Optical element, optical system having the same, and optical device

Abstract

To provide an anti-reflective coating that is easy to manufacture. [Solution] An anti-reflective film 100 formed on the optical surface of a substrate 200, having first to fourth layers arranged sequentially from the substrate 200 side, wherein the refractive index of the fourth layer 4 decreases as it moves away from the substrate 200, and when the refractive indices of the first to third layers at a wavelength of 550 nm are n1, n2, and n3 respectively, and the maximum refractive index of the fourth layer 4 at a wavelength of 550 nm is n4, then n1 > n2, n2<n3、n3> The condition n4 is satisfied.

Description

Technical Field

[0001] The present invention relates to an antireflection film, and is suitable for optical devices such as digital still cameras, digital video cameras, cameras for silver halide films, telescopes, and the like.

Background Art

[0002] Patent Document 1 describes an antireflection film composed of two layers whose respective refractive indices decrease as they depart from the base material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The antireflection film described in Patent Document 1 is designed such that the refractive index of the first layer adjacent to the base material is less than or equal to the refractive index of the base material, and the refractive index of the second layer is less than or equal to the refractive index of the first layer. Therefore, it is necessary to change the type and composition ratio of the materials constituting each layer according to the material of the base material, and since the degree of freedom in material selection at that time is low, it is difficult to manufacture the antireflection film.

[0005] An object of the present invention is to provide an antireflection film that is easy to manufacture.

Means for Solving the Problems

[0006] An antireflection film according to one aspect of the present invention for achieving the above object is an antireflection film formed on an optical surface of a base material, and has first to fourth layers arranged in order from the side of the base material. The refractive index of the fourth layer decreases as it moves away from the substrate. When the refractive indices of the first to third layers at a wavelength of 550 nm are n1, n2, and n3, respectively, and the maximum refractive index of the fourth layer at a wavelength of 550 nm is n4, then n1 > n2, n2<n3、n3> It is characterized by satisfying the condition n4. [Effects of the Invention]

[0007] According to the present invention, an anti-reflective coating that is easy to manufacture can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of the anti-reflective coating according to the first embodiment and a diagram showing an example of refractive index change. [Figure 2] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 1. [Figure 3] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 2. [Figure 4] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 3. [Figure 5] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 4. [Figure 6] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 5. [Figure 7] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 6. [Figure 8] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 7. [Figure 9] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 8. [Figure 10] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 9. [Figure 11] Schematic diagram of the anti-reflective coating according to the second embodiment [Figure 12] Figure showing the refractive index change and reflectance characteristics of the anti-reflective coating according to Example 10. [Figure 13] Schematic diagram of the optical system according to this embodiment [Figure 14] Schematic diagram of an imaging device according to an embodiment

Embodiments for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that each drawing may be drawn at a scale different from the actual for convenience. Also, in each drawing, the same members are denoted by the same reference numerals, and redundant explanations are omitted.

[0010] FIG. 1(a) shows a schematic diagram of an optical element 300 having an antireflection film 100 and a substrate (transparent substrate) 200 according to the first embodiment, and FIG. 1(b) is a schematic diagram showing an example of the refractive index change (refractive index structure) of the optical element 300. In FIG. 1(a), the direction from the side of the substrate 200 toward the air side (film thickness direction) is defined as the Z direction, and the directions perpendicular to the Z direction (radial directions) are defined as the X direction and the Y direction.

[0011] The antireflection film 100 has, on the surface (optical surface) of the substrate 200, a first layer (first thin film layer) 1, a second layer (second thin film layer) 2, a third layer (third thin film layer) 3, and a fourth layer (refractive index change layer) 4 arranged in this order from the side of the substrate 200. The fourth layer 4 is a refractive index change layer (graded layer) whose refractive index decreases as it moves away from the substrate. In the present embodiment, as the refractive index change layer, an uneven layer (uneven structure) in which a plurality of convex portions (structures) are arranged in the radial direction is adopted. Each convex portion has a shape in which the volume decreases in the film thickness direction, so that the space occupancy rate of each convex portion decreases (the space occupancy rate of air increases) in the film thickness direction. As a result, as shown in FIG. 1(b), the effective refractive index (average refractive index) of the uneven layer decreases in the film thickness direction. In order to improve the antireflection performance of the antireflection film 100, it is desirable that the refractive index of the fourth layer 4 changes monotonically, and it is more preferable that the change is continuous. However, the refractive index of the fourth layer 4 may be changed intermittently as necessary.

[0012] In the fourth layer 4 according to this embodiment, the arrangement interval (pitch) p of the plurality of convex portions is shorter than the wavelength of the light used (the wavelength used). The pitch p corresponds to the interval between adjacent convex portions (the interval between valleys) as shown in FIG. 1(a). By making the pitch p shorter than the wavelength used, the concavo-convex layer can provide the same effect as a refractive index change layer in which no plurality of convex portions exist with respect to the light used. At this time, the pitch p is not limited as long as it is shorter than the wavelength used, but considering the general environment in which the antireflection film 100 is used, it is desirable to set the pitch p to 400 nm or less. Note that the arrangement interval of the plurality of convex portions may or may not have periodicity.

[0013] According to the fourth layer 4, the refractive index at the interface between the antireflection film 100 and air can be changed in the film thickness direction. At this time, most of the reflected light generated within the concavo-convex structure cancels each other out. Therefore, if the fourth layer 4 is provided directly on the substrate 200, reflection will occur only at the interface between the fourth layer 4 and the substrate 200 in the antireflection film 100. Therefore, in order to cancel this reflection, it is desirable to increase the number of interfaces by providing a plurality of layers between the fourth layer 4 and the substrate 200 and design so that the reflected light generated at each interface cancels each other out.

[0014] Therefore, the antireflection film 100 according to this embodiment is designed such that the number of interfaces is 4 or more. Specifically, interfaces are formed between the substrate 200 and the first layer 1, between the first layer 1 and the second layer 2, between the second layer 2 and the third layer 3, and between the third layer 3 and the fourth layer 4, respectively.

