JP2006267561A - Optical element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a lens provided with an antireflection film, which is high in durability and high in moisture blocking capability. <P>SOLUTION: A plastic lens has the antireflection film made by forming a hard coat layer directly on a base material, wherein the antireflection film is a multilayer film comprising a low-refractive index film or a middle-refractive index film and high-refractive index films, and at least one of the high-refractive index films is formed of a layer consisting of a simple compound of silicon nitride. By adopting the layer consisting of the simple compound of silicon nitride as one of the multilayer film of the antireflection film, the plastic lens which takes advantage of characteristics of amorphous silicon having high durability, can suppress the effect of ultraviolet ray and moisture to the lens base material and the other layers and has high heat resistance and light resistance can be provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical element such as a spectacle lens having an antireflection film and a method for manufacturing the same.

  In the process of manufacturing lenses used for eyeglasses etc., antireflection is used to suppress light reflection and increase light transmission on glass or resin substrates directly or on a hard coat layer. A film is formed. Furthermore, in order to obtain an effective antireflection effect in the visible light region even in an optical element or component such as a spectacle lens, a material having an appropriate refractive index is thinned and laminated over a plurality of layers. A multilayer antireflection film is widely formed.

As the film configuration of the multilayer antireflection film, in the case of a three-layer film, the thickness of each layer is set to 1 / 4λ (λ = design wavelength), or the first layer and the third layer are set to 1 / 4λ, the second layer A configuration in which only λ is 1 / 2λ is often used. The substance constituting the antireflection film when the base material of the optical component is made of a synthetic resin has an appropriate refractive index so that an antireflection effect can be sufficiently obtained, and the quality of the formed film (hardness, It is necessary to select a substance that can provide transparency. As such a substance, silicon oxide such as SiO ₂ or SiOx is used for the low refractive index layer, and ZrO ₂ (zirconium oxide), Ta ₂ O ₅ (tantalum oxide), TiO ₂ (oxidation) is used for the high refractive index layer. Titanium) and the like are used. The middle refractive index layer is a laminated film of Al ₂ O ₃ (aluminum oxide) or the like, or a low refractive index material such as SiO ₂ or SiOx, and a high refractive index material such as ZrO ₂ , Ta ₂ O ₅ or TiO _2. An equivalent membrane layer composed of is used.

When an antireflection film is formed on a plastic base material (synthetic resin base material), in order to improve the adhesion to the base material, the first layer (lowermost layer) on the base material is particularly an SiO ₂ film. By doing so, it has a role as an adhesive layer. At this time, the film thickness of SiO ₂ needs to be about 1 / 4λ or 1 / 2λ in order to obtain adhesion. Further, when the base material is a synthetic resin material (plastic), a hard coat layer is provided on the base material because it is weak in scratch resistance and easily scratched, and an antireflection film is formed thereon. . Even in such a case, an SiO ₂ film is provided as a first layer on the hard coat layer so as to obtain adhesion. As a method for forming the antireflection film, a vacuum deposition method in which a substance constituting the antireflection film is heated and melted with an EB (electron gun) in a vacuum and laminated on a substrate is often performed. .
JP-A-3-84501

As a coating layer that covers the optical element, particularly in an optical element based on plastic, in addition to the antireflection effect, the antireflection film is durable as a coating layer that covers the surface or is close to the surface. Sex is also required. For this reason, for example, in Patent Document 1, an antireflection film is used, a composite material of Si ₃ N ₄ and SiO ₂ is used for the first layer, and a dielectric having a refractive index of 2.0 to 2.2 is used for the second layer. It is disclosed that the optical properties and durability can be improved by using SiO _{2 in} the third layer. As an example of the second layer, it is disclosed that a material such as TiO ₂ , CeO ₂ , Ta ₂ O ₅ , ZrO ₂ —TiO ₂ is used.

However, considering from the viewpoint of improving the durability of the antireflection film, materials such as TiO ₂ are easy to crystallize, and generally have a problem of forming a columnar structure crystal at a low temperature (from room temperature to about 200 ° C.). . For this reason, there is a concern that moisture and gas can easily permeate from the crystal grain boundary and adversely affect the plastic substrate. Further, when a material such as Zr—Ti is employed, there is a concern that moisture and gas can easily pass through because the density of the film is low.

