metal film 15 was made of aluminum, with a film thickness of 70 nm on the top surface of the microstructure 13 and a film thickness of 20 nm on the sides. The reflective polarizing element was fabricated in the same manner as in Example 4 for other configurations and manufacturing methods.

[0053] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no delamination of the adhesion layer 41 and the metal film 15 was observed. Furthermore, when the optical properties were evaluated, the P-polarization transmittance was worsened by approximately 8.3% compared to the case without the convex structure 14, but this was within a range that was acceptable for product performance. The configuration and characteristics are shown in Table 1.

[0054] (Example 6) The resin substrate 11 was made of polyester resin (refractive index: 1.65), and the microstructure 13 was a line-and-space structure with a pitch of 130 nm, a line width of 50 nm, and a line height of 100 nm. The convex structure 14 had a width of 55 nm in the line direction, a width of 50 nm in the pitch direction, and a height of 30 nm, and the proportion of the convex structure 14 was set to 30%.

[0055] Cr was used as the adhesion layer 41 and formed with a thickness of approximately 10 nm to cover the base 12, microstructure 13, and convex structure 14. Furthermore, the metal film 15 was made of aluminum, with a top film thickness of 100 nm and a side film thickness of 40 nm for the microstructure 13. The reflective polarizing element was fabricated in the same manner as in Example 4 for other configurations and manufacturing methods.

[0056] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no delamination of the adhesion layer 41 and the metal film 15 was observed. Furthermore, when the optical properties were evaluated, the P-polarization transmittance was worsened by approximately 9.4% compared to the case without the convex structure 14, but this was within a range that was acceptable for product performance. The configuration and characteristics are shown in Table 1.

[0057] (Example 7) As shown in Figure 4, an optical element was fabricated in which a convex structure 14 was provided in the middle of the side surface of a microstructure 13. A polyester resin (refractive index: 1.65) was used for the resin substrate 11, and the microstructure 13 was a line-and-space structure with a pitch of 250 nm, a line width of 70 nm, and a line height of 300 nm. The convex structure 14 had a width of 30 nm in the line direction, a width of 40 nm in the pitch direction, and a height of 26 nm, with the proportion of the convex structure 14 being 5%. The metal film 15 was made of aluminum, with a film thickness of 100 nm on the top surface of the microstructure 13 and a film thickness of 40 nm on the side surface. The other configurations and manufacturing methods were the same as in Example 1 to fabricate a reflective polarizing element. However, in the same injection molding as in Example 1, the convex structure 14 would get caught in the mold during demolding. Therefore, the resin temperature was lowered by 5°C compared to normal during demolding to cause thermal shrinkage of the molded product for demolding. As a result, the amount of deformation of the molded product during demolding can be kept within the elastic deformation range, and the convex structure 14 can be formed without damage during demolding.

[0058] When a heat cycle test was performed on the reflective polarizing element in this embodiment, no peeling of the metal film 15 was observed. Furthermore, as a result of evaluating the optical properties, the P-polarization transmittance was worsened by approximately 1.4% compared to the case without the convex structure 14, but this was within a range that was acceptable for product performance. The configuration and characteristics are shown in Table 1.

[0059] (Comparative Example 1) A reflective polarizing element was fabricated in the same manner as in Example 1, except that the convex structure 14 was omitted and COP resin was used as the resin material. The configuration is shown in Figure 5. Figure 5(a) is a schematic plan view, and (b) is a schematic cross-sectional view of the A-A' region in (a). The dashed line in Figure 5(a) shows the side view of the microstructure 13 of the resin substrate 11 when the metal film 15 is removed.

[0060] In the heat cycle test of the reflective polarizing element in this comparative example, delamination of the metal film 15 occurred from the corner formed by the microstructure 13 and the base 12. The structure and characteristics are shown in Table 1.

[0061] (Comparative Example 2) Reflective polarizing elements were fabricated by modifying the microstructure 13 and convex structure 14, using COP resin as the resin material, and maintaining the same abundance ratio as in Example 3. The abundance ratio was 40%, the same as in Example 3. Specifically, the microstructure 13 was a line-and-space structure with a pitch of 150 nm, a line width of 50 nm, and a line height of 200 nm, while the convex structure 14 had a width of 25 nm in the line direction, a width of 56 nm in the pitch direction, and a height of 60 nm. The configuration and characteristics are shown in Table 1.

