Optical element and optical device including same

Abstract

To provide an optical element that can achieve excellent reflection prevention property and excellent durability to environments, and an optical device including the optical element.SOLUTION: An optical element 300 includes a substrate 200 made of a resin material and a reflection prevention film 100, and the reflection prevention film 100 includes: a dielectric layer 11 on the substrate 200; and a porous layer 10 on the dielectric layer 11. The dielectric layer 11 includes: a first layer containing silicon oxide; and a second layer containing tantalum oxide. The porous layer 10 contains silicon oxide or magnesium fluoride.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical element, which is suitable for optical devices such as digital still cameras, digital video cameras, cameras for silver halide film, and telescopes. [Background technology]

[0002] Patent Document 1 discloses an optical element in which an antireflection film is provided on a substrate made of a resin material, the antireflection film being formed by sequentially laminating a multilayer including a silicon oxide layer and a tantalum oxide layer, a homogeneous layer made of magnesium fluoride, and a homogeneous layer made of silicon oxide. Patent Document 1 employs a material that can be formed without heating as the multilayer provided on the substrate, thereby suppressing deformation of the substrate due to heat. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication 2017-134404 Summary of the Invention [Problem to be solved by the invention]

[0004] However, strong tensile stress is generated in the homogeneous layer made of magnesium fluoride according to Patent Document 1, which may cause film cracks or peeling depending on environmental changes such as temperature. Also, in the anti-reflection film according to Patent Document 1, a homogeneous layer made of silicon oxide is provided on the homogeneous layer made of magnesium fluoride, making it difficult to improve the anti-reflection performance.

[0005] An object of the present invention is to provide an optical element capable of achieving good anti-reflection performance and environmental durability, and an optical device including the same. [Means for solving the problem]

[0006] To achieve the above object, one aspect of the present invention provides an optical element having a substrate made of a resin material and an antireflection film, the antireflection film including a dielectric layer formed on the substrate and a porous layer formed on the dielectric layer, the dielectric layer including a first layer containing silicon oxide and a second layer containing tantalum oxide, and the porous layer including silicon oxide or magnesium fluoride. the first layer is adjacent to the second layer, the second layer is adjacent to the porous layer, and the first layer comprises 90% or more by weight of silicon oxide and 10% or less by weight of aluminum. It is characterized by: Effect of the Invention

[0007] According to the present invention, it is possible to provide an optical element capable of achieving good anti-reflection performance and environmental durability, and an optical device including the same. [Brief description of the drawings]

[0008] [Figure 1] Schematic diagram of an optical element according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing the reflectance characteristics of an optical element according to Example 1 of the present invention. [Diagram 3] FIG. 11 is a diagram showing the reflectance characteristics of an optical element according to Example 2 of the present invention. [Figure 4] FIG. 11 is a diagram showing the reflectance characteristics of an optical element according to Example 3 of the present invention. [Diagram 5] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 4 of the present invention. [Figure 6] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 5 of the present invention. [Figure 7] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 6 of the present invention. [Figure 8] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 7 of the present invention. [Figure 9] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 8 of the present invention. [Figure 10] FIG. 13 is a diagram showing the reflectance characteristics of an optical element according to Example 9 of the present invention. [Figure 11] FIG. 16 is a diagram showing the reflectance characteristics of an optical element according to a tenth embodiment of the present invention. [Figure 12] FIG. 16 is a diagram showing the reflectance characteristics of an optical element according to Example 11 of the present invention. [Figure 13] FIG. 16 is a diagram showing the reflectance characteristics of an optical element according to Example 12 of the present invention. [Figure 14] FIG. 1 is a diagram showing the reflectance characteristics of an optical element according to Comparative Example 1. [Figure 15] FIG. 1 is a diagram showing the reflectance characteristics of an optical element according to Comparative Example 1. [Figure 16] Schematic diagram of an optical system according to an embodiment of the present invention. [Figure 17] Schematic diagram of an optical device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] 1 is a schematic diagram (cross-sectional view) of an optical element 300 according to an embodiment of the present invention. The optical element 300 has a substrate (resin substrate) 200 made of a resin material, and an anti-reflection film 100 formed on the substrate 200. Note that the resin material according to this embodiment refers to a material whose main component is a resin (organic substance), i.e., a material in which the proportion of resin is the largest, and includes a mixture of multiple resins and a resin in which inorganic material particles are dispersed (organic composite).

[0011] The anti-reflection coating 100 is composed of a dielectric layer 11 consisting of a plurality of dielectric thin films formed on a substrate 200, and a porous layer 10 formed on the dielectric layer 11. The dielectric layer 11 is composed of layers 1, 2, 3, 4, 5, and 6 arranged in this order from the substrate 200 side, one of which is a layer containing silicon oxide (first layer) and the other is a layer containing tantalum oxide (second layer).

