JP7343750B2 - Antireflection film, its manufacturing method, and optical member using the same - Google Patents

Description

The present invention relates to an antireflection film having either water-repellent or hydrophilic functionality, a method for manufacturing the anti-reflection film, and an optical member using the anti-reflection film.

Interchangeable lenses such as single focus lenses and zoom lenses used in imaging devices such as photographic and broadcast cameras are made up of multiple lenses in a lens barrel. The reflected light is amplified by multiple lenses. Therefore, when the amount of reflected light on each lens surface is large, not only is there a large loss in the amount of transmitted light, but also flare and ghosting due to multiple reflections within or between lenses are likely to occur, resulting in low contrast. Furthermore, with digitalization, the imaging portion of cameras and the like has been replaced with an imaging device instead of film, and light reflected from the surface of the imaging device has also become a cause of flare and ghosts.

In order to suppress the amount of reflected light on each lens surface, an antireflection film is provided on the surface of an optical element such as an interchangeable lens or an image sensor. For example, by combining dielectric thin films with different refractive indexes and setting the film thickness of each layer to 1/2λ or 1/4λ with respect to the design center wavelength λ, interference effects can be used to create a relationship between air and the thin film. An antireflection film with a multilayer structure is provided, which is designed to cancel out reflected light generated at each interface: an interface, an interface between thin films, and an interface between a thin film and a substrate. Magnesium fluoride (MgF ₂ ) with a refractive index of 1.38 is commonly applied to the outermost layer of the multilayer antireflection film to improve antireflection performance.

However, with the advent of AIoT in recent years, imaging devices used as digital devices such as sensing cameras such as digital cameras, network cameras, and in-vehicle cameras are required not only to have optical performance but also to be able to capture clear images in any location or situation. There is a demand for functionalities such as water/oil repellency, hydrophilicity/antifogging, and antifouling properties.

For example, as a method for imparting water repellency, a method is known in which a water repellent layer consisting of an SiO ₂ layer and a fluorine-containing silicon layer is formed on the outermost layer of an antireflection film by vacuum deposition. However, it is extremely difficult to control the optical film thickness of the SiO ₂ layer and the water-repellent layer to a film thickness that does not affect optical performance, and there is a problem that anti-reflection performance varies depending on the manufacturing lot. Ta.

JP-A-7-104102 (Patent Document 1) discloses that an antireflection layer with _two MgF layers as the outermost layer is formed on a glass substrate, and a SiO ₂ adhesion layer (with an optical thickness of 5 nm or less) is formed on the antireflection layer. This patent discloses a water-repellent anti-reflection film formed by forming a fluorine-containing silicon water-repellent layer (refractive index of about 1.38) with an optical thickness of 5 nm or less on top of the film.

The water-repellent anti-reflection film disclosed in _Patent Document 1 uses a SiO ₂ layer as an interaction (bonding part) to ensure adhesion between the MgF ₂ layer and the fluorine-containing silicon water-repellent layer. The ratio is high at 1.46, and the antireflection performance (degree of freedom in design) decreases. In addition, the optical thickness of the SiO ₂ layer and the fluorine-containing silicon layer is kept to 5 nm or less each to suppress the effect _on optical properties. Since the film is formed by vacuum evaporation, it is extremely difficult to control the optical film thickness to 5 nm or less without affecting optical performance, and the problem of variations in antireflection performance depending on the manufacturing lot has not been resolved. do not have.

Japanese Patent Application Publication No. 7-104102

Therefore, an object of the present invention is to provide an antireflection film that has excellent reflection spectral characteristics, excellent adhesion, and can impart water repellency or hydrophilicity.

Another object of the invention is to provide a method for manufacturing such antireflection coatings with high precision.

Yet another object of the present invention is to provide an optical member provided with such an antireflection film.

As a result of intensive research in view of the above issues, the present inventors formed an inorganic dense layer consisting of one or more layers whose outermost layer is fluoride, and had water repellency with a refractive index of 1.35 to 1.50 on the fluoride layer. We have discovered that by directly forming a silica fine particle layer, water repellency can be imparted without deteriorating antireflection performance, and it is also possible to convert the function to hydrophilicity, leading to the idea of the present invention.

That is, the anti-reflection film according to one embodiment of the present invention is an anti-reflection film that has an inorganic dense layer formed on the surface of a base material and consisting of one or more layers, and a silica fine particle layer formed thereon. hand,
The outermost layer of the inorganic dense layer is a fluoride,
The silica fine particle layer has an alkylsilyl group and/or an alkenylsilyl group on the surface, a refractive index of 1.35 to 1.50 , a porosity of 5 to 25%, and a water contact angle of 70 to 115°. It is characterized by

An anti-reflection film according to another embodiment of the present invention is an anti-reflection film having an inorganic dense layer formed on the surface of a base material and consisting of one or more layers, and a silica fine particle layer formed thereon. ,
The outermost layer of the inorganic dense layer is a fluoride,
The silica fine particle layer has an alkylsilyl group and/or an alkenylsilyl group on the surface, a refractive index of 1.35 to 1.50, and a porosity of 5 to 25%,
The silica fine particle layer further has a silanol group on the surface,
A hydrophilic film having a betaine structure and a silanol group is formed on the silica fine particle layer,
Characterized by a water contact angle of less than 15° .

The fluorides that make up the outermost layer of the inorganic dense layer include magnesium fluoride (MgF ₂ ), bismuth fluoride (BiF ₃ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), and thiolite (Na ₅ Al). ₃ F ₁₄ ), cryolite (Na ₃ AlF ₆ ), lanthanum fluoride (LaF ₃ ), lead fluoride (PbF ₂ ), lithium fluoride (LiF), neodymium fluoride (NdF ₃ ) or sodium fluoride (NaF ) is preferable. The materials of the inorganic dense layer other than fluoride include SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , ZnO, Ta ₂ O ₅ , Nb ₂ O ₅ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ Preferably, it is at least one selected from the group consisting of O ₃ , Y ₂ O ₃ , Pr ₆ O ₁₁ and Sb ₂ O ₃ .