[0015] <0OO0101>Here, when the refractive indices of the first layer 1, the second layer 2, and the third layer 3 at a wavelength of 550 nm (reference wavelength) are n1, n2, and n3, respectively, and the maximum value of the refractive index of the fourth layer 4 at a wavelength of 550 nm is n4, it is desirable to satisfy the following conditional expressions (1) to (3). By satisfying the conditional expressions (1) to (3), it becomes easy to satisfactorily cancel the reflected light generated at each interface. n1>n2(1) n2<n3(2) n3>n4(3)

[0016] Generally, it is known that it is desirable to change the refractive index of the anti-reflective coating so that it decreases monotonically from the substrate side towards the air side. However, as mentioned above, depending on the material of the substrate, it may be difficult to select appropriate materials for each layer of the anti-reflective coating (low degree of freedom in material selection), and it may be difficult to provide an appropriate anti-reflective coating for the substrate. Therefore, as described above, by making the fourth layer 4 a refractive index changing layer and configuring it to satisfy the conditions (1) to (3), good anti-reflective performance can be obtained without monotonically changing the refractive index of the anti-reflective coating 100. In other words, the degree of freedom in material selection for the anti-reflective coating 100 can be improved.

[0017] Specifically, by satisfying condition (1), the refractive index of the first layer 1, which is the layer closest to the substrate 200, becomes relatively high, making it easier to select an appropriate material for the general optical material used as the substrate 200. Furthermore, by satisfying conditions (1) and (2), the refractive index of the second layer 2 becomes lower than that of the adjacent first layer 1 and third layer 3. This makes it easier to cancel out the reflected light generated at the interface between the substrate 200 and the first layer 1 with the reflected light generated at the interface between the second layer 2 and the first layer 1 and third layer 3. In other words, it becomes easier to obtain good anti-reflective performance without having to make the refractive index of the first layer 1 less than or equal to the refractive index of the substrate 200, as described in Patent Document 1 above.

[0018] Furthermore, in a configuration that satisfies conditions (1) to (3), it is preferable that the following conditions (4) to (6) are also satisfied. 1.52 ≤ n1 ≤ 1.85 (4) 1.25 ≤ n² < 1.45 (5) 1.40 ≤ n3 ≤ 1.60 (6)

[0019] By selecting materials for each layer that satisfy the conditions (4) to (6), the ease of manufacturing and anti-reflective performance can be improved. For the fourth layer 4, it is sufficient if it is a refractive index changing layer whose maximum refractive index is lower than that of the third layer 3. Furthermore, it is preferable that the following conditions (4a) to (6a) are satisfied. 1.55 ≤ n1 ≤ 1.75 (4a) 1.30 ≤ n² < 1.40 (5a) 1.45 ≤ n3 ≤ 1.55 (6a)

[0020] Furthermore, when the film thicknesses of the first layer 1, the second layer 2, the third layer 3, and the fourth layer 4 are d1, d2, d3, and d4, respectively, it is desirable that the following conditions (7) to (9) be satisfied. However, the film thickness here refers to the physical film thickness, without considering the refractive index (not the optical film thickness), on the reference axis (optical axis, central axis) passing through the vertex of the optical surface. 3nm ≤ d1 ≤ 90nm (7) 5nm ≤ d2 ≤ 45nm (8) 100nm ≤ d3 + d4 ≤ 350nm (9)

[0021] By appropriately setting the film thickness of each layer to satisfy conditions (7) to (9), the anti-reflective performance can be further improved. Furthermore, it is preferable to satisfy the following conditions (7a) to (9a) and (9b). 5nm ≤ d1 ≤ 50nm (7a) 10nm ≤ d2 ≤ 40nm (8a) 3nm ≤ d3 ≤ 50nm (9a) 150nm ≤ d4 ≤ 300nm (9b)

[0022] Furthermore, the refractive index of the substrate is n sub In this case, it is preferable that the following condition (10) is satisfied. By satisfying condition (10), it becomes easy to obtain good anti-reflective performance even without making the refractive index of the first layer 1 less than or equal to the refractive index of the substrate 200, as described in Patent Document 1 above. n2 <n sub <n1(10)

[0023] However, if anti-reflective performance is prioritized over the freedom of material selection, the system may be configured to satisfy the following condition (11) as needed. n2 <n1<n sub (11)

[0024] The first layer 1 and the second layer 2 according to this embodiment can be formed by a dry deposition method (dry coating) such as vacuum deposition or sputtering, or by a wet deposition method (wet coating) such as the sol-gel method. In this case, in order to suppress variations in film thickness within the plane of each layer, it is desirable to form each layer by a wet deposition method in which a coating liquid is applied to the coating surface and then dried or baked. In particular, among wet deposition methods, it is preferable to employ the spin coating method in which the coating liquid is applied while the coating surface is rotated.

[0025] The first layer 1 is preferably made of a material containing an organic compound having at least one of an aromatic ring and an imide ring. Here, an organic compound refers to a carbon-containing compound, excluding compounds with simple structures such as carbon monoxide and carbon dioxide. Materials containing organic compounds can be easily formed by a wet film deposition method. Furthermore, since organic compounds (polymers) having aromatic rings and imide rings have a planar structure, in layers having these structures in the main chain, the molecular chains tend to orient parallel to the coating surface during film deposition. Therefore, the presence of aromatic rings and imide rings can improve the uniformity of the film thickness and refractive index of the first layer 1.

[0026] Furthermore, these materials possess high mechanical properties even without curing by high-temperature treatment, making them suitable for the bottom layer (the layer adjacent to the base material 200) when laminating multiple layers on the base material 200. Moreover, polymers with such a planar structure can be easily peeled off the base material 200 by wiping it with a solvent in the radial direction parallel to the surface of the base material 200 (solvent wiping). Therefore, even if defects occur during manufacturing, the base material 200 can be easily restored by solvent wiping.

