JPH07198902A - Water-repellent optical element and its production - Google Patents

Abstract

PURPOSE:To obtain a highly durable optical element fulfilling optical performance and having a water-repellent surface by providing specified first and second layers and a fluoride layer on the surface of an optical element substrate. CONSTITUTION:This optical element is provided with a first anti-reflection layer 3 consisting of a single layer or plural layers provided on the surface of an optical element substrate 1, a second layer 2 of carbon having <=5nm thickness and formed on the first layer 3 and a fluoride layer having a covalent bond with the carbon of the outermost surface of the second layer 2. In this case, a region, where the first layer 2 and the second layer 3 are not formed, is provided, and a fluorine-resistant protective film can be formed on the region. The carbon of the second layer 2 is formed by physical vapor deposition, chemical vapor deposition, plasma CVD, etc. Since the fluorination is performed while keeping the vacuum used when the carbon film of the second layer 2 is formed, the carbon film is not exposed to the atmosphere, and a C-0 bond is not formed because the surface of the carbon film is not oxidized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical elements such as lenses, prisms, filters, cover glasses, and viewing windows which utilize the transparency of a glass substrate and have water repellency, antifouling properties and antireflection properties. The present invention relates to a required water repellent optical element and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to impart water repellency to a glass substrate, a water repellent substance is generally provided as a film. For example, Japanese Patent Application Laid-Open No. 1-126244 proposes a method in which polydimethylsiloxane is applied as a water-repellent substance by a spray method, a dipping method, or the like, and heated to crosslink. In addition, JP-A-4-48068 and JP-A-4-48068
No. 240133, a method of forming a film of a Teflon resin as a water-repellent substance by a sputtering method and a PF.
A method has been proposed in which resin particles A are applied, heated, and baked to coat a fluororesin. Furthermore, JP-A-4-
Japanese Patent No. 305037 discloses a technique in which a mixed film of a metal oxide and carbon and a carbon film are provided on a glass substrate and the film is formed by sputtering in CF ₄ gas.

[0003]

However, these conventional techniques have the following drawbacks. Japanese Patent Laid-Open No. 1-1262
In the technique described in Japanese Patent Laid-Open No. 44, the film strength and the film adhesion are not sufficient. For this reason, there is a problem in that even if it has water repellency in the initial stage, its durability is low and its performance deteriorates with time. As a technique utilizing this, there is a coating agent for the front window of a vehicle, but it has a short effect and must be repeatedly treated.

The methods of forming a film of a Teflon resin by sputtering in JP-A-4-48068 and JP-A-4-240133 or coating PFA resin particles and heating and baking a fluorine resin for coating are described below.
Since a stable material excellent in water repellency that does not bond to the substrate is used, the adhesion to the substrate and the film strength are insufficient, and the film peels off or the film is damaged. Therefore, durability is low.

In the method of providing a mixed film of a metal oxide and carbon and a carbon film in JP-A-4-305037 and fluorinating the surface, when the mixed film and the carbon film are combined, the film thickness becomes 50 nm, Since it absorbs visible light, it is not suitable for optical applications. Furthermore, since there is no countermeasure against reflection on the surface, it is difficult to apply it to an optical element that requires precision. Moreover, as the surface fluorination method, since carbon is provided by sputtering in CF ₄ gas, only CF ₄ is incorporated into the carbon film, and a bond between fluorine and carbon that serves as a matrix does not occur, which is stable. It does not become a state. In addition, since the content of fluorine is not so high as about 20%, there is a problem in the level of water repellency and antifouling effect and its sustainability.

The present invention has been made in consideration of the problems of these conventional techniques, and satisfies the optical performance and
An object of the present invention is to provide an optical element having a water-repellent surface having high durability and a method for producing the same.