The antireflection film of the present invention may further have a silanol group on the surface of the silica fine particle layer, and a hydrophilic film having a betaine structure and a silanol group may be formed on the silica fine particle layer. Preferably, such a hydrophilic antireflection film has a water contact angle of less than 15°. The optical thickness of the hydrophilic film is preferably 5 nm or less.

The above method for producing a hydrophilic antireflection film involves forming an inorganic dense layer on a base material, and forming a silica fine particle layer having an alkylsilyl group and/or an alkenylsilyl group on the inorganic dense layer by a wet process. After the film is fired and a silanol group is formed on the surface of the silica fine particle layer by irradiation with oxygen plasma, a hydrophilic member having a betaine structure and a silanol group is applied to the surface of the silica fine particle layer and fired. The hydrophilic film is formed by this. It is preferable that the silica fine particle layer is fired at a temperature of 150°C or higher and 400°C or lower, and the hydrophilic film is fired at a temperature of 80°C or higher and lower than 130°C.

The optical element of the present invention is characterized in that the above antireflection film is formed on the surface of a base material. Preferably, the refractive index of the base material is 1.45 to 1.95. The base material is preferably made of glass, quartz, silicon, or chalcogenide, and is preferably flat or lenticular.

It is preferable that the haze value of the optical element is 0.3% or less. Further, it is preferable that the optical element be used for light rays having a wavelength range of 300 nm to 2000 nm.

According to the present invention, an inorganic dense layer consisting of one or more fluoride layers is formed as the outermost layer, and a water-repellent silica fine particle layer with a refractive index of 1.35 to 1.50 is directly formed on the fluoride layer. As a result, water repellency can be imparted without deteriorating antireflection performance, and functional conversion to hydrophilicity is also possible.

FIG. 1 is a diagram showing an optical member provided with an antireflection film according to an embodiment of the present invention. FIG. 7 is a diagram showing an optical member provided with an antireflection film according to another embodiment of the present invention. 3 is a graph showing the spectral reflectance of Example 1. 3 is a graph showing the spectral reflectance of Example 2. 3 is a graph showing the spectral reflectance of Reference Example 1. 3 is a graph showing the spectral reflectance of Example 3. 3 is a graph showing the spectral reflectance of Example 4. 3 is a graph showing the spectral reflectance of Example 5. 3 is a graph showing the spectral reflectance of Comparative Example 2. 3 is a graph showing the spectral reflectance of Comparative Example 3.

[1] First Embodiment FIG. 1 is a diagram showing an optical element equipped with a water-repellent antireflection film according to an embodiment of the present invention. The optical element shown in FIG. 1 includes a base material 10 and an antireflection film 20 formed on the surface of the base material 10. The antireflection film 20 includes, in order from the base material 10, an inorganic dense layer 21 whose outermost layer is a fluoride, and a silica fine particle layer 22 having an alkylsilyl group and/or an alkenylsilyl group.

(1) Base material Although the base material 10 shown in FIG. 1 has a flat plate shape, the present invention is not limited thereto, and may be in the shape of a lens, and can be applied to any base material used for an optical element. For example, it may be a lens, prism, light guide, film, or diffraction element that has a curvature on its surface. The base material 20 preferably has a refractive index of 1.45 to 1.95 with respect to the d-line (hereinafter simply referred to as "d-line") of a He light source having a wavelength of 587.56 nm.

The material of the base material 10 is not particularly limited, but glass, quartz, silicon, chalcogenide, etc. may be used. Specifically, FK03, FK5, BK7, SK20, SK14, LAK7, LAK10, LASF016, LASF04 SFL03, LASF08, NPH2, TAFD4, S-FPL53 (registered trademark), S-PSL5 (registered trademark), S-BSL7 ( Optical glass such as (registered trademark), S-BAL50 (registered trademark), S-BSM14 (registered trademark), S-LAL7 (registered trademark), S-LAL10 (registered trademark), Pyrex (registered trademark) glass, quartz, synthetic Examples include quartz, blue plate glass, white plate glass, Lumicera (registered trademark), Zerodur (registered trademark), fluorite, sapphire, and the like.

(2) Inorganic dense layer The inorganic dense layer 21 consists of at least one dense inorganic layer, and the outermost layer is a fluoride. Examples of fluorides include magnesium fluoride (MgF ₂ ), bismuth fluoride (BiF ₃ ), calcium fluoride (CaF ₂ ), cerium fluoride (CeF ₃ ), thiolite (Na ₅ Al ₃ F ₁₄ ), and cryofluoride. Examples include light (Na ₃ AlF ₆ ), lanthanum fluoride (LaF ₃ ), lead fluoride (PbF ₂ ), lithium fluoride (LiF), neodymium fluoride (NdF ₃ ), or sodium fluoride (NaF). Magnesium fluoride (MgF ₂ ) is particularly preferred.

The inorganic dense layer 21 may be a single layer of an inorganic layer made of fluoride, or may be a plurality of layers of two or more layers including an inorganic layer made of fluoride as the outermost layer. When the inorganic dense layer 21 is composed of multiple layers, the inorganic layer other than fluoride may be a single oxide of an inorganic material commonly used as a dielectric film of an antireflection film, or may be a mixture or a compound. For example, _SiO2 , _{Al2O3 ,} TiO2, _ZrO2 , _ZnO , _Ta2O5 , _Nb2O5 , _{HfO2 , CeO2} , _SnO2 , _{In2O3 , Y2O3 , Pr6O . 11} and at least one selected from the group consisting of Sb ₂ O ₃ . The above-mentioned fluoride may be used as the material for the inorganic layers other than the outermost layer.

The layer structure and film thickness of the inorganic dense layer 21 can be appropriately determined according to the optical characteristics and desired optical function of the silica fine particle layer 22 by a method such as determining an optimum value using computer simulation.

(3) Silica fine particle layer The silica fine particle layer 22 is a porous layer made of silica fine particles, and includes an alkylsilyl group and/or an alkenyl group formed by bonding an alkyl group and/or alkenyl to a silicon atom forming a skeleton of at least some of the silica fine particles. /or an alkenylsilyl group is present. Therefore, the hydrophobic alkylsilyl group and/or alkenylsilyl group are oriented on the surface side of the silica fine particle layer 22, thereby imparting a water-repellent function to the antireflection film 20.