[0012] In this embodiment, the dielectric layer 11 is configured with six layers, but the number of layers of the dielectric layer 11 is not limited to this, and any number of layers may be used as long as the dielectric layer 11 has at least a layer containing silicon oxide and a layer containing tantalum oxide. As shown in FIG. 1(b), other layers such as a water-repellent layer, an oil-repellent layer, and a protective layer (protective film) for protecting the porous layer 10 may be provided on the anti-reflection film 100. In this case, multiple layers may be provided on the anti-reflection film 100. Examples of layers provided on the anti-reflection film 100 include paint containing fluorine and paint containing silicon oxide.

[0013] Generally, resin materials are prone to deformation and discoloration at high temperatures. Therefore, when performing heating deposition or baking to form the anti-reflection film 100 on the substrate 200, it is desirable to set the temperature at 200°C or less, preferably 120°C or less, and more preferably 80°C or less. In addition, resin materials have a larger linear expansion coefficient than inorganic materials such as glass, and tend to expand with increasing temperature. Therefore, when a film that generates tensile stress in the opposite direction to the expansion direction of the resin material is formed on the substrate 200, there is a risk of film cracking or film peeling. Therefore, it is desirable to use a material for the anti-reflection film 100 that can be deposited without heating or with low heating at 80°C or less, and that has sufficient film strength and compressive stress.

[0014] Therefore, in this embodiment, silicon oxide and tantalum oxide are adopted as materials that satisfy this condition. Specifically, the dielectric layer 11 has a layer (first layer) containing silicon oxide and a layer (second layer) containing tantalum oxide. With this configuration, good anti-reflection performance can be obtained by combining silicon oxide with a low refractive index and tantalum oxide with a high refractive index, and film cracking and peeling due to expansion of the substrate 200 can be suppressed by generating compressive stress in the first layer and the second layer.

[0015] In order to cope with the large expansion of the substrate 200, it is desirable to use a material that generates a strong compressive stress. As a result of intensive research, the inventors of the present application have found that the compressive stress of silicon oxide can be increased by adding a certain amount of aluminum (Al) to silicon oxide. Therefore, it is desirable to use a material containing silicon oxide with a weight ratio of 90% or more and aluminum with a weight ratio of 10% or less for the first layer. The inventors of the present application have found that the effect of improving environmental durability can be obtained even if the aluminum content (addition amount) is small. In this case, the weight ratio of aluminum to be added to the first layer is preferably 0.001% or more.

[0016] Furthermore, examples of high refractive index materials that can provide sufficient film strength even when vapor-deposited without heating or with low-temperature heating at 80° C. or less include titanium oxide, lanthanum oxide, and zirconium oxide in addition to tantalum oxide. Therefore, the second layer may be made of a material that contains at least one of titanium oxide, lanthanum oxide, and zirconium oxide in addition to tantalum oxide.

[0017] In order to further improve environmental durability, it is preferable that the layer 1 of the dielectric layer 11 arranged at a position closest to the substrate 200 is the first layer or the second layer. Furthermore, it is preferable that the dielectric layer 11 is composed of first and second layers alternately stacked. That is, it is preferable that the dielectric layer 11 is composed of one or more first layers and two or more second layers, or two or more first layers and one or more second layers. In this case, it is more preferable that the dielectric layer 11 is composed of a plurality of first layers and a plurality of second layers. According to these configurations, deformation or discoloration of the substrate 200, or film cracking or peeling of the dielectric layer 11 can be more effectively suppressed.

[0018] The method of forming the dielectric layer 11 is not particularly limited, and physical vapor deposition methods such as vapor deposition, sputtering, and ion plating can be used. Examples of methods for heating the deposition material in the vapor deposition method include resistance heating, electron beam deposition, and laser deposition. The electron beam deposition method is preferable in terms of suppressing temperature rise and contamination of the substrate 200 because the deposition material can be directly heated. In addition, in order to generate sufficient compressive stress in the first layer and the second layer, it is also desirable to use an ion beam assisted method. In the ion beam assisted method, an independent ion source plays a role in assisting the deposition, so a film with low absorption and scattering and high strength can be formed.

[0019] It is generally known that the lower the refractive index of the material of the top layer (the layer farthest from the substrate) in an anti-reflection film, the better the anti-reflection performance. Therefore, in this embodiment, the top layer of the anti-reflection film 100 is a porous layer 10 having voids therein. This makes it possible to significantly reduce the refractive index of the top layer compared to a case where the top layer does not have voids therein. Furthermore, in this embodiment, silicon oxide or magnesium fluoride, which has a relatively low refractive index, is used as the material for the porous layer 10. This makes it possible to sufficiently reduce the refractive index of the top layer in the anti-reflection film, making it possible to achieve good anti-reflection performance.