[0007]

A water-repellent optical element of the present invention comprises a single layer or a plurality of layers provided on the surface of an optical element substrate, the first layer having an antireflection function, and the first layer. A second layer made of carbon and having a thickness of 5 nm or less on the first layer, and a fluorinated layer formed so as to covalently bond with the carbon on the outermost surface of the second layer. It is characterized by

Here, a region where the first layer and the second layer are not formed can be provided, and a fluorine-resistant protective film can be formed in the region. As the protective film, metal, metal oxide,
One or more of metal nitride, metal fluoride, metal sulfide, and metal carbide can be used. As the first layer having an antireflection function, Al, Al ₂ O ₃ , T
_{iO 2, ZrO 2, B 2} O 3, BN, ZnS and other materials can be used, by using the organometallic compound such as various metal alkoxides and Borazan as starting materials, can be generated.

The carbon of the second layer can be formed by physical vapor deposition, chemical vapor deposition, sputtering, plasma CVD or the like. This carbon has extremely high adhesion to the optical element substrate and can be uniformly provided, so that the surface shape of the optical element does not change. As the gas for fluorinating carbon, F ₂ gas or HF gas can be selected, and F ₂ gas is particularly preferable.

Since the carbon film of the second layer has absorption in the visible region, it is necessary to make the film thickness as thin as possible for use in optical applications. Practically, 5 nm or less is suitable. When the optical element provided with the second layer is heated in vacuum and fluorine gas or fluoride gas is introduced, these gases are very rich in reactivity and react with carbon (C) to form a covalent bond. A compound containing C-F is produced. As a result, the carbon on the surface of the second layer is covered with fluorine (F). Thereby, the fluorine concentration on the outermost surface can be made extremely high. Here, substances such as fluororesins having a C—F bond (PTFE (polytetrafluoroethylene: trade name Teflon), PFA, PCTFE, etc.) and graphite fluoride (CF ₂ , CF ₃ ) are all chemical. It is highly stable and has high water repellency due to the property of reducing the surface energy of fluorine.

Further, the C—F bond has a feature that it has a high bonding force, is stable thermally, and has high durability. For example, the adhesion between ordinary adhesives and organic binders, and the intermolecular force (van der Waals force) that governs strength is 5K.
While the covalent bond energy of C-F is about 100 Kcal / mol and that of C-C bond is about 80 Kcal / mol, it is a very strong bond.

On the other hand, the carbon film of the second layer is made of PVD or CV.
Since the film is formed by D or the like, it has high adhesion to the optical element. Moreover, the carbon film itself has a high bond energy of C-C and C = C (the respective bond energies are about 80 and 110K).
Since it has a cal / mol), it has high durability.

In the present invention, since the carbon film of the second layer is fluorinated while maintaining the degree of vacuum at the time of film formation, the carbon film is not exposed to the atmosphere and the surface of the carbon film is oxidized. Does not form a C-O bond. Since the reaction rate is slow at room temperature, the entire surface is not oxidized even when exposed to the atmosphere, but the oxidized part is stable (the binding energy is about 80 Kca).
(1 / mol), it cannot bond with fluorine and the concentration of fluorine on the surface is slightly lowered, but this is not the case.

Further, when the antireflection film and the carbon film are not provided outside the optically effective surface, or when there is a portion where the film cannot be provided due to the method of holding the substrate during film formation, the fluorination treatment is performed. The fluorine gas used attacks the exposed part of the glass substrate of the optical element.
Since the coating is performed with the protective film made of nitride or sulfide, the fluorination treatment can be performed without damaging the base material.

[0015]

First Embodiment FIG. 1 is a sectional view showing a first embodiment of the present invention. An optical element substrate 1 is formed of a glass material BSL7 (Ohara Optical Co., Ltd.), and MgF ₂ as a first layer having an antireflection function has a thickness of 1 on the surface of the optical element substrate 1.
It is provided with a thickness of 30 nm (nd), and a carbon film 2 as a second layer is provided thereon with a thickness of 5 nm. In the manufacture of this example, first, the optical element substrate 1 is placed in a vacuum container,
The inside of the container is vacuum-sucked to maintain a pressure of 6 × 10 ⁻⁴ Pa,
After heating the substrate to 250 ° C., an antireflection film is deposited.
Next, carbon is vapor-deposited on the antireflection film. After that, while maintaining the pressure in the container at 6 × 10 ⁻⁴ Pa, the optical element was
Fluorine gas is added to 1
It is introduced until it reaches a pressure of 01 KPa, the pressure of the fluorine gas in the system is kept at 101 ± 1 KPa for 5 minutes, and fluorination is performed.

