Antireflection film, optical element, optical system, and optical device

Abstract

This antireflection film is formed by laminating a plurality of layers on a resin substrate, and comprises: an alternately laminated layer which is formed on the substrate and in which a layer having a refractive index between 1.35 and 1.55, inclusive, and a layer having a refractive index between 2.00 and 2.35, inclusive, at a wavelength of 550 nm are alternately laminated; a magnesium fluoride layer which is formed on the alternately laminated layer and which contain magnesium fluoride; and an uppermost layer, being a layer formed on the magnesium fluoride layer and having a refractive index of 1.55 or less at the wavelength of 550 nm and an optical film thickness corresponding to the wavelength of 550 nm between 3 nm and 110 nm, inclusive. The layer located farthest on the substrate side from among the layers of the alternately laminated layer has a refractive index between 1.35 and 1.55, inclusive, at the wavelength of 550 nm, has compressive stress, and has an optical film thickness corresponding to the wavelength of 550 nm between 135 nm and 490 nm, inclusive.

Description

Anti-reflective coating, optical element, optical system, and optical device

[0001] This invention relates to an anti-reflective coating, an optical element, an optical system, and an optical apparatus. This invention claims priority to Japanese Patent Application No. 2025-003533, filed on 9 January 2025, and in designated countries where incorporation by reference is permitted, the contents described in that application are incorporated into this application by reference.

[0002] Patent Document 1 describes an anti-reflective film formed by laminating a first, second, third, fourth, fifth, and sixth layer in that order from the substrate side on a substrate, wherein the refractive index of the substrate is 1.40 to 2.10 at a reference wavelength λ = 520 nm, the optical film thickness of the first layer is 0.045λ or more and 0.971λ or less and is a high refractive index material with a refractive index of 1.60 or more and 2.50 or less, the optical film thickness of the second layer is 0.025λ or more and 0.166λ or less and is a low refractive index material with a refractive index of 1.30 or more and 1.50 or less, and the optical film thickness of the third layer is 0.038λ The above describes an anti-reflective coating characterized in that the material is a high refractive index material with a refractive index of 1.60 or more and 2.50 or less at 0.375λ or less, the optical film thickness of the fourth layer is a low refractive index material with a refractive index of 1.30 or more and 1.50 or less at 0.048λ or more and 0.152λ or less, the optical film thickness of the fifth layer is a high refractive index material with a refractive index of 1.80 or more and 2.50 or less at 0.045λ or more and 0.119λ or less, and the optical film thickness of the sixth layer is an ultra-low refractive index material with a refractive index of 1.10 or more and 1.30 or less at 0.228λ or more and 0.331λ or less.

[0003] Japanese Patent Publication No. 2018-101132

[0004] One aspect of the present invention is an anti-reflective film comprising a plurality of layers laminated on a resin substrate, the film comprising: an alternating laminated layer formed on the substrate, in which layers having a refractive index of 1.35 or more and 1.55 or less at a wavelength of 550 nm and layers having a refractive index of 2.00 or more and 2.35 or less are alternately laminated; a magnesium fluoride layer containing magnesium fluoride formed on the alternating laminated layer; and an uppermost layer formed on the magnesium fluoride layer, in which the refractive index at a wavelength of 550 nm is 1.55 or less and the optical film thickness corresponding to a wavelength of 550 nm is 3 nm or more and 110 nm or less, wherein the layer of the alternating laminated layer that is closest to the substrate has a refractive index of 1.35 or more and 1.55 or less at a wavelength of 550 nm, has compressive stress, and has an optical film thickness corresponding to a wavelength of 550 nm is 135 nm or more and 490 nm or less.

[0005] Another aspect of the present invention is an anti-reflective film comprising a plurality of layers laminated on a resin substrate, the layers being a first layer, a second layer, a third layer, a fourth layer, a fifth layer, a sixth layer, a seventh layer, and an eighth layer from the layer in contact with the substrate, wherein at a reference wavelength λ = 550 nm, the first layer is silicon oxide, and the optical film thickness (n λ ×d) is 135 nm to 490 nm, the second layer is titanium oxide, and the optical film thickness (n λ ×d) is 8 nm to 50 nm, the third layer is silicon oxide, and the optical film thickness (n λ ×d) is 30 nm or more and 100 nm or less, the fourth layer is titanium oxide, and the optical film thickness (n λ ×d) is 55 nm to 180 nm, and the fifth layer is silicon oxide, and the optical film thickness (n λ ×d) is 3 nm to 65 nm, and the sixth layer is titanium oxide, and the optical film thickness (n λ ×d) is 60 nm to 160 nm, and the seventh layer is magnesium fluoride, and the optical film thickness (n λ ×d) is 13 nm to 150 nm, and the 8th layer is silicon oxide, and the optical film thickness (n λ ×d) is between 3 nm and 110 nm.