[0020] Here, the refractive index of the porous layer 10 at the d line is n d 10 In this case, it is desirable to satisfy the following conditional expression (1):

[0021] 1.15≦n d 10 ≦1.35 (1) The refractive index n of the porous layer 10 is determined from the ratio of the material and voids constituting the porous layer 10 and their refractive indices. That is, the greater the ratio of voids in the porous layer 10, the higher the refractive index n d 10is low. By satisfying conditional formula (1), the refractive index of the porous layer 10 can be sufficiently low while maintaining sufficient strength of the porous layer 10, so that both environmental durability and good antireflection performance can be achieved. Furthermore, it is more preferable to satisfy the following conditional formula (1a).

[0022] 1.20≦n d 10 <= 1.31 (1a) The method for forming the porous layer 10 includes, for example, the sol-gel method. The method for applying the coating liquid in the sol-gel method is not particularly limited, and dip coating, spin coating, spray coating, roll coating, etc. can be adopted, but among these, it is preferable to adopt the relatively easy spin coating method. The sol-gel method includes a heat treatment process, but since it is possible to perform baking at a low temperature by using a solvent with a low boiling point, it is preferable from the viewpoint of suppressing deformation and discoloration of the substrate 200. Therefore, it is preferable that the material of the porous layer 10 is a material that hardens at a low temperature of 80°C or less.

[0023] The solvent used for forming the porous layer 10 is 1.0 mg / cm 2 , which has at least one of an ether bond and an ester bond, has a carbon number of 4 to 7, and has a branched structure. 3 More than 2.8mg / cm 3 The following alcohols are preferable. Examples of the alcohol include 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, 1-butoxy-2-propanol, 2-isopropoxyethanol, and 3-methoxy-1-butanol. Alternatively, methyl lactate or ethyl lactate may be used. The alcohol used as the solvent may be one type or two or more types. The alcohol used as the solvent remains inside the porous layer 10 and also plays a role in controlling the size of the pores.

[0024] In order to form voids in the porous layer 10, it is desirable that the porous layer 10 has a plurality of particles made of silicon oxide and a binder that binds the plurality of particles together. In this case, the plurality of particles may be spherical solid particles or hollow particles, ring-shaped or hook-shaped solid particles, etc. However, in order to increase the proportion of air (voids) in the porous layer 10 and reduce the refractive index of the porous layer 10, it is preferable to use hollow particles or ring-shaped or hook-shaped solid particles. When solid particles are used, the particles are bonded (linked) to each other in a chain shape to form a chain structure (particles), so that sufficient strength can be secured while forming many voids.

[0025] The average refractive index of the resin material constituting the substrate 200 at the d line is denoted by nd 200 , the linear expansion coefficient is α(10 -5 / °C), it is desirable to satisfy at least one of the following conditional expressions (2) and (3). By using a resin material that satisfies at least one of the conditional expressions (2) and (3) for the substrate 200, it is possible to achieve both freedom in designing the optical element 300 and ease of manufacture and optical performance of the substrate 200.

[0026] 1.48≦nd 200 ≦1.80 (2) 1.5≦α≦30.0 (3) Specific examples of the present embodiment will be described below, however, each example is merely an example of the present embodiment, and the present invention is not limited to the scope of each example.

[0027] [Example 1] First embodiment An optical element 300 according to the present invention will be described below. The configuration of the optical element 300 according to the present embodiment is the same as that of the embodiment shown in FIG.

[0028] The material of the substrate 200 in this embodiment is ZEONEX manufactured by Zeon Corporation, which is a cycloolefin polymer (COP) resin with a refractive index of 1.53 at the d-line. The material of the dielectric layer 11 in this embodiment is SiO2 as silicon oxide and Ta2O5 as tantalum oxide. The material of the porous layer 10 in this embodiment is chain particles (chain silica) made of SiO2.

[0029] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 1.

[0030] [Table 1] A method for forming the anti-reflection coating 100 according to this embodiment will be described.

[0031] (a) Method for forming dielectric layer 11 The substrate 200 was placed on a deposition jig in a deposition chamber (vacuum chamber), and deposition materials, granular SiO2 and Ta2O5, were placed in a crucible. -3 The chamber was evacuated without heating until it reached a high vacuum of approximately 1×10 Pa. After it was confirmed that the inside of the deposition chamber had reached a high vacuum, Ar was introduced into the ion gun as an inert gas, and the ion gun was discharged. After the ion gun reached a stable state, oxygen was introduced into the deposition chamber, and the vacuum pressure reached 1×10 -2 When the pressure reached about 100 Pa, ion beam assisted deposition was performed using oxygen ions.