[0027] The polymer used in the first layer 1 may be any polymer having at least one of an aromatic ring and an imide ring in its main chain, and may be either a thermosetting resin or a thermoplastic resin. However, considering that the refractive index and film thickness do not change under baking conditions and that there is little residue of uncured monomers, it is desirable to use a thermoplastic resin. Examples of such thermoplastic resins include thermoplastic polyimide (polyimide resin), aromatic polyamide, melamine polymer, polymaleimide (maleimide resin), aromatic polyethers such as polyether ketone and polyether sulfone, aromatic polyesters such as polyethylene terephthalate, aromatic polycarbonate, aromatic polyurethane, and aromatic polyurea. Of these, thermoplastic polyimide is particularly preferred because the base material 200 can be easily regenerated by solvent wiping.

[0028] The second layer 2 is preferably made of a material containing an organic compound that can be easily formed by a wet film deposition method. Here, since the second layer 2 needs to have a lower refractive index than the other layers, it is desirable to make it out of a material containing fine particles in order to easily achieve a low refractive index. In this case, the second layer 2 preferably contains solid particles, and more preferably contains solid particles (solid silica particles) made of silicon dioxide (SiO2). As for the solid silica particles, it is preferable to use those bound with a binder having a structure such as a siloxane bond.

[0029] The organic solvents that can be used in the coating solutions for the first layer 1 and the second layer 2 are not particularly limited and can be selected within a range that does not impair coating properties or performance. Examples of organic solvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropanol, 1-pentanol, 2-pentanol, cyclopentanol, 2-methylbutanol, 3-methylbutanol, 1-hexanol, 2-hexanol, 3-hexanol, 4-methyl-2-pentanol, 2-methyl-1-pentanol, 2-ethylbutanol, 2,4-dimethyl-3-pentanol, 3-ethylbutanol, and 1-heptanol. Monohydric alcohols such as 2-heptanol, 1-octanol, and 2-octanol; dihydric or higher alcohols such as ethylene glycol and triethylene glycol; ether alcohols such as methoxyethanol, ethoxyethanol, propoxyethanol, isopropoxyethanol, butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and 1-propoxy-2-propanol; dimethoxyethane, diglyme, tetrahydrofuran, dioxane, di Examples include ethers such as isopropyl ether, dibutyl ether, and cyclopentyl methyl ether; esters such as ethyl formate, ethyl acetate, n-butyl acetate, methyl lactate, ethyl lactate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and propylene glycol monomethyl ether acetate; various aliphatic or alicyclic hydrocarbons such as n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane; various aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; various ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; chlorinated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, and tetrachloroethane; and aprotic polar solvents such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and ethylene carbonate.Furthermore, a mixture of two or more solvents may be used as the coating solution.

[0030] The third layer 3 in this embodiment can also be formed by a dry or wet deposition method, similar to the first and second layers. On the other hand, for the deposition method of the fourth layer 4, examples include a method for forming an uneven structure by nanoimprinting or etching, or a method for forming plate-like crystals by the gelatinization of aluminum oxide (alumina). In this case, to simplify the manufacturing process of the anti-reflective film 100, it is desirable to adopt a method using the gelatinization of aluminum oxide. With this method, the third layer 3 and the fourth layer 4 can be formed simultaneously.

[0031] Let me explain a specific example of this method. First, a porous layer containing amorphous aluminum oxide is formed by drying or calcining an aluminum oxide precursor sol. Then, by immersing the porous layer in hot water, a bumpy structure consisting of protruding crystals (plate-like crystals) mainly composed of aluminum oxide is formed. At this time, the entire porous layer after immersion in hot water does not become a bumpy structure; a part of it remains as a porous layer. Therefore, this remaining porous layer becomes the third layer 3, and the layer containing the bumpy structure becomes the fourth layer 4. Thus, it is desirable that both the third layer 3 and the fourth layer 4 contain aluminum oxide. Furthermore, it is preferable that the third layer 3 is a porous layer containing aluminum oxide, and that the fourth layer 4 is a bumpy layer mainly composed of aluminum oxide.

[0032] The thickness of the porous layer, which is the third layer 3, can be adjusted by the composition of the aluminum oxide precursor sol, the temperature of the hot water, and the immersion time in the hot water. Depending on these film formation conditions, it is possible to make the third layer 3 extremely thin. The method for forming the porous layer before the hot water treatment is not particularly limited. However, for the reasons mentioned above, it is desirable to use a wet film formation method, similar to the first and second layers, and it is particularly preferable to use a spin coating method. This allows the three layers, the first layer 1, the second layer 2, and the porous layer, to be formed sequentially by the spin coating method, thereby simplifying the manufacturing process of the anti-reflective film 100.

[0033] A functional layer having a specific function may be provided on the upper (air side) of the fourth layer 4, as needed. Examples of functional layers include an antifouling layer to prevent dirt, a hydrophilic or hydrophobic layer to reduce the effects of water droplet adhesion, an adhesive layer for bonding to other layers or substrates, and a protective layer to improve durability. For the antifouling layer, a layer containing a fluoropolymer, a fluorosilane monolayer, or a layer containing titanium dioxide particles is preferred. For the hydrophilic layer, a hydrophilic polymer layer is preferred, and a layer containing a polymer having amphoteric hydrophilic groups such as sulfobetaine groups, carbobetine groups, or phosphoroline groups is particularly preferred. For the adhesive layer, a layer with high permeability after curing is desirable, and it is preferably composed of acrylic resin or epoxy resin. For the protective layer, a layer containing phosphoric acid is preferred.

