JPH0836101A - Antireflection film of optical parts made of synthetic resin - Google Patents

Abstract

PURPOSE:To provide an antireflection film which is formed of a three-layered structure on the surface of optical parts made of a synthetic resin and with which as-designed optical characteristics are obtainable by simple optical designing and environmental resistance is excellent. CONSTITUTION:This antireflection film is formed by depositing a chromium layer 2 having a film thickness <=15nm (ideally <=5nm) as a first layer, a cerium dioxide layer 3 as a second layer and a silicon dioxide layer 4 as a third layer on the surface of an acrylic substrate (optical parts) 1. Although the antireflection film is physically formed of the three-layered structure, the chromium layer 2 is extremely thinly formed and, therefore, the execution of the optical designing by taking only the refractive indices and layer thicknesses of the cerium dioxide layer 3 and the silicon dioxide layer 4 suffices. The as- designed stable optical characteristics (spectral reflectivity) is thus obtd. and the environmental resistance performance is improved by the excellent affinity and adhesion property of the chromium layer 2 to the acrylic resin substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film for synthetic resin optical parts, which is made of synthetic resin objective lenses used in optical pickups for CD players and various synthetic resin such as video cameras and still cameras. The present invention relates to a structure of an antireflection film which is applied to optical parts and also serves as a surface protective film for those parts.

[0002]

2. Description of the Related Art Inorganic glass has been used for optical components such as lenses, but recently synthetic resins such as acrylic are used as optical component materials because they are easy to process, lightweight and inexpensive. Is often applied as. In this case, the optical component made of synthetic resin has a high light reflectance as in the case of the inorganic glass and is easily scratched due to its low hardness, so that an antireflection film that also serves as a protective film is applied.

Although a single layer antireflection film is generally made of magnesium fluoride (MgF ₂ ), various antireflection films having a three-layer structure have been proposed in order to improve spectral reflection characteristics. ing. For example, on the surface of an optical component made of acrylic resin, silicon dioxide is sequentially formed from the surface side.
(SiO ₂ ) layer, zirconium dioxide (ZrO ₂ ) layer and silicon dioxide (SiO ₂ ) layer formed, or silicon dioxide (SiO ₂ ) layer, aluminum trioxide (Al ₂ O ₃ ) layer and silicon dioxide ( Si
O ₂ ) layer formed (the above is JP-A-59-204801),
Silicon dioxide (SiO ₂₎ layer and magnesium fluoride (MgF ₂₎ layer and the silicon dioxide that was deposited (SiO ₂₎ layer (JP 60-1297
01), silicon dioxide (SiO ₂ ) layer and cerium dioxide (Ce)
There has been proposed one in which an O ₂ ) layer and a silicon dioxide (SiO ₂ ) layer are formed.

Further, the spectral reflectance of each of the above antireflection films is 2.8 for incident light having a wavelength range of 740 to 840 nm.
However, in Japanese Patent Laid-Open No. 63-121801, as shown in FIG. 3, a silicon monoxide (SiO) layer 12 and a cerium dioxide (SiO 2) layer are formed on the surface of the acrylic resin substrate 1. CeO ₂ )
We have proposed an antireflection film in which the layer 13 and the silicon dioxide (SiO ₂ ) layer 14 are formed. According to the proposal, the spectral reflectance of incident light in the same wavelength range as described above is 0.5% or less. It is possible to

Generally, a vacuum deposition method is adopted as a method of forming an antireflection film, and in the case of inorganic glass, it is 2
The substrate is heated at 00 to 400 ° C. to obtain a strong vapor-deposited film. However, in the case of synthetic resin, deterioration and decomposition occur due to heating. Therefore, vacuum vapor deposition should be performed at a temperature of 60 ° C. or lower. I am trying to do it.

[0006]

By the way, Japanese Patent Laid-Open No. 63-1
The antireflection film of No. 21801 seems to have obtained an extremely excellent spectral reflectance, but when designing the spectral reflection characteristics, silicon monoxide (SiO) formed as the first layer on the surface of the acrylic resin substrate 1 The refractive index of the layer 12 must be taken into account strictly. Actually, an antireflection film having a three-layer structure designed based on almost the same specifications (specifications of the following Table 1) as in the example of JP-A-63-121801 was prepared, but the refractive index and the film thickness were If a slight design / manufacturing error occurs, the above spectral reflection characteristics cannot be obtained, and the weather resistance test (60 ° C, 90%, 168h) and thermal shock test (70 ° C to -30 ° C, 1h, 200 cycles)
As a result, many cracks were generated in the antireflection film, and a practically satisfactory product was not obtained.