[0032] (b) Method for forming the porous layer 10 law

[0033] (b-1) Preparation of chain silica coating solution and binder solution First, a dispersion containing chain silica particles and a solvent (chain silica dispersion) was prepared. The solvent was 2-propanol (IPA), Nissan Chemical Industries' IPA-ST-UP (average particle size 12 nm, solid content concentration 15 mass%), which was replaced with 1-propoxy-2-propanol using an evaporator. The solvent ratio in the chain silica dispersion was IPA:1-propoxy-2-propanol = 7.5:92.5.

[0034] Next, a solution (binder solution) containing components necessary for forming a binder was prepared. Specifically, 18.5 g of tetraethoxysilane (TEOS) from Tokyo Chemical Industry Co., Ltd. and 16.0 g of 0.1 wt% phosphinic acid (10 equivalents relative to TEOS) as catalytic water were mixed and stirred in a water bath at 20°C for 60 minutes.

[0035] Further, 33.4 g of the binder solution was added to 251.3 g of the chain silica dispersion, 174.5 g of 1-propoxy-2-propanol, and 546.5 g of ethyl lactate were added, and the mixture was stirred for 60 minutes to prepare a chain silica coating liquid.

[0036] (b-2) Coating method for the porous layer 10 The chain silica coating liquid was dropped onto the dielectric layer 11 formed on the substrate 200, and spin-coated at 4000 rpm for 20 seconds. Thereafter, the porous layer 10 was formed by baking for 10 minutes in a hot air circulating oven at 25°C.

[0037] Fig. 2 shows the reflectance characteristics of the optical element 300 according to this embodiment. Fig. 2 shows the relationship between the reflectance and the wavelength of the incident light when the angle of incidence of the incident light to the optical element 300 is 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees. As shown in Fig. 2, the reflectance when the angle of incidence is 0 degrees is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0038] [Example 2] Second Embodiment An optical element 300 according to a second embodiment of the present invention will be described below. Regarding this embodiment, the description of the same configuration as in the above-described first embodiment will be omitted.

[0039] The material of the substrate 200 is the same COP resin as in Example 1. The material of the dielectric layer 11 is SiO2 containing 0.001% by weight of Al, and Ta2O5. The material of the porous layer 10 is chain silica as in Example 1. The dielectric layer 11 in this example is composed of seven layers, unlike Example 1. The method of forming the dielectric layer 11 and the porous layer 10 is the same as in Example 1.

[0040] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 2.

[0041] [Table 2] Fig. 3 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1 (Fig. 2). As shown in Fig. 3, the reflectance when the incident angle is 0 degrees is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0042] [Example 3] Third embodiment An optical element 300 according to a third embodiment of the present invention will be described below. The configuration of the optical element 300 according to this embodiment is the same as that of the embodiment shown in FIG.

[0043] The material of the substrate 200 is the same COP resin as in Example 1. The material of the dielectric layer 11 is a mixture of SiO2 containing 3.0% by weight of Al, and Ta2O5 and TiO2. The material of the porous layer 10 is chain silica. On the porous layer 10, a protective layer 20 mainly composed of TEOS is provided. The method of forming the dielectric layer 11 is the same as in Example 1.

[0044] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 3.

[0045] [Table 3] A method for forming the porous layer 10 and the protective layer 20 according to this embodiment will be described.

[0046] (c) Method of forming the porous layer 10 and the protective layer 20 law

[0047] (c-1) Preparation of chain silica coating liquid The chain silica coating liquid according to this example was prepared in the same manner as in Example 1(b-1).

[0048] (c-2) Preparation of protective layer coating solution 26.0g of TEOS from Tokyo Chemical Industry Co., Ltd. and 22.5g of 0.01M diluted hydrochloric acid (10 equivalents to TEOS) as catalytic water were added to 7.7g of 1-ethoxy-2-propanol from Kishida Chemical Co., Ltd., and mixed and stirred for 60 minutes. Furthermore, this mixture was stirred for 40 minutes in an oil bath at 60°C. After that, 1-ethoxy 2-propanol and 2-ethylbutanol were added to the mixture so that the solid concentration of silica was 0.8 wt%, to prepare a coating liquid for the protective layer. The ratio of 1-ethoxy 2-propanol to 2-ethylbutanol was 3:7.

[0049] (c-3) Coating method for the porous layer 10 and the protective layer 20 0.2 ml of the chain silica coating liquid was dropped onto the dielectric layer 11 formed on the substrate 200, and spin-coated at 4000 rpm for 20 seconds. Then, 0.2 ml of the protective layer coating liquid was dropped onto the dielectric layer 11 coated with the chain silica coating liquid, and spin-coated at 4000 rpm for 20 seconds. After that, the porous layer 10 and protective layer 20 were formed by baking for 10 minutes in a hot air circulating oven at 25°C.