[0006] Another aspect of the present invention is an optical element comprising the anti-reflective film described above. Another aspect of the present invention is an optical element having the anti-reflective film described in any one of claims 1 to 13 on a substrate, wherein the substrate comprises at least one of acrylic resin, COP (cycloolefin polymer) resin, polyethylene resin, polypropylene resin, polyester resin, ethylene vinyl copolymer resin, polyvinyl chloride resin, cellulose resin, polyamide resin, polyimide resin, polycarbonate resin, polystyrene resin, and vinyl acetate resin.

[0007] Another aspect of the present invention is an optical system including the optical elements described above.

[0008] Another aspect of the present invention is an optical device including the optical system described above.

[0009] This is an example of a cross-sectional view of the anti-reflective coating in this embodiment. This is a perspective view showing an example in which the optical device according to this embodiment is used as an imaging device. This is a front view of the imaging device CAM. This is a rear view of the imaging device CAM. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 1. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 2. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 3. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 4. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 5. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 6. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 7. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 8. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 9. This is a graph showing the relationship between wavelength (nm) and reflectance (%) in Example 10. This graph shows the relationship between wavelength (nm) and reflectance (%) in Example 11. This graph shows the relationship between wavelength (nm) and reflectance (%) in Comparative Example 1. This graph shows the relationship between wavelength (nm) and reflectance (%) in Comparative Example 3.

[0010] Hereinafter, embodiments according to the present invention (hereinafter referred to as "the present embodiment") will be described. The following present embodiment is an exemplification for explaining the present invention and is not intended to limit the present invention to the following content. The present invention can be appropriately modified and implemented within the scope of its gist.

[0011] In the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios. Also, the "cross-section" in the "cross-sectional view" or "cross-sectional perspective" refers to a cross-section orthogonal to the horizontal plane.

[0012] Also, the term "upper" used when explaining the lamination indicates the positional relationship assuming that the side to be laminated is "lower", and is not limited to a configuration in which the lamination side is located above in the vertical direction.

[0013] FIG. 1 is an example of a cross-sectional view of the antireflection film 1 in the present embodiment. The antireflection film 1 in the present embodiment is formed by laminating a plurality of layers on a base material 10. The antireflection film 1 includes a base material 10, an alternately laminated layer 20, a magnesium fluoride layer 30, and an uppermost layer 40.

[0014] The base material 10 is made of resin, and for example, one or more of acrylic resin, COP (cycloolefin polymer) resin, polyethylene resin, polypropylene resin, polyester resin, ethylene vinyl copolymer resin, polyvinyl chloride resin, cellulose resin, polyamide resin, polyimide resin, polycarbonate resin, polystyrene resin, and vinyl acetate resin can be used.

[0015] The alternately laminated layer 20 is laminated on the base material 10 and is a layer in which a low refractive index layer 21 and a high refractive index layer 22 are alternately laminated. The low refractive index layer 21 has a refractive index (n λ ) of 1.35 or more and 1.55 or less at a reference wavelength λ = 550 nm. For example, the low refractive index layer 21 includes silicon oxide (SiO ２ , SiO, etc.), aluminum oxide (Al ２ O ３One or more of the above can be used in combination. The refractive index is more preferably 1.40 or higher, and even more preferably 1.45 or higher. The refractive index is more preferably 1.53 or lower, and even more preferably 1.50 or lower.

[0016] The high refractive index layer 22 has a refractive index (n) at a reference wavelength λ = 550 nm. λ The layer has a refractive index of 2.00 to 2.35. For example, the high refractive index layer 22 contains titanium oxide (TiO ２ (e.g.), zirconium oxide (Zr ２ O etc.), tantalum oxide (Ta ２ O ５ One or more of the above can be used in mixtures. The refractive index is more preferably 2.03 or higher, and even more preferably 2.05 or higher. In order to obtain better anti-reflective properties, a particularly high refractive index TiO is used. ２ It is particularly preferable to use [this].

[0017] In Figure 1, the alternating laminated layer 20 has a total of six layers, consisting of a low refractive index layer 21 and a high refractive index layer 22. However, the number of layers in the alternating laminated layer 20 is not limited to this example. Since a smaller number of layers tends to make it more difficult to reduce reflectivity, and a larger number of layers tends to increase manufacturing costs, in this embodiment, the total number of low refractive index layers 21 and high refractive index layers 22 in the alternating laminated layer 20 is preferably six to ten layers.

[0018] The magnesium fluoride layer 30 is a layer laminated on top of the alternating layer 20, and is made of magnesium fluoride (MgF ２ This is a layer containing ). The top layer 40 is a layer that is laminated on top of the magnesium fluoride layer 30. Note that the magnesium fluoride layer 30 does not have to be in contact with the alternating laminated layer 20, and other layers may be interposed between them. Also, the top layer 40 does not have to be in contact with the magnesium fluoride layer 30, and other layers may be interposed between them.