[0034] Furthermore, if the third layer 3 is a porous layer, a portion of the functional layer may penetrate into the interior (pores) of the third layer 3. For example, when a protective layer is provided as a functional layer, a portion of the material of that protective layer may also be included in the third layer 3. In this case, it is desirable to use a material for the functional layer that does not hinder the anti-reflective performance of the third layer 3 as much as possible. For example, when providing a protective layer, it is desirable to use a material containing phosphorus. In this case, the third layer 3 will also contain phosphorus, but good anti-reflective performance can be maintained.

[0035] The material of the substrate 200 can be any transparent material (light-transmitting material) and is not particularly limited. For example, the substrate 200 can be an inorganic material such as glass or an organic material such as resin (plastic). The shape of the substrate 200 can be appropriately selected according to the application of the optical element 300, and may be a flat plate, a curved plate, or a film. That is, the surface on the substrate 200 where the anti-reflective film 100 is formed (coated surface) may be a flat surface or a curved surface, and in the case of a curved surface, it may be concave, convex, or aspherical.

[0036] The following are specific examples of this embodiment. However, these are merely examples of this embodiment, and the present invention is not limited to the scope of each embodiment.

[0037] [Example 1] Figure 2(a) shows the refractive index change in the optical element 300 according to Example 1, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100.

[0038] The substrate 200 in this embodiment is made of S-BSL7 (manufactured by OHARA Corporation) with a refractive index of 1.52. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0039] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0040] <Formation of polyimide coating solution 1> 200 g of 4,4'-methylenebis(aminocyclohexane) (hereinafter referred to as DADCM: manufactured by Tokyo Chemical Industry Co., Ltd.) was gradually dissolved by adding hexane under reflux. After stopping the heating and leaving it at room temperature for several days, the precipitate was filtered off and dried under reduced pressure. 58 g of a white solid alicyclic diamine DADCM was obtained.

[0041] Three types of diamines—the alicyclic diamine DADCM, the aromatic diamine 4,4'-bis(4-aminophenoxy)biphenyl (product name BODA: manufactured by Wakayama Seika Kogyo), and the siloxane-containing diamine 1,3-bis(3-aminopropyl)tetramethyldisiloxane (product name PAM-E: manufactured by Shin-Etsu Chemical Co., Ltd.)—were dissolved in N,N-dimethylacetamide (hereinafter referred to as DMAc) to a total volume of 12 mmol.

[0042] Approximately 12 mmol of dianhydride was added to this diamine solution while cooling it with water. The dianhydride used was 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride (product name TDA-100: manufactured by Shin Nippon Rika). The amount of DMAc was adjusted so that the total mass of the diamine and dianhydride was 20% by weight.

[0043] The solution was stirred at room temperature for 15 hours to carry out the polymerization reaction. Further dilution with DMAc to an 8% by weight concentration was performed, followed by the addition of 7.4 ml of pyridine and 3.8 ml of acetic anhydride. The mixture was stirred at room temperature for 1 hour. The mixture was then stirred in an oil bath at 60-70°C for 4 hours. The polymerization solution was reprecipitated in methanol to extract the polymer, which was then washed several times in methanol. After drying at 60°C for 24 hours, a white to pale yellow powdered polyimide was obtained. The obtained polyimide was dissolved in cyclohexanone to a solid content concentration of 2.5% by mass to obtain polyimide coating solution 1.

[0044] <Formation of solid silica coating solution 1> Solid silica coating solution 1 was obtained by adding 300 g of 1-methoxy-2-propanol and 4 g of silica sol 1 to 25 g of silica particle dispersion PL-1 (manufactured by Fuso Chemical).

[0045] <Production of aluminum oxide precursor coating solution> 14.8 g of aluminum-sec-butoxide (ASBD, manufactured by Kawaken Fine Chemicals), 3.42 g of 3-methyl-2,4-pentanedione, and 2-ethylbutanol were mixed and stirred until homogeneous. 1.94 g of 0.01 M dilute hydrochloric acid was dissolved in a mixed solvent of 2-ethylbutanol / 1-ethoxy-2-propanol, and then slowly added to the aluminum-sec-butoxide solution, and stirred for a while. The final solvent obtained was a mixed solvent of 36.9 g of 2-ethylbutanol and 15.8 g of 1-ethoxy-2-propanol. The mixture was further stirred in an oil bath at 120°C for 2 to 3 hours or more to obtain an aluminum oxide precursor coating solution.

[0046] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 1, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0047] First, 0.2 ml of polyimide coating solution 1 was dropped onto the surface of substrate 200 and spin-coated at 4000 rpm for 20 seconds to form the first layer 1. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of substrate 200 and spin-coated at 4000 rpm for 25 seconds to form the second layer 2. Furthermore, 0.2 ml of aluminum oxide precursor coating solution was dropped onto the surface of substrate 200 and spin-coated at 4000 rpm for 20 seconds. Next, the substrate was heated at 140°C for 60 minutes to cure, then immersed in 80°C hot water for 20 minutes, and then dried at 60°C for 15 minutes.

[0048] The surface and cross-section of the substrate 200 were observed using FE-SEM, and it was confirmed that a fourth layer 4, which is an uneven layer in which fine plate-like crystals mainly composed of aluminum oxide are randomly formed, and a third layer 3, which is a residual layer mainly composed of aluminum oxide, were present.

[0049] Table 1, described below, shows the detailed configuration of the substrate 200 and anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-described conditions (1) to (10). As shown in Figure 2(a), the refractive index of the fourth layer 4 is 1.47 at the bottom (interface with the third layer 3) and changes continuously in the film thickness direction down to 1.00 (air) at the top.

[0050] Figure 2(b) shows the reflectance characteristics of the anti-reflective coating 100 of this embodiment 1. In Figure 2(b), the reflectance of the anti-reflective coating 100 for light of various wavelengths incident at incident angles from 0 to 60 degrees with respect to the intersection of the optical surface of the substrate 200 and the reference axis (optical axis, central axis) is shown. As shown in Figure 2(b), the reflectance of the anti-reflective coating 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less for wavelengths from 400 nm to 700 nm, indicating that good anti-reflective performance is obtained.