In the case of an optical element using a plastic substrate, particularly a moisture permeable plastic, the inventors of the present application consider that there are the following two disadvantages due to the permeation of moisture. For one, plastic substrates generally tend to absorb moisture, and when moisture penetrates, the coefficient of thermal expansion increases and the glass transition point tends to decrease. Therefore, there is a problem that the heat resistance of the plastic lens, that is, the temperature at which cracks are generated on the surface of the antireflection film is lowered. This is because the thermal expansion coefficient of the plastic lens substrate (2 to 12 × 10 ⁻⁵ / ° C.) is large, and the inorganic substance constituting the antireflection film has a thermal expansion coefficient (quartz: 5 × 10 ⁻⁷ / ° C.). Because of its small size, it is based on the phenomenon that when the lens expands due to heat, it cannot withstand the expansion and cracks occur in the antireflection film.

  Another problem is that when the moisture reaches the plastic substrate through crystal grain boundaries and fine cracks, partial swelling or refractive index change occurs, and the lens surface is visually observed as distorted. There is.

The presence of moisture further adversely affects the optical element not only in the lens substrate but also in the context of the hard coat layer. That is, since the base plastic is softer than glass and has poor adhesion to an inorganic substance, a primer or a hard coat is generally formed on the surface in many cases. It is required to use a plastic substrate having a high refractive index to make it thin and light, and accordingly, the hard coat is also required to have a high refractive index. For this reason, TiO ₂ sol is often used for the hard coat, but when TiO ₂ is irradiated with ultraviolet rays and moisture is present in the vicinity, the moisture is decomposed by the photoactivity of TiO ₂ , and decomposed OH, O, etc. Ions or radicals decompose organic matter (plastic). As a result, the hard coat and the like are peeled off.

  Therefore, in the present invention, an optical element having an antireflection film that has high durability, can withstand a difference in thermal expansion coefficient, is resistant to cracking, and has an excellent function of preventing moisture from entering, and its manufacture It aims to provide a method.

  In order to obtain a function that can withstand the difference in coefficient of thermal expansion, has high durability, is resistant to cracking, and prevents moisture from entering stably, the strength of the film It is desirable to form a film with a high crystallinity and low crystallinity, that is, in an amorphous state. From such a viewpoint, when the film configuration of the antireflection film was examined, it was found that there was a problem with the material used for the high refractive index layer as described above.

  Therefore, in the present invention, the high refractive index layer is formed of a layer made of a simple compound of silicon nitride. Silicon nitride (sometimes referred to as SiN in this specification) has a refractive index of about 2.1, high hardness, and is difficult to crystallize when deposited. Therefore, since the durability is high and there is no grain boundary, moisture and the like can be completely shielded, and an antireflection film with high water stopping performance can be configured. However, there is a problem in that the bond between silicon and nitrogen tends to be insufficient during film formation, and transparency is lowered. For this reason, even though silicon nitride is conventionally used as a material for an antireflection film, it is formed as a composite material (composite compound) with SiO, and transparency is ensured by bonding silicon to oxygen. Therefore, a high refractive index layer having silicon nitride as one composition is not formed.

  By increasing the thickness of the medium refractive index layer containing silicon nitride, durability and water stoppage may be obtained. However, in terms of the optical design of the antireflection film, increasing the thickness of the medium refractive index layer results in a decrease in optical performance and a decrease in productivity.

  On the other hand, the problem of opaqueness due to insufficient bonding between silicon and nitrogen during film formation can be solved by employing RF sputtering deposition or the like when coating (depositing) an optical substrate. I understood. In addition, it has been found that plastic substrates in recent years are not damaged even when a high energy vapor deposition method such as RF sputtering vapor deposition is adopted. It has been found that a layer made of a simple compound of silicon nitride can be formed on the material. Therefore, silicon nitride can be used for the high-refractive index layer, and an antireflection film containing a sufficient amount of silicon nitride can be generated without degrading optical properties or productivity.

