JPH07318703A - Optical thin film material and antireflection film using that - Google Patents

Abstract

PURPOSE:To obtain an optical thin film material with which an optical thin film excellent in antireflection characteristics and durability can be formed and to obtain an antireflection film using this material by using a metal oxide containing tantalum and titanium as metal elements. CONSTITUTION:This optical thin film material is metal oxide containing tantalum and titanium as metal elements. This antireflection film is a thin film of metal oxide containing tantalum and titanium formed on a plastic optical element. The thin film of metal oxide containing tantalum and titanium is preferably produced by mixing a ditantalum pentoxide powder and a titanium oxide powder, sintering or fusing the mixture, and vapor depositing the material by an electron gun heating method. Ditantalum pentoxide and titanium oxide used in this method are not limited but any state of these can be used. Especially, for sintering, a powdery state having a proper particle size is preferable for easy sintering. Further, it is preferable to mix the two powders before sintering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film formed on an optical thin film material and an optical element made of plastic, and more particularly to an antireflection film having improved antireflection properties and durability.

[0002]

2. Description of the Related Art Optical elements made of plastics are used for eyeglass lenses, camera lenses, CRT filters, etc. because of their light weight, excellent impact resistance and easy processing. In such an optical element, the reflection from the surface of the optical element lowers the light transmissivity and causes unnecessary reflection called flare, ghost, etc. to deteriorate the optical characteristics. Therefore, in order to prevent reflection, a multi-layer antireflection film is widely applied to the surface by a vacuum deposition method or a sputtering method.

[0003]

In these multilayer antireflection films, the type of the film is determined so as to satisfy the film thickness and the refractive index calculated by the theory of the optical thin film, but the refractive index actually exists. Since the refractive index of the substance is limited, it is not always possible to form an antireflection film having a sufficient antireflection effect. In particular, a multilayered antireflection film for a plastic substrate having a high refractive index of more than 1.60 currently used is desired to have a refractive index of 2.00 or more, particularly 2.10 or more as a high refractive index thin film material. Rarely, zirconium oxide, titanium oxide, tantalum pentoxide, cerium oxide, etc. are preferably used. However, since zirconium oxide has a low refractive index of 1.95 to 2.00, a sufficient antireflection effect cannot be obtained, and titanium oxide and cerium oxide have a refractive index of 2.05 to 2.15, but the film is soft. Also, tantalum pentoxide, which has low thermal shock resistance, has a refractive index of 2.
However, good characteristics cannot be obtained because absorption occurs in the thin film and the transmittance becomes low.

To solve these problems, Japanese Unexamined Patent Publication No.
291502 discloses the use of a sintered mixture of ditantalum pentoxide, zirconium oxide and yttrium oxide. However, in this sintered body, when an electron gun is used during vacuum vapor deposition, the material scatters violently, and some of the scattered material becomes large particles that adhere to the optical element, which may cause defects. It cannot be said to be sufficient, and when using any of the materials, a hard coat layer of an organosilicon compound is often provided between the substrate and the multilayer antireflection film to increase the strength of the thin film, but the thermal shock resistance is not sufficient. Was not.

As described above, the multilayer film deposited on the plastic has problems that the antireflection property is not sufficient and the thermal shock resistance is weak because the refractive index of the high refractive material is not sufficiently high. Therefore, the problem to be solved by the present invention is that the optical characteristics and thermal shock resistance are not sufficient on the plastic substrate.

[0006]

The present invention has been made to solve the above problems, and an antireflection film according to the present invention is an antireflection film formed on a plastic substrate. Is a thin film of a metal oxide containing tantalum and titanium. Further, the present invention is an optical thin film material, which is a metal oxide containing tantalum and titanium as metal elements.