[0019] In this embodiment, a resin is used for the base material 10. Since the base material 10 will undergo irreversible deterioration if heated too much, it is preferable to avoid excessive temperature increase compared to the case where glass is used for the base material 10 during the film formation of each film. On the other hand, if the temperature increase is suppressed during the film formation of the magnesium fluoride layer 30, crystallization will be impaired, which will affect the strength of the magnesium fluoride layer 30 and may reduce the scratch resistance, becoming a cause of scratches and the like. The antireflection film 1 in this embodiment can protect the magnesium fluoride layer 30 and suppress the load on the magnesium fluoride layer 30 by providing the top layer 40.

[0020] The top layer 40 preferably has a refractive index low enough to maintain the antireflection performance of the antireflection film 1. The refractive index (n <0oo0020>) of the top layer 40 at the reference wavelength λ = 550 nm is preferably 1.55 or less, more preferably 1.53 or less, and even more preferably 1.50 or less. In view of the types of materials that can be used in this field, the refractive index (n λ ) of the top layer 40 at the reference wavelength λ = 550 nm can be, for example, 1.35 or more.

[0021] The antireflection film 1 preferably has a reflectance of 0.3% or less, more preferably 0.25% or less, and even more preferably 0.2% or less for light with a wavelength of 450 nm or more and 650 nm or less. Also, the total physical film thickness, which is the sum of the physical film thicknesses of the alternating laminated layer 20, the magnesium fluoride layer 30, and the top layer 40, the smaller it is, the less material is used and the cost can be reduced. On the other hand, if it is too small, sufficient antireflection performance tends not to be obtained. From the above viewpoints, the total physical film thickness is preferably 350 nm or more, more preferably 370 nm or more, and even more preferably 385 nm or more. Also, the total physical film thickness is preferably 600 nm or less, more preferably 510 nm or less, and even more preferably 420 nm or less.

[0022] Hereinafter, among the layers constituting the alternating laminated layer 20, an example will be described in which the layer located closest to the base material 10 side is defined as the first layer, and the layer number increases as it approaches the uppermost layer 40. In the example shown below, as shown in FIG. 1, the first layer is the low refractive index layer 21, and the second layer is the high refractive index layer 22.

[0023] Among the alternating laminated layer 20, the first layer preferably has compressive stress. Since MgF contained in the magnesium fluoride layer 30 is generally known to have tensile stress, by providing a layer having compressive stress in the first layer, the tensile stress of the magnesium fluoride layer 30 can be reduced. That is, if the physical film thickness of the first layer is too small, it cannot resist the tensile stress of the magnesium fluoride layer 30, and cracks may occur. On the other hand, if the physical film thickness is too large, wrinkles may occur due to the influence of compressive stress. Examples of the film-forming material having compressive stress include silicon oxide (SiO ２ , SiO, etc.). The refractive index (n ２ ) of the first layer at the reference wavelength λ = 550 nm is preferably 1.35 or more and 1.55 or less, and the optical film thickness (n λ ×d) is preferably 135 nm or more and 490 nm or less. The optical film thickness of the first layer at the reference wavelength λ = 550 nm is preferably 135 nm or more, more preferably 160 nm or more, and even more preferably 190 nm or more. The optical film thickness of the first layer at the reference wavelength λ = 550 nm is preferably 490 nm or less, more preferably 380 nm or less, and even more preferably 270 nm or less.

[0024] Note that the present embodiment is not limited to the configuration in which the layer in contact with the base material 10 is the first layer of the alternating laminated layer 20. For example, other layers may be interposed between the base material 10 and the first layer of the alternating laminated layer 20.

[0025] In order for the antireflection film 1 to obtain good antireflection performance, when the alternating laminated layer 20 has a total of six low refractive index layers 21 and high refractive index layers 22, the second layer to the sixth layer preferably have the following configurations, respectively.

[0026] The second layer is the high refractive index layer 22. The optical film thickness (n​​λ The optical thickness (n) of the second layer at the reference wavelength λ = 550 nm is preferably 8 nm or more, more preferably 12 nm or more, and even more preferably 25 nm or more. λ The refractive index (n) of the second layer is preferably 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less. λ ) is preferably 2.00 or more and 2.35 or less.

[0027] The third layer is a low refractive index layer 21. The optical thickness of the third layer at a reference wavelength λ = 550 nm (n λ The optical thickness (n) of the third layer at the reference wavelength λ = 550 nm is preferably 30 nm or more, more preferably 32 nm or more, and even more preferably 35 nm or more. λ The refractive index (n) of the third layer is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 50 nm or less. λ ) is preferably 1.35 or more and 1.55 or less.