The presence of alkylsilyl groups and/or alkenylsilyl groups on the surface of the silica fine particle layer 22 also provides excellent adhesion to the fluoride in the outermost layer of the inorganic dense layer 21. In other words, when silica sol and silane coupling agents used in wet processes such as the sol-gel method are formed on MgF ₂ , the coating is repelled by the MgF ₂ , making it difficult to form a film and having poor adhesion. However, by using a coating liquid in which fine silica particles contain an alkylsilyl group and/or an alkenylsilyl group, the film forming property on MgF ₂ is improved, and the adhesion with MgF ₂ after baking and hardening is improved. and provides excellent mechanical strength. This is considered to be because the remaining alkoxysilane or siloxane skeleton or silanol group forms an oxide layer of SiO ₂ at the interface with MgF ₂ and is physically adsorbed with MgF ₂ . Therefore, the silica fine particle layer of the present invention can be formed directly on MgF ₂ without the need to interpose a metal oxide such as SiO ₂ as an interaction (bonding part) in advance, so it does not impair antireflection properties. Functionality such as water repellency or hydrophilicity can be imparted without the need for water repellency or hydrophilicity.

In order to simplify the manufacturing process, either an alkylsilyl group or an alkenylsilyl group is preferably present on the surface of the silica fine particle layer 22, and from the viewpoint of functionality and adhesion, an alkylsilyl group is preferable. .

The alkylsilyl group may be a monoalkylsilyl group in which one alkyl group is bonded to a silicon atom, or a dialkylsilyl group in which two alkyl groups are bonded, but the mechanical strength is maintained due to the Si-O bond of the silica fine particles. However, in order to impart excellent functionality and adhesion, a monoalkylsilyl group is preferred. Specific examples of the alkyl group include ethyl group, propyl group, n-butyl group, etc., with methyl group being particularly preferred.

Like the alkylsilyl group, the alkenylsilyl group may be a monoalkenylsilyl group in which one alkenyl group is bonded to a silicon atom, or it may be a dialkenylsilyl group in which two alkenyl groups are bonded; It is preferable to have one. Specific examples of the alkenyl group include a vinyl group, an allyl group, and the like, with a vinyl group being particularly preferred.

The alkylsilyl group and/or alkenylsilyl group may be present throughout the surface side of the silica fine particle layer 22, but 20 to 80% of the silicon atoms on the surface of the silica fine particle layer 22 are the alkylsilyl group and/or Preferably, it constitutes an alkenylsilyl group. If it is less than 20%, the water repellent effect will be low and the contact angle of pure water will be low, and if it is more than 80%, the number of siloxane bonds formed between the silica fine particles will decrease, resulting in a decrease in the mechanical strength of the silica fine particle layer.

The refractive index of the silica fine particle layer 22 for the d-line is 1.35 to 1.50. If the refractive index of the silica fine particle layer 22 formed on the surface of the inorganic dense layer 21 exceeds 1.50, the antireflection performance (degree of freedom in design) will decrease. In addition, when the refractive index is less than 1.35, the porosity of the silica fine particle layer 22 becomes high, so that the mechanical strength (scratch resistance) deteriorates. The refractive index of the silica fine particle layer 22 is preferably 1.38 to 1.46, more preferably 1.38 to 1.41.

The porosity of the silica fine particle layer 22 is a parameter that is appropriately determined depending on the refractive index; when the porosity of the silica fine particle layer 22 is high, the refractive index is low, and when the porosity is low, the refractive index is high. The porosity of the silica fine particle layer 22 is preferably 5 to 25%. When the porosity is less than 5%, the refractive index approaches that of a dense silica layer, and the antireflection performance (degree of freedom in design) decreases. Moreover, if the porosity exceeds 25%, mechanical strength (scratch resistance) will deteriorate. The porosity of the silica fine particle layer 22 is more preferably 5 to 20%, and even more preferably 10 to 15%.

Although the water repellency of the surface of the silica fine particle layer 22 can be set as appropriate, it is preferable that the contact angle of water on the surface is 70 to 115°. If the water contact angle is less than 70°, a sufficient water repellency effect cannot be obtained. Furthermore, in order to obtain a good balance between antireflection performance and water repellency, the upper limit of the water contact angle is preferably about 115°. Although the degree of hydrophilicity of the surface of the hydrophilic film 33 on the surface of the silica fine particle layer 22 can be set as appropriate, it is preferable that the contact angle of water on the surface is less than 15°. If the contact angle of water is more than 15°, a sufficient hydrophilic effect cannot be obtained. Further, in order to improve the visibility when water droplets are attached, it is desirable that the contact angle of water is 5° or less.

The optical thickness of the silica fine particle layer 22 is preferably 20 to 100 nm. If the film thickness is less than 20 nm, the water repellent function cannot be sufficiently exhibited. Furthermore, if the film thickness exceeds 100 nm, optical performance will deteriorate. The optical thickness of the silica fine particle layer 22 is more preferably 25 to 50 nm.

It is preferable that the optical element provided with such an antireflection film 20 has a haze value (haze value) of 0.3% or less. As a result, sufficient antireflection properties can be obtained even when the lens barrel is configured with a plurality of lenses, such as an interchangeable lens. Further, it is desirable that the optical element has sufficient anti-reflection properties for light in the wavelength range of 300 nm to 2000 nm and can be used suitably.

(4) Manufacturing method
(4-1) Method of forming the inorganic dense layer The inorganic dense layer 21 is formed by a dry process such as a PVD method or a CVD method such as a vacuum evaporation method or a sputtering method, or a wet process such as a sol-gel method or SOG (Spin on glass). can be formed. From the viewpoint of optical properties and economical efficiency, vacuum evaporation is particularly preferred.