In the present invention, the metal oxide thin film containing tantalum and titanium is preferably a thin film obtained by vapor-depositing a mixture of ditantalum pentoxide powder and titanium oxide powder, and sintering or melting compound, by an electron gun heating method. is there. The tantalum pentoxide and titanium oxide used here are not particularly limited and any of them can be used, but in particular, in the case of sintering, a powdery material having an appropriate particle diameter is preferable so that it can be easily sintered. It is desirable that the average particle diameter of these is about 0.5 to 1 μm for ditantalum pentoxide and about 0.2 to 0.3 μm for titanium oxide. Furthermore, it is desirable to mix both of them in advance before sintering, and as a mixing method, there is a method such as using a ball mill.
For sintering, the powder is made into pellets by a method such as pressing in advance, and the pellets are baked in an electric furnace or the like. Heating temperature is 100
It is preferably 0 ° C or higher. In the case of melting, it is desirable that the two should be mixed in advance with a ball mill or the like so that they are sufficiently mixed and then melted. As a melting method, high frequency melting, electron beam melting, or the like is used. The composition ratio of the mixture or the compound obtained by mixing the powders is preferably 95% ditantalum pentoxide and 5% titanium oxide. The vapor-deposited film thus obtained does not absorb like a tantalum pentoxide film, and has a much better thermal shock resistance than a titanium oxide film,
Especially, it has very good durability in hot water test.
Further, the refractive index shows a high numerical value of 2.15, for example, which is effective from the viewpoint of film design. A preferable mixing ratio is 100 to 0.5 parts by weight of titanium oxide with respect to 100 parts by weight of tantalum pentoxide.
The amount of 0 parts by weight or less is preferable in that the material is less scattered, and the amount of 0.5 parts by weight or more is preferable in that the thin film is less absorbed and sufficient permeability is obtained. As titanium oxide,
TiO ₂ , Ti ₂ O ₃ and Ti ₃ O ₅ are used.

The structure of the antireflection film is λ / 2-λ / 4
A large-layer antireflection film such as a two-layer film of λ / 4-λ / 2-λ / 4 and a three-layer film of λ / 4-λ / 2-λ / 4 can be considered, but a multilayer film of four layers or more is also possible to further improve the antireflection property. is there.

In the multilayer antireflection film in which the low refractive index film and the high refractive index film are alternately laminated, the high refractive index film is preferably a thin film of a metal oxide containing tantalum and titanium. It is preferable to use a silicon dioxide film as the low refractive index film from the viewpoint of physical characteristics.

The plastic used as the base material of the antireflection film used in the present invention is a methyl methacrylate homopolymer, a copolymer containing methyl methacrylate and at least one other monomer as a monomer component, and diethylene glycol bisallyl carbonate alone. Polymer, copolymer containing diethylene glycol bisallyl carbonate and at least one other monomer as a monomer component, sulfur-containing copolymer, halogen-containing copolymer, polycarbonate, polystyrene, polyvinyl chloride, unsaturated polyester, polyethylene Examples include plastic optical substrates such as terephthalate and polyurethane. Further, it is also possible to include those in which a hard coat layer containing an organic silicon compound is provided on these plastic substrates.

Further, as a method for forming the antireflection film, an ion plating method, a sputtering method or the like can be included in addition to the vacuum vapor deposition method.

[0012]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited thereto.

Example 1 A tantalum pentoxide powder (average particle size 0.7 μm) and titanium oxide (TiO ₂ ) powder (average particle size 0.25 μm) were used in a ball mill at a weight ratio of 95: 5. After mixing and press molding, 10 in the atmosphere
Sintering was performed at 00 ° C. for 4 hours to obtain pellets for vapor deposition. This was set on the hearth for vapor deposition of an electron gun (JEBG102 made by JEOL) placed in a vacuum chamber (BMC850 made by SYNCHRON), and the inside of the apparatus was evacuated to 1 × 10 ⁻⁵ Torr, then by an electron beam. These were dissolved and evaporated, and an optical film thickness nd = 125 nm was deposited on a plastic plate made of a polymer of diethylene glycol bisallyl carbonate set in advance in a vacuum chamber. After completion of vapor deposition, the plastic flat plates were taken out, and the absorption and the refractive index were calculated from the transmittance and the reflectance of the thin film obtained from a spectrophotometer (Hitachi U-3400 type). Equation 1 was used to calculate the absorption, and Equation 2 was used to calculate the refractive index. Formula 1 (Absorption) = 100-((Transmittance) + (Reflectance))

[0014]

[Outer 1] As a result of this evaluation, it was found that the thin film material of the present invention could obtain a high refractive index of 2.0 or more without absorption as shown in Table 1.