[0028] The fourth layer is a high refractive index layer 22. The optical thickness of the fourth layer at the reference wavelength λ = 550 nm (n λ The optical thickness of the fourth layer (n) at the reference wavelength λ = 550 nm is preferably 55 nm or more, more preferably 95 nm or more, and even more preferably 130 nm or more. λ The refractive index (n) of the fourth layer is preferably 180 nm or less, more preferably 171 nm or less, and even more preferably 160 nm or less. λ ) is preferably 2.00 or more and 2.35 or less.

[0029] The fifth layer is a low refractive index layer 21. The optical thickness of the fifth layer at a reference wavelength λ = 550 nm (n λ The optical thickness (n) of the fifth layer at the reference wavelength λ = 550 nm is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. λThe refractive index (n) of the fifth layer is preferably 65 nm or less, more preferably 35 nm or less, and even more preferably 22 nm or less. λ ) is preferably 1.35 or more and 1.55 or less.

[0030] The sixth layer is a high refractive index layer 22. The optical thickness of the sixth layer at the reference wavelength λ = 550 nm (n λ The optical thickness of the sixth layer (n) at the reference wavelength λ = 550 nm is preferably 60 nm or more, more preferably 62 nm or more, and even more preferably 65 nm or more. λ The refractive index (n) of the sixth layer is preferably 160 nm or less, more preferably 130 nm or less, and even more preferably 84 nm or less. λ ) is preferably 2.00 or more and 2.35 or less.

[0031] To obtain good anti-reflective performance, the optical thickness of the magnesium fluoride layer 30 at a reference wavelength λ = 550 nm (n λ The optical thickness (n) of the magnesium fluoride layer 30 at a reference wavelength λ = 550 nm is preferably 13 nm or more, more preferably 60 nm or more, and even more preferably 90 nm or more. λ ×d) is preferably 150 nm or less, more preferably 140 nm or less, and even more preferably 137 nm or less. Note that when there are six alternating laminated layers 20, the magnesium fluoride layer 30 is the seventh layer, but the preferred optical film thickness of the magnesium fluoride layer 30 described above is not limited to the case where the magnesium fluoride layer 30 is the seventh layer (i.e., when there are six alternating laminated layers 20).

[0032] In order to obtain good anti-reflective performance while protecting the magnesium fluoride layer 30, the optical thickness of the uppermost layer 40 at a reference wavelength λ = 550 nm (n λ The optical thickness (n) of the uppermost layer 40 at the reference wavelength λ = 550 nm is preferably 3 nm or more, more preferably 4 nm or more, and even more preferably 5 nm or more. λ×d) is preferably 110 nm or less, more preferably 58 nm or less, and even more preferably 18 nm or less. Note that when there are six alternating laminated layers 20, the top layer 40 is the eighth layer, but the preferred optical film thickness of the top layer 40 described above is not limited to the case where the top layer 40 is the eighth layer (i.e., when there are six alternating laminated layers 20).

[0033] A first indicator for evaluating the properties of the anti-reflective coating 1 is the ratio of the physical thickness of the magnesium fluoride layer 30 to the total physical thickness. The first indicator is preferably a value that provides good anti-reflective performance and where compressive stress and tensile stress are in appropriate balance. If the physical thickness of the magnesium fluoride layer 30 is too small relative to the total physical thickness, it will lead to a decrease in the overall anti-reflective performance of the anti-reflective coating 1. Conversely, if the physical thickness of the magnesium fluoride layer 30 is too large relative to the total physical thickness, tensile stress will become dominant, leading to cracks and delamination of the coating. The first indicator is preferably 0.01 or more and 0.35 or less. The first indicator is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.09 or more. The first indicator is preferably 0.35 or less, more preferably 0.32 or less, and even more preferably 0.28 or less.

[0034] A second indicator for evaluating the properties of the anti-reflective coating 1 is the ratio of the physical thickness of the magnesium fluoride layer 30 to the sum of the physical thicknesses of the low refractive index layer 21 and the uppermost layer 40 of the alternating laminated layer 20. The second indicator is preferably a value that provides good anti-reflective performance and where compressive stress and tensile stress are in appropriate balance. If the physical thickness of the magnesium fluoride layer 30 is too small compared to the sum of the physical thicknesses of the low refractive index layer 21 and the uppermost layer 40, it will lead to a decrease in the overall anti-reflective performance of the anti-reflective coating 1. Conversely, if the physical thickness of the magnesium fluoride layer 30 is too large compared to the sum of the physical thicknesses of the low refractive index layer 21 and the uppermost layer 40, tensile stress will become dominant, leading to cracks and delamination of the coating. The second indicator is preferably 0.03 or more and 0.63 or less. It is preferably 0.03 or more, more preferably 0.16 or more, and even more preferably 0.31 or more. The second indicator is preferably 0.63 or less, more preferably 0.57 or less, and even more preferably 0.50 or less.