[0051] Furthermore, the reflectance of the anti-reflective film 100 is preferably 0.5% or less, and more preferably 0.2% or less, for light incident at an incident angle of 0 degrees in the wavelength range of 450 nm to 650 nm. In addition, the reflectance of the anti-reflective film 100 is preferably 1.0% or less, and more preferably 0.8% or less, for light incident at an incident angle of 30 degrees in the wavelength range of 450 nm to 650 nm.

[0052] [Example 2] Figure 3(a) shows the refractive index change in the optical element 300 according to Example 2, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0053] The substrate 200 in this embodiment is made of S-BSM14 (manufactured by OHARA Corporation) with a refractive index of 1.60. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0054] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0055] <Formation of polyimide coating solution 2> Two types of diamines, the aromatic diamine 4,4'-bis(4-aminophenoxy)biphenyl (product name BODA: manufactured by Wakayama Seika Kogyo) and the siloxane-containing diamine 1,3-bis(3-aminopropyl)tetramethyldisiloxane (product name PAM-E: manufactured by Shin-Etsu Chemical Co., Ltd.), were dissolved in N,N-dimethylacetamide (hereinafter referred to as DMAc) to a total volume of 12 mmol.

[0056] Approximately 12 mmol of dianhydride was added to this diamine solution while cooling it with water. 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride (product name TDA-100: manufactured by Shin Nippon Rika) was used as the dianhydride. The amount of DMAc was adjusted so that the total mass of the diamine and dianhydride was 20% by weight.

[0057] The solution was stirred at room temperature for 15 hours to carry out the polymerization reaction. Further dilution with DMAc to an 8% by weight concentration was performed, followed by the addition of 7.4 ml of pyridine and 3.8 ml of acetic anhydride. The mixture was stirred at room temperature for 1 hour. The mixture was then stirred in an oil bath at 60-70°C for 4 hours. The polymerization solution was reprecipitation in methanol to extract the polymer, which was then washed several times in methanol. After drying at 60°C for 24 hours, a white to pale yellow powdered polyimide was obtained. The obtained polyimide was dissolved in cyclohexanone to a solid content concentration of 1.8% by mass to obtain polyimide coating solution 2.

[0058] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 2 obtained in the above process, the solid silica coating solution 1, and the aluminum oxide precursor coating solution.

[0059] First, 0.2 ml of polyimide coating solution 2 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 30 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 30 seconds. The method for forming the third layer 3 and the fourth layer 4 is the same as in Example 1 and will therefore be omitted.

[0060] Table 1, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 3(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 2(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 750 nm, indicating that good anti-reflective performance is obtained.

[0061] [Example 3] Figure 4(a) shows the refractive index change in the optical element 300 according to Example 3, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0062] The substrate 200 in this embodiment is made of S-TIL26 (manufactured by OHARA Corporation) with a refractive index of 1.57. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin and branched melamine resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0063] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0064] <Formation of a blend polymer coating solution 1 of branched melamine polymer and polyimide> A branched melamine polymer light-curing coating (product name Hypertech UR101: manufactured by Nissan Chemical Corporation) was diluted to a concentration of 2.5% by mass with a cyclopentanone / cyclohexanone mixed solvent to obtain a branched melamine polymer solution. 30.0 g of the branched melamine polymer solution and 25.0 g of the polyimide coating solution 1 obtained in Example 1 were stirred and mixed at room temperature to obtain a blended polymer coating solution 1 of branched melamine polymer and polyimide.

[0065] <Film formation of each layer> An anti-reflective film 100 was formed using the blended polymer coating solution 1, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in the above-described process.

[0066] First, 0.2 ml of blended polymer coating solution 1 was dropped onto the surface of substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 25 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 20 seconds. The method for forming the third layer 3 and the fourth layer 4 is the same as in Example 1 and will therefore be omitted.

[0067] Table 1, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 4(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 4(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 750 nm, indicating that good anti-reflective performance is obtained.

[0068] [Example 4] Figure 5(a) shows the refractive index change in the optical element 300 according to Example 4, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0069] The substrate 200 in this embodiment is made of S-BSL7 (manufactured by OHARA Corporation) with a refractive index of 1.52. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin and branched melamine resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0070] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0071] <Formation of solid silica coating solution 2> 25 g of silica particle dispersion PL-1 (manufactured by Fuso Chemical Co., Ltd.) was mixed with 300 g of 1-methoxy-2-propanol and 5 g of silica sol 1 to obtain solid silica coating solution 2.

[0072] <Formation of Blend Polymer Coating Solution 2 of Branched Melamine Polymer and Polyimide> A branched melamine polymer photocuring coating (product name Hypertech UR101: manufactured by Nissan Chemical Corporation) was diluted to a concentration of 1.0% by mass with a cyclopentanone / cyclohexanone mixed solvent to obtain a branched melamine polymer solution. 30.0 g of the branched melamine polymer solution and 15.0 g of the polyimide coating solution 2 obtained in Example 2 were stirred and mixed at room temperature to obtain a blended polymer coating solution 2 of branched melamine polymer and polyimide.

[0073] <Film formation of each layer> An anti-reflective film 100 was formed using the blended polymer coating solution 2, solid silica coating solution 2, and aluminum oxide precursor coating solution obtained in the above-described process.

[0074] First, 0.2 ml of the blended polymer coating solution 2 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 20 seconds. Next, 0.2 ml of the solid silica coating solution 2 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 25 seconds. The method for forming the third layer 3 and the fourth layer 4 is the same as in Example 1 and will therefore be omitted.

[0075] Table 1, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 5(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 5(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 700 nm, indicating that good anti-reflective performance is obtained.

[0076] [Example 5] Figure 6(a) shows the refractive index change in the optical element 300 according to Example 5, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0077] The substrate 200 in this embodiment is made of quartz with a refractive index of 1.46. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0078] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0079] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 1, solid silica coating solution 2, and aluminum oxide precursor coating solution obtained in the above-described process.