(4-2) Method for Forming Silica Fine Particle Layer The silica fine particle layer 22 is preferably formed by a wet method, particularly a sol-gel method. That is, it is formed by applying a coating liquid obtained from a hydrolyzed polycondensate of a trifunctional alkoxysilane such as methyltrialkoxysilane or a tetrafunctional alkoxysilane such as tetraethoxysilane, followed by drying and baking. Examples of the sol-gel method include WO 2002/018982, WO 2006/030848, JP 2006-3562, JP 2006-215542, JP 2007-94150, and JP 2008-225210. No., JP 2008-233403, JP 2009-75583, JP 2009-258711, "Journal of Sol-Gel Science and Technology", 2000, It can be obtained by the method described in Vol. 18, pp. 219-224.

Using a mixed solution of a first sol consisting of a silica skeleton-forming compound of alkoxysilane and a second sol consisting of a silica skeleton-forming compound of alkoxysilane modified with an alkyl group and/or alkenyl group, silica Although the method for forming the fine particle layer will be described in detail, the present invention is not limited thereto.

The method of forming a silica fine particle layer using a mixed liquid includes (i) a step of preparing a first sol by hydrolyzing and polycondensing an alkoxysilane under an acidic catalyst, and (ii) a step of preparing a first sol using an alkyl group and/or an alkenyl group. A step of preparing a second sol by hydrolyzing and polycondensing a group-modified alkoxysilane under an acidic catalyst, and (iii) preparing a coating liquid by mixing the first sol and the second sol. (iv) applying the obtained mixed sol onto a substrate; and (v) firing.

(i) First sol preparation process
(a) Alkoxysilane The starting material alkoxysilane is preferably a tetraalkoxysilane monomer or oligomer (condensation product). When a tetrafunctional alkoxysilane is used, a sol of colloidal silica particles having a relatively large particle size can be obtained. Tetraalkoxysilane is represented by Si(OR) ₄ [R is an alkyl group having 1 to 5 carbon atoms (methyl, ethyl, propyl, butyl, etc.) or an acyl group having 1 to 4 carbon atoms (acetyl, etc.)] Preferably. Specific examples of tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane, and the like. Among them, tetramethoxysilane and tetraethoxysilane are preferred.

(b) Organic solvent As the organic solvent, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butyl alcohol are preferred, and ethanol, 2-propanol, and 1-butanol are preferred. More preferred.

(c) Hydrolysis and polycondensation in the presence of an acidic catalyst Hydrolysis and polycondensation proceed by adding an organic solvent, an acidic catalyst, and water to alkoxysilane. Examples of acidic catalysts include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and acetic acid. The sol containing the acidic catalyst is preferably heated and stirred at 10 to 90°C for about 15 minutes to 24 hours. Hydrolysis and polycondensation progresses by heating and stirring.

The quantitative ratio of the organic solvent to the alkoxysilane is preferably set so that the concentration of the alkoxysilane is 0.1 to 70% by mass (silica concentration) in terms of SiO ₂ . When the silica concentration exceeds 70% by mass, the particle size of the silica particles in the resulting sol becomes too large, the viscosity increases, and gelation progresses. On the other hand, if the silica concentration is less than 0.1, the particle size of the silica particles in the resulting sol will be too small. Note that the molar ratio of organic solvent/alkoxysilane is preferably in the range of 1×10 ⁻¹ to 1×10 ³ .

The molar ratio of water/alkoxysilane is preferably 1 to 40. If the molar ratio of water/alkoxysilane exceeds 40, the hydrolysis reaction proceeds too quickly, making it difficult to control the reaction and making it difficult to obtain uniform silica particles. On the other hand, if it is less than 1, hydrolysis of the alkoxysilane will not occur sufficiently.

The median diameter of the silica particles in the first sol is 150 nm or less, preferably 10 to 50 nm. The median diameter is measured by dynamic light scattering.

(ii) Second sol preparation step
(a) Alkoxysilane The starting material is preferably an alkoxysilane monomer or oligomer (condensation product) modified with an alkyl group and/or an alkenyl group. One alkyl group and/or alkenyl group may be bonded to the alkoxysilane, or two alkyl groups may be bonded to the alkoxysilane.

Specific examples of alkoxysilanes with one alkyl group bonded include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, and n-butyltrimethoxysilane. Examples include alkyltrialkoxysilanes such as silane. Specific examples of alkoxysilanes having one alkenyl group bonded to them include alkenyltrialkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, and allyltriethoxysilane. Specific examples of alkoxysilanes in which two alkyl groups are bonded include dialkyldialkoxysilanes such as dimethyldimethoxysilane and dimethyldiethoxysilane.

(b) Organic solvent As the organic solvent, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butyl alcohol are preferred, and ethanol, 2-propanol, and 1-butanol are preferred. More preferred.

(c) Hydrolysis and polycondensation in the presence of an acidic catalyst Hydrolysis and polycondensation proceed by adding an organic solvent, an acidic catalyst, and water to alkoxysilane. Examples of acidic catalysts include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and acetic acid. The sol containing the acidic catalyst is preferably heated and stirred at 10 to 90°C for about 15 minutes to 24 hours. Hydrolysis and polycondensation progresses by heating and stirring.

The quantitative ratio of the organic solvent to the alkoxysilane is preferably set so that the concentration of the alkoxysilane is 0.1 to 70% by mass (silica concentration) in terms of SiO ₂ . When the silica concentration exceeds 70% by mass, the particle size of the silica particles in the resulting sol becomes too large, the viscosity increases, and gelation progresses. On the other hand, if the silica concentration is less than 0.1, the particle size of the silica particles in the resulting sol will be too small. Note that the molar ratio of organic solvent/alkoxysilane is preferably in the range of 1×10 ⁻¹ to 1×10 ³ .

The molar ratio of water/alkoxysilane is preferably 1 to 40. If the molar ratio of water/alkoxysilane exceeds 40, the hydrolysis reaction proceeds too quickly, making it difficult to control the reaction and making it difficult to obtain uniform silica particles. On the other hand, if it is less than 1, hydrolysis of the alkoxysilane will not occur sufficiently.

The median diameter of the colloidal silica particles in the second sol is between 1 and 150 nm, preferably between 10 and 50 nm.