Example 2 A plastic eyeglass lens made of a polymer of diethylene glycol bisallyl carbonate was added to 300 g of 2-ethoxyethanol, 470 g of colloidal silica dispersed with 2-methoxyetalol, and 185 g of α-glycidoxypropyltrimethoxysilane. A flow control agent (0.03 g) and a 0.05N aqueous hydrochloric acid solution (50 g) were added, and the solution was stirred at room temperature for 2 hours to form a hard coat layer on the substrate to be vapor-deposited, and the pellets for vapor deposition prepared in Example 1 were used. After melted silicon dioxide (manufactured by Optron) having a particle size adjusted to 1 to 3 mm was set in each of the hearths for electron gun vapor deposition placed in a vacuum chamber, and the inside of the apparatus was evacuated to 1 × 10 ⁻⁵ Torr. , Multi-layered reflection with film structure as shown in Table 2 by melting and evaporating them with an electron gun It has created a stop film. In order to evaluate the durability of the thus prepared multilayer antireflection film, the appearance of the lens, the adhesion of the thin film, and the thermal shock resistance were compared in the following manner.

Appearance There should be no cracks, cracks, wrinkles, and no light scattering when visually observing the lens by illuminating it with the slide projector as the light source.

Adhesion: The lens surface is cross-cut so as to be 100 mm at intervals of 1 mm, and cellophane tape (made by Sekisui, trade name Cellotape No. 252) is strongly adhered to it 45
The multilayer antireflection film, the hard coat layer, and the surface of the substrate were peeled off rapidly at an angle of 10 degrees, and the presence or absence of peeling was examined.

Thermal shock resistance (hot water test) A lens provided with a multilayer antireflection film was alternately immersed in warm water and cold water kept at 20 ° C. for 10 seconds each, and this was repeated 5 times.
The temperature of the warm water was increased from 60 ° C. by 5 ° C. at a time, and the test was conducted until abnormalities such as cracks and wrinkles occurred in the appearance.

As shown in Table 3, the results of these evaluations are good in all the items, and it was found that the material of the present invention is very excellent in durability, particularly in thermal shock resistance.

Example 3 A tantalum pentoxide powder (average particle size 0.7 μm) and titanium oxide (TiO ₂ ) powder (average particle size 0.5 μm) were used in a ball mill at a weight ratio of 95: 5. After mixing and press-molding, melt reaction using an electron beam to produce a compound of ditantalum pentoxide and titanium oxide, and crushing it into 1-3 mm
A multilayer antireflection film was formed by the same method as in Example 2 on the same plastic substrate as in Example 2 with the film configuration shown in the table.
It evaluated by the method similar to. The results obtained were good as shown in Table 3.

(Example 4) The substrate of Example 2 was replaced with a thiourethane resin, and a multilayer antireflection film was formed and evaluated in the same manner as in Example 2, and it was good as shown in Table 3. .

Comparative Example 1 The ditantalum pentoxide powder of Example 1 and the titanium oxide powder were mixed, pressed and sintered at a weight ratio of 50:50, and melted in the same apparatus as in Example 1 to cause bumping. Was severe, and the particles that jumped up were attached to the substrate, which was not desirable in appearance.

Comparative Example 2 When only the ditantalum pentoxide powder of Example 1 was pressed and sintered and dissolved and evaporated in the same apparatus as in Example 1, absorption occurred in the thin film and brown coloring was observed. The appearance was not preferable.

(Comparative Example 3) Only the titanium oxide powder of Example 2 was press-molded and fired, and then, on the same plastic substrate as in Example 2 with the film constitution shown in Table 2, by the same method as in Example 2. A multilayer antireflection film was formed and evaluated in the same manner as in Example 2. The results obtained were inferior in thermal shock resistance as shown in Table 3.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

As described above, according to the present invention, in a multilayer antireflection film formed by alternately laminating a low refractive index film and a high refractive index film on a plastic lens, the high refractive index film contains a metal containing tantalum and titanium. By using a thin film of oxide, it has become possible to significantly improve its properties and durability.

Claims (6)

[Claims] 1. An optical thin film material, which is a metal oxide containing tantalum and titanium as metal elements. 2. The optical thin film material according to claim 1, wherein the metal oxide is a sintered body of ditantalum pentoxide and titanium oxide. 3. The metal oxide is a melt of ditantalum pentoxide and titanium oxide.
Optical thin film material. 4. Titanium oxide is 100 to 0.5 parts by weight with respect to 100 parts by weight of ditantalum pentoxide.
Or the optical thin film material of 3. 5. An antireflection film formed on a plastic optical element, wherein the antireflection film is a thin film of a metal oxide containing tantalum and titanium. 6. The antireflection film according to claim 5, wherein a hard coat layer of an organic silicon compound is provided on the plastic optical element, and the antireflection film is formed thereon.