  That is, in the present invention, an optical element having an antireflection film formed directly on an optical substrate or sandwiching at least one other layer, the antireflection film being a low refractive index layer Alternatively, the optical element is a multilayer film including a medium refractive index layer and a high refractive index layer, and at least one of the high refractive index layers is a layer made of a simple compound of silicon nitride. In this optical element, since the antireflection film includes a high refractive index layer made of one or more simple compounds of silicon nitride, the antireflection film has high durability and sufficiently contains amorphous silicon nitride. Thus, the optical substrate and the hard coat layer can be covered. As a result, even if there is a difference in coefficient of thermal expansion, the strength is high and the antireflection film has compressive stress, so cracks are difficult to occur, and moisture is partially transmitted even if it is not crystallized. Since the optical base material can be covered with the antireflection film having no antireflection, the antireflection film can sufficiently block the influence of ultraviolet rays and moisture on the optical base material and other layers under the antireflection film. For this reason, according to the present invention, an optical element having high heat resistance and high light resistance can be provided.

  As described above, the present invention includes an optical element in which an antireflection film is formed directly on an optical substrate or with at least one other layer interposed therebetween. Hard coat layer to protect the optical substrate and improve the adhesion of the anti-reflective film with the inorganic substance between the film, and further improve the adhesion between the hard coat layer and the optical substrate And an optical element having a primer layer for improving impact resistance. Furthermore, an optical element in which a film having water repellency and antifogging properties is formed on the surface of the antireflection film is also included in the scope of the present invention.

  In one embodiment of the present invention, the antireflection film has a three-layer structure, and from the optical substrate side, a medium refractive index layer made of a composite material of silicon nitride and silicon oxide and a high compound made of a simple compound of silicon nitride. The optical element includes a refractive index layer and a low refractive index layer made of a simple compound of silicon oxide. By adopting a medium refractive index layer made of a composite material of silicon nitride and silicon oxide as the first layer, an antireflection film containing a large amount of silicon nitride can be formed with a small layer structure. Further, in manufacturing, when the number of layers is small, the time required for gas switching or the like is shortened, so that throughput can be shortened. From this point, a three-layer structure is desirable.

  The structure of the antireflection film is a multilayer structure of five layers or more in which a low refractive index layer made of silicon oxide and a high refractive index layer made of a simple compound of silicon nitride are laminated from the optical substrate side. Also good.

  In an optical element according to one aspect of the present invention, the optical base is a lens having a plastic lens base. For example, as an optical substrate (lens substrate), acrylic resin, thiourethane resin, methacrylic resin, allyl resin, episulfide resin, polycarbonate, polystyrene, diethylene glycol bisallyl carbonate (CR-39), polyvinyl chloride , Halogen-containing copolymers, sulfur-containing copolymers and the like are useful. By adopting the antireflection film of the present invention using such a plastic material as a base material, it is possible to prevent moisture from entering the base material, so that the thermal expansion law of the base material is increased and the glass transition point is decreased. Problems can be prevented and the heat resistance and durability of the plastic lens, which is an optical element, can be improved.

  Furthermore, the present invention relates to a method for producing an optical element having an antireflection film formed directly on an optical substrate or sandwiching at least one other layer, wherein the optical element has a low refractive index layer or a medium refractive index. An antireflection film forming step of forming an antireflection film by a multilayer film including a refractive index layer and a high refractive index layer. The antireflection film formation step is performed by a simple compound of silicon nitride, and has a high refractive index. The manufacturing method of the optical element provided with the high refractive index layer formation process which forms a layer is included. In the manufacturing method for manufacturing an antireflection film having a three-layer structure, the antireflective film forming step includes forming a medium refractive index layer by using a composite material of silicon nitride and silicon oxide before the high refractive index layer forming step. After the refractive index layer forming step and the high refractive index layer forming step, a low refractive index layer forming step of forming a low refractive index layer with a simple compound of silicon oxide is included.

  With this manufacturing method, it is possible to manufacture an antireflection film that includes a large amount of silicon nitride with a small layer structure, is highly durable, and has a high ability to prevent the ingress of moisture, and as a result, it is possible to manufacture a highly durable optical element. .

  In the high refractive index layer forming step, a suitable vapor deposition method is an RF sputtering vapor deposition method. In this vapor deposition method, since nitrogen or oxygen can be introduced as a reactive gas in addition to argon as a sputtering gas, a highly transparent silicon nitride film can be formed. Also, direct current sputtering, CVD (chemical vapor deposition), electron beam evaporation, ion plating, which can perform the formation process of metal film and the irradiation process of ions or radicals for oxidation or nitridation in a short cycle Is a suitable vapor deposition method in the high refractive index layer forming step.