The surface of the optical element of this embodiment has a carbon film,
The outermost surface thereof has a C—F bond fluorinated by highly reactive fluorine gas. Since such a surface has high water repellency and high adhesion to the substrate, it acts as a highly durable water repellent layer. Further, since the carbon film of the second layer is extremely thin, there is almost no optical influence, and the antireflection film provided as the base of the carbon film has good optical characteristics. In this embodiment, the surface of the carbon film provided by vapor deposition is fluorinated without being exposed to the atmosphere, so the carbon film is not oxidized and fluorination is not hindered. Therefore, high water repellency can be efficiently imparted.

In this example, the contact angle with respect to water droplets was measured to be about 115 ° C. Also, 300 g / cm
^When the durability was tested by rubbing with sillbon paper under a friction condition of 1,000 reciprocations under a load of ^2, the water repellency did not change.

FIG. 2 shows the reflectance characteristic of this embodiment, which has a good antireflection function. When a dummy sample similarly provided with a water-repellent film was evaluated by XPS with respect to a flat plate-shaped sample of the same material as that of the optical element of this example, fluorine and a large amount of carbon could be detected, and fluorine was a chemical substance. it was confirmed that the shift has a binding _{C-F, C-F 2} , C-F 3. Also, because the carbon film is very thin,
The MgF ₂ peak of the substrate could also be detected. From the above, it is considered that the extreme surface (1 nm or less) of the carbon film is fluorinated, and the fluorine bonds with carbon and is fixed in a stable state. Therefore, the outermost surface has a very high fluorine concentration and high water repellency.

[0019]

Second Embodiment FIG. 3 shows a second embodiment of the present invention. The optical element substrate 1 is made of glass material LAL14 (Ohara Optical Co., Ltd.), on the surface of which a first layer 3 having a plurality of layers having an antireflection function is provided, and a carbon film is formed on the first layer 3. The second layer 2 is provided with a thickness of 5 nm (nd), and the outermost surface of the carbon film is fluorinated. In the present embodiment, the first layer 3 is made of Al ₂ O ₃ (nd = 130n) from the base material side.
m), TiO ₂ (nd = 260 nm), MgF ₂ (nd
= 130 nm).

In the manufacture of this embodiment, an antireflection film is vapor-deposited under vacuum (6 × 10 ⁻⁴ Pa) on the molding surface of the optical element substrate 1, and then a carbon film is vapor-deposited in the same manner. At this time, the substrate was heated at 250 ° C. Further, while keeping the vacuum in the vapor deposition apparatus, the optical element substrate is heated to about 450 ° C., and when the temperature is stable, fluorine gas is introduced until the pressure reaches 101 KPa, and the pressure of fluorine gas in the system is kept at 101 ° C. ±
Hold at 1 Pa for 5 minutes to fluorinate.

Also in this embodiment, an optical element having both antireflection effect and water repellency can be obtained. FIG. 4 shows a reflectance characteristic diagram of this embodiment. A glass material having a high refractive index (nd = 1.7), such as a lanthanum glass material.
In the case of 0), since the reflection on the surface becomes large, a higher antireflection effect is required, but the antireflection film of this example has a multi-layer structure and can suppress reflection in a wider wavelength range. it can. When the contact angle of the optical element obtained in this example with respect to a water drop was measured, it was about 115 °.
Also in this embodiment, 1000 g is applied with a load of 300 g / cm ^2.
Durability test conducted by rubbing with sillbon paper under reciprocating friction condition showed no change in water repellency. FIG. 8 shows an optical element formed in the same manner as this example without providing an antireflection film,
In this case, since the reflection is less than 7%, it cannot be used as an optical element.

[0022]

[Embodiment 3] This embodiment is the same as Embodiment 2 except that the antireflection film of the first layer is different. The antireflection film of the present embodiment is Ta ₂ O ₅ (nd = 20 nm), S
iO ₂ (nd = 40 nm), Ta ₂ O ₅ (nd = 260)
nm) and SiO ₂ (nd = 130 nm) are laminated in this order, and MgF ₂ (nd = 20n) from the base material side.
m), ZrO ₂ (nd = 25 nm), MgF ₂ (nd =
20 nm), ZrO ₂ (nd = 270 nm), MgF ₂
There are two types of five-layer structure in which (nd = 130 nm) is sequentially laminated.