[0007]

[Table 1] (Note) PMMA: Polymethylmethacrylate

In particular, since silicon monoxide (SiO) is a metastable oxide, it is rare that it is formed as a pure compound in which oxygen atoms are bonded to silicon atoms in a ratio of 1: 1. When exposed to a medium atmosphere, the number of moles of oxygen atoms tends to decrease, and the variation causes the refractive index of the layer of silicon monoxide (SiO) to change, resulting in an antireflection film. There was a tendency that the spectral reflectance of was unstable.

On the other hand, it is natural that the objective lens of an optical pickup and various optical parts such as a video camera and a still camera should have a small spectral reflectance, but the average of incident light in the wavelength range of 700 to 840 nm is desirable. To 5
It is sufficient that the content is ˜6% or less, rather it is more important that the design of the optical thin film is simple and that the antireflection film having stable optical characteristics can be formed based on the design. Therefore,
The present invention focuses on the fact that chromium (Cr) is a stable material and is optimal as a film forming material for the first layer formed on the surface of an optical component made of acrylic resin, and has solved the problems of the prior art. It was created with the aim of providing a barrier.

[0010]

The present invention provides a synthetic resin having a three-layer structure in which a first layer, a second layer and a third layer are laminated on a surface of a synthetic resin optical component in order from the surface side. In the antireflection film of the optical component, the first layer has a thickness of 15 n.
The present invention relates to an antireflection film for a synthetic resin optical component, characterized in that the second layer is a cerium dioxide layer and the third layer is a silicon dioxide layer.

[0011]

The first chrome layer has extremely good adhesion and affinity with the synthetic resin, contributes to the prevention of cracks (film cracks) as the base layer, and the film damage of all three layers due to film stress is The compressive stress of the first chrome layer, the tensile stress of the second cerium dioxide layer, and the compressive stress of the third silicon dioxide layer are balanced to prevent film breakage in a stable state as a whole. . The cerium dioxide layer and the silicon dioxide layer have an antireflection function at the used wavelength, and the silicon dioxide layer on the outermost surface side functions as a protective film having environmental resistance.

In particular, in the case of the present invention, it is possible to stably form the first chromium layer as a thin film having a thickness of tens of nanometers or less and to have a negligible optical characteristic, and to physically form a three-layer structure. However, the optical design can be performed by considering only the refractive index and the layer thickness of the second cerium dioxide layer and the third silicon dioxide layer, which simplifies the design and stabilizes the design. The obtained optical characteristics can be obtained.

[0013]

EXAMPLES Examples of the "antireflection film for synthetic resin optical components" of the present invention will be described in detail below with reference to FIGS. The antireflection film of this example has a three-layer structure as shown in FIG. 1, and comprises a chromium (Cr) layer 2 and a chromium (Cr) layer 2 in order from the surface side of an acrylic resin substrate 1 corresponding to an optical component such as a lens.
Cerium dioxide (CeO ₂ ) layer 3 and silicon dioxide (SiO ₂ ) layer 4
Are formed.

In the production thereof, each layer is first applied to the surface of the acrylic resin substrate 1 by an electron gun vapor deposition method in a high vacuum (1/10 ⁵ Torr or less) / normal temperature (23 to 25 ° C.) atmosphere. Chromium layer 2 is vapor-deposited as a layer and the chromium layer 2
A cerium dioxide layer 3 is vapor-deposited as a second layer thereon, and a silicon dioxide layer 4 is vapor-deposited as a third layer on the cerium dioxide layer 3 to form a three-layer structure. In that case, the vapor deposition control is performed so that the first chromium layer 2 has a thickness of 15 nm or less, preferably 5 nm or less. The thickness of the second layer cerium dioxide layer 3 and the third layer silicon dioxide layer 4 is λ (= 700-
840 nm) and its optical film thickness (= refractive index × film thickness)
Is controlled to be about (λ / 4).

The refractive index of the acrylic resin substrate 1 and the film thickness of the chromium layer 2 and the refractive index and film thickness of the cerium dioxide layer 3 and the silicon dioxide layer 4 in this example are as shown in Table 2 below.

[Table 2]

The feature of this embodiment is that the chromium layer 2 is used as described above.
Is extremely thin, and the effect of the optical refractive index can be ignored while obtaining a sufficient transmittance. That is, such a condition can be realized by forming the chrome layer 2 as thin as possible within the range of 15 nm or less,
Moreover, chromium (Cr) itself has a good affinity with the acrylic resin (PMMA) and cerium dioxide (CeO ₂ ), and exhibits excellent adhesion between the acrylic resin substrate 1 and the cerium dioxide layer 3.