  Hereinafter, the present invention will be further described based on examples in which a spectacle lens is manufactured as an optical element according to the present invention.

Example 1
As a lens base material (optical base material), a refractive index of 1.67, manufactured by Seiko Epson Corporation, a product name: a lens base material for Seiko Super Sovereign, a spectacle lens provided with a hard coat layer and an antireflection layer Produced.

(Hard coat layer)
A coating solution (coating solution) for forming a hard coat layer (another layer) on the lens substrate was prepared as follows. First, in a reaction vessel equipped with a stirrer, 74.93 g of γ-glycidoxypropyltrimethoxysilane, 37.61 g of γ-glycidoxypropylmethyldimethoxysilane, and 38.2 g of 0.1 N aqueous hydrochloric acid solution were charged. Stir for 60 minutes. Next, 275.11 g of distilled water was added and the mixture was further stirred for 60 minutes. Thereafter, a composite sol of anatase-type titanium oxide / zirconium oxide / silicon oxide (manufactured by Catalyst Kasei Kogyo Co., Ltd., trade name “OPTRAIK 1820Z (U-25 / A8)”) as a sol of inorganic oxide fine particles, After adding 0.30 g of a silicone-based surfactant (trade name “L-7604” manufactured by Nippon Unicar Co., Ltd.) and stirring sufficiently, a coating liquid (HC liquid) for a hard coat layer was obtained.

  This coating solution HC was applied to the convex surface of the lens substrate by spin coating, and heated and cured at 135 ° C. for 0.5 hours. Thereafter, the coating liquid HC was also applied to the concave surface of the lens substrate by spin coating, and heated and cured at 135 ° C. for 2.5 hours. As a result, a lens (work) having a hard coat layer formed on both surfaces of the lens substrate was obtained.

(Formation of antireflection film)
An antireflection film was formed on the workpiece by a film forming apparatus (sputtering apparatus) 1 shown in FIG. This sputtering apparatus 1 has a vacuum chamber (chamber) 2, a substrate support 11 for supporting a work 70 in the vacuum chamber 2, a silicon target 13 disposed at a position facing this, and a space between them. A shutter 12 that opens and closes is provided. By moving the shutter 12 to the open / close position, the timing of vapor deposition is measured, and a film having a desired thickness is formed on the surface of the work 70. A high frequency power source 17 is connected to the target 13. At the time of cleaning the work 70, the high frequency power source is switched to and connected to the substrate support base 11.

  First, the work 70 is set on the substrate support 11 of the vacuum chamber 2 of the apparatus 1. Next, a cleaning process is performed. In this process, while the shutter 12 is moved between the target 13 on which silicon is placed and the substrate support 11, the inside of the apparatus 1 is evacuated and oxygen 14 is introduced into the vacuum chamber 2 for replacement. To do. In this state, a high frequency power source 17 was connected to the substrate support 11 to apply high frequency power, and an oxygen plasma cleaning process was performed on the surface of the work 70 for 120 seconds.

  Next, the high frequency power supply 17 is connected to the target 13 to form each layer of the antireflection film. Specific film forming conditions are collectively shown in FIG. In this example, the antireflection film is formed with a three-layer structure of a medium refractive index layer, a high refractive index layer, and a low refractive index layer. First, in the middle refractive index layer forming step of forming a middle refractive index layer with a composite material (SiON) of silicon nitride and silicon oxide of the first layer, after adjusting the pressure of the apparatus 1 to 0.6 Pa, FIG. The medium refractive index of the composite material of silicon nitride and silicon oxide is formed on the workpiece 70 by RF sputtering vapor deposition using high frequency power while introducing oxygen 14, nitrogen 15 and argon 16 under the conditions shown in FIG. A SiON film is formed. The flow rate of oxygen is 5 sccm, the flow rate of nitrogen is 10 sccm, the flow rate of argon is 15 sccm, and the high-frequency power is 500 W.

  Next, in the high refractive index layer forming step of forming a high refractive index layer with a simple compound of silicon nitride, oxygen 14 is stopped and nitrogen 15 and argon 16 are introduced under the conditions shown in FIG. On the other hand, a high refractive index SiN film is formed on the workpiece 70 by a simple compound of silicon nitride by an RF sputtering vapor deposition method using high frequency power. The flow rate of nitrogen is 10 sccm, the flow rate of argon is 15 sccm, and the high frequency power is 800 W.