Also in this embodiment, as in the second embodiment, an optical element having both an antireflection function and water repellency on the surface can be formed. FIG. 5 is a reflectance characteristic diagram of the optical element having the above-mentioned four-layer structure, and FIG. 6 is a reflectance characteristic diagram of the layer structure. There are merits suitable for.

[0024]

Fourth Embodiment FIG. 7 shows a fourth embodiment of the present invention. Glass material PB
The optical element substrate 1 is formed of M18 (Ohara Optical Co., Ltd.), and the antireflection film 3 as the first layer is formed on the incident and outgoing optical surfaces of the substrate 1 by the same steps as in Example 1. It is provided. Further, a carbon film 2 as a second layer is provided on the incident surface side of the base material 1. Further, an alumina film 4 is provided on the surface (side surface) of the optical element substrate 1 on which the antireflection film is not provided.

In the manufacture of this embodiment, first, as in the case of Embodiment 1, the antireflection film 3 is provided on the emission surface, and then the antireflection film 3 is also provided on the incident surface side. After that, a solution containing aluminum alcoholate and ethanol is applied to the side surface of the optical element substrate 1 and baked in the atmosphere at 300 ° C. for 2 hours. By this firing, a 100 nm alumina film 4 was obtained. Next, a carbon film is provided on the incident side of the optical element substrate 1 in the same manner as in Example 1, and the outermost surface thereof is fluorinated. Note that the aluminum nitride film may be formed as a protective film by heating in nitrogen instead of firing in the atmosphere described above.

The aluminum alcoholate applied to the side surface in this embodiment is heated to form alumina (Al).
₂ O ₃ ) thin film is formed. As a result, the entire surface of the optical element substrate 1 is covered with a thin film of MgF ₂ or Al ₂ O ₃ , and the SiO ₂ component contained in the optical element substrate 1 is not corroded by F ₂ and HF gas used for the fluorination treatment. The fluorination process becomes possible.

[0027]

INDUSTRIAL APPLICABILITY As described above, the present invention is an optical element having both high water repellency and an excellent antireflection function, and thus is an optical element most suitable for applications exposed to the outside world. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a reflectance characteristic diagram of Example 1.

FIG. 3 is a sectional view of the second embodiment.

FIG. 4 is a reflectance characteristic diagram of Example 2.

FIG. 5 is a reflectance characteristic diagram in the case of four layers in Example 3.

FIG. 6 is a reflectance characteristic diagram in the case of five layers of Example 3.

FIG. 7 is a sectional view of the fourth embodiment.

FIG. 8 is a reflectance characteristic diagram of a comparative example.

[Explanation of symbols]

 1 Optical element base material 2 2nd layer 3 1st layer

Claims (4)

[Claims] 1. A single layer or a plurality of layers having an antireflection function provided on the surface of an optical element substrate, and carbon formed on the first layer to a thickness of 5 nm or less. 2. A water-repellent optical element, comprising: a second layer consisting of: and a fluorinated layer formed so as to covalently bond with carbon on the outermost surface of the second layer. 2. The surface of the optical element substrate is provided with a region where the first layer and the second layer are not formed, and the region is covered with a fluorine-resistant protective film. The water-repellent optical element according to claim 1. 3. A step of forming a first layer comprising a single layer or a plurality of layers and having an antireflection function on the surface of an optical element substrate, and a second layer of carbon having a thickness of 5 nm or less as the first layer. A step of depositing on the first layer, and a step of heating while maintaining the vacuum atmosphere at the time of forming the second layer and introducing fluorine gas or fluoride gas into the vacuum atmosphere to covalently bond the carbon on the outermost surface with fluorine. And a method for manufacturing a water-repellent optical element. 4. A fluorine-resistant protective film is formed by applying a fluorine-resistant compound solution prior to covalently bonding the fluorine and then heating in an atmosphere or nitrogen. A method for producing the water-repellent optical element as described above.