[0080] First, 0.2 ml of polyimide coating solution 1 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 20 seconds. Next, 0.2 ml of solid silica coating solution 2 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 20 seconds. The methods for forming the third layer 3 and the fourth layer 4 are the same as in Example 1 and will therefore be omitted.

[0081] Table 1, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 6(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 6(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less at wavelengths from 410 nm to 680 nm, indicating that good anti-reflective performance is obtained.

[0082] [Table 1]

[0083] [Example 6] Figure 7(a) shows the refractive index change in the optical element 300 according to Example 6, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0084] The substrate 200 in this embodiment is made of S-BAH32 (manufactured by OHARA Corporation) with a refractive index of 1.67. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0085] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0086] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 1, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0087] First, 0.2 ml of polyimide coating solution 1 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 30 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 15 seconds. The methods for forming the third layer 3 and the fourth layer 4 are the same as in Example 1 and are therefore omitted.

[0088] Table 2, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (9) and (11). Figure 7(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 7(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 800 nm, indicating that good anti-reflective performance is obtained.

[0089] [Example 7] Figure 8(a) shows the refractive index change in the optical element 300 according to Example 7, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0090] The substrate 200 in this embodiment is made of S-BAH28 (manufactured by OHARA Corporation) with a refractive index of 1.72. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0091] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0092] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 2, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0093] First, 0.2 ml of polyimide coating solution 2 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 30 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 10 seconds. The methods for forming the third layer 3 and the fourth layer 4 are the same as in Example 1 and will therefore be omitted.

[0094] Table 2, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (9) and (11). Figure 8(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 8(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 800 nm, indicating that good anti-reflective performance is obtained.

[0095] [Example 8] Figure 9(a) shows the refractive index change in the optical element 300 according to Example 8, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0096] The substrate 200 in this embodiment is made of S-TIH53 (manufactured by OHARA Corporation) with a refractive index of 1.85. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin and branched melamine resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0097] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0098] <Film formation of each layer> An anti-reflective film 100 was formed using the blended polymer coating solution 1, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0099] First, 0.2 ml of blended polymer coating solution 1 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 30 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 10 seconds. The methods for forming the third layer 3 and the fourth layer 4 are the same as in Example 1 and will therefore be omitted.

[0100] Table 2, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (9) and (11). Figure 9(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 9(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 800 nm, indicating that good anti-reflective performance is obtained.

[0101] [Example 9] Figure 10(a) shows the refractive index change in the optical element 300 according to Example 9, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 100. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0102] The substrate 200 in this embodiment is made of K22R (manufactured by ZEONEX) with a refractive index of 1.53. In the anti-reflective film 100 in this embodiment, the first layer 1 is made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0103] The method for forming the anti-reflective coating 100 in this embodiment is as follows.

[0104] <Film formation of each layer> An anti-reflective film 100 was formed using the polyimide coating solution 2, solid silica coating solution 2, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0105] First, 0.2 ml of polyimide coating solution 2 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 20 seconds. Next, 0.2 ml of solid silica coating solution 2 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 22 seconds. The methods for forming the third layer 3 and the fourth layer 4 are the same as in Example 1 and will therefore be omitted.

[0106] Table 2, described below, shows the detailed configuration of the substrate 200 and the anti-reflective film 100 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 10(b) shows the reflectance characteristics of the anti-reflective film 100 of this embodiment 1. As shown in Figure 10(b), the reflectance of the anti-reflective film 100 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range of 400 nm to 700 nm, indicating that good anti-reflective performance is obtained.

[0107] [Table 2]

[0108] Although the first embodiment described an anti-reflective film composed of four layers, the present invention is not limited thereto, and an anti-reflective film composed of five or more layers may be used. By increasing the number of layers that make up the anti-reflective film, the design flexibility of the anti-reflective film can be further improved. As a result, depending on the material of the substrate, it may be possible to improve the anti-reflective performance compared to an anti-reflective film composed of four layers.

[0109] Figure 11 is a schematic diagram of an optical element 301 having an anti-reflective film 101 and a substrate (transparent substrate) 200 according to the second embodiment. The anti-reflective film 101 has a first layer (first thin film layer) 1, a second layer (second thin film layer) 2, an intermediate layer (third thin film layer) M, a third layer (fourth thin film layer) 3, and a fourth layer (refractive index changing layer) 4, arranged in order from the substrate 200 side toward the air side. Specific examples of this embodiment are shown below. However, this is merely one example of this embodiment, and the present invention is not limited to the scope of these examples.

[0110] [Example 10] Figure 12(a) shows the refractive index change in the optical element 301 according to Example 10, i.e., the refractive index structure of the substrate 200 and the anti-reflective film 101. In this example, the same configuration and manufacturing method as in the other examples described above will not be explained.

[0111] The substrate 200 in this embodiment is made of S-BSL7 (manufactured by OHARA Corporation) with a refractive index of 1.52. In the anti-reflective film 101 in this embodiment, the first layer 1 and the intermediate layer M are made of a material mainly composed of polyimide resin, the second layer 2 is made of a material mainly composed of solid silica, and the third layer 3 and the fourth layer 4 are made of a material mainly composed of aluminum oxide.

[0112] The method for forming the anti-reflective film 101 in this embodiment is as follows.

[0113] <Film formation of each layer> An anti-reflective film 101 was formed using the polyimide coating solution 1, solid silica coating solution 1, and aluminum oxide precursor coating solution obtained in each of the above-described steps.