Further, in the low refractive index layer forming step of forming a low refractive index layer with a simple compound of silicon oxide, the nitrogen 15 is stopped and oxygen 14 and argon 16 are introduced under the conditions shown in FIG. A low-refractive-index SiO ₂ film is formed on the workpiece 70 by a simple compound of silicon oxide by an RF sputtering vapor deposition method using electric power. The flow rate of oxygen is 5 sccm, the flow rate of argon is 15 sccm, and the high-frequency power is 400 W.

Thus, from the lens substrate side, a middle refractive index layer of SiON (refractive index 1.65) having an optical thickness of 9.5 nm and SiN (refractive index 2.05) having an optical thickness of 120.2 nm are formed. A three-layer antireflection film composed of a high refractive index layer and a low refractive index layer of SiO ₂ (refractive index 1.45) having an optical thickness of 86.2 nm is formed on both surfaces of the workpiece 70. The design center wavelength indicating the center of the transmission band of this antireflection film is 500 nm, and the reflectance spectrum (optical characteristics) of the antireflection film is shown in FIG.

(Example 2)
In this example, similarly to Example 1, a lens having an antireflection film consisting of five layers was manufactured using a work in which a hard coat layer was formed on the lens substrate (both sides). The film formation conditions at that time are summarized in FIG. After the work 70 is set in the apparatus 1 and the cleaning process is finished, in the low refractive index layer forming step of forming a low refractive index layer with a simple compound of silicon oxide, the nitrogen 15 is stopped under the conditions shown in FIG. Then, while introducing oxygen 14 and argon 16, a first low-refractive-index SiO ₂ film is formed on the workpiece 70 by a silicon oxide simple compound by RF sputtering vapor deposition using high-frequency power. The flow rate of oxygen is 5 sccm, the flow rate of argon is 15 sccm, and the high-frequency power is 400 W.

  Next, in the high refractive index layer forming step of forming a high refractive index layer with a simple compound of silicon nitride, oxygen 14 is stopped and nitrogen 15 and argon 16 are introduced under the conditions shown in FIG. Then, a high refractive index SiN film is formed on the workpiece 70 by a simple compound of silicon nitride by an RF sputtering vapor deposition method using high frequency power. The flow rate of nitrogen is 10 sccm, the flow rate of argon is 15 sccm, and the high frequency power is 800 W.

By repeating these steps, a low refractive index layer of SiO ₂ (refractive index 1.45) with an optical thickness of 8.6 nm and SiN (refractive index of optical thickness of 53.6 nm) are formed from the lens substrate side. 2.05) high refractive index layer, 9.0 nm optical thickness SiO ₂ (refractive index 1.45) low refractive index layer, 54.2 nm optical thickness SiN (refractive index 2.05). ) And a low refractive index layer of SiO ₂ (refractive index 1.45) having an optical thickness of 89.7 nm were formed on both surfaces of the work 70. The design center wavelength of this five-layer antireflection film is 500 nm, and FIG. 5 shows the reflectance spectrum (optical characteristics) of the antireflection film.

(Comparative Example 1)
Further, in order to compare with the above-described examples, SiO ₂ (refractive index: 1.46) is obtained by electron beam evaporation on the workpiece in which the hard coat layer is formed on the lens substrate (both sides) by changing the target. A lens provided with a five-layer antireflection film made of ZrO ₂ (refractive index of 2.05) was manufactured. This antireflection film has a design center wavelength λ of 500 nm and is λ / 4-λ / 4-λ / 4 (1 to 3 layers are equivalent films). From the lens substrate side, 19.6 nm of SiO ₂ Low refractive index layer, 43.4 nm ZrO ₂ high refractive index layer, 8.71 nm SiO ₂ low refractive index layer, 72.17 nm ZrO ₂ high refractive index layer, 85.81 nm SiO 2 _An antireflection film was formed by 5 layers with ₂ low refractive index layers.