[0035] A third indicator for evaluating the properties of the anti-reflective film 1 is the ratio of the physical film thickness of the magnesium fluoride layer 30 to the physical film thickness of the first layer, which is the layer located closest to the substrate 10 among the layers of the alternating laminated layer 20. The third indicator is preferably a value that has good anti-reflective performance and in which compressive stress and tensile stress are in appropriate balance. If the physical film thickness of the magnesium fluoride layer 30 is too small compared to the physical film thickness of the first layer, it will lead to a decrease in the overall anti-reflective performance of the anti-reflective film 1. Also, if the physical film thickness of the magnesium fluoride layer 30 is too large compared to the physical film thickness of the first layer, tensile stress will become dominant, which will cause cracks and delamination of the film. The third indicator is preferably 0.05 or more and 1.2 or less. The third indicator is preferably 0.05 or more, more preferably 0.2 or more, and even more preferably 0.40. The third indicator is preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.72 or less.

[0036] A fourth indicator for evaluating the properties of the anti-reflective film 1 is the ratio of the physical film thickness of the first layer, which is located closest to the substrate 10 among the layers of the alternating laminated layer 20, to the sum of the physical film thicknesses of the low refractive index layer 21 and the uppermost layer 40 of the alternating laminated layer 20. The fourth indicator is preferably a value that has good anti-reflective performance and in which compressive stress and tensile stress are in appropriate balance. If the physical film thickness of the first layer is too large compared to the sum of the physical film thicknesses of the low refractive index layer 21 and the uppermost layer 40, it will lead to a decrease in the overall anti-reflective performance of the anti-reflective film 1. Also, if the physical film thickness of the first layer is too small compared to the sum of the physical film thicknesses of the low refractive index layer 21 and the uppermost layer 40, the tensile stress of the magnesium fluoride layer 30 will become dominant, which will cause cracks and delamination of the film. The fourth indicator is preferably 0.4 or more and 0.95. The fourth indicator is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.66 or more. The fourth indicator is preferably 0.95 or less, more preferably 0.89 or less, and even more preferably 0.86 or less.

[0037] A fifth indicator for evaluating the properties of the anti-reflective coating 1 is the ratio of the physical thickness of the top layer 40 to the physical thickness of the magnesium fluoride layer 30. The fifth indicator is preferably a value that provides good anti-reflective performance and sufficient strength to the coating surface. If the physical thickness of the top layer 40 is too large compared to the physical thickness of the magnesium fluoride layer 30, it will lead to a decrease in the overall anti-reflective performance of the anti-reflective coating 1. Conversely, if the physical thickness of the top layer 40 is too small compared to the physical thickness of the magnesium fluoride layer 30, sufficient strength cannot be obtained on the coating surface, leading to scratches and other issues. The fifth indicator is preferably 0.02 or more and 4.3 or less. The fifth indicator is preferably 0.02 or more, more preferably 0.03 or more, and even more preferably 0.05 or more. The fifth indicator is preferably 4.3 or less, more preferably 1 or less, and even more preferably 0.1 or less.

[0038] If the alternating laminated layers 20 consist of 8 layers, the 1st, 3rd, 5th, and 7th layers are low refractive index layers 21, the 2nd, 4th, 6th, and 8th layers are high refractive index layers 22, the 9th layer is a magnesium fluoride layer 30, and the 10th layer is the top layer 40. If the alternating laminated layers consist of 10 layers, the 1st, 3rd, 5th, 7th, and 9th layers are low refractive index layers 21, the 2nd, 4th, 6th, 8th, and 10th layers are high refractive index layers 22, the 11th layer is a magnesium fluoride layer 30, and the 12th layer is the top layer 40.

[0039] By forming the anti-reflective film 1 according to this embodiment onto a desired resin optical material, an optical element with good anti-reflective performance can be obtained. Such optical elements include, for example, lenses, prisms, filters, etc. The optical material on which the anti-reflective film 1 according to this embodiment is formed only needs to have a resin surface. Therefore, the entire optical material may be made of resin, or optical materials other than resin (glass, ceramics, etc.) may be bonded to the portion on which the anti-reflective film 1 according to this embodiment is not formed. Furthermore, examples of optical systems in which the above optical element is used include objective lenses, focusing lenses, imaging lenses, interchangeable lenses for cameras, etc. These optical systems can be suitably used in various optical devices such as imaging devices such as interchangeable-lens cameras and non-interchangeable-lens cameras, and microscope devices such as fluorescence microscopes and multiphoton microscopes. Such optical devices are not limited to the imaging devices and microscopes mentioned above, but also include, but are not limited to, telescopes, binoculars, laser rangefinders, projectors, etc. An example of these will be described below.