[0050] Fig. 4 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 4, the reflectance when the incident angle is 60 degrees is 2.5% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0051] [Example 4] Fourth embodiment An optical element 300 according to a fourth embodiment of the present invention will be described below. Regarding this embodiment, the description of the same configuration as each of the above-mentioned embodiments will be omitted.

[0052] The material of the substrate 200 is the same COP resin as in Example 3. The material of the dielectric layer 11 is a mixture of SiO2 containing 10.0% by weight of Al, and Ta2O5 and TiO2. The material of the porous layer 10 is chain silica as in Example 3. The material of the protective layer 20 is a material mainly composed of TEOS as in Example 3. The dielectric layer 11 in this example is composed of seven layers, unlike Example 3. The methods of forming the dielectric layer 11, the porous layer 10, and the protective layer 20 are the same as in Example 3.

[0053] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 4.

[0054] [Table 4] Fig. 5 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 5, the reflectance when the incident angle is 60 degrees is 2.5% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0055] [Example 5] Fifth embodiment An optical element 300 according to a fifth embodiment of the present invention will be described below. Regarding this embodiment, the description of the same configuration as each of the above-mentioned embodiments will be omitted.

[0056] The material of the substrate 200 in this embodiment is EP-5000 manufactured by Mitsui Gas Chemical Co., Ltd., which is a special polycarbonate (PC) resin with a refractive index of 1.64 at the d-line. The material of the dielectric layer 11 is SiO2 and a mixture of Ta2O5 and ZrO2. The material of the porous layer 10 is chain silica similar to that in the first embodiment. The method of forming the dielectric layer 11 and the porous layer 10 is similar to that in the first embodiment.

[0057] Table 5 shows the detailed configuration of the optical element 300 according to this embodiment.

[0058] [Table 5] Fig. 6 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 6, the reflectance when the incident angle is 0 degree is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0059] [Example 6] Sixth embodiment An optical element 300 according to a sixth embodiment of the present invention will be described below. Regarding this embodiment, the description of the same configuration as each of the above-mentioned embodiments will be omitted.

[0060] The material of the substrate 200 is the special PC resin similar to that of Example 5. The material of the dielectric layer 11 is a mixture of SiO2 containing 0.001% by weight of Al, and Ta2O5 and ZrO2. The material of the porous layer 10 is chain silica similar to that of Example 1. The dielectric layer 11 of this example is composed of five layers, unlike that of Example 5. The method of forming the dielectric layer 11 and the porous layer 10 is similar to that of Example 1.

[0061] Table 6 shows the detailed configuration of the optical element 300 according to this embodiment.

[0062] [Table 6] Fig. 7 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 7, the reflectance when the incident angle is 0 degree is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0063] [Example 7] Seventh embodiment An optical element 300 according to a seventh embodiment of the present invention will be described. Regarding this embodiment, the description of the same configuration as each of the above-mentioned embodiments will be omitted.

[0064] The material of the substrate 200 is the special PC resin similar to that of the fifth embodiment. The material of the dielectric layer 11 is SiO2 containing 0.03% by weight of Al, and Ta2O5. The material of the porous layer 10 is hollow particles (hollow silica) made of SiO2. The method of forming the dielectric layer 11 is similar to that of the first embodiment.

[0065] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 7.

[0066] [Table 7] A method for forming the porous layer 10 according to this embodiment will be described.

[0067] (d) Method for forming the porous layer 10 law

[0068] (d-1) Preparation of hollow silica coating solution and binder solution First, 6.00 g of a dispersion containing hollow silica particles and a solvent (hollow silica dispersion) was diluted with 28.17 g of 1-methoxy-2-propanol to prepare a hollow silica coating liquid (solid content concentration 3.60% by mass). As the hollow silica dispersion, Suluria 1110 (average particle size 55 nm, solid content concentration 20.50% by mass) manufactured by JGC Catalysts and Chemicals Co., Ltd., which is a dispersion using IPA as the solvent, was used.

[0069] Next, a binder solution for hollow silica was prepared. Specifically, 26.0g of TEOS from Tokyo Chemical Industry Co., Ltd. and 22.5g of 0.01M diluted hydrochloric acid (10 equivalents to TEOS) as catalytic water were added to 7.7g of 1-ethoxy-2-propanol from Kishida Chemical Co., Ltd., and the mixture was mixed and stirred for 60 minutes. Furthermore, this mixture was stirred for 40 minutes in an oil bath at 60°C. After that, 1-ethoxy 2-propanol and 2-ethylbutanol were added so that the solid concentration of silica was 0.8 wt%, to prepare a binder solution. The ratio of 1-ethoxy 2-propanol to 2-ethylbutanol was 3:7.