[0114] First, 0.2 ml of polyimide coating solution 1 was dropped onto the surface of the substrate 200 and the first layer 1 was formed by spin coating at 4000 rpm for 13 seconds. Next, 0.2 ml of solid silica coating solution 1 was continuously dropped onto the surface of the substrate 200 and the second layer 2 was formed by spin coating at 4000 rpm for 18 seconds. Next, 0.2 ml of polyimide coating solution 1 was continuously dropped onto the surface of the substrate 200 and the intermediate layer M was formed by spin coating at 4000 rpm for 24 seconds. The method for forming the third layer 3 and the fourth layer 4 is the same as in Example 1 and will therefore be omitted.

[0115] In this way, by constructing the first layer 1 and the intermediate layer M from the same material, the film formation methods for each can be standardized, making it easier to manufacture the anti-reflective film 101. At this time, the film thickness d of the intermediate layer M m It is desirable to make the thickness of the first layer 1 thinner than the film thickness d1.

[0116] Table 3, described later, shows the detailed configuration of the substrate 200 and anti-reflective film 101 according to this embodiment. The refractive index and film thickness of each material satisfy the above-mentioned conditions (1) to (10). Figure 12(b) shows the reflectance characteristics of the anti-reflective film 101 of this embodiment 1. As shown in Figure 12(b), the reflectance of the anti-reflective film 101 of this embodiment 1 at an incident angle of 0 degrees is 0.2% or less in the wavelength range from 420 nm to 700 nm, indicating that good anti-reflective performance is obtained.

[0117] [Table 3]

[0118] [Optical systems and optical devices] Next, an optical system 400 and an optical device 500 as embodiments will be described.

[0119] Figure 13 shows a schematic cross-sectional view of the optical system 400 according to this embodiment, including the optical axis (dash-dotted line). The optical system 400 has a plurality of optical elements (lenses) G401 to G416 and an aperture diaphragm 402, and is an imaging optical system that forms an image of an object on the image plane 403. The anti-reflective coating 100 according to the above embodiment is provided on at least one of the incident surface and the exit surface of at least one of the optical elements G401 to G416. In order to obtain good anti-reflective performance in the entire optical system 400, it is desirable that the anti-reflective coating 100 be provided on all optical elements, and it is even more preferable that the anti-reflective coating 100 be provided on both the incident surface and the exit surface of each optical element. It is also desirable to provide the anti-reflective coating 100 on prisms, filters, etc. when using optical elements.

[0120] Figure 14 shows a schematic diagram of an imaging device (digital camera) 500 as an optical device according to this embodiment. The imaging device 500 has a lens unit 501 equipped with an optical system 400 and a main unit 502 equipped with an image sensor 503. Each optical element constituting the optical system 400 is held by a holding member (lens barrel) in the lens unit 501. The image sensor 503 is an element that captures an image of an object by receiving light from the optical system 400, and can employ a photoelectric conversion element such as a CCD sensor or a CMOS sensor. The image sensor 503 is positioned so that its imaging surface (light-receiving surface) coincides with the image plane 403 of the optical system 400.

[0121] The lens unit 501 may be integrated with the main body unit 502, or it may be configured to be detachable (replaceable) from the main body unit 502. When the lens unit 501 and the main body unit 502 are detachable from each other, the lens unit 501 can be considered as a single optical device (lens device), and the main body unit 502 can be considered as a single optical device (imaging device). The optical elements according to each embodiment are not limited to use in the imaging device described above, but can be applied to various optical devices such as binoculars, projectors (projection devices), and telescopes.

[0122] [Differentiation] Although preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of its gist.

[0123] In the embodiments described above, a textured layer is used as the uppermost refractive index changing layer, but other refractive index changing layers may also be used. For example, in a layer containing fine particles such as solid particles or hollow particles, a refractive index changing layer may be formed by impregnating another material between each fine particle and changing the space occupancy of the material in the film thickness direction. Even when such a configuration is adopted, it is possible to form the refractive index changing layer by a wet film deposition method such as the spin coating method described above.

[0124] The embodiments of the present invention include the following configurations.

[0125] (Composition 1) An anti-reflective coating formed on the optical surface of a substrate, The substrate has first to fourth layers arranged in order from the side thereof, The refractive index of the fourth layer decreases as it moves away from the substrate. When the refractive indices of the first to third layers at a wavelength of 550 nm are n1, n2, and n3, respectively, and the maximum refractive index of the fourth layer at a wavelength of 550 nm is n4, n1 > n2 n2 <n3 n3>n4 An anti-reflective coating characterized by satisfying the following condition.

[0126] (Configuration 2) The first layer comprises an organic compound having at least one of an aromatic ring and an imide ring, The second layer contains an organic compound, The anti-reflective film according to configuration 1, characterized in that each of the third and fourth layers contains aluminum oxide.

[0127] (Composition 3) An anti-reflective coating formed on the optical surface of a substrate, The substrate has first to fourth layers arranged in order from the side thereof, The refractive index of the fourth layer decreases as it moves away from the substrate. The first layer comprises an organic compound having at least one of an aromatic ring and an imide ring, The second layer contains an organic compound, The anti-reflective coating is characterized in that each of the third and fourth layers contains aluminum oxide.

[0128] (Composition 4) 1.52 ≤ n1 ≤ 1.85 1.25 ≤ n² < 1.45 1.40 ≤ n3 ≤ 1.60 An anti-reflective film according to any one of configurations 1 to 3, characterized by satisfying the following conditional expression.

[0129] (Composition 5) When the film thicknesses of the first to fourth layers are d1, d2, d3, and d4, respectively, 3nm ≤ d1 ≤ 90nm 5nm ≤ d2 ≤ 45nm 100nm ≤ d3 + d4 ≤ 350nm An anti-reflective film according to any one of configurations 1 to 4, characterized by satisfying the following conditional expression.

[0130] (Composition 6) 3nm ≤ d3 ≤ 50nm 150nm ≤ d4 ≤ 300nm The anti-reflective film according to configuration 5, characterized in that it satisfies the following conditional expression.

[0131] (Composition 7) The refractive index of the substrate is n sub In that case, n2 <n sub <n1 An anti-reflective film according to any one of configurations 1 to 6, characterized by satisfying the following conditional expression.

