JPS59208501A - Five layer reflection preventive film - Google Patents

Abstract

PURPOSE:To widen a low reflection wavelength area, and also to obtain durability which is excellent physically and chemically, by using two kinds of materials of high and low refractive indexes for forming the first, the third and the fifth layers, and the second and the fourth layers by a low refractive layer and a high refractive layer, respectively. CONSTITUTION:The first layer, the third layer and the fifth layer, counting from the air side to a substrate side, of a reflection preventive film consisting of a thin film of five layers provided on the surface of the substrate whose refractive index is within a range of 1.4-1.85 consists of a substance of the same low refractive index whose refractive index is within a range of 1.35-1.47, for instance, MgF2, and the second layer and the fourth layer are formed by a substance of the same high refractive index whose refractive index is within a range of 2.0-2.4, for instance, ZrO2. Also, each optical film thickness n1d1-n5d5 of the first - the fifth layers is optimized so as to have each value of n1d1=(0.25+ or -0.2)lambda0, n2d2=(0.55+ or -0.05)lambda0, n3d3= (0.1+ or -0.05)lambda0, n4d4= (0.1+ or -0.05)lambda0, and n5d5=(0.1+ or -0.8)lambda0(lambda0 is a design wavelength). In this way, by the lambda/4-lambda/2-lambda/4 constitution fundamentally, the lambda/4 layer contacting with the substrate is formed by placing the high refractive index layer between the low refractive index layers, and a good reflection preventive film is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an anti-reflection film for optical bodies used in the visible light region, which is composed of a five-layer interference thin film provided on a substrate with a refractive index of about 1.4 to 1.85. It concerns membranes.

BACKGROUND ART Conventionally, it has been widely practiced to apply an antireflection film to reduce surface reflection on camera lenses, eyeglasses, and the like. In this case, the structure of the anti-reflection film is a single-layer anti-reflection film in which a thin film of a low refractive index material is formed to an optical thickness of approximately 1/4 of the wavelength to be prevented from reflection, or a film with two types of refractive index, low and high. A two-layer anti-reflection film made of a material sequentially formed from the air side to a thickness of (λ/4-λ/2), and furthermore, 3's in low and high! Materials with refractive indexes of λ/4-λ/
A three-layer anti-reflection film formed to a thickness of 2-λ/4 and a material with a low, high, medium and low refractive index are layered from the air side, making the film thickness of each layer 2/4.
-λ/2-λ/4-λ/4 four-layer antireflection film is known as a typical example.

Among these antireflection films, an antireflection film having three or more layers is required in order to achieve low reflectance in a wide wavelength range such as the entire visible light range. However, in order to obtain a three-layer or four-layer antireflection film as described above, three types of materials are required whose refractive indexes have an appropriate relational expression, and furthermore, the relational expression should be Since the refractive index of the substrate is included, if you try to obtain an optimal solution for different substrates, you will have to prepare film materials with different refractive indexes depending on the refractive index of the substrate. .

In view of this point, the present inventor has developed the conventionally known λ
/4-λ/2-2/a three-layer antireflection film,
Various studies were conducted on a structure that satisfies the above characteristics by replacing the two layers and four layers of intermediate refractive index in contact with the substrate with three-layer symmetrical equivalent films.

In this case, there are two methods for forming the symmetrical bilayer: a low refractive index material is sandwiched between high refractive index materials, or a high refractive index material is sandwiched between low refractive index materials. These two methods have exactly the same effect at the center wavelength used for design, but different effects at the peripheral wavelengths. US Pat. No. 3,565,509 discloses the former method, that is, an example using symmetrical equivalent films in which a low refractive index material is sandwiched between high refractive index materials. In this case, the optical properties are improved compared to the original three-layer film, and the high refractive index material layer on the opposite side of the substrate of the symmetrical five-layer film is continuous with the original second layer. has the advantage in terms of production that it can have a four-layer structure. However, it has been found that the desired low reflectance characteristics cannot be obtained at peripheral wavelengths, and that the durability between the fifth layer of high refractive index material following the substrate and the substrate is insufficient. It was done.

