JP3426286B2 - Moisture resistant anti-reflective coating - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component such as a lens and a prism constituting an optical apparatus, and more particularly to an antireflection film for an optical component used in a high humidity atmosphere. 2. Description of the Related Art Conventionally, an antireflection film used for an optical component such as a lens or a prism constituting an optical apparatus is made of, for example, MgF ₂ as a low refractive index material and ZrO as a high refractive index material. ₂ is used. More specifically, on the optical glass substrate (BK7) 4 a refractive index of 1.52, as shown in FIG. 3, at the design wavelength lambda ₀ = 550 nm, the consisting MgF ₂ having an optical thickness of lambda _0/16 more 3a, the second layer 3b made of ZrO ₂ having an optical thickness of λ _0/8, the third layer 3c made of MgF ₂ having an optical thickness of λ _0/16, an optical film thickness lambda
_0/4 of the fourth layer 3d formed of ZrO _2, the anti-reflection film 3 is formed, further comprising a fifth layer 3e consisting of MgF ₂ having an optical thickness of lambda _0/4. However, in such an antireflection film, in a high-humidity atmosphere where water droplets are formed on the film surface, when the water droplets evaporate over a long period of time, a white cloudy flow mark appears on the portion where the water droplets are formed. Remains. This flow mark has a problem that it does not easily fall off even when wiped with a solvent such as alcohol. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to easily wipe off the flow marks remaining after evaporation after water droplets are formed on the surface of the antireflection film by exposure to a high humidity atmosphere. It is an object of the present invention to provide an antireflection film having a high moisture resistance. SUMMARY OF THE INVENTION As a result of intensive studies, the present inventors have found that HfO ₂ is used as a high refractive index material and SiO _{2 is} used as a low refractive index material.
It has been found that the above object can be achieved by using. The present invention has been completed based on such findings. That is, the antireflection film according to the present invention is characterized in that it has a layer using HfO ₂ as a high refractive index material and a layer using SiO ₂ as a low refractive index material. As described above, the antireflection film according to the present invention is formed by combining a layer using HfO ₂ as a high refractive index material and a layer using SiO ₂ as a low refractive index material. And an appropriate optical film thickness in accordance with the desired reflection characteristics. The method for forming the film is not particularly limited, and examples thereof include a vacuum deposition method and a sputtering method. FIG. 1 shows an example of the configuration of the antireflection film of the present invention. In FIG. 1, the antireflection film 1 is composed of five layers,
Optical film thickness λ _0/1 at design wavelength λ ₀ on optical glass substrate 2
The first layer 1a made of 2 of SiO _2, an optical film thickness lambda _0/12
Second layer 1b consisting of HfO _2, the third layer 1c made of SiO ₂ having an optical thickness of λ _0/12, having an optical thickness of λ _0/4 Hf
Fourth layer 1d consisting of O _2, SiO ₂ having an optical thickness of lambda _0/4
The fifth layer 1e made of is sequentially formed. [0008] HfO ₂ and SiO ₂ are excellent in moisture resistance, and by forming an appropriate film structure using them, desired antireflection characteristics and moisture resistance can be obtained. Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. Example 1 One of the crown glasses BK7 (refractive index = 1.5
The glass substrate composed of 2) is heated to 250 ° C., and the optical film thickness λ ₀ at a design wavelength λ ₀ = 550 nm by a vacuum evaporation apparatus.
/ 12 first layer of SiO ₂ of the optical thickness of lambda _0/12
Second layer consisting of HfO _2, Si having an optical thickness of lambda _0/12
Third layer consisting of O _2, the fourth layer of HfO ₂ having an optical thickness of λ _0/4, successively forming a fifth layer of SiO ₂ having an optical thickness of λ _0/4, to prepare an anti-reflection film . The reflectance characteristic of this antireflection film has a wavelength of 470 to 6 as shown in FIG.
It shows excellent antireflection characteristics with a reflectance of 0.5% or less in a range of 20 nm. [0011] Comparative Example 1 the BK7 glass substrate was heated to 250 ° C., optical thickness at a design wavelength lambda ₀ = 550 nm by a vacuum vapor deposition apparatus lambda _0/16
The first layer of the MgF _2, ZrO optical film thickness lambda _0/8
Second layer consisting of _2, a third layer of MgF ₂ having an optical thickness of lambda _0/16, a fourth layer of ZrO ₂ having an optical thickness of lambda _0/4, further optical film thickness lambda _0/4 of MgF ₂ Was sequentially formed to form an antireflection film. The reflectance characteristic of this antireflection film has a wavelength of 470 to 62 as shown in FIG.
In the range of 0 nm, the reflectance is 0.5% or less, indicating excellent antireflection characteristics. [0012] Moisture resistance test After water droplets made of pure water were placed on the antireflection films prepared in the above Examples and Comparative Examples, the film was allowed to stand in an atmosphere of a temperature of 65 ° C and a relative humidity of 95% for 14 hours to evaporate the water droplets. Observation of the traces showed that small flow marks remained on the anti-reflection film formed in Example 1, but when the portions were wiped with alcohol, the flow marks disappeared. On the other hand, in the anti-reflection film formed in Comparative Example 1, a large flow mark remained on the trace of the evaporation of the water droplet, and the flow mark remained without disappearing even if the portion was wiped with alcohol. Therefore, it is understood that the antireflection film of the present invention is comparable in reflection characteristics to the conventional one, and has remarkably improved in moisture resistance. The antireflection film of the present invention has a wavelength of 470-6.
Exhibits an antireflection effect with a reflectance of 0.5% or less at 20 nm,
Moreover, it has an excellent moisture resistance effect. Therefore, the antireflection film of the present invention is most suitable as an antireflection film for an optical component used in a high humidity atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing a configuration of an antireflection film showing one embodiment of the present invention. FIG. 2 is a graph showing a reflectance characteristic of an antireflection film formed in Example 1 of the present invention. FIG. 3 is an explanatory view showing a configuration of a conventional antireflection film. FIG. 4 is a graph showing a reflectance characteristic of an anti-reflection film prepared in Comparative Example 1. [Description of Signs] 1 Anti-reflection film 1a First layer 1b Second layer 1c Third layer 1d Fourth layer 1e Fifth layer 2 Glass substrate 3 Anti-reflection film 4 Glass substrate

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-128829 (JP, A) JP-A-1-246502 (JP, A) JP-A-4-42201 (JP, A) JP-A-5-205 173216 (JP, A) JP-A-61-159602 (JP, A) JP-A-58-35501 (JP, A) JP-A-63-81404 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) G02B 1/11

Claims (1)

(57) [Claims 1 optical anti-reflection film formed on a glass substrate, an optical film thickness lambda _0/12 from the optical glass substrate side first layer when the design wavelength is lambda ₀ SiO ₂ layer, HfO ₂ layer of the second layer having an optical thickness λ _0/12, SiO ₂ layer of the third layer having an optical thickness λ _0/12, HfO fourth layer is an optical film thickness lambda _{0/4 two} layers, moisture antireflection film fifth layer is characterized by being composed of five layers is SiO ₂ layer having an optical thickness of λ _0/4.