[0132] (Composition 8) The anti-reflective film according to any one of configurations 1 to 7, characterized in that the first layer comprises a polyimide resin or a maleimide resin.

[0133] (Composition 9) The anti-reflective film according to any one of configurations 1 to 8, characterized in that the first layer contains thermoplastic polyimide.

[0134] (Composition 10) The anti-reflective film according to any one of configurations 1 to 9, characterized in that the second layer contains particles made of silicon dioxide.

[0135] (Composition 11) The anti-reflective film according to any one of configurations 1 to 10, characterized in that the third layer is a porous layer containing aluminum oxide.

[0136] (Composition 12) The anti-reflective film according to any one of configurations 1 to 11, characterized in that the third layer contains phosphorus.

[0137] (Composition 13) The anti-reflective film according to any one of configurations 1 to 12, characterized in that the fourth layer includes a plurality of protrusions arranged at a pitch shorter than the wavelength used.

[0138] (Composition 14) An anti-reflective film according to any one of configurations 1 to 13, characterized in that, in the wavelength range of 450 nm to 650 nm, the reflectance for light incident at an incident angle of 0 degrees at the intersection of the optical surface and the reference axis of the optical surface is 0.5% or less.

[0139] (Composition 15) An anti-reflective film according to any one of configurations 1 to 14, characterized in that, in the wavelength range of 450 nm to 650 nm, the reflectance for light incident at an incident angle of 30 degrees at the intersection of the optical surface and the reference axis of the optical surface is 1.0% or less.

[0140] (Composition 16) An optical element characterized by having an anti-reflective film according to any one of configurations 1 to 15 and the substrate.

[0141] (Composition 17) An optical system characterized by having a plurality of optical elements, including the optical element described in configuration 16.

[0142] (Composition 18) An optical device characterized by having an optical element described in configuration 16 and a holding member for holding the optical element.

[0143] (Composition 19) An imaging device characterized by having an optical element as described in configuration 16 and an image sensor that receives light from the optical element. [Explanation of Symbols]

[0144] 1. The first layer 2. Second layer 3. The third layer 4. The fourth layer 100 Anti-reflection coating 200 Base material

Claims

1. An anti-reflective coating formed on the optical surface of a substrate, The substrate has first to fourth layers arranged in order from the side thereof, The refractive index of the fourth layer decreases as it moves away from the substrate. The refractive indices of the first to third layers at a wavelength of 550 nm are each n １ , n ２ , n ３ The maximum refractive index of the fourth layer at a wavelength of 550 nm is set to n ４ In that case, n １ >n ２ n ２ <n ３ n ３ >n ４ An anti-reflective coating characterized by satisfying the following condition.

2. The first layer comprises an organic compound having at least one of an aromatic ring and an imide ring. The second layer contains an organic compound, The anti-reflective film according to claim 1, characterized in that each of the third and fourth layers contains aluminum oxide.

3. An anti-reflective coating formed on the optical surface of a substrate, The substrate has first to fourth layers arranged in order from the side thereof, The refractive index of the fourth layer decreases as it moves away from the substrate. The first layer comprises an organic compound having at least one of an aromatic ring and an imide ring. The second layer contains an organic compound, The anti-reflective coating is characterized in that each of the third and fourth layers contains aluminum oxide.

4. 1.52≦n １ ≦1.85 1.25≦n ２ <1.45 1.40≦n ３ ≦1.60 The anti-reflective film according to any one of claims 1 to 3, characterized in that it satisfies the following conditional expression.

5. The film thickness of the first to fourth layers is d １ d ２ d ３ d ４ In that case, 3nm≦d １ ≦90nm 5nm≦d ２ ≦45nm 100nm≦d ３ +d ４ ≦350nm The anti-reflective film according to claim 4, characterized in that it satisfies the following condition.

6. 3nm≦d ３ ≦50nm 150nm≦d ４ ≦300nm The anti-reflective film according to claim 5, characterized in that it satisfies the following condition.

7. The refractive index of the substrate is n ｓｕｂ In that case, n ２ <n ｓｕｂ <n １ The anti-reflective film according to any one of claims 1 to 3, characterized in that it satisfies the following conditional expression.

8. The anti-reflective film according to any one of claims 1 to 3, characterized in that the first layer comprises a polyimide resin or a maleimide resin.

9. The anti-reflective film according to any one of claims 1 to 3, characterized in that the first layer comprises thermoplastic polyimide.

10. The anti-reflective film according to any one of claims 1 to 3, characterized in that the second layer contains particles made of silicon dioxide.

11. The anti-reflective film according to any one of claims 1 to 3, characterized in that the third layer is a porous layer containing aluminum oxide.

12. The anti-reflective film according to claim 11, characterized in that the third layer contains phosphorus.

13. The anti-reflective film according to any one of claims 1 to 3, characterized in that the fourth layer includes a plurality of protrusions arranged at a pitch shorter than the wavelength of use.

14. The anti-reflective film according to any one of claims 1 to 3, characterized in that, in the wavelength range of 450 nm to 650 nm, the reflectance for light incident at an incident angle of 0 degrees at the intersection of the optical surface and the reference axis of the optical surface is 0.5% or less.

15. The anti-reflective film according to any one of claims 1 to 3, characterized in that, in the wavelength range of 450 nm to 650 nm, the reflectance for light incident at an incident angle of 30 degrees at the intersection of the optical surface and the reference axis of the optical surface is 1.0% or less.

16. An optical element characterized by having an anti-reflective film according to any one of claims 1 to 3 and the substrate.

17. An optical system characterized by having a plurality of optical elements, including the optical element described in claim 16.

18. An optical device comprising an optical element as described in claim 16 and a holding member for holding the optical element.

19. An imaging device characterized by having an optical element as described in claim 16 and an image sensor that receives light from the optical element.

Images