(Comparative Example 2)
Furthermore, SiO ₂ (refractive index of 1.46) and TiO ₂ (refractive index of 2.39) are changed by electron beam vapor deposition instead of the target on the work having a hard coat layer formed on the lens substrate (both sides). A lens having an antireflection film consisting of 7 layers was produced. This antireflection film has a design center wavelength λ of 500 nm and λ / 4-λ / 4-λ / 4 (1 to 3 layers and 4 to 6 layers are equivalent films), and is 20 nm from the lens substrate side. A low refractive index layer of SiO _2, a high refractive index layer of 14.0 nm TiO ₂ , a low refractive index layer of 31.0 nm SiO _2, a high refractive index layer of 51.0 nm TiO ₂ ; An antireflection film was formed by seven layers of a low refractive index layer of SiO ₂ of 0 nm, a high refractive index layer of TiO ₂ of 35.0 nm, and a low refractive index layer of SiO ₂ of 89.0 nm.

(Evaluation method and evaluation criteria)
The plastic lenses with antireflection films produced in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated for heat resistance and durability (heat / light) by the following methods. The results are summarized in FIG.

(Heat resistance test)
The sample lens substrate used for the heat resistance test has a -5.00 degree and a center thickness of about 1 mm. First, regarding the heat resistance, the outer periphery of each of the obtained lenses was shaved so that the lens would fit within the frame of the spectacle lens, and the shaved lens was attached to the spectacle frame. In this state, the temperature at which cracks occur when heated in an atmospheric oven was defined as the heat resistant temperature. In the oven, the temperature was increased from 50 ° C. every 5 ° C., and after treatment at each temperature for 30 minutes, the presence or absence of cracks was observed. To determine the crack, the lens was held over a normal fluorescent lamp and the presence or absence of the crack was visually determined.

  “Initial” indicates a sample in which the lens after preparation is attached to the frame, and “humidification” indicates a sample in which the lens after being left to stand for one week in an environment of 40 ° C. and 80% humidity is attached to the frame. Indicates.

(Constant temperature and humidity test)
The sample lens substrate used in the constant temperature and humidity test has a -3.00 degree and a center thickness of about 1 mm. Each sample was allowed to stand in an atmosphere of 60 ° C. and 100% humidity after production, and the state after 1 day, 3 days, and 7 days was visually observed. The degree of change in the appearance of each sample was visually evaluated in the following stages. “○” indicates that no change is observed, “△” indicates that fine irregularities appear on the surface (less than half area), and “×” indicates that fine irregularities are present on the surface. It shows that it appears to have occurred (entire surface).

(Light resistance test)
The sample lens substrate used in the light resistance test has a -3.00 degree and a center thickness of about 1 mm. Each sample was exposed to a sunshine weather meter (manufactured by Suga Test Co., Ltd .; WEL-SUN-HC) using a xenon lamp for 80 hours, and the degree of change in the surface state was visually evaluated in the following stages. “◎” indicates that no change is observed, “◯” indicates that white turbidity has occurred, “Δ” indicates that a crack has occurred, and “×” indicates that peeling has occurred. Show.

(Evaluation results)
In the heat resistance test, Example 1 and Example 2 showed high heat resistance in both “initial stage” and “humidification”. In contrast, in Comparative Example 1, the “initial” heat resistance temperature was low, and in “humidification”, the heat resistance temperature significantly decreased. Also, in Comparative Example 2, the heat resistance temperature at the “initial stage” was low, and the heat resistance temperature decreased at “humidification”.

  In the constant temperature and humidity test, the appearance of Example 1, Example 2 and Comparative Example 1 did not change. On the other hand, in Comparative Example 2, irregularities occurred on the lens surface.

  In the light resistance test, Example 1, Example 2, and Comparative Example 2 showed no change. In contrast, in Comparative Example 1, peeling occurred.

  The following phenomena can be explained from the above evaluation results. In Examples 1 and 2, an antireflection film having a simple compound layer of silicon nitride is formed. First, the reason why the heat resistance of the samples of Examples 1 and 2 is higher by about 10 to 30 ° C. than the samples of Comparative Examples 1 and 2 is that the silicon nitride film has a very strong compressive stress. It is considered that no cracks were observed. In addition, since the silicon nitride film is dense and amorphous, it can prevent moisture and the like from passing therethrough. Therefore, it is considered that not only heat resistance but also temporal change and light resistance in a constant temperature and humidity test are excellent. Furthermore, silicon nitride also has the property of absorbing ultraviolet rays, which prevents the ultraviolet rays from reaching the hard coat layer or lens base material, and the light activity of Ti sol is generated in combination with the low moisture penetration. Without light resistance.