(iii) Mixing step The first sol and second sol obtained as described above are mixed to prepare a coating liquid. After mixing the first and second acidic sols, it is preferable to stir the mixture at room temperature of 10 to 30°C for about 10 minutes to 3 hours.

The second sol may be added to the first sol, or the first sol may be added to the second sol. In order to adjust the concentration and fluidity of the coating liquid and improve its coating suitability, the first sol and the second sol may be added to the developing solvent. At that time, after adding the first sol and the second sol, it is preferable to stir at room temperature of 10 to 30°C for about 10 minutes to 3 hours. Examples of the developing solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butyl alcohol. The silica concentration of the alkoxysilane in the mixed liquid in terms of SiO ₂ is preferably 0.05 to 10% by mass. If the silica concentration in the liquid mixture exceeds 10% by mass, the viscosity will be high, resulting in poor film-forming properties and poor leveling properties. On the other hand, if the silica concentration is less than 0.05% by mass, the solid content concentration will be too low and the film thickness during film formation will be too thin, making it difficult to impart functionality such as water repellency and hydrophilicity to the substrate. .

The solid content mass ratio of the first sol/second sol is preferably 0.05 to 10. If this ratio is less than 0.05, a large amount of alkylsilyl groups or alkenylsilyl groups will be formed in the silica particles, reducing the bonding strength of the silica particles and reducing the scratch resistance. If this ratio exceeds 10, water repellency will not be sufficient because there are few alkylsilyl groups and/or alkenylsilyl groups present on the surface of the silica fine particle layer. The solid content mass ratio of the first sol/second sol is more preferably 0.1 to 2.

(iv) Application process Methods for applying the coating liquid to the surface of the base material include dip coating, spray coating, spin coating, printing, and the like. When applying to a three-dimensional structure such as a lens, a dipping method is preferred. Preferably, the pulling speed in the dipping method is about 0.1 to 10 mm/sec. The concentration of silica in the coating liquid is preferably 0.05 to 10% by mass.

(v) Firing process The firing conditions for the coating film are appropriately selected depending on the desired porosity and water repellency. The porosity (refractive index) of the silica fine particle layer can be controlled by the temperature at which the silica sol is baked and solidified after being formed into a film. Furthermore, when the firing temperature of the silica sol is high, the amount of residual hydroxyl groups is reduced, and the degree of water repellency is increased. The firing temperature is preferably 250 to 400°C. If the firing temperature is less than 250°C, scratch resistance and water repellency will be insufficient. If the firing temperature exceeds 400°C, the porosity of the silica fine particle layer will decrease, the refractive index will increase, and the alkyl group and/or alkenyl group of the alkylsilyl group and/or alkenylsilyl group will be burned out. Water repellent effect is reduced. More preferably, the firing temperature is 300 to 350°C.

[2] Second Embodiment FIG. 2 is a diagram showing an optical element equipped with a hydrophilic antireflection film according to another embodiment of the present invention. The optical element shown in FIG. 2 includes a base material 10 and an antireflection film 30 formed on the surface of the base material 10. The antireflection film 30 includes, in order from the base material 10, an inorganic dense layer 31 whose outermost layer is fluoride, a silica fine particle layer 32 having an alkylsilyl group and/or an alkenylsilyl group and a silanol group, and a silica fine particle layer 32. It has a hydrophilic film 33 having a betaine structure and silanol groups formed on the surface.

(1) Base material, inorganic dense layer The base material 10 and the inorganic dense layer 31 can be the same as the base material 10 and the inorganic dense layer 21 of the first embodiment.

(2) Silica fine particle layer The silica fine particle layer 32 has a silanol group on the outer surface opposite to the surface in contact with the inorganic dense layer 31. The inorganic dense layer 31 can be the same as the inorganic dense layer 21 of the first embodiment except that it has silanol groups on the outer surface. A silanol group formed by bonding a hydroxyl group to a silicon atom existing as a skeleton is provided on the outer surface side of the silica fine particle layer 32. This provides excellent adhesion between the betaine structure and the hydrophilic film 33 having silanol groups.

The silanol group may be present on the entire outer surface side of the silica fine particle layer 32, but it is preferable that the silanol group is present at a ratio of 20 to 80% of the silicon atoms present as a skeleton on the outer surface side. If it is less than 20%, the number of siloxane bonds formed with the betaine structure will decrease, making it difficult to impart hydrophilicity, resulting in a decrease in hydrophilicity. If it exceeds 80%, the silanol groups are not used for the siloxane bonds formed between the silica fine particles, resulting in fewer siloxane bonds and a decrease in the mechanical strength of the silica fine particle layer. Furthermore, as will be described later, even if a silanol group is formed by substituting an alkylsilyl group and/or an alkenylsilyl group, and almost no alkylsilyl group and/or alkenylsilyl group remains on the outer surface side of the silica fine particle layer 32, It is good and preferably present in a proportion of 20 to 60%.

(3) Hydrophilic Film The hydrophilic film 33 has a betaine structure that can exhibit excellent hydrophilicity and a terminal silanol group that has excellent adhesion to the silica fine particle layer 32. The betaine structure is not particularly limited as long as it is one commonly used as a hydrophilic polymer, and examples include methacrylic acid esters containing a betaine group. Examples of betaine groups include carboxybetaine groups.

Hydrophilicity can be imparted simply by providing silanol groups in the silica fine particle layer 32, but if left in the atmosphere, the silanol groups become contaminated with time and the hydrophilicity deteriorates. Therefore, a compound having a silanol group and a betaine structure in the molecule is bonded to this silanol group by dehydration condensation of the silanols to form a hydrophilic betaine structure on the outer surface of the silica fine particle layer 32. Thereby, the hydrophilic effect can be continuously expressed.

The optical thickness of the hydrophilic film 33 is preferably 10 nm or less. If the film thickness exceeds 10 nm, the antireflection properties will deteriorate. Moreover, if the film thickness is less than 3 nm, hydrophilicity is insufficient. More preferably, the optical thickness of the hydrophilic film 33 is 3 to 7 nm.