[0040] <Imaging Device> Figure 2 is a perspective view showing an example in which the optical device according to this embodiment is used as an imaging device. The imaging device DSLR is a so-called digital single-lens reflex camera (interchangeable lens camera), and the photographic lens 103 (optical system) is equipped with optical elements including an anti-reflective coating according to this embodiment. The lens barrel 102 is detachably attached to the lens mount (not shown) of the camera body 101. The light passing through the lens 103 of the lens barrel 102 is then imaged onto the sensor chip (solid-state image sensor) 104 of the multi-chip module 106 located on the back side of the camera body 101. This sensor chip 104 is a bare chip such as a so-called CMOS image sensor, and the multi-chip module 106 is a COG (Chip On Glass) type module in which the sensor chip 104 is bare-chip mounted on a glass substrate 105.

[0041] Figures 3 and 4 are schematic diagrams showing another example in which the optical device according to this embodiment is used as an imaging device. Figure 3 shows a front view of the imaging device CAM, and Figure 4 shows a rear view of the imaging device CAM. The imaging device CAM is a so-called digital still camera (non-interchangeable lens camera), and the photographic lens WL (optical system) is equipped with optical elements including an anti-reflective coating according to this embodiment.

[0042] When the power button (not shown) of the imaging device CAM is pressed, the shutter (not shown) of the photographic lens WL is opened, and light from the subject (object) is collected by the photographic lens WL and formed on the image sensor located on the image plane. The image of the subject formed on the image sensor is displayed on the LCD monitor M located behind the imaging device CAM. The photographer determines the composition of the subject image while looking at the LCD monitor M, then presses down the release button B1 to capture the subject image with the image sensor and saves it to memory (not shown).

[0043] The imaging device CAM is equipped with an auxiliary light emitter EF that emits auxiliary light when the subject is dark, and function buttons B2 used for setting various conditions of the imaging device CAM, etc.

[0044] In optical systems used in digital cameras and the like, an anti-reflective coating with high anti-reflective performance is required to suppress ghosting and flare. The anti-reflective coating according to this embodiment is suitable as an anti-reflective coating to be formed on resin optical materials in such optical devices. In other words, by using the anti-reflective coating according to this embodiment, ghosting and flare caused by resin optical materials can be suppressed. That is, it can be said that this also contributes to obtaining the advantages of using resin optical materials (for example, weight reduction and cost reduction of optical devices). The optical devices to which this embodiment can be applied are not limited to the imaging devices described above, but can also include projectors, for example. The optical elements are not limited to lenses, but can also include prisms, for example.

[0045] <Examples> Next, examples and comparative examples of the present invention will be described. However, the present invention is not limited in any way by the following examples.

[0046] <Examples 1 and 2> A flat plate-shaped cycloolefin polymer (COP resin) was used as the substrate 10. The refractive index of the cycloolefin polymer used at a wavelength of 550 nm was 1.54. SiO was added to the low refractive index layer 21. ２ Using TiO ２ A total of six alternating layers 20 were laminated onto the substrate 10 with the physical film thicknesses shown in the table below. Subsequently, a magnesium fluoride layer 30 and an uppermost layer 40 with the physical film thicknesses shown in the table below were laminated. The alternating layers 20, magnesium fluoride layer 30, and uppermost layer 40 were each laminated by vacuum deposition. In the table, "layer 7" refers to the magnesium fluoride layer 30, and "layer 8" refers to the uppermost layer 40. ２ The refractive index at a wavelength of 550 nm is 1.46, MgF ２ The refractive index at a wavelength of 550 nm is 1.38, TiO ２The refractive index at a wavelength of 550 nm was 2.04 for the second layer and 2.13 for the fourth and sixth layers. Since film deposition on resin substrates is performed under relatively lower heating conditions compared to film deposition on glass substrates, it is thought that the temperature inside the deposition apparatus gradually increased due to radiant heat when the deposition material is melted, causing the refractive index to fluctuate between layers close to and far from the substrate. In addition, the spectral reflectance of light at an incident angle of 0 degrees was determined by simulation.

[0047] After film formation, the presence or absence of cracks was visually checked. In addition, a dry piece of Silbon paper was folded into eight and rubbed against the surface with loads of 200g, 300g, 400g, and 500g using a rubbing tester, and the same area was rubbed back and forth 20 times. After that, the surface was visually observed to check for the occurrence of scratches. <Examples 3-9> The spectral reflectance of light at an incident angle of 0 degrees was determined by simulation when each layer having the physical film thickness described in the attached table was laminated on the substrate 10 (software used: TFCalc). In Example 3, the value obtained was obtained when acrylic resin was used for the substrate 10. The refractive index of the acrylic resin at a wavelength of 550 nm was assumed to be 1.49.