[0070] (d-2) Coating method for the porous layer 10 A hollow silica coating solution was dropped onto the dielectric layer 11 formed on the substrate 200, and spin-coated at 3000 rpm for 20 seconds to form a layer of hollow silica fine particles. A binder solution was then dropped onto the layer of hollow silica fine particles, and spin-coated at 4500 rpm for 20 seconds. Thereafter, the layer was baked for 10 minutes in a hot air circulating oven at 25°C to form a porous layer 10.

[0071] Fig. 8 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 8, the reflectance when the incident angle is 60 degrees is 0.21% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0072] [Example 8] An optical element 300 according to an eighth embodiment of the present invention will be described below. Regarding this embodiment, the description of the same configuration as each of the above-mentioned embodiments will be omitted.

[0073] The material of the substrate 200 is the special PC resin, which is the same as in Example 5. The material of the dielectric layer 11 is a mixture of SiO2 containing 10.0% by weight of Al, and Ta2O5. The material of the porous layer 10 is hollow silica, which is the same as in Example 7. The dielectric layer 11 in this example is composed of five layers, unlike in Example 7. The method of forming the dielectric layer 11 and the porous layer 10 is the same as in Example 7.

[0074] Table 8 shows the detailed configuration of the optical element 300 according to this embodiment.

[0075] [Table 8] Fig. 9 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 9, the reflectance when the incident angle is 60 degrees is 0.21% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0076] [Example 9] Ninth embodiment An optical element 300 according to a ninth embodiment of the present invention will be described. In this embodiment, the description of the same configuration as in each of the above-mentioned embodiments will be omitted.

[0077] The material of the substrate 200 in this embodiment is EP-9000 manufactured by Mitsui Gas Chemical Co., Ltd., which is a special polycarbonate (PC) resin with a refractive index of 1.67 at the d-line. The material of the dielectric layer 11 is SiO2 and Ta2O5. The material of the porous layer 10 is hollow silica similar to that of the seventh embodiment. On the porous layer 10, a protective layer 20 containing TEOS as a main component is provided. The method of forming the dielectric layer 11 is similar to that of the first embodiment.

[0078] Table 9 shows the detailed configuration of the optical element 300 according to this embodiment.

[0079] [Table 9] A method for forming the porous layer 10 and the protective layer 20 according to this embodiment will be described.

[0080] (e) Method of forming the porous layer 10 and the protective layer 20 law

[0081] (e-1) Preparation of hollow silica coating solution and binder solution The hollow silica coating solution and the binder solution according to this example were prepared in the same manner as in Example 7(d-1).

[0082] (e-2) Preparation of protective layer coating solution The protective layer coating liquid according to this example was prepared in the same manner as in Example 3(c-1). Note that the protective layer coating liquid in Example 3 and the binder solution in Example 7 were the same.

[0083] (e-3) Coating method for the porous layer 10 and the protective layer 20 0.2 ml of hollow silica coating liquid was dropped onto the dielectric layer 11 formed on the substrate 200, and spin-coated at 3000 rpm for 20 seconds. 0.2 ml of binder solution was then dropped onto the dielectric layer 11 coated with the hollow silica coating liquid, and spin-coated at 4000 rpm for 20 seconds. After that, the porous layer 10 was formed by baking for 10 minutes in a hot air circulating oven at 25°C. Furthermore, 0.2 ml of protective layer coating liquid was dropped onto the porous layer 10, and spin-coated at 4000 rpm for 20 seconds, and then baked for 10 minutes in a hot air circulating oven at 25°C to form the protective layer 20.

[0084] Fig. 10 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 10, the reflectance when the incident angle is 0 degrees is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0085] [Example 10] Tenth embodiment An optical element 300 according to the present invention will be described. In this embodiment, the description of the same configuration as in each of the above-mentioned embodiments will be omitted.

[0086] The material of the substrate 200 is the special PC resin, which is the same as in Example 9. The material of the dielectric layer 11 is a mixture of SiO2 containing 0.001% by weight of Al, and Ta2O5 and TiO2. The material of the porous layer 10 is hollow silica, which is the same as in Example 7. The material of the protective layer 20 is a material mainly composed of TEOS, which is the same as in Example 9. The dielectric layer 11 in this example is composed of five layers, unlike in Example 9. The method of forming the dielectric layer 11 and the porous layer 10 is the same as in Example 7.

[0087] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 10.

[0088] [Table 10] Fig. 11 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 11, the reflectance when the incident angle is 0 degrees is 0.15% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained.

[0089] [Example 11] An optical element 300 according to an eleventh embodiment of the present invention will be described. In this embodiment, the description of the same configuration as in each of the above-mentioned embodiments will be omitted.