[0062] In this comparative example, the reflective polarizing element had a larger convex structure 14, resulting in a lower P-change transmittance of approximately 18.8% compared to comparative example 1, which did not have a convex structure 14. Therefore, it failed to meet the required product performance. The configuration and characteristics are shown in Table 1.

[0063] (Comparative Example 3) A reflective polarizing element was fabricated in the same manner as in Example 1, except that the microstructure 13 and convex structure 14 were modified and COP resin was used as the resin material. The microstructure 13 was a line-and-space structure with a pitch width of 130 nm, a line width of 40 nm, and a line height of 100 nm. The convex structure 14 had a width of 50 nm in the line direction, a width of 55 nm in the pitch direction, and a height of 30 nm, with a presence ratio of 40%. The configuration and characteristics are shown in Table 1.

[0064] In this comparative example, the reflective polarizing element had a large proportion of the convex structure 14, resulting in a P-change transmittance of approximately 12.5% ​​compared to comparative example 1, which did not have the convex structure 14, and thus failing to meet the required product performance. The configuration and characteristics are shown in Table 1.

[0065] [Table 1] [Explanation of symbols]

[0066] 11: Resin substrate, 12: Base, 13: Microstructure, 14: Convex structure, 15: Metal film, 41: Adhesion layer

Claims

1. An optical element comprising a resin substrate having a base and a microstructure protruding from the base, and a metal film formed on at least a portion of the side surface of the microstructure, Multiple convex structures are provided on the side surface where the metal film is formed, and the average volume of the multiple convex structures is 14,800 nm. 3 83000nm or more 3 An optical element characterized by the following:

2. The optical element according to claim 1, characterized in that the convex structure is formed at the corner formed by the side surface and the surface of the base.

3. The optical element according to claim 1, characterized in that the area of ​​the interface in which the resin substrate contacts the metal film is 160% or more and 680% or less of the area of ​​the interface in the case where there is no convex structure.

4. The optical element according to claim 1, characterized in that, in a plan view taken from the normal direction of the surface of the base on which the microstructure is formed, the proportion of the convex structure, indicated by the ratio of the upper surface area of ​​the convex structure formed in the region where the metal film is formed within the evaluation area to the area of ​​the evaluation area, is 1% or more and 35% or less.

5. An optical element comprising a resin substrate having a base and a microstructure protruding from the base, an adhesion layer covering the surface of the resin substrate, and a metal film formed on at least a portion of the side surface of the microstructure via the adhesion layer, The surface of the base portion is provided with a plurality of convex structures, and the average volume of the plurality of convex structures is 14,800 nm. 3 83000nm or more 3 An optical element characterized by the following:

6. The optical element according to claim 5, characterized in that, in a plan view taken from the normal direction of the surface of the base on which the microstructure is formed, the proportion of the convex structure, indicated by the ratio of the upper surface area of ​​the convex structure to the area of ​​the evaluation area, is 1% or more and 35% or less.

7. The optical element according to claim 5, characterized in that the area of ​​the interface in which the resin substrate contacts the adhesion layer is 160% or more and 680% or less of the area of ​​the interface in the case where there is no convex structure.

8. The optical element according to any one of claims 1 to 7, characterized in that the microstructure is a line-and-space structure.

9. The optical element according to claim 8, characterized in that the metal film is formed on one side and the top surface of each line of the microstructure.

10. The optical element according to claim 9, characterized in that the metal film is an obliquely vapor-deposited film.

11. The optical element according to any one of claims 1 to 7, characterized in that the microstructure is made of a resin material.

12. The optical element according to any one of claims 1 to 7, characterized in that the base is made of a resin material.

13. The optical element according to claim 12, characterized in that the microstructure and the base are integrally molded.

14. The optical element according to any one of claims 1 to 7, characterized in that the metal film is made of aluminum.

15. One of the surface areas of the aforementioned convex structure is 2620 nm 2 9230nm or more 2 The optical element according to any one of claims 1 to 7, characterized in that it is as follows:

16. The optical element according to any one of claims 1 to 7, characterized in that the height of the convex structure is 12 nm or more and 68 nm or less.

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