Although the hydrophilicity of the surface of the hydrophilic film 33 can be set as appropriate, it is preferable that the contact angle of water on the surface is less than 15°. If the contact angle of water is more than 15°, a sufficient hydrophilic effect cannot be obtained. Further, in order to improve the visibility when water droplets are attached, it is desirable that the contact angle of water is 5° or less.

(4) Manufacturing method
(4-1) Method for forming an inorganic dense layer The inorganic dense layer 31 can be formed in the same manner as the inorganic dense layer 21 of the first embodiment.

(4-2) Method for Forming Silica Fine Particle Layer The silica fine particle layer 32 is formed in the same manner as the silica fine particle layer 22 of the first embodiment, and then a step of forming silanol groups on the outer surface is performed. The method for forming silanol groups is, for example, by irradiating the outer surface of the silica fine particle layer 32 with oxygen plasma to break the Si-C bonds of the alkylsilyl groups and/or alkenylsilyl groups on the outer surface, and then newly forming the silanol groups thereon. Examples include a method of forming a silanol group. Oxygen plasma is irradiated with oxygen plasma for 0.5 to 10 minutes at an irradiation intensity of 100 to 1500 W under a reduced pressure of 10 to 100 Pa while supplying oxygen at a flow rate of 50 to 100 cc/min using a plasma cleaner, for example. is preferable.

(4-3) Method for forming a hydrophilic film A sol for forming a hydrophilic film is applied as a coating liquid to the surface of the silica fine particle layer 32. Examples of the coating method include a dip coating method, a spray coating method, a spin coating method, and a printing method. When the base material 10 is applied to a three-dimensional structure such as a lens, a dipping method is preferred. Preferably, the pulling speed in the dipping method is about 0.1 to 10 mm/sec.

The applied coating liquid is baked to produce a hydrophilic film. The firing temperature is preferably 80°C or higher and lower than 130°C. If the firing temperature is less than 80°C, the adhesion will be weak and the hydrophilic function will tend to deteriorate. If the firing temperature is 130°C or higher, the hydrophilic functional groups will be altered and the hydrophilic function will deteriorate. The firing time is preferably 1 minute to 1 hour. The obtained hydrophilic membrane may be washed if necessary. Cleaning can be performed, for example, by rinsing with pure water.

The anti-reflection film of the present invention has excellent refractive index characteristics and excellent functionality such as water repellency or hydrophilicity, and can be suitably used for optical members used for light rays in the wavelength range of 300 nm to 2000 nm. can. Such optical members include, for example, lenses, prisms, filters, etc. mounted on optical equipment such as television cameras, video cameras, digital cameras, vehicle-mounted cameras, microscopes, and telescopes.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. The optical film thickness and refractive index of the samples prepared in Examples and Comparative Examples were measured using a lens reflectance measuring device (model number: USPM-RU, manufactured by Olympus Corporation). The results obtained are shown in Table 1.

Example 1
[1-1 Formation of dense layer]
_MgF2 monomers were deposited on a BK7 glass flat plate (diameter: 30 mm, refractive index: 1.518) using a vacuum evaporation method using a vacuum evaporation apparatus equipped with an electron beam evaporation source so as to have the layer structure shown in Table 1. Formed a dense layer of layers.

[1-2 Preparation of water-repellent silica sol]
3.91 g of tetraethoxysilane and 1.35 g of an aqueous hydrochloric acid solution of pH 2 were placed in a 100 ml two-necked eggplant flask, and an Allene condenser was attached, followed by stirring and refluxing at 60°C for 2 hours. To the sol thus obtained, 4.62 g of ethanol and 10.73 g of 2-propanol were added and stirred for 10 minutes to obtain sol A in which tetraethoxysilane was hydrolyzed and polymerized. Next, a new 100 ml two-necked eggplant flask was prepared, and 10.3 g of methyltriethoxysilane and 3.04 g of a pH 3 acetic acid aqueous solution were added thereto, an Allene condenser was attached, and the mixture was stirred and refluxed at 60°C for 2 hours. . To the sol thus obtained, 1.08 g of ethanol and 2.52 g of 2-propanol were added and stirred for 10 minutes to obtain sol B in which methyltriethoxysilane was hydrolyzed and polymerized. Separately, 64.71 g of 2-propanol and 7.42 g of 1-butanol were placed in a 100 ml disposable beaker and stirred to prepare a developing solvent for water-repellent silica sol in advance. To this developing solvent, 4.12 g of Sol A and 3.33 g of Sol B produced above were added, and the mixture was further stirred for 10 minutes to produce a water-repellent silica sol.

[1-3 Preparation of water-repellent anti-reflection film]
The prepared water-repellent silica sol was dip-coated onto a BK7 glass substrate on which a MgF ₂ film was vacuum-deposited at a pulling speed of 1 mm/sec, and the resulting film-formed substrate was placed in an inert oven and heated at 200°C. After baking for 1.5 hours, a water-repellent antireflection film 20 having a silica fine particle layer having methylsilyl groups formed on the surface as shown in FIG. 1 was produced.

Example 2
A water-repellent anti-reflection film 20 was produced in the same process as in Example 1 except that the firing temperature was 350°C.

Reference example 1
A water-repellent anti-reflection film 20 was produced in the same manner as in Example 1, except that an electric furnace was used instead of an inert oven and the firing temperature was 500°C.

Example 3
Same as Example 2 except that the glass substrate was changed to an FK5 glass flat plate (diameter: 30 mm, refractive index: 1.489), and the dense layer was changed to a 6-layer dense layer shown in Table 1, the outermost layer of which is a MgF ₂ film. In the second step, a water-repellent anti-reflection film 20 was produced.

Example 4
The water-repellent anti-reflection film 20 produced in the same process as in Example 2 was heated for 48 hours while supplying oxygen at a flow rate of 100 cc/min using a plasma cleaner (model number: PDC210) manufactured by Yamato Scientific Co., Ltd. Oxygen plasma was irradiated for 5 minutes at an irradiation intensity of 500 W under a reduced pressure of Pa. This film-forming substrate was lifted into a solution in which a hydrophilic film-forming sol (LAMBIC-771W, manufactured by Osaka Organic Chemical Industry Co., Ltd.) made of a hydrophilic polymer containing a betaine group and a silanol group was diluted twice with pure water. A hydrophilic antireflection film 30 was prepared by dip coating at a speed of 3.0 mm/sec, heating the film-forming substrate at 120° C. for 30 minutes, and rinsing with pure water.