[0048] <Example 10> The spectral reflectance of light at an incident angle of 0 degrees when a total of 8 alternating laminated layers 20 are laminated on the substrate 10 was determined by simulation. In the attached table, "Layer 9" is the magnesium fluoride layer 30, and "Layer 10" is the top layer 40. The rest is the same as in Example 3.

[0049] <Example 11> The spectral reflectance of light at an incident angle of 0 degrees when a total of 10 alternating laminated layers 20 are laminated on the substrate 10 was determined by simulation. In the attached table, "Layer 11" is the magnesium fluoride layer 30, and "Layer 12" is the top layer 40. The rest is the same as in Example 3.

[0050] Figures 5 to 15 are spectral reflectance graphs showing the relationship between wavelength (nm) and reflectance (%) for each of Examples 1 to 11. The following table shows the film deposition data and test results for each example. In the abrasion test of Example 1, no scratches were observed at loads of 200g, 300g, 400g, and 500g.

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059] <Comparative Example 1> Similar to Example 3, a cycloolefin polymer was used for the base material 10, and the values ​​were simulated when the alternating laminated layers 20 shown in the table below were laminated. In this comparative example, the magnesium fluoride layer 30 and the top layer 40 were not laminated.

[0060] <Comparative Examples 2 and 3> In Comparative Examples 2 and 3, the alternating laminate layers 20 described in the table were laminated onto the cycloolefin polymer substrate 10, similar to Example 1. However, the top layer 40 was not laminated onto the anti-reflective film 1. The anti-reflective film 1 in Comparative Example 2 was evaluated for post-deposition cracking in the same manner as in Example 1. The anti-reflective film 1 in Comparative Example 3 was evaluated for post-deposition cracking and the presence or absence of scratches in the same manner as in Example 1.

[0061] Figures 16 and 17 are graphs of spectral reflectance of light at an incident angle of 0 degrees, showing the relationship between wavelength (nm) and reflectance (%) for Comparative Example 1 and Comparative Example 3, respectively. The following table shows the film deposition data and test results for each comparative example. In the abrasion test of Comparative Example 3, scratch formation was confirmed at loads of 200g, 300g, 400g, and 500g.

[0062]

[0063]

[0064]

[0065] <Evaluation> According to Examples 1 to 11, it was confirmed that a suitable low reflectivity can be obtained with the anti-reflective film 1 in this embodiment. Furthermore, according to Examples 10 and 11, even when the alternating laminated layers 20 consist of 8 and 10 layers, an anti-reflective film 1 with suitable anti-reflective performance can be obtained.

[0066] Furthermore, Comparative Example 1 confirmed that an anti-reflective film without the magnesium fluoride layer 30 and the top layer 40 could not obtain satisfactory anti-reflective performance. Furthermore, Comparative Example 2 confirmed that cracks occurred after film formation when the first layer was not made of a material with compressive stress. According to Comparative Example 3, it was confirmed that when the top layer 40 was not provided, the film was unsuitable for friction tests and could not obtain sufficient strength.

[0067] 1: Anti-reflective coating, 10: Substrate, 20: Alternating laminated layers, 21: Low refractive index layer, 22: High refractive index layer, 30: Magnesium fluoride layer, 40: Top layer, DSLR / CAM: Imaging device, 101: Camera body, 102: Lens barrel, 103: Imaging lens, 104: Sensor chip, 105: Glass substrate, 106: Multi-chip module, B1: Release button, B2: Function button, EF: Auxiliary light emitter, M: LCD monitor, WL: Imaging lens

Claims

1. An anti-reflective film comprising a plurality of layers laminated on a resin substrate, comprising: an alternating laminated layer formed on the substrate, in which layers having a refractive index of 1.35 or more and 1.55 or less at a wavelength of 550 nm and layers having a refractive index of 2.00 or more and 2.35 or less are alternately laminated; a magnesium fluoride layer containing magnesium fluoride formed on the alternating laminated layer; and an uppermost layer formed on the magnesium fluoride layer, having a refractive index of 1.55 or less at a wavelength of 550 nm and an optical film thickness of 3 nm or more and 110 nm or less corresponding to a wavelength of 550 nm, wherein the layer of the alternating laminated layer located closest to the substrate has a refractive index of 1.35 or more and 1.55 or less at a wavelength of 550 nm, has compressive stress, and an optical film thickness of 135 nm or more and 490 nm or less corresponding to a wavelength of 550 nm.

2. The anti-reflective film according to claim 1, wherein the total physical film thickness, which is the sum of the physical film thicknesses of the alternating laminated layer, the magnesium fluoride layer, and the uppermost layer, is 350 nm or more and 600 nm or less.

3. The anti-reflective film according to claim 2, wherein the ratio of the physical film thickness of the magnesium fluoride layer to the total physical film thickness is 0.01 or more and 0.35 or less.