The present inventor paid attention to this point, and basically, λ/4-
λ in contact with the substrate of the 5-layer anti-reflection film with λ/2-λ/4 configuration
It has been found that the above drawbacks can be improved by replacing the /4 layer with a symmetrical three-layer equivalent film in which a high refractive index material layer is sandwiched between low refractive index layers. Furthermore, in the present invention, the present invention does not stop at simply replacing both films with the same film, but by using the five-layer structure obtained as described above as the original structure, and further optimizing the film thickness of each layer, the first to fifth layers are In addition to specifying the optical film thickness within a predetermined range, the 1st, 3rd and 5th layers should be made of the same low refractive index material, and the 2nd and 4th layers should be made of the same high refractive index material, reflectance characteristics, It has been found that it is possible to obtain an antireflection film that is very satisfactory in terms of productivity, durability, etc.

That is, the gist of the present invention is an antireflection film consisting of a five-layer thin film provided on the surface of a transparent substrate having a refractive index in the range of 1.40 to 1.85, the air side of the antireflection film being The first layer, the third layer, and the fifth layer counting from the side toward the substrate are made of the same low refractive index material having a refractive index in the range of 1.35 to 1.47, and the second layer and The fourth layer has a refractive index of 2.0
The optical film thickness of the first layer, second layer, third layer, fourth layer, and fifth layer is n1(!1 tlJd! +n1( 11,214 (1
4t''56s relates to a five-layer antireflection film that satisfies the following range.

nl a! x (0,25±0,2)λOs n Snow d Goose= (0,55±0.05')λ0nBdl=(
0,1±o,os)λo+n4a4=(0,1±
O, [15) λ0n5d5-(0,100, Oa) λ0
(λ0 is the design wavelength) The present invention will be explained in more detail below.

FIG. 1 is a cross-sectional view of an optical body according to an embodiment of the present invention, in which a five-layer antireflection film is applied on a transparent substrate having a refractive index in the range of 1.4 to 1.85. Yes, in the figure,
1 is a transparent or translucent substrate, 2 is a first layer, 5 is a second layer, 4 is a fifth layer, 5 is a fourth layer, and 6 is a fifth layer.

The five-layer antireflection film of the present invention is the three-layer antireflection film (λ
/4-λ/2-2/a) is the prototype. As shown in FIG. 2, this three-layer anti-reflection film is formed as a first layer 12 on the surface of the substrate 11 with an optical film thickness of λ/, counting from the air side.
A layer of a low refractive index substance having a refractive index of 1.35 to 1.47 is formed as the second layer #15, and a layer of a low refractive index material with an optical thickness of λ/2 is formed as the second #15.
A layer of a material with a high refractive index of 0 to 2.4 is formed, and a layer of an intermediate refractive index material with an optical thickness of 2/4 is formed as the third layer 14. For example, when the substrate is glass with a refractive index of 1.52 and the low refractive index material of the first layer is MfF2 with a refractive index of 1.38, the refractive index of the third layer 14 described above is a three-layer antireflection film. According to the condition (t's = nt 1'n6), approximately 1
．． An intermediate refractive index of 38 x 6 = 1.70 is often required, and the substrate is glass with a refractive index of 1.73, and the first
When the low refractive index material of the layer is MfF2 with a refractive index of 1.38, the condition of the three-layer antireflection film (n3=nly'; ) is approximately 1.38 rate will be required. The structure of the former three-layer antireflection film is as shown in Table 1, and its antireflection properties are as shown in curve 21 in FIG. 3.

Further, the structure of the latter three-layer antireflection film is rough as shown in Table 2, and its antireflection properties are consistent with curve 31 in FIG.

As is clear from the curve 21 in FIG. 3 and the curve 51 in FIG. 4, it is recognized that such a three-layer antireflection film has a narrow low reflection wavelength region.

Table 1 Table 2 Invention (Koji) The third layer with an intermediate refractive index of λ/4 of the three-layer antireflection film described above is combined with the high refractive index layer of 2.0 to 2.4 with a refractive index of 1. Symmetry 3 sandwiched between low refractive index layers of 35 to 1.47
It is characterized by approximation using a layered film, and the configuration of a specific example thereof is shown in Table 5.4.