Example 5
A hydrophilic anti-reflection film 30 was produced in the same process as in Example 4, except that the water-repellent anti-reflection film 20 produced in the same process as in Example 3 was used.

Comparative example 1
The substrate prepared in [1-1] of Example 1, in which the MgF ₂ film was vacuum-deposited on the BK7 glass substrate, was used as the sample of Comparative Example 1.

Comparative example 2
[(1-1) Preparation of organically modified silica wet gel (surface modification with TMCS)]
(1-1-1) Preparation of silica wet gel 5.90 g of methyl silicate 51 (average tetramer of tetramethoxysilane) manufactured by Fuso Chemical Industries, Ltd. and 50.55 g of methanol (special grade) manufactured by Wako Pure Chemical Industries, Ltd. 3.20 g of 0.10 N aqueous ammonia prepared from 28% ammonia (special grade) manufactured by Wako Pure Chemical Industries, Ltd. was added to the mixture of 100 g and stirred for 10 minutes. Thereafter, the mixture was allowed to stand at room temperature for 3 days to accelerate the hydrolysis polycondensation reaction and was aged.

(1-1-2) Solvent replacement of silica wet gel The silica wet gel prepared in step (1-1-1) was cut into a size of about 2 cm square, placed in a crystallizing dish, and washed at Wako Pure Chemical Industries, Ltd. Ethanol (special grade) manufactured by Co., Ltd. was added thereto, and the mixture was slowly stirred for one day at 300 rpm using a magnetic stirrer to replace the solvent in the silica wet gel with ethanol. By decantation after substitution, a wet silica gel in which the ethanol solvent had been substituted was obtained. Ethanol used for solvent replacement was added at a ratio of 100 ml to 20 g of silica wet gel.

Next, 4-methyl-2-pentanone (special grade) manufactured by Wako Pure Chemical Industries, Ltd. was added to the silica wet gel whose solvent had been replaced with ethanol, and the mixture was slowly stirred at 300 rpm using a magnetic stirrer for 1 day. , the solvent in the silica wet gel was replaced with 4-methyl-2-pentanone. By decantation after substitution, a silica wet gel in which the solvent was substituted with 4-methyl-2-pentanone was obtained. 4-Methyl-2-pentanone used for solvent replacement was added at a ratio of 100 ml to 20 g of silica wet gel.

(1-1-3) Surface modification of silica wet gel 60 g of the wet gel prepared in step (1-1-2) was placed in a crystallizing dish, and trimethylchlorosilane from Tokyo Chemical Industry Co., Ltd. and Wako Pure Chemical Industries, Ltd. A liquid mixture consisting of 4-methyl-2-pentanone (special grade) manufactured by ) was added and stirred slowly at 300 rpm for 1 day using a magnetic stirrer to organically modify the silicon oxide terminals in the silica wet gel. An organically modified silica wet gel was obtained by decantation after organic modification. A mixed solution of trimethylchlorosilane and 4-methyl-2-pentanone was prepared by mixing them at a volume ratio of 5 ml:95 ml. For the organic modification of the silica wet gel, 100 ml of a mixture of trimethylchlorosilane and 4-methyl-2-pentanone was added to 20 g of the silica wet gel.

(1-1-4) Washing of organically modified silica wet gel 60 g of the wet gel prepared in step (1-1-3) was placed in a crystallizing dish, and 4-methyl-2-pentanone manufactured by Wako Pure Chemical Industries, Ltd. (special grade) was added thereto and slowly stirred for one day at 300 rpm using a magnetic stirrer to wash the organically modified silica wet gel. Thereafter, by decantation, an organically modified wet gel from which the organic modifier and by-products were removed was obtained. 4-Methyl-2-pentanone used for washing was added at a ratio of 100 ml to 20 g of silica wet gel.

[(1-2) Preparation of ultrasonic dispersion of organically modified silica wet gel]
Place the organically modified silica wet gel prepared in step (1-1) in a 100 ml disposable beaker, add 4-methyl-2-pentanone (special grade) manufactured by Wako Pure Chemical Industries, Ltd., and stir using a magnetic stirrer for 700 ml. Ultrasonic dispersion was carried out for 2 hours using an ultrasonic dispersion device (rated output: 600 W, oscillation frequency: 19.5 KHz ±1 KHz) manufactured by Nippon Seiki Seisakusho Co., Ltd. while stirring at rpm. The concentration of the dispersion solution was adjusted to 3.5 wt% in terms of solid content to obtain a coating solution for producing a porous silica membrane. The solid content concentration of the dispersion solution was prepared from the solid content calculated from the mass before and after drying when the organically modified silica wet gel was dried by placing it in a 120°C blower constant temperature oven (inert oven) for 2 hours.

[(1-3) Application of sol to substrate and hardening of coating film]
On the MgF ₂ film vacuum-deposited on the BK7 glass substrate prepared in step [1-1] of Example 1, the coating solution for preparing the porous silica film prepared in step (1-2) above was spin-coated. A sample of Comparative Example 2 was obtained by applying the coating according to the method and air drying.

Comparative example 3
The sample prepared in Comparative Example 2 was placed in an electric furnace and fired at 400° C. for 1.5 hours to obtain a sample for Comparative Example 3.

[Measurement of spectral reflectance]
The spectral reflectance of the samples prepared in Examples 1 to 5, Reference Example 1, and Comparative Examples 2 and 3 was measured. The spectral reflectance was measured at an incident angle of 0° in the wavelength range of 380 to 780 nm using a lens reflectance measuring device (model number: USPM-RU, manufactured by Olympus Corporation). In addition, for the above Examples, Reference Examples, and Comparative Examples, the spectral reflectance of the base material and the spectral reflectance when a single MgF ₂ layer was formed on the base material were also measured in the same manner. The obtained results are shown in Figures 3 to 10.