[0090] The material of the substrate 200 is the special PC resin, which is the same as in Example 9. The material of the dielectric layer 11 is a mixture of SiO2 containing 3.0% by weight of Al, and Ta2O5 and ZrO2. The material of the porous layer 10 is hollow silica, which is the same as in Example 7. The material of the protective layer 20 is a material mainly composed of TEOS, which is the same as in Example 9. The methods of forming the dielectric layer 11, the porous layer 10, and the protective layer 20 are the same as in Example 9.

[0091] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 11.

[0092] [Table 11] Fig. 12 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 12, the reflectance when the incident angle is 60 degrees is 2.5% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0093] [Example 12] An optical element 300 according to a twelfth embodiment of the present invention will be described. In this embodiment, the description of the same configuration as in each of the above-mentioned embodiments will be omitted.

[0094] The material of the substrate 200 is the special PC resin, which is the same as in Example 9. The material of the dielectric layer 11 is a mixture of SiO2 containing 10.0% by weight of Al, and Ta2O5 and ZrO2. The material of the porous layer 10 is hollow silica, which is the same as in Example 7. The material of the protective layer 20 is a material mainly composed of TEOS, which is the same as in Example 9. The methods of forming the dielectric layer 11, the porous layer 10, and the protective layer 20 are the same as in Example 9.

[0095] The detailed configuration of the optical element 300 according to this embodiment is shown in Table 12.

[0096] [Table 12] Fig. 13 shows the reflectance characteristics of the optical element 300 according to this embodiment, similar to Example 1. As shown in Fig. 13, the reflectance when the incident angle is 60 degrees is 2.5% or less in the visible wavelength range of 420 to 700 nm, and it is understood that good anti-reflection performance is obtained even when the incident angle is large.

[0097] [Comparative Example 1] In order to explain the effects of the present invention, an optical element 300 according to Comparative Example 1 will be described. The optical element 300 according to Comparative Example 1 differs from Example 1 in that the uppermost layer is not a porous layer but a magnesium fluoride (MgF2) dielectric layer 11.

[0098] The material of the substrate 200 is the same COP resin as in Example 1. The material of the dielectric layer 11 is the same as in Example 1, with SiO2 and Ta2O5, and MgF2 as the uppermost layer. The method of forming the dielectric layer 11 is the same as in Example 1.

[0099] Table 13 shows the detailed configuration of the optical element 300 according to this comparative example.

[0100] [Table 13] Fig. 14 shows the reflectance characteristics of the optical element 300 according to this comparative example, similar to Example 1. As shown in Fig. 14, the reflectance when the incident angle is 0 degrees is 0.15% or less in the visible wavelength range of 420 to 700 nm. However, compared to the reflectance characteristics of the optical element 300 according to Example 1 (Fig. 2), it can be seen that the wavelength band where the reflectance is sufficiently low is narrow, and the reflectance increases when the incident angle is large.

[0101] [Comparative Example 2] In order to explain the effects of the present invention, an optical element 300 according to Comparative Example 2 will be described. The optical element 300 according to Comparative Example 2 differs from Comparative Example 1 in that the uppermost layer of the dielectric layer 11 is SiO2 instead of magnesium fluoride.

[0102] The material of the substrate 200 is the same COP resin as in Example 1. The materials of the dielectric layer 11 are the same SiO2 and Ta2O5 as in Example 1. The method of forming the dielectric layer 11 is the same as in Example 1.

[0103] Table 14 shows the detailed configuration of the optical element 300 according to this comparative example.

[0104] [Table 14] Fig. 15 shows the reflectance characteristics of the optical element 300 according to this comparative example, similar to Example 1. As shown in Fig. 15, the reflectance when the incident angle is 0 degrees is about 0.5% in the visible wavelength range of 420 to 700 nm, and it is clear that the reflectance is increased compared to the reflectance characteristics (Fig. 2) of the optical element 300 according to Example 1.

[0105] Next, a method for durability testing conducted to confirm the durability of the antireflection coating 100 according to each of the examples and comparative examples under various conditions will be described.

[0106] (High temperature and humidity storage test) A sample of the manufactured optical element 300 was left in a thermostatic chamber set at a temperature of 60° C. and a humidity of 90% for 1000 hours, and then the appearance of the antireflection film 100 was visually observed.

[0107] (Low temperature storage test) A sample of the produced optical element 300 was left in a thermostatic chamber set at a temperature of −30° C. for 1000 hours, and then the appearance of the antireflection film 100 was visually observed.

[0108] (High temperature storage test) A sample of the produced optical element 300 was left in a thermostatic chamber set at a temperature of 70° C. for 12 hours, and then the appearance of the antireflection film 100 was visually observed.

[0109] Table 15 shows a summary of the antireflection performance of the antireflection film 100 according to each of the examples and comparative examples, and the results of the durability test.