4. The anti-reflective film according to any one of claims 1 to 3, wherein the ratio of the physical film thickness of the magnesium fluoride layer to the sum of the physical film thicknesses of the layers with a refractive index of 1.35 or more and 1.55 or less among the alternating laminated layers and the uppermost layer is 0.03 or more and 0.63 or less.

5. The anti-reflective film according to any one of claims 1 to 4, wherein the ratio of the physical film thickness of the magnesium fluoride layer to the physical film thickness of the layer located closest to the substrate among the alternating layers is 0.05 or more and 1.2 or less.

6. The anti-reflective film according to any one of claims 1 to 5, wherein the ratio of the physical film thickness of the layer located closest to the substrate among the layers of the alternating laminate to the sum of the physical film thicknesses of the layer having a refractive index of 1.35 or more and 1.55 among the layers of the alternating laminate is 0.4 or more and 0.95 or less.

7. The anti-reflective film according to any one of claims 1 to 6, wherein the ratio of the physical film thickness of the uppermost layer to the physical film thickness of the magnesium fluoride layer is 0.02 or more and 4.3 or less.

8. The alternating laminated layer consists of a first layer, a second layer, a third layer, a fourth layer, a fifth layer, and a sixth layer from the layer closer to the substrate. At a reference wavelength λ = 550 nm, the refractive index (n λ ) of the first layer is 1.35 or more and 1.55 or less, and the optical film thickness (n λ × d) is 135 nm or more and 490 nm or less. The refractive index (n λ ) of the second layer is 2.00 or more and 2.35 or less, and the optical film thickness (n λ × d) is 8 nm or more and 50 nm or less. The refractive index (n λ ) of the third layer is 1.35 or more and 1.55 or less, and the optical film thickness (n λ × d) is 30 nm or more and 100 nm or less. The refractive index (n λ ) of the fourth layer is 2.00 or more and 2.35 or less, and the optical film thickness (n λ × d) is 55 nm or more and 180 nm or less. The refractive index (n λ ) of the fifth layer is 1.35 or more and 1.55 or less, and the optical film thickness (n λ × d) is 3 nm or more and 65 nm or less. The refractive index (n λ ) of the sixth layer is 2.00 or more and 2.35 or less, and the optical film thickness (n λ × d) is 60 nm or more and 160 nm or less. The optical film thickness (n λ × d) of the magnesium fluoride layer is 13 nm or more and 150 nm or less. The antireflection film according to any one of claims 1 to 7.

9. The anti-reflective film according to any one of claims 1 to 8, wherein the alternating laminated layers consist of 6 to 10 layers.

10. The anti-reflective film according to any one of claims 1 to 9, wherein the layer having a refractive index of 2.0 or more and 2.30 or less is titanium oxide.

11. The anti-reflective film according to any one of claims 1 to 10, wherein the layer with a refractive index of 1.35 or more and 1.55 or less is a silicon oxide.

12. An anti-reflective film comprising multiple layers laminated on a resin substrate, wherein the layers are numbered from the layer in contact with the substrate, namely the first, second, third, fourth, fifth, sixth, seventh, and eighth layers, and at a reference wavelength λ = 550 nm, the first layer is silicon oxide, and the optical film thickness (n λ ×d) is 135 nm to 490 nm, the second layer is titanium oxide, and the optical film thickness (n λ ×d) is 8 nm or more and 50 nm or less, the third layer is silicon oxide, and the optical film thickness (n λ ×d) is 30 nm or more and 100 nm or less, the fourth layer is titanium oxide, and the optical film thickness (n λ ×d) is 55 nm to 180 nm, and the fifth layer is silicon oxide, and the optical film thickness (n λ ×d) is 3 nm or more and 65 nm or less, and the sixth layer is titanium oxide, and the optical film thickness (n λ ×d) is 60 nm to 160 nm, and the seventh layer is magnesium fluoride, and the optical film thickness (n λ ×d) is 13 nm to 150 nm, and the 8th layer is silicon oxide, and the optical film thickness (n λ An anti-reflective coating in which ×d) is between 3 nm and 110 nm.

13. The anti-reflective film according to any one of claims 1 to 12, wherein the reflectance for light with a wavelength of 450 nm or more and 650 nm or less is 0.3% or less.

14. An optical element comprising an anti-reflective coating according to any one of claims 1 to 13.

15. An optical element having an anti-reflective film according to any one of claims 1 to 13 on a substrate, wherein the substrate comprises at least one of acrylic resin, COP (cycloolefin polymer) resin, polyethylene resin, polypropylene resin, polyester resin, ethylene vinyl copolymer resin, polyvinyl chloride resin, cellulose resin, polyamide resin, polyimide resin, polycarbonate resin, polystyrene resin, and vinyl acetate resin.

16. An optical system comprising the optical element described in claim 14 or 15.

17. An optical apparatus including the optical system described in claim 16.

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