[Measurement of HAZE value and water contact angle]
The HAZE value (haze value) of the samples prepared in Examples, Reference Examples, and Comparative Examples was measured using Murakami Color Research Institute Co., Ltd._HM-150, and the contact angle of pure water was measured using Kyowa Kagaku Co., Ltd. The measurement was carried out using a contact angle measurement device manufactured by Manufacturer Co., Ltd. The results obtained are shown in Table 2.

[Evaluation method of scratch resistance and adhesion]
The anti-reflection film on the surface of the base material was coated with a 20 mm x 20 mm nonwoven fabric (trade name "Spic Lens Wiper", manufactured by Ozu Sangyo Co., Ltd.) at a speed of 3600 mm/min while applying a pressure of 1 kg/cm ² for 30 minutes. Rubbing, surface scratches, and peeling conditions were visually confirmed and evaluated based on the following criteria. The results obtained are shown in Table 2.
<Judgment criteria>
A part of the anti-reflection film was scratched, but it did not peel off...○
The anti-reflective film was scratched and some parts peeled off or the reflective color changed...△
The anti-reflection film has completely peeled off...×

As shown in Tables 1 and 2 and Figures 3 to 10, the antireflection films of Examples 1 to 5 have excellent scratch resistance and adhesion while maintaining excellent antireflection properties, and are water repellent or hydrophilic. It also had the functionality of In Reference Example 1, the silica fine particle layer was fired at a temperature of 500°C, so the methylsilyl groups on the surface were burned out and the layer became hydrophilic. The antireflection film of Comparative Example 1 in which no silica fine particle layer was formed had a pure water contact angle of 41° and did not have either water repellency or hydrophilic functionality. Comparative Examples 2 and 3 having a silica airgel film as the outermost layer had poor scratch resistance and adhesion.

10... Base material 20, 30... Antireflection film 21, 31... Inorganic dense layer 22, 32... Silica fine particle layer 33... Hydrophilic film

Claims (17)

An antireflection film comprising an inorganic dense layer formed on the surface of a base material and consisting of one or more layers, and a silica fine particle layer formed thereon,
The outermost layer of the inorganic dense layer is a fluoride,
The silica fine particle layer has an alkylsilyl group and/or an alkenylsilyl group on the surface, a refractive index of 1.35 to 1.50, and a porosity of 5 to 25%,
An anti-reflection film characterized by a water contact angle of 70 to 115°. 2. The antireflection film according to claim 1, wherein 20 to 80% of the silicon atoms on the surface of the silica fine particle layer constitute an alkylsilyl group and/or an alkenylsilyl group. An anti-reflection film comprising an inorganic dense layer formed on the surface of a base material and consisting of one or more layers, and a silica fine particle layer formed thereon,
The outermost layer of the inorganic dense layer is a fluoride,
The silica fine particle layer has an alkylsilyl group and/or an alkenylsilyl group on the surface, a refractive index of 1.35 to 1.50, and a porosity of 5 to 25%,
The silica fine particle layer further has a silanol group on the surface,
A hydrophilic film having a betaine structure and a silanol group is formed on the silica fine particle layer,
Anti-reflection coating characterized by a water contact angle of less than 15°. 4. The antireflection film according to claim 3, wherein the hydrophilic film has an optical thickness of 5 nm or less. 5. The antireflection film according to claim 1, wherein the silica fine particle layer has an optical thickness of 20 to 100 nm. 6. The antireflection film according to claim 1, wherein the fluoride is magnesium fluoride (MgF ₂ ), bismuth fluoride (BiF ₃ ), calcium fluoride (CaF ₂ ), or cerium fluoride (CeF 2 ). ₃ ), thiolite (Na ₅ Al ₃ F ₁₄ ), cryolite (Na ₃ AlF ₆ ), lanthanum fluoride (LaF ₃ ), lead fluoride (PbF ₂ ), lithium fluoride (LiF), neodymium fluoride (NdF) ₃ ) or an antireflection film characterized by being made of sodium fluoride (NaF). In the antireflection film according to any one of claims 1 to 6, the material of the inorganic dense layer other than the fluoride is SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , ZnO, Ta ₂ O ₅ , A reflection characterized by being at least one member selected from the group consisting of Nb ₂ O ₅ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ O ₃ , Y ₂ O ₃ , Pr ₆ O ₁₁ and Sb ₂ O ₃ Prevention membrane. A method for manufacturing the antireflection film according to claim 3 or 4, comprising:
Forming an inorganic dense layer on the base material,
After forming a silica fine particle layer having an alkylsilyl group and/or an alkenylsilyl group on the inorganic dense layer by a wet process and firing,
Forming silanol groups on the surface of the silica fine particle layer by irradiating oxygen plasma,
A method for producing an anti-reflection film, characterized in that the hydrophilic film is formed by applying a hydrophilic member having a betaine structure and a silanol group to the surface of the silica fine particle layer and baking it. The method for manufacturing an antireflection film according to claim 8,
In the silica fine particle layer formed on the inorganic dense layer after firing and before irradiation with oxygen plasma , 20 to 80% of the silicon atoms on the surface constitute an alkylsilyl group and/or an alkenylsilyl group. A method for producing an antireflection film, characterized by: 10. The method for producing an antireflection film according to claim 8 or 9, wherein the silica fine particle layer is fired at a temperature of 150°C or higher and 400°C or lower. 11. The method for producing an anti-reflection film according to claim 10, wherein the hydrophilic film is fired at a temperature of 80°C or higher and lower than 130°C. An optical element comprising a base material and the antireflection film according to any one of claims 1 to 7 formed on the surface of the base material. 13. The optical element according to claim 12, wherein the base material has a refractive index of 1.45 to 1.95. The optical element according to claim 12 or 13, wherein the optical element has a haze value of 0.3% or less. 15. The optical element according to claim 12, wherein the base material is made of glass, quartz, silicon, or chalcogenide. 16. The optical element according to claim 12, wherein the base material has a flat plate shape or a lens shape. 17. The optical element according to claim 12, wherein the optical element is used for light having a wavelength range of 300 nm to 2000 nm.

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