[0110] [Table 15] As shown in Table 15, in each of the Examples, no film cracking or peeling occurred in any of the durability tests, and it was confirmed that good anti-reflection performance and high environmental durability were achieved at the same time. On the other hand, in Comparative Example 1, since MgF2 with a large tensile stress is used as the top layer, it was confirmed that film cracking and peeling occurred in each durability test. In addition, in Comparative Example 2, although no film cracking or peeling occurred, it was confirmed that good anti-reflection performance was not obtained as described above.

[0111] [Optical systems and optical devices] Next, an optical system 400 and an optical device 500 according to an embodiment of the present invention will be described.

[0112] FIG. 16 shows a schematic diagram of a cross section including an optical axis (dash line) of an optical system 400 according to this embodiment. The optical system 400 is an imaging optical system having a plurality of optical elements (lenses) G401 to G411 and an aperture 402, and forms an image of an object on an image plane 403. At least one of the entrance surface and the exit surface of at least one of the optical elements G401 to G411 is provided with the anti-reflection film 100 according to the above-mentioned embodiment. In order to obtain good anti-reflection performance in the entire optical system 400, it is desirable that all optical elements are provided with the anti-reflection film 100, and more preferably, both the entrance surface and the exit surface of each optical element are provided with the anti-reflection film 100. In addition, when a prism, a filter, or the like is used as an optical element, it is desirable to provide the anti-reflection film 100 on them.

[0113] 17 is 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 including the optical system 400, and a main body unit 502 including an imaging element 503. Each optical element constituting the optical system 400 is held by a holding member (lens barrel) in the lens unit 501. The imaging element 503 is an element that captures an image of an object by receiving light from the optical system 400, and may be, for example, a photoelectric conversion element such as a CCD sensor or a CMOS sensor. The imaging element 503 is disposed so that its imaging surface (light receiving surface) coincides with the image plane 403 of the optical system 400.

[0114] Lens unit 501 may be integrated with main body unit 502, or may be configured to be detachable from main body unit 502. When lens unit 501 and main body unit 502 are configured to be detachable from each other, lens unit 501 can be regarded as one optical device (lens device), and main body unit 502 can be regarded as one optical device (imaging device). Note that the optical element according to each embodiment can be applied not only to the above-mentioned imaging device, but also to various optical devices such as binoculars, projectors, and telescopes.

[0115] Although the 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 the gist of the present invention. [Explanation of symbols]

[0116] 10 Porous layer 11 Dielectric layer 100 Anti-reflection coating 200 Substrates 300 Optical Elements

Claims

1. An optical element having a substrate made of a resin material and an anti-reflection film, the anti-reflection film comprises a dielectric layer formed on the substrate and a porous layer formed on the dielectric layer, the dielectric layer includes a first layer including silicon oxide and a second layer including tantalum oxide; the porous layer comprises silicon oxide or magnesium fluoride; the first layer is adjacent to the second layer, the second layer is adjacent to the porous layer; 1. An optical element, wherein the first layer contains 90% or more by weight of silicon oxide and 10% or less by weight of aluminum.

2. When the refractive index of the porous layer at the d line is nd 10, 1.15≦nd10≦1.35 2. The optical element according to claim 1, which satisfies the following condition:

3. 3. The optical element according to claim 1, wherein the second layer contains at least one of titanium oxide, lanthanum oxide, and zirconium oxide.

4. 4. The optical element according to claim 1, wherein the porous layer comprises a plurality of particles made of silicon oxide and a binder that binds the plurality of particles to one another.

5. 5. The optical element according to claim 4, wherein each of the plurality of particles is a spherical hollow particle.

6. 5. The optical element according to claim 4, wherein each of the plurality of particles is a solid particle, and the plurality of particles are bonded to each other in the form of a chain.

7. The porous layer has a density of 1.0 mg / cm ３ More than 2.8 mg / cm ３ 7. The optical element according to claim 1, comprising the following alcohol, the alcohol having at least one of an ether bond and an ester bond, a carbon number of 4 to 7, and a branched structure:

8. When the average refractive index of the resin material at the d line is nd200, 1.48≦nd200≦1.80 8. The optical element according to claim 1, which satisfies the following condition: 1.0<x<1 / 2.0<x<1 / 2.

0.

9. The linear expansion coefficient of the resin material is α(10 －５ / ℃), １．５≦α≦３０．０ 9. The optical element according to claim 1, which satisfies the following condition: 1.0<x<1.0<x<1.

10. 10. The optical element according to claim 1, comprising the substrate and the anti-reflection film.

11. 10. The optical element according to claim 1, comprising: the substrate; the anti-reflection film; and a protective layer provided on the anti-reflection film.

12. 12. An optical device comprising: the optical element according to claim 1; and a holding member for holding the optical element.

13. 12. An optical device comprising: the optical element according to claim 1; and an image sensor that receives light from the optical element.

Images