In Table 5, the optical film thickness 1, which is the initial value of the film thickness of each layer of the five-layer antireflection film, was optimized using a computer. The antireflection properties of the five-layer antireflection coating having the initial value of optical thickness l with the configuration shown in Table 3 are as shown by the curve 22 in FIG. The antireflection properties of the five-layer antireflection film having a thickness of 1 are as shown by curve 23 in FIG.

Similarly, in Table 4, the optical film thickness is a book in which the optical film thickness (2), which is the initial value of the film thickness of each layer of the five-layer antireflection film, is optimized using a computer. The antireflection properties of the five-layer antireflection coating having the initial value of optical thickness 1 and having the configuration shown in Table 4 are as shown by curve 32 in FIG. The antireflection properties of the five-layer antireflection film having the following properties are as shown by curve 55 in FIG. Third
Curve 25 in the figure is compared to curves 21 and 22, and curve 33 in Figure 4 is compared to curves 31 and 32, indicating that sufficiently low reflectance can be achieved over the entire visible range. It is recognized that it is a very satisfactory anti-reflection film as the reflected color is hardly perceptible due to its flat properties.

The material forming the low refractive index layer used for the first and third layers having a refractive index of 1.35 to 1.47 in the present invention is MtF.
2, Na5A11'6, 5in1, etc. are used.

Among them, is MV the best material for the low refractive index layer? , is stability.

It is ideal because it has excellent abrasion resistance, moisture resistance, and other physical and chemical properties, and it is easy to form a film. In addition, materials for forming the high refractive index layer used for the third and fifth layers with a refractive index of 2.0 to 2.4 include Zr0B, Y2O3, and Oa0.
2, 0r103 HTa! Og, T1.02,
Tt)02, ZnS, a mixture thereof, etc. are used. Among them, ZrO2 or ZrO2 is the main component and T10! Those containing the above are particularly excellent in terms of ease of film formation and stability.

In particular, in the present invention, the 1st, 3rd, and 5th layers of the 5-layer antireflection film are made to have low levels, so that the amount of materials used can be reduced, stable layers can be easily obtained, and the 1C flexibility can be improved. The same material is used for the refractive index material and the high refractive index materials for the second and fourth layers, so that a five-layer anti-reflection film consisting of two types of high and low refractive index materials is constructed.

As explained above, according to the five-layer antireflection film of the present invention in which the optical thickness and refractive index range of the first to fifth layers are specified, the low refractive index layer of the first to fifth layers is The second and fourth high refractive index layers are made of only two types of materials with high and low refractive indexes, and have a wide low reflection wavelength range for substrates with a refractive index of 1.4 to 1.85. Moreover, it is possible to obtain an antireflection film that has high physical and chemical durability and also has good productivity.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a five-layer antireflection film according to the present invention, Figure 2
The figure is a cross-sectional view of a conventional three-layer antireflection coating, and FIG. FIG. 4 is a graph showing spectral reflectance curves of the antireflection films of the conventional example and the example of the present invention listed in Tables 2 and 4. 1: Substrate, 2: First layer, 3: Second layer, 4: Third layer, 5:
4th layer, 6; 5th layer. αJ Sail Trapsai Nibegawa. Q, 6 0. /.

Claims (1)

[Claims] (1) An antireflection film consisting of a 95-layer thin film provided on the surface of a substrate having a refractive index in the range of 1.4 to 1.85,
Counting from the air side to the substrate side of the antireflection film, the first, third, and fifth layers have a refractive index of 1.35 to 1.4.
The second layer and the fourth layer are made of the same high refractive index material with a refractive index in the range of 2.0-2.4, and the first layer is made of the same high refractive index material with a refractive index in the range of 2.0-2. layer. Optical film thickness of 2nd layer, 3rd layer, 4th layer and 5th layer nl d
l + nldl + “8dM + n4d4 T
``1ldll is characterized by satisfying the following range 5
layer anti-reflective coating. nldlm (Q, 25±0.2)λ(1+ Jdl−
(α55±0.05)λOnmdm-(aI±0.05
)λ6, n4d4sx (0,1±0.05)λ
. 11Bds== (Q, 1±0.08)λ0 (λ0
is the design wavelength) (2) The low refractive index material is MflF, and the high refractive index material is Z r O! or Tie, Z containing
The five-layer antireflection film according to claim 1, characterized in that it is rO2.