Further, the cerium dioxide layer 3 and the silicon dioxide layer 4
Has an antireflection function in the wavelength range of incident light used, and the silicon dioxide layer 4 serves as a protective film for environmental resistance. In the antireflection film of this embodiment, the chromium layer 2 has almost no influence on the optical characteristics as described above.
If the thickness is less than or equal to nm, the layer has a physically three-layer structure, but only the cerium dioxide layer 3 and the silicon dioxide layer 4 function for antireflection, and it can be optically regarded as a two-layer structure. Therefore,
In designing the antireflection film, the cerium dioxide layer is provided on condition that the chromium layer 2 is formed extremely thin as described above.
It suffices to consider only the refractive index and the film thickness of 3 and the silicon dioxide layer 4.

The antireflection film of this embodiment manufactured based on the design specifications of Table 2 and the antireflection film of JP-A-63-121801 manufactured based on the design specifications of Table 1 are as follows: The wavelength λ of the incident light is 400 to 1000 n, respectively.
It was changed to m and the transmittance was measured. The result is shown in Figure 2.
The antireflection film of the present embodiment is almost 94 in the wavelength range (λ = 700 to 840 nm) targeted for various optical parts such as an objective lens of an optical pickup and a video camera.
It shows a transmittance of not less than% (corresponding to 6% or less in the spectral reflectance). Further, regarding the antireflection film of this example, a weather resistance test (60 ° C., 90%, 168 h) and (70 ° C., 90%, 504 h) were performed.
h), and thermal shock test (70 ° C to -30 ° C, 1h, 20
(0 cycle), the rate of occurrence of cracks in the deposited film was extremely low in each test.

On the other hand, in the case of the antireflection film of JP-A-63-121801, the results (λ = 780-8
The spectral reflectance at 20 nm is less than 0.5%).
As shown in FIG. 7, the antireflection film of this example has a more excellent average spectral reflectance in the above wavelength range. Incidentally, in the results of the weather resistance test and the thermal shock test for the antireflection film of JP-A-63-121801, the crack occurrence rate was high as described above.

Further, in the antireflection film of JP-A-63-121801, there is a tendency for the spectral reflectance to become unstable, which is considered to be due to the change in the refractive index of the first silicon monoxide (SiO) layer. But,
With the antireflection film of this example, an extremely stable spectral reflectance as designed was obtained, and the transmittance of several manufactured antireflection films was measured under the same conditions as described above. The characteristics were almost the same, and no variation occurred.

[0021]

EFFECTS OF THE INVENTION The "antireflection film of synthetic resin optical component" of the present invention has the above-mentioned constitutions, so that the following effects can be obtained. According to the invention of claim 1, since the first layer is a chromium layer having a film thickness of 15 nm or less, it has a physically three-layer structure, but has a second cerium dioxide layer and a third layer. Considering only the refractive index and layer thickness related to the silicon dioxide layer of the layer, optical design can be easily performed within the range that has no practical effect, and it has stable optical characteristics as designed and also has environmental resistance performance. An excellent antireflection film can be obtained. According to the invention of claim 2, the first chromium layer is the synthetic resin optical component and the antireflection film (the second cerium dioxide layer and the third chromium layer).
The antireflection film which has almost no optical influence can be realized only by ensuring the adhesion to the silicon dioxide layer).

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an antireflection film of a synthetic resin optical component according to an embodiment of the present invention.

FIG. 2 is a graph showing the transmittance characteristics of the antireflection film according to the example of the present invention and the antireflection film of the related art, with the wavelength λ of the incident light on the horizontal axis and the transmittance on the vertical axis. Is.

FIG. 3 is a cross-sectional view of a conventional antireflection film.

[Explanation of symbols]

1 ... Acrylic resin substrate (synthetic resin optical component), 2 ... Chrome layer (first layer), 3,13 ... Cerium dioxide layer (second layer), 4, 14 ...
Silicon dioxide layer (third layer), 12 ... Silicon monoxide layer (first layer).

Claims (2)

[Claims] 1. An antireflection film for a synthetic resin optical component, which has a three-layer structure in which a first layer, a second layer, and a third layer are laminated on the surface of the synthetic resin optical component in order from the surface side. The first layer is a chrome layer having a thickness of 15 nm or less, the second layer is a cerium dioxide layer, and the third layer is a silicon dioxide layer. Anti-reflection film for parts. 2. The antireflection film for a synthetic resin optical component according to claim 1, wherein the thickness of the chromium layer as the first layer is 5 nm or less.