In Comparative Example 1, since both SiO ₂ and ZrO ₂ transmit moisture, the heat resistance in “humidification” is remarkably reduced, and ultraviolet rays are also transmitted, so that the hard coat or substrate is destroyed by the photoactivity of Ti sol. Therefore, it is considered that the light resistance is lowered. However, no change in appearance at constant temperature and humidity has occurred despite the permeation of moisture. This is because the entire membrane permeates moisture, and the substrate itself contains moisture, but the change is evenly generated in the lens surface, but a change in the visual appearance is observed. It is thought that it is not.

In Comparative Example 2, since TiO ₂ shields moisture and ultraviolet rays, the change in heat resistance of “humidification” is small and light resistance is also obtained as in the example. However, since TiO ₂ has a columnar crystal structure, a very small amount of moisture enters from the grain boundaries. For this reason, the base material partially absorbs water (swells). Therefore, it is considered that a portion that is not a water-absorbed portion exists in the surface, and irregularities can be confirmed by visual inspection. In terms of heat resistance, it is thought that the “humidification” in particular is slightly reduced due to the influence of a small amount of moisture.

  As described above, the performance of the optical element in terms of durability and the like is almost equal between the sample of Example 1 in which the three-layer antireflection film is formed and the sample of Example 2 in which the five-layer antireflection film is provided. it is conceivable that. If such performance is almost determined by the amount of silicon nitride contained in the antireflection film, the antireflection film having a three-layer structure in which the middle refractive index layer containing silicon nitride is formed in the first layer. The method is superior in that it is easy to manufacture and can shorten the throughput because the time for gas switching and the like is shortened.

  In the above, the antireflection film according to the present invention is formed by high-frequency sputtering vapor deposition. However, it is possible to perform the formation process of the metal film and the irradiation process of ions or radicals for oxidation or nitridation in a short cycle. A silicon nitride film can also be formed by using direct current sputtering, CVD (chemical vapor deposition), electron beam evaporation, ion plating, or the like.

  Further, in addition to the antireflection film, the surface can be subjected to water repellent treatment with a fluorine-based silane compound or the like, and the influence of moisture can be further prevented. Further, the present invention can be applied even when glass is used as the lens substrate.

The figure which shows the apparatus which forms the antireflection film which concerns on this invention. The figure which shows the film-forming conditions of Example 1 which concerns on this invention. 2 is a graph showing optical characteristics of the lens obtained in Example 1. The figure which shows the film-forming conditions of Example 2 which concerns on this invention. 5 is a graph showing optical characteristics of the lens obtained in Example 2. The figure which summarized the evaluation result regarding Examples 1 and 2 and Comparative Examples 1 and 2.

Explanation of symbols

  1 device, 70 workpieces (lens substrate)

Claims (6)

An optical element having an antireflection film formed directly on an optical substrate or sandwiching at least one other layer,
The antireflection film is a multilayer film including a low refractive index layer or a medium refractive index layer, and a high refractive index layer,
The optical element, wherein at least one of the high refractive index layers is a layer made of a simple compound of silicon nitride.   2. The antireflection film according to claim 1, wherein the antireflection film has a three-layer structure, and the medium refractive index layer made of a composite material of silicon nitride and silicon oxide and the simple compound of silicon nitride from the optical substrate side. An optical element comprising a high refractive index layer and the low refractive index layer made of a simple compound of silicon oxide.   3. The optical element according to claim 1, wherein the optical substrate is a plastic lens substrate. A method for producing an optical element having an antireflection film formed directly on an optical substrate or sandwiching at least one other layer,
An antireflection film forming step of forming the antireflection film by a multilayer film including a low refractive index layer or a medium refractive index layer and a high refractive index layer;
The antireflection film forming step includes a high refractive index layer forming step of forming the high refractive index layer with a simple compound of silicon nitride. In claim 4, the antireflection film forming step comprises:
A medium refractive index layer forming step of forming the medium refractive index layer with a composite material of silicon nitride and silicon oxide before the high refractive index layer forming step;
And a low refractive index layer forming step of forming the low refractive index layer with a simple compound of silicon oxide after the high refractive index layer forming step.   6. The method of manufacturing an optical element according to claim 4, wherein, in the high refractive index layer forming step, the high refractive index layer is formed by an RF sputtering